Auralex Acoustic Pyramid Foam is an all time classic when it comes to sound deadening foam panels. You will find this foam in anechoic chambers and in professional recording studios. It covers the walls of many home recording studios as well.

The purpose of this review is to fully investigate the real usefulness of Auralex Studiofoam Pyramid. You’ll find out what type of pyramid foam is best for your recording studio, and where the best placement for Auralex Acoustic Pyramid foam is. In addition, we’ll suggest how to supplement the pyramid foam with other types of sound deadening foam. You can supplement with narrow wedge sound deadening foam panels, regular wedge foam panels, and vertical wedge panels. Also, we will see that acoustic pyramid foam plays well with home recording studio package offers such as Auralex Roominators.

Questions About Auralex Studiofoam Pyramid Answered

Are you equipping a professional recording studio, or want your DIY home recording studio sound like a big, professional studio? Then you should be taking advantage of the Auralex Pyramid sound deadening foam. But you still have questions, such as:

• Is it possible to get great sound treatment with Auralex Pyramids?
• How much foam is right for my space?
• Where on the walls and ceilings should place the foam panels?
• What thickness of the pyramid sound deadening foam is best?
• How to orient the panels for best absorption?
• What are the ways get good absorption at lower frequencies, such as fundamental frequencies of human voice?
• How to maximize the available space in the recording studio?

These questions and more will be answered in this post. Keep reading!

Dimensions, Thickness, Studiofoam Sound Deadening Foam Material

Auralex Acoustic Pyramid Foam comes in two thicknesses, 2 inch and 4 inch thickness. This is important as, especially for low frequencies absorption. At low frequency, increased thickness will significantly increase the absorption. On the other hand, 4″ thick foam will take up a lot of room on the walls. Thick foam layer could significantly reduce the amount of available space in the studio.

The panel dimensions are 2 ft by 2 ft for both 2 in and 4 in Studiofoam Pyramid Foam. According to the company, the wedges in 4 in. foam are 3 inches tall while the wedges in the 2 in. foam are 1.5 inches tall. The foam is made of durable, polyurethane open cell foam material. Open cell structure is important for effective sound absorption. Even though Studiofoam Pyramid foam is termed “high density”, it is still very light and easy to handle and install.

Low And Variable Speed Of Sound In Sound Deadening Acoustic Foams

Speed of sound in open cell polyurethane foams behaves different than in other materials like solids. Speed of sound in a foam depends strongly on frequency of the sound. This differentiates it from other forms of matter such as solid, liquid, or gas. In these, speed of sound is to a large degree independent of frequency. The figure below

schematically shows the dependence of the speed of sound (c) in the foam on frequency (f). Speed of sound is measured in meters per second. Frequency is measured in Hertz (Hz). We can see that, speed of sound for all frequencies up to 4000 Hz is less than speed of sound in the air, which is around 330 m/s in normal conditions. Also, for frequencies below 1000 Hz, the speed of sound in this foam will drop dramatically with frequency. We will simulate such low speed of sound and show that it influences the absorption and reflection properties such as diffusion of the reflected waves, below. Low speed of sound allows “packing” of a larger portion of the sound wavelength into the foam, which is claimed to increase absorption as well.

Noise Reduction Coefficient, NRC, And Sound Absorption Coefficients, Experimentally Determined

In Table below, we present the results from the measurements of noise reduction coefficient, NRC, and sound absorption coefficients at a variety of sound frequencies. They were measured by Riverbank Acoustical Laboratories using standardized procedures ASTM C423-90a and E795-92. The method used is called Room Reverberation Method.

Comparison: 2″ Vs. 4″ Foam

We observe that both 2 in. and 4 in. Auralex Studiofoam Pyramid foams have excellent sound absorption coefficient. It has nearly perfect value above 500 Hz for the 4″ Pyramid Foam and above 900 Hz for the 2″ Pyramid Foam. The absorption coefficient drops down below these frequencies. Overall, the 2″ thick Auralex Studiofoam Pyramids has noise reduction coefficient, NRC, of 0.80 and the 4″ thick Pyramids has NRC of 0.95. NRC is a special average of sound absorption coefficients for discrete frequencies between 125 Hz and 4000 Hz.

Overall, we can see that, for the relevant frequencies below 500 Hz, the 4″ Pyramid Foam has up to three times higher noise absorption coefficient. This means three times more absorption at these frequencies, despite only twice the thickness. Also, as observed in the pyramids vs wedge acoustic foam comparison post that the sound absorption coefficient is highly variable in the popular 2″ pyramid foam. In that foam it varies by 50% between 0.09 and 0.13 for frequencies between 125 Hz and 200 Hz. We also observe that sound absorption coefficient is relatively constant between 0.21 and 0.28 for frequencies between 100 Hz and 160 Hz in the 4″ Auralex Studiofoam Pyramids foam.

It is important to note that these sound absorption measurements were made under specific conditions. The measurements predominantly measure absorption under normal incidence. Here the sound impinges onto the foam surface perpendicularly, under a right angle. We will look into simulations of these foams under a great variety of angles of incidence between 0 and 90 degrees.

Pyramid Foam Has Great Diffusion In 3D

Compared to most other popular sound deadening foams such as Auralex Wedge, Auralex Wedgies, the Studiofoam Pyramid foams have better diffusion in 3D. What is the significance of high diffusion? Diffusion is reflection of an incoming sound wave which comes in a single direction, into many outgoing directions. In reviews of other foam geometries we have seen that foams differ widely in their diffusion. However, when the incoming sound direction is perpendicular to the ridge of the wedge in Studiofoam Wedge type foams, the sound will only reflect in directions inside the plane defined by that wedge and the incoming wave direction. Thus the diffusion will be only two dimensional, thus not so high.

Diffusion in 3D with the pyramid foam means that parts of the incoming wave will reflect in directions that do not all lie in the same plane. That is a much more significant diffusion.

High diffusion is important in preventing formation of powerful standing waves which distort the recordings strongly at discrete frequencies.

Analysis Of Reflection “To The Side” In 3D

In the figure below

we illustrate how an incoming wave in a normal incidence can reflect in two different directions depending on where exactly the incoming wave hits the side of the pyramid. As a comparison we present the same incoming wave impinging on a wedge soundproofing foam on the right.

Here we see that the incoming wave refracts, bounces off the bottom of the foam, and exits through the other side of the wedge. It therefore travels back into the room exactly in the opposite direction from where it came from. In pyramid foam, however, that same normally impinging incoming wave will again refract through the side of the pyramid, bounce off the bottom of the pyramid, but then, instead of hitting the other, opposite, side of the pyramid, it hits the neighboring side of the pyramid on the way out. It then refracts out back into the room under an angle that is not normal to the base anymore. That is a perfect example of enhanced 3D diffusion that just does not happen in wedge foam.

Surely, it depends on where exactly the normally impinging wave hits the side of the pyramid. If the incoming wave hits the side of the pyramid close to the middle of the base, then the reflected wave will still be normal, that is, perpendicular to the base, on its way out. That is because that part of the wave will not go out through the neighboring side of the pyramid. Instead, it will go out through the opposite side of the pyramid. However, at least a part of the wave will hit the neighboring side of the pyramid. That part will exit through the neighboring side, and be reflected off the normal, incoming direction.

For More Info…

We have compared diffusion in pyramid foam vs wedge foam in more detail in this post: Sound Proof Foam Panels: Pyramid Acoustic Foam Vs Wedge Acoustic Foam.

This 3D diffusion in normal incidence will be important when we discuss below where exactly the pyramid foam is best used when turning a room into a sound recording studio.

Absorption And Reflection Off A Pyramid Foam Under Different Angles Of Incidence

We will present simulations of reflection and absorption of sound off of Auralex Studiofoam Pyramid under the following conditions, as an example of what is happening. You can see more information about what software we used in our simulations here: Sound Proof Foam Panels: Pyramid Acoustic Foam Vs Wedge Acoustic Foam.

We will assume, for the sake of giving example, that the speed of sound in the foam is 140 m/s and that the speed of sound in the air is 330 m/s. This will give us correct bending of sound rays in simulations. In reality, speed of sound in foam varies with frequency. For low frequencies it could be as low as 80 m/s and as high as 200 m/s. Further, we will assume that the wave enters on one side of the pyramid and exits on the other, that is, we will consider only two-dimensional reflection and diffusion. The 3D diffusion adds to the total diffusion. The effect of 3D diffusion has been considered above.

Normal Incidence

Figure below

shows a typical pattern of refraction of a normally incident foam onto a pyramid shaped foam. The assumption about the speed of sound is given above. There are multiple reflections, including total internal reflections, and multiple refractions. A good portion of wave energy is reflected straight back, in the direction straight up in the figure. This makes sense as the symmetry and the law reflection demands that the angle of reflection is the same as the angle of incidence.

Again, the image does not include 3D effects, so in reality, more of the wave energy is diffused “sideways”, into the 3rd dimension, not pictured in the image. But still, a lot of sound energy will be reflected straight back. This is the reason why, despite good 3D diffusion, we recommend to use the 4″ Auralex Studiofoam Pyramid foam where the sound waves will likely impact on the wall under the 90 degree angle. This way, the portion of the sound reflected straight back will be minimized. The strong, unwanted standing waves at discrete frequencies will not be present as much as they would be with the 2″ pyramid foam.

15 Degree Angle Of Incidence

Figure below

shows the situation where the angle of incidence of a sound wave is 15 degrees. The incoming wave is starting at the top right corner of the image. As we follow the path of the wave, we see that wave first refracts into the foam on the side of the pyramid. Then the wave reflects internally and totally off the bottom of the foam. After that it makes its way to the left side of the pyramid 2 pyramids away. Finally it refracts back into the air.

Overall, that path follows the law of reflection. This means that the outgoing wave is 15 degrees to the normal, just like the incoming wave was. Needless to say, to such path, another possible path should be added. In that other path the wave refracts through the neighboring side, making its way into the 3rd dimension, out of the plane of the image. This contributes to more sound diffusion.

Figure below

shows a similar 15 degree angle of incidence impact, but emphasizes the path of the part of the wave that initially reflects off of the side of the pyramid. That wave makes its way into the foam by refracting on the side of the neighboring pyramid after initial reflection. The propagation angle at this moment is very flat, or horizontal. This ensures a long path nearly horizontally through the foam. When that part of the sound wave eventually exits the foam and makes its way back into the room, it will be significantly attenuated, or absorbed. In addition to possible reflection/refraction paths presented, again, there will be additional paths out of the plane of the image which will certainly improve diffusion due to a greater variety of reflected angles.

30 Degree Angle Of Incidence

Our simulations of sound rays show similar patterns of reflection and refraction for 30 degree angle of incidence as in 15 degree angle of incidence case. We do not present images here. They are identical as the ones presented in Auralex Studiofoam Wedge Panels Soundproofing Foam Panels Review for the same, 30 degree, angle of incidence.

The major difference to reflection and absorption in Auralex Wedge panels is that the Auralex Pyramids will again reflect into the 3rd dimension. This will definitely increase diffusion. The exact increase of added diffusion on overall absorption is unclear. Assuming the amount of absorption is otherwise the same, the increased diffusion means that the sound will reflect in many different directions. It will have many more opportunities to be absorbed in sound deadening foam on other walls of the recording studio, before it will make its way to the microphone. This way, increased diffusion indirectly increases overall absorption.

45 Degree Angle Of Incidence

Our simulations show that under the 45 angle of incidence, overall, the initially refracted and initially reflected wave both end up traveling through the foam under more horizontal angles, thereby increasing the path inside the foam, and, overall, increasing absorption. So we like the Auralex Studiofoam Pyramid foam more for expected angles of incidence of 45 degrees. Figure

shows the expected refractions and reflections of an incoming wave with angle of incidence of 45 degrees. The wave is assumed not to hit the neighboring sides of the pyramid. It is assumed to stay in the plane of the image. Parts of the wave will certainly leave the plane of the image. This will increase the diffusion into the 3rd dimension in a pyramid foam. This does not happen in the regular wedge foam. We can see in the figure how the initially refracted wave makes it into the foam on the left. The wave then reflects back three pyramids down to the right. The final outgoing angle is 45 degrees to the normal. This obeys the law of reflection.

The other part of the incoming wave which initially reflects off of the pyramid side will, to a large degree, make its way into the next pyramid. It will then internally reflect down to the bottom of the foam. Then it will make another cycle bottom-to-pyramid before it exits the foam. This increases the total path through the foam and thus increases absorption.

60 Degree Angle Of Incidence

Figure below

shows what happens under the 60 degree angle of incidence of the sound wave. Due to the impact into the side of the pyramid being nearly normal incidence, a locally 0 degree angle, the wave refracts straight through. Due to the pyramid top angle, the wave internally reflects straight down, and then from the bottom of the foam, straight back up, and then retraces its way backwards.

The wave exits the foam along exactly the same path it came in from. Therefore, the initially refracted wave will bounce right back in the opposite direction, after one loop back and forth through the thickness of the foam. The initially reflected wave will, due to normal impact, reflect straight back also. Both of these paths are highly undesirable. Reflection straight back will have a huge potential to form short standing waves in the room. These will cause distortions.

The only redeeming feature of the pyramid foam as compared with the regular wedge foam is that, at least some of the wave will not follow the path back as depicted, but will escape into the 3rd dimension, and exit the pyramid on the side, out of the plane of the image. This part of the wave will not be forming standing waves described in the previous paragraph.

Overall, we do not recommend using pyramid foam for expected angles of incidence of 60 degrees.

75 Degree Angle Of Incidence

Figure below

shows what the refraction and reflection pattern that happens when the sound impinges on the pyramid sound deadening foam under the 75 degree angle of incidence. The majority of the sound energy refracts into the foam. This is due to the near-normal incidence onto the side of the pyramid. Then, the wave propagates to the other, left, side of the pyramid and totally internally reflects off of it. It then goes nearly straight down toward the bottom of the foam. There it internally reflects from the bottom of the foam or from the wall. It then follows the symmetric path back to the tip of the pyramid where it exits under the 75 degree angle, for the most part.

Of course, as always in the reflection/refraction images above, we have assumed here that the wave has not hit the neighboring side of the entrance side of the pyramid, but it has hit the opposite side to the entrance side of the pyramid. If the wave did hit the neighboring side, it would travel out of the plane of the image. This would produce a bit more diffusion into out of plane directions.

Overall, looking at the figure, the length of the path of the sound wave under the 75 degree incidence is not very long. Dispersion is not great either. We do not recommend using the pyramid foam for these angles of incidence.

Overall Assessment Of Reflection And Absorption Properties Of Pyramid Foam

As our simulations indicate, pyramid foam such as Auralex Studiofoam Pyramid will perform best in the range of angles of incidence between 15 and 30 degrees. In this range, as well as for normal incidence, it should outperform foams with wedge geometries due to its extra diffusion into the 3rd dimension. We additionally recommend the 4″ pyramid foam over the 2″ pyramid foam for extra absorption.

Placement Of Pyramid Sound Deadening Foam Panels In A Recording Studio

Based on our simulations, above, we can see Auralex Studiofoam Pyramid Foam placed on walls and ceilings in a recording studio predominantly in placement where the expected angle of sound incidence is up to 30 degrees. Even in such placements you should preferably use the thicker, 4″ thick, foam panels. This is because of overall better absorption for important frequencies of about 100 Hz – about 500 Hz. Absorption of these frequencies is up to 3x greater with the 4″ thick pyramid foam.

Fire Retardancy And Durability

Auralex Studiofoam Pyramids sound deadening foam is made of open cell polyurethane foam material that contains no melanine. Lack of melanine makes for good durability. Open cell cellular structure increases the absorption. This is due to energy transfer from sound energy to thermal energy via turbulent airflow through the open cells.

Availability, Colors

Both the 2″ and the 4″ thick Auralex Studiofoam Pyramids sound deadening foam is available in three colors: Purple, Burgundy, and Charcoal.

One of these colors should match the decor of your room and the other sound deadening foams you may place on the walls and ceilings.

When a musician decides to turn a room into a recording studio, she will encounter a lot of contradicting and confusing information. What is the best way to treat a room and turn it into a recording studio? Auralex has stepped up and combined two of its successful sound absorbing foam products to help a musician and a DIY acoustic foam design enthusiast. With the help of Auralex, the musician will be able to quickly and effortlessly sound treat any room. She will be able to significantly improve the quality of the recorded sound.

We will review Auralex Project 2 Roominator Kit sound absorbing foam (available at Walmart) in order to support that DIY recording studio enthusiast. She will be able to set up her recording studio with minimal cost, best possible materials, with no outside help of expensive “experts”. We will talk about optimal placement and orientation of the panels that you will find in the kit.  Additional optional upgrades will be discussed. We will base our suggestions on the sound simulations that we showed in other posts on this site.

Contents OF Auralex Project 2 Roominator Sound Absorbing Foam Kit

The Auralex Roominator Kit contains Auralex 24 Studiofoam Wedge Panels with dimensions 2′ (H) x 2′ (W) of 2″ thickness. You can attach these to walls and the ceiling. In addition, the kit contains 8 pieces of Auralex LENRD Bass Traps. These are panels that fit in the corners of the room. You will also find 144 EZ-Stick Pro Adhesives for easy install. Due to the lightness of the Studiofoam sound absorbing foam you will find installation of the kit effortless.

The Regular Wedge Panels, Their Absorption And Diffusion

The surface shape of the Wedge Panels is one of what we termed “regular wedge” in this review post: Auralex Studiofoam Wedge Panels Soundproofing Foam Panels Review. We found these regular wedge panels to absorb sufficiently well for mid to high frequencies above 500 Hz. For adequate absorption at lower frequencies, between 100 Hz and 500 Hz, which are also important, we found that the “regular wedge” type foam such as Auralex Studiofoam Wedge, included in Project 2 Roominator Kit, is best suitable, absorption-wise, for angles of incidence around 30 degree to 45 degree. These are the mid-range angles of incidence.

What determines the angle of incidence? One must approximately figure where the most common location of the sound source will be. Then, draw a straight line from the source to the position at the wall. At that position of the wall, one draws a normal line, which is perpendicular to the wall at that point. The angle of incidence is then defined as the angle between the line of incoming wave, and the normal line. Typically, the incidence will be “normal” at the position on the wall which is closest to the sound source. As one goes farther away from that position, the angle of incidence increases. The largest angles of incidence will be at the very far end of the side wall in the room.

Further Improving Absorption And Diffusion

The upshot of this is that, the “regular wedge” type panels such as Auralex Studiofoam Wedge panels included in the Roominator Kit will still work in all placements in the room, but for better absorption and better diffusion, you may want to consider supplementing them for the placement on the wall closest to the sound source with the Auralex Pyramid Foam reviewed here: Sound Deadening Foam Panels With Diffusion: Review Of Auralex Acoustic Pyramid Foam, or the Auralex DST-type foams reviewed here: Best Acoustic Foam: Acoustic Wedge Foam Auralex DST 112, DST 114 Review. Likewise, for placement in the far-end sides of the room (angle of incidence 60 degrees and over) you will improve absorption by substituting with the Auralex DST-type foams.

What about the orientation of the Auralex Wedge sound absorbing foam included in this Kit? The Wedge foam comes in 2 ft by 2 ft square panels. Thus, you can orient it in any direction. We recommend orienting it such that the ridge of the wedges are perpendicular to the direction from the sound source. That way, one side of the wedge will face in the direction of the sound source, which will maximize the transmission of sound into the foam, and thus, the absorption will be maximal. We have discussed this in the post on placement of sound absorbing foam in the recording studio here: Acoustic Sound Foam Placement In Recording Studio. Part 2, Oblique Incidence.

Bottom line, by heeding the advice in this section, the sound impinging on the wedge panels will be maximally absorbed. The remaining sound that will still be reflected back into the room will be diffused. This means that the sound will go back into the room in random directions. This will allow the sound to be absorbed in other wedge panels mounted on other walls in the room, or on the ceiling. In addition, the sound that impinges onto the corners of the room will be absorbed by the second component of the Auralex Project 2 Roominator Kit, the LENRD Bass Traps.

LENRD Bass Traps, Their Role In Sound Absorption And Diffusion, And Placement

LENRD Bass Traps are the second important component of Auralex Roominator Kit. LENRDs  absorb and diffuse the sound that hits the corners of the room. Why are LENRDs so important?  And what is their best placement?

Sound Absorption Of LENRD Bass Traps

Table below shows the Noise Reduction Coefficient, NRC, and Sound Absorption Coefficients for a variety of relevant frequencies from 100 Hz on.

As you can see, the sound absorption coefficients for LENRD are over 1.00 for frequencies between 100 Hz and 5000 Hz. This indicates full absorption at these frequencies. Surely, this is due to LENRD high thickness. You should place LENRD foams in corners of the recording studio.There, LENRDs won’t take up much of the useful space.

The basic physics of mirrors explains what happens when a sound impinges on a corner of the room where the three walls that are coming together are at a 90 degree angles relative to one another. The sound will bounce once off of each wall. Due to the law of reflection, the sound will bounce back exactly in the opposite direction from where it came from.

Such perfect back reflections are detrimental for the room acoustics. Back reflections enable creation of back-and-forth reflections from one corner of the room to another. This then builds up standing waves at certain discrete frequencies. At these discrete frequencies, the sound will be disproportionately amplified. The sound recording will suffer due to unusual amplification at these frequencies.

So it is best to avoid the buildup of such standing waves bouncing off the corners of the room. Absorbing as much sound as possible in the corners of the room will do the trick. This is the role of Auralex LENRD Bass Traps, included in the kit.

Placement Of LENRD Bass Traps

Based on this, the best positioning of the LENRD Bass Traps is in the corners of the room that are closest to the sound source. The reason for positioning them as close as possible to the sound source is so that the sound is absorbed in them when it is most intense. The sound is most intense closest to the source, before it reflects off of any wall.

Assuming good, thick, sound absorbing carpeting in the room, it would then be advisable to place LENRD Bass Traps in the upper corners of the room, the corners closest to the sound source. If you have any Bass Traps left over, installing these in the bottom corners of the room would make sense also.

What about diffusion of the reflected sound that reflects off the LENRDs? Well, since the absorption of the sound anywhere between 100 Hz and 4,000 Hz is so complete, there is hardly any reflected sound. Thus, the amount of diffusion of that sound is not very important.

Material’s Fire Retardancy And Durability

The material that both Wedges and LENRD foams are made of are open-cell polyurethane foams. They are light, yet absorb mid to high frequencies above 500 Hz practically 100%. For frequencies below 500 Hz, the proper positioning of Wedges as described above will allow for maximal absorption there too. The LENRD foams are much thicker than the Wedges.  LENRD foam will have much better absorption at lower frequencies 100 Hz – 500 Hz. Practically all relevant sound impinging on them will be absorbed.

The polyurethane foams are Class-A rated as far as fire retardancy. Before installation, you should still check with the local laws as far as restrictions on installation.

Appearance, Colors Available

Auralex Project 2 Roominator Kit comes in Purple, Burgundy, and Charcoal color. If you decide to combine Roominator Kit components with Auralex Pyramid Panels or Auralex DST Panels as suggested above, the color combinations will match.

See Auralex Project 2 Roominator Kit at Walmart.com.

Note: It has come to our attention that, recently, Auralex Project 2 Roominator Kit has been out of stock. We recommend looking into the Auralex Roominator D36-DST here at Walmart instead.

Studiofoam Wedge soundproofing foam panels are some of the most popular, widely  used, soundproofing foam panels in the world. Auralex primarily designed them to improve sound inside your recording studio. The Studiofoam Wedge panels are great for absorbing echoes, reverb, and prevent buildup of standing waves in a recording studio. All this improves the recorded sound. Studiofoam Wedge foams are most popular among the sound engineers as well as among DIY recording studio enthusiasts.

We review sound absorption performance of Studiofoam Wedge panels in a variety of conditions. We emphasize absorption of highly relevant frequencies in the range of 100 – 300 Hz. This is the range where human voice fundamental frequencies lie. This is also where fundamental frequencies of numerous musical instruments are. Soundproofing foams notoriously absorb relatively less in this frequency domain. These foams absorb much better in the mid to high frequencies above 500 Hz. Their absorption there is nearly 100%.

We put emphasis on the absorption under a variety of angles of incidence. We simulate angles from normal incidence where the measurements are usually performed. In our simulations we are also able to simulate oblique incidence of sound at a range of incident angles. In most real life circumstances, the soundproofing panel will have sound impinging on it under an oblique angle. Our investigation is therefore relevant. Different soundproofing foam behave differently under different angles of incidence. A particular soundproofing foam would be most useful in a particular placement in a recording studio.

Studiofoam Wedge Dimensions, Weight, Density

Auralex Studiofoam Wedge comes in three thicknesses, 2″, 3″ and 4″. By far the most popular is the 2 inch thickness. Surely, this is because of lighter weight, and a lesser space requirement and lighter weight. 2″ foam carries a lower price tag too. Regardless of thickness, Studiofoam Wedge are light and easy to install, even for a non-professional.

Studiofoam Wedge foam panels come in two sizes, 2 ft by 4 ft and 2 ft by 2 ft. They are a workhorse of recording studio wall treatment, and thus come in relatively large sizes, as opposed to Auralex Wedgies soundproofing foam, which come in 1 ft by 1 ft dimension only.

Wedges, as all Studiofoam panels are made of polyurethane, which is a high-density (still very light 1.5-1.7 lb/ft³), open-cell foam. According to the ASTM report on Auralex site, the surface density of the foam is 0.18 lb/ft² for the 2″ thick foam.

Speed Of Sound And Dispersion

Speed of sound is the speed with which sound propagates, or moves through the material. In air, the speed of sound is about 330 meters per second, and it is to a large degree independent of the frequency of sound. In foam, however, there is dispersion. This means that speed of sound varies with frequency of sound, which is unusual for regular gases, liquids and solids, but is common in foams. While there is no published data for Studiofoam, a similar foam has the dependence of speed of sound on frequency as depicted in Figure below adopted from reference Jones:

We can see that speed of sound for low frequencies tends toward zero, and it grows slowly with frequency. We will, for the purpose of this report, work with the frequency of about 240 Hz, which corresponds to speed of sound of about 140 meters per second. The important thing is, besides the exact value of the speed, also the fact that the speed of sound in the foam is actually less than the speed of sound in the air. This will determine the amount of absorption and directions in which the sound reflects off of the foam back into the room. This is called diffusion.

Sound Absorption Measurements By Frequency And Noise Reduction Coefficient

Table below shows a comparison of noise reduction coefficients (NRC) for the three thicknesses of Auralex Studiofoam Wedge. The NRC is obtained as average of sound absorption coefficients measured at different sound frequencies. These measurements are standardized and are given in the table as well. We can see that for mid to high frequencies above 500 Hz, all three thicknesses have practically 100% sound absorption. Absorption coefficient around 1.00 means nearly 100% absorption. For lower frequencies, the 4″ Wedges absorb more. However, since the 4″ foam is heavier, more expensive, we will investigate how to make the most even of a thinner, more manageable, and more accessible 2″ foam.

Studiofoam Wedges Sound Absorption At Various Angles Of Incidence

The experimental measurements of sound absorption coefficients given in the table above are done following a special protocol. In this protocol, the sound is directed toward the foam surface directly, not at an angle. This is called normal incidence. We use the ability to simulate other angles of incidence besides normal incidence, using a simulation available online at PHET. Let’s investigate how a foam like Studiofoam Wedge performs at normal incidence and other, oblique angles of incidence, in order to figure out where this foam would work best for sound absorption.

Normal Incidence

Normal incidence is important, especially in regards to reflection of sound straight back. The sound that impinges perpendicularly to the surface can, when reflected straight back, do the same on the other side of the room, and, since most recording rooms have opposite walls parallel to each other, cause a buildup of powerful standing waves. Standing waves appear at discrete frequencies that then become disproportionately highly amplified in the recordings, therefore causing distortion. Such wall-to-wall standing waves can be amplified best because of the shortest end-to-end distance, allowing highest fundamental and first overtone frequencies to become resonant, and causing distortion in recordings.

Figure below shows a wave impinging on a side of a “regular wedge”, or a wedge with

a relatively large wedge angle, such as Studiofoam Wedges have. We notice that, due to the large wedge angle, a large fraction of the impinging wave gets transmitted (or, refracts) into the foam. It then bounces off the bottom of the foam. It then exits through a side of a wedge two wedges away from the original wedge. The direction in which the wave exist is the opposite of the incoming direction. That is, the significant portion of the wave is directed straight back in the opposite direction of where it came from. This is expected due to the symmetry of the regular wedge foam geometry and due to normal incidence.

The part of the impinging wave that reflects off the first wedge surface hits under a 90 degree angle the surface of the neighboring wedge. Most of that wave transmits through the surface into the second wedge. Then, as shown in the image, it bounces of the lower left corner of the foam. It then exits the foam (accidentally) through the same wedge, but the opposite side. Then it reflects off the neighboring wedge. Then it reflects back directly in the opposite direction where it came from. While this is accidental, it shows the possibility that a large fraction of the waves will be reflected directly in the backward direction.

Comparison To Other Types Of Wedge Foam For Normal Incidence

This reflection straight back does not make the regular wedge foam a good candidate to be used on the parts of the wall where we expect normal incidence of the waves from the sound source. For such locations, one should look into these foams: Sound Deadening Foam With Great Diffusion – Pyramids, Narrow Wedge/Wedgies or Vertical Wedge Acoustic Foam. To be fair, part of the wave inside the foam will make a couple of back-and-forth loops inside the foam before it exits. It will exit at angles other than straight back. Most prominent loop is the part of the wave that initially refracts into the foam, then bounces off the bottom of the foam. Then, instead of exiting on the side of the wedge, it internally reflects back into the wedge. Then it makes a loop back to the bottom of the foam due to internal reflections. However, we have seen more of that behavior when we simulated normal incidence in a foam that resembles Auralex Wedgies. We thus conclude that a narrow wedge soundproof foam has better diffusion and better absorption for the speed of sound simulated.

Overall, we prefer vertical wedge acoustic foams for normal incidence situation. See also Soundproof Foam Panel Placement In Recording Studio.

15 Degree Angle Of Incidence

First we focus on the wave that impinges onto the wedge surface under an 15 degree angle and then refracts, or is transmitted into the foam. Figure below

focuses on this situation. The incoming wave (from the right) refracts into the foam, bounces off the bottom, and, for the most part, exits via the symmetric route on the left, at an reflected angle of 15 degrees. There is only limited absorption via this route as this route is quite short.

The wave that upon the first 15-degree-angle-of-of-incidence encounter with the foam reflects off the side of the wedge is focused on in the figure below

We notice that the initially reflected wave proceeds in nearly horizontal direction through the air. It then enters the neighboring side of the wave, and proceeds, still nearly horizontally, through the foam. Upon a bounce from the bottom of the foam, it continues under a nearly horizontal direction. Later on, it even makes a loop or two around, from the wedge side to the bottom and back. This makes the initially reflected wave go a large distance through the foam. That part of the wave will get absorbed significantly.

This behavior is similar to what we observed in the “narrow wedge” type soundproofing foam Auralex Wedgies Review. However, with the “narrow wedge” at 15 degree wave incidence, both the initially reflected wave and the initially refracted wave took paths that were relatively close to horizontal. Large portions of both parts of the wave were able to make loops inside the foam. So for 15 degree incidence, we still prefer the narrow wedge type foam for maximum absorption.

30 Degree Angle Of Incidence

Figure below

shows the incoming under the 30 degree angle of incidence. It comes into the foam parallel to one of the sides of the wedge. It then hits the other side of the wedge. The refracted part is significant. It experiences one total reflection bounce off the bottom of the foam. It then exits two wedges down under the same angle of 30 degrees as it entered. This complies with the law of reflection.

The initially reflected part of the wave bounces back to the left, in an almost horizontal direction. It then passes through the neighboring wedge. Then, it continues its path nearly horizontally through the foam. This horizontal motion increases absorption as it makes the path of the wave through the foam very long. This part of the wave may even reflect off the side of the foam and continue backwards, then eventually up toward the wedges, and cycle back down. Again, this part of the wave will be absorbed well.

In the figure above, we do not see much of a diversity in outgoing angles, the diffusion is not significant with this angle of incidence.

45 Degree Angle Of Incidence

Figure

shows an impact of a sound wave from the right at a 45 degree angle of incidence. The initially refracted wave retains most of the original power as it impinges on the side of the wedge as the angle of incidence locally there is nearly 90 degrees. This refracted part of the wave then bounces completely off the bottom of the foam. It then exits on the right through a wedge, making a final angle of 45 degrees with the normal. Overall, this is expected by the law of reflection.

A smaller part of the wave impinging onto the side of the wedge will initially reflect. It will then enter into the foam through a side of the neighboring wedge. Afterwards, most of that part of the wave will internally reflect inside the wedge. It will then bounce off the bottom of the foam, and possibly circle back and forth between the top and the bottom of the wedge foam one or more times before exiting the foam. That initially reflected part should be well absorbed in the foam due to multiple back-and-forth paths. However, as we stated, this part of the wave does not represent most of the energy of the incoming wave.

60 Degree Angle Of Incidence

Figure

shows what happens when sound impinges onto the soundproofing foam of the “regular wedge” type with an angle of incidence of 60 degrees. The side of the wedge is at an angle of 60 degrees off the horizontal also. Thus, the wave impinges onto the side of the wedge as a normally incident wave. Most of the wave goes straight through, then totally reflects off the other side of the wedge. Then, most of the wave goes straight down, then bounces off the bottom of the foam or the wall behind it. The wave then retraces its path back out. Therefore, the initially refracted part of the original wave makes a back-and-forth through the thickness of the foam. Then that part of the wave comes back at the same place, in the backward direction.

The initially reflected wave bounces straight back also.

Together, regardless of the exact speed of sound, or frequency, most of the energy of the wave impinging under the 60 degree angle will reflect straight back. The diffusion of the wave is nil. Furthermore, a backward reflecting wave is most likely to allow for a powerful standing wave in the room. The natural frequencies of the standing wave will be amplified and will distort the recordings.

To conclude, placing “regular wedge” soundproofing foam such as Auralex Studiofoam Wedges such that they would mostly experience incoming waves under 60 degree angle of incidence or similar is not advisable.

75 Degree Angle Of Incidence

Figure below

shows a simulation of a wave impinging under the 75 degree angle to the normal on a “regular wedge” type soundproofing foam such as Studiofoam Wedge. Notice that the angle of incidence onto the actual side of the wedge is just 15 degrees off normal. The transmission will therefore be efficient. After that, the wave totally internally reflects off the opposite side of the same wedge. Then, the wave proceeds nearly vertically down to the bottom of the foam. There it reflects, either internally from the bottom of the foam, or from the neighboring wall. Then, it starts its way back up, and exits through the opposite side of the same wedge. The angle under which the wave exits is the same 75 degree angle.

The part of the impinging wave initially reflected off the side of the wedge reflects back under an angle of about 45 degrees.

Overall, there are thus just two significant angles of reflection. The diffusion in this situation is low. Likewise, no significant back-and-forth paths of the wave inside the foam are created. The absorption will not be out of the ordinary at 75 degrees angle of incidence.

Fire Retardancy

Auralex Studiofoam Wedges have A Rating for fire retardancy, based on the recent ASTM E-84 Fire Rating Test Report.

Durability

Auralex Studiofoam has open cell cellular structure for good absorption. It is made of polyurethane and it does not contain melamine. That makes Studiofoam very durable.

Colors Available

Studiofoam Wedges are the workhorse of Auralex recording studio treatments. Auralex Studiofoam Wedge soundproofing foam panels are available in purple, burgundy, and charcoal. At least one of them should match the overall color scheme of your studio.

Pros

One of the main advantages of Studiofoam Wedge is its availability in large panels, such as 2′ by 4′. Also, Studiofoam Wedge have become very popular and have been around for a long time.

Cons

However, in our simulations we have found at various angles of sound incidence that [vertical wedges] and narrow wedge soundproofing foam panels should work better, that is, will give more absorption and more diffuse reflection of sound. At an angle of incidence of 60 degrees we found that the back reflection will be strong at all frequencies. This virtually guarantees generation of standing waves and associated recorded sound distortion.

Sizes Available

Typically, Auralex Studiofoam Wedges are purchased as 2′ by 4′ by 2″ panels. If needed, they can easily be cut down to a 2′ by 2′ size.

Checkout the availability of sizes of Auralex Wedge soundproofing foam at the Sam Ash music store through this link:
Auralex At Walmart.com

Acoustic Soundproofing Foam Reduces External Noises

Acoustic soundproofing foam is predominantly used as the sound treatment foam. It is intended to improve the sound produced inside the recording studio. However, sound absorbing foam contributes to sound insulation from the outside noises as well. Naturally, the foam absorbs sounds hitting it from either front or back side. Contrary to widespread opinion, depending on the source of external noise, and depending on the extent of the wall coverage, sound absorbing foam panels can be used for effective sound insulation from the outside noises.

Sources Of External Noises In A Recording Studio

The sources of external noises vary. In buildings, the main sources are vibrations of the windows and vibrations of the walls. Vibrations of the windows are caused directly by the outside noise that reaches the window panes. Vibrations of the walls are often caused by the vibrations of the frame of the building. The vibration of the frame, in turn, is caused by the vibration of the surrounding earth. The earth vibrates because of the nearby traffic, or similar sources.

How Does Acoustic Soundproofing Foam Reduce External Noise?

How can sound absorbing foam panels significantly reduce external noise in a recording studio? As we will see below, for a certain range of frequencies, soundproof foams are a nearly perfect absorber of sound. For noise concentrated in that frequency range, all you need to do is place soundproofing foam panels at the sources of the external noise. These sources could either be the windows, or the walls where most of the noise is originating. You will be placing acoustic soundproof foam on or near the walls and windows anyways for sound treatment. This will automatically reduce the level of external noises as well. Just keep in mind that, in order to reduce the external noise significantly, all sources of noise must be covered with soundproof foam. This should include all the walls, windows and doors. Sometimes this will mean covering all of the wall surface with soundproofing foam panels.

How We Investigated Noise Reduction For Most Popular Sound Deadening Foams

We performed computer simulations of sound propagation through external noise deadening foams.

In simulations that follow we will assume that the noise is coming either from the window or from the wall. We will assume that the noise waves are directed perpendicularly (in the normal direction) to the window or wall surface. This is much different than the sound that is created inside the recording studio. The sound created in the studio hits on the panels possibly from a variety of directions. In order for sound to really be coming perpendicularly from the wall, the foam must be attached directly to the wall. For instance, it could be, as is customary, glued to the wall.

The consequence here will be that the external sounds are incoming toward the bottom side of the soundproofing foam panels, perpendicular to the bottom side of the foam tile. This, again, is much different than the sound generated inside the recording studio. The sound generated inside the studio will reach the top side of the foam panels first.

What type of sound absorbing foam is best to reduce external noises? We have simulated several types of soundproofing foam panels. The foams simulated include: flat foam, regular wedge foam, pyramid foam, narrow wedge, and vertical wedge foams.

Experimentally Established Sound Absorption Coefficients For Popular Acoustic Foams

All types of acoustic foam do a nearly perfect job absorbing noise with frequencies over 800 Hz at predominantly normal incidence. We can see that in the table below.

Source: Webarchive.

Great Absorption Of External Noise Over 800 Hz Of Sound Insulation Foam

These measurements were done based on the sound absorption standard (link) which measures absorption of the sound hitting the top surface of the sound proof foam panel. This is not true for the external noise. Nevertheless, we will still be able to use the above results for frequencies above 800 Hz. We will assume that for frequencies above 800 Hz, absorption of all the commercially available panels is nearly perfect regardless whether the sound is hitting the panel from the top (as measured in the table above) or from the bottom, as in the case of external noise coming from the window or wall. So external noise with frequencies above 800 Hz should be adequately absorbed by any type of sound proof panels above.

Absorption Of External Noise With Frequencies Below 800 Hz

What about frequencies below 800 Hz? Frequencies below 800 Hz are crucial for recording studios because fundamental frequencies of human voice, as well as fundamental frequencies of many musical instruments lie in this frequency region. Likewise, the first few overtone frequencies fall below 800 Hz as well. Microphones will be very sensitive to these frequency region. Therefore, as much external noise as possible must be eliminated at these frequencies.

We see in the table above that some foams absorb as little as 10% of the noise at frequencies around 100-200 Hz. However, absorption itself does not tell the whole story. It is also important what happens to the noise that is allowed through the foam. Does that noise diffuse in different directions, or does it go straight out? The noise that is significantly diffused has a better chance of being absorbed to a significant degree in some other sound absorbing foam before it hits the microphone.

Speed Of Sound Variation In Sound Deadening Foam Below 800 Hz

For frequencies of noise below 800 Hz, an interesting phenomenon occurs. The speed of sound in the foam starts to drop as the frequency drops below 800 Hz. The speed of sound can be as low as 140 m/s at 200 Hz and as low as 90 m/s at 100 Hz. For such low speeds of sound, much lower than speed of sound in the air, strong internal reflection of sound can occur when the sound or noise is approaching the foam panel from the bottom side.

We performed a number of computer simulations to that regard, using bending of light simulation software at PHET. The simulations were designed to represent bending of light. However they apply to bending of sound waves as well as long as the speed of sound is properly chosen. This is because laws of reflection and refraction apply equally to both sound and light. The simulations we had access to correspond to sound frequency of 200 Hz in the sound absorbing foam and to speed of sound in the foam of 140 m/s. They correspond to speed of sound in the air of 330 m/s.

Due to low speed of sound for frequencies below 800 Hz, internal reflection of the sound can still cause significant absorption of sound even though the sound absorption coefficient for such frequencies is low.

Let’s look at how different shapes of sound deadening foam can cause different levels of internal reflection. Bear in mind that large internal reflection for certain foam shapes will cause sound to spend longer time, and longer paths inside the sound deadening foam, which in turn will increase the total sound and noise absorption.

We’ll look into these sound deadening foam shapes: Flat, pyramid, regular wedge, narrow wedge, vertical wedge.

Flat Acoustic Sound Absorbing Foam: Some Internal Reflection, No Diffusion

We simulate sound propagation in flat foam such as Auralex Sonoflat, pictured above. The figure below shows the simulated sound rays.

 

The figure shows a simulation of paths of five initially parallel sound rays. All five rays are coming from below in the direction straight up, normally to the bottom surface of the flat foam. The internal reflection is present but most of the sound will just go through the flat foam once and exit straight up, with no diffusion whatsoever.

Pyramid Wedge Sound Absorbing Foam: No Internal Reflections, Diffusion In Four Directions

In the figure below

 

we simulate sound propagation in a pyramid sound deadening foam. Speed of sound is 140 m/s. As you can see, the sound rays are penetrating into the foam from the bottom side, below. Also, notice that, as the sound ray hits the pyramid edge, it refracts, and leaves the foam and enters the room. The refraction will either be to the left or to the right, depending on what pyramid foam surface the ray hits on. There is no internal reflection at this speed of sound. We do get diffusion of sound, both to the left and right as pictured. In addition, in the pyramid sound absorbing foam the diffusion in the third dimension out of the screen and into the screen is possible. Altogether there are four directions in which sound will diffuse into, left, right, in and out.

Regular Wedge Sound Absorbing Foam: No Internal Reflections, Diffusion In Two Directions

The picture of the simulated sound propagation is the same as in figure above. By “regular wedge” we mean that the angle at the top vertex of the wedge is rather large, perhaps as large as 60 degrees or larger. We will contrast this with the “narrow wedge” foam which will have a top vertex angle less than 60 degrees. The noise will propagate straight up through the foam only once, and then refract on transmission into the air in the room. The sound will diffuse into two directions only, left and right.  You can see that in the figure above. There will be no diffusion in and out of the screen. Therefore, there is less diffusion with regular wedge sound absorbing foam.

Narrow Wedge Sound Proof Insulation Foam: Two Internal Reflections, Wide Diffusion In Two Directions

We simulated sound propagation through a narrow wedge sound proof insulation foam. You can see the result of the simulation in the figure below.

Notice that the sound enters the foam from below, internally reflects off the side of the wedge, and then internally reflects once again on the other side. Afterwards, sound exits close to the top vertex of the wedge, and at a relatively large angle. Because of two internal reflections, and the relatively long path through the wedge, the sound absorption will be quite good. In addition, the large angle diffusion will cause the noise from the outside propagate along the walls for a longer while. This gives more absorption of the noise along the studio walls before reaching the microphone.

Vertical Wedge Sound Proof Insulation Foam: Three Or More Internal Reflections, Complete Noise Bounce Back

Our simulation of a vertical wedge sound proof foam in figure below

 

shows a possibility of a complete internal reflection from the slanted side of the wedge, followed by the internal reflection off of the vertical side. The two internal reflections send the sound back into the foam. This forces the sound to travel a significant distance through the foam. Then, the sound reflects off the bottom, and then again reflects internally off the slanted side of the wedge. After that the sound goes straight down, that is, in the direction back to the wall. At this point the sound can either go back out through the wall, or go on a repeated internal loop through the foam. Repeated long internal loops will cause significant absorption in the foam.

We have seen (ref Jones) that the speed of sound goes down as the frequency of sound goes down from 200 Hz toward sub-100 Hz. This means that this internal reflection will play a role for sub-200 Hz frequencies. For higher frequencies, however, the complete internal reflection as depicted in figure above will turn into partial internal reflection and partial transmission. Partial transmission and partial internal reflection will make overall absorption of external noises as studied here less pronounced. This will happen for frequencies higher than 200 Hz.

Conclusion: Best Sound Absorbing Foam To Absorb External Noise, Based On Noise Absorption And Noise Diffusion

Based on our assumptions of the noise coming from the wall and impinging normally from the bottom of the sound absorbing foam, it appears, that for absorption of frequencies of 200 Hz and below, the vertical wedge foam will be best. See our review of vertical wedge acoustic foam here. For frequencies higher than 200 Hz, the internal reflection effect will be diminished. Then, the absorption will be strongest for the foam with the most volume given the same thickness. For higher frequencies, the flat foam will win out.

Another consideration is external noise diffusion. When the foam’s geometry is causing high diffusion of noise, it increases the chance of the external noise hitting on other sound absorption foams in the recording studio. This adds to overall noise absorption. The narrow wedge sound proof insulation foam has the highest noise diffusion among the foams studied in this post. Find the review of our recommended narrow wedge soundproof foam here.

As you can see, different foams will absorb different amounts of external noise. Also, they will diffuse the external noise into the room differently. Vertical wedge foam will absorb the most external noise, while the narrow wedge will diffuse the external noise the most.

When designing your recording studio, you should take these result into account, depending on the severity of the external noise.

In addition, we recommend different types of soundproofing foam in different parts of the recording studio. That way you will achieve the best absorption of sounds generated in the studio. You will reduce echo, flutter, and resonant standing wave buildup as much as possible. We go into more detail about this and present our recommendations here.

Sound Proof Foam Panels For Best Recording Possible

Are you a musician wondering how to achieve best recording studio acoustics? Maybe you are recording your own podcast? You may have tried setting up a recording studio or a sound booth to record your performances. You have then probably come across the unwanted echoes, flutter, or similar noises and sound distortions. Surely you have noticed these distortions degrading or downright destroying the quality of your recordings. You looked around and realized that sound proof foam will be light weight, flexible, and will be easy to install. You have checked them online and you have asked around. Now you wonder what type of sound proof foam panels to use, and how to place these panels in the recording studio or your sound booth. Look no further. You will find actionable advice below.

Ambitious Goal: Detailed Discussion Of Sound Treatment With Soundproof Foam

We have an ambitious goal for this article to compare and contrast two of the most commonly used types of acoustic foam panels. These are pyramid acoustic foam and wedge acoustic foam. We will point out at important qualities you need to look for in both, and which sound proof foam panel works better, given the requirements. You will know what to do to remove the artifacts such as unwanted echoes, reverb, spurious resonances and the like. Your recordings will reach the quality of your live voice or the live sound of your musical instruments. We will review the best available pyramid acoustic foams and wedge acoustic foams. We will also point to a discussion of what type of sound proof foam panels you need and where to place them in the recording room to achieve the very best sound in your recordings.

Important Qualities Of Sound Proof Foam Panels: Sound Absorption Average, Directionality, Diffusion

For quality recordings, the most important qualities of sound proof foam are sound absorption average, noise reduction coefficient, sound absorption coefficient. In addition, directionality of reflected sound waves, and associated diffusion are important.

Sound Absorption Average, SAA, Of Open Cell Acoustic Foam

The most important quality of sound proof foam is the amount of sound absorption. When the sound proof panels absorb just the right amount of sound and at all relevant frequencies, then there is sufficient feedback for the performer, yet not too much of the echo in the recording. Finding balance is the key.

Sound absorption by soundproof foam panels is represented by Sound Absorption Average, SAA. SAA can reach or even exceed the value of 1 for certain frequencies, which guarantees hundred percent absorption. Such high absorption is in part due to open cell structure of the foam. Open cell acoustic foam has foam bubbles that have several open (unfilled) sides. Open cell foam structure allows the air enter the foam as the sound wave hits, thus allowing sound energy conversion into heat as the atoms of air flow past the open cell walls.

Sound Absorption Average and Noise Reduction Coefficient For Pyramid Foam And Wedge Foam

Modern standard in sound absorption measurements is SAA, Sound Absorption Average (Source). SAA has replaced the noise reduction coefficient NRC (Source).
SAA is more accurate and detailed. Both NRC coefficient and SAA coefficiant have values between 0 and 1 where 0 represent perfect reflection of all sound and 1 represent perfect absorption of all sound.

However, SAA or NRC measurement standards do not offer a complete description of absorption properties of sound proof foams such as pyramid shaped foam or wedge shaped foam. The absorption coefficients are measured exclusively around discrete frequencies and they are mostly measured for normal (perpendicular) incidence onto the soundproof foam panels (see Source). In this article we will provide a broader view which, however, will still include the SAA and NRC data.

Table Of Experimental SAA And NRC Data For Auralex Wedges And Pyramids

Comparing NRC for the most popular Auralex Wedges with 2 in. thickness with Auralex Pyramids with the same thickness, we first notice that the Wedges have NRC of 0.8 and the Pyramids have NRC of 0.7 (see table below).

	100	125	160	200	250	315	400	500	630	800	1000	1250	1600	2000	2500	3150	4000	5000	NRC	Fire	Dimensions
2″ Wedges	0.17	0.11	0.16	0.24	0.3	0.45	0.64	0.91	1.01	1.06	1.05	1.02	1.03	0.99	0.97	0.95	1	1.05	0.8	A	2’x4’x2″ Foam Panel
2″ Pyramids	0.11	0.13	0.09	0.13	0.18	0.27	0.34	0.57	0.73	0.9	0.96	1.05	1.07	1.03	0.98	0.96	0.98	1.05	0.7	A	2’x4’x2″ Foam Panel

(Source: archive.org)

Major Difference At Lower Frequencies

Both foams seem to absorb sound pretty good overall. The only significant difference lies in absorption at low frequencies. At 500 Hz, the Wedges’ absorption coefficient is still 0.91 while the Pyramids’ is down to 0.57. Frequencies below 1,000 Hz, however, are the most important frequencies for most recording studios and sound booths. This is because the fundamental frequency range of a male voice is between 85 Hz and 155 Hz, and the fundamental frequency of a female voice ranges between 165 Hz and 255 Hz. (Source: msu.edu).

The reason for the wedge acoustic foam having a greater NRC than the pyramid acoustic foam is the greater volume. For the same surface area of the tile, defined as width times length of the tile, the pyramid acoustic foam has a lesser volume than the equally thick wedge acoustic foam. Since the sound absorption happens in the cells of the foam, generally this means that the greater the volume, the greater the absorption.

The Volume Difference

Consider the pyramid acoustic foam and the wedge acoustic foam that have the same base a and the same height (thickness) h, as in figure below

Both the pyramid foam and the wedge foam have the same room-facing surface area equal to A = 2*a*sqrt(h²+a²/4) However, their volumes differ. The volume of the pyramid is V = 1/3 a² h and the volume of the wedge is V = 1/2 a² h. Therefore the wedge has 50% more volume. The amount of absorption is proportional to the volume therefore it is natural to expect that the wedge acoustic foam would absorb more. This is apparent in the absorption coefficient table above. The table shows absorption coefficients for both 2″ Auralex Studiofoam Wedges and 2″ Auralex Studiofoam Pyramids for a variety of frequencies under the standard, mostly normal incidence conditions.

We find that both foams have perfect absorption for normal incidence for all frequencies above 1,000 Hz. For frequencies between 1,000 Hz and 200 Hz, the wedge foam has an advantage of up to 30% higher absorption coefficient. Overall, we see that 2″ Studiofoam Wedges have NRC of 0.80 while 2″ Studiofoam Pyramids has the NRC of 0.70.

A surprising result occurs, however, for the absorption measurement at 125 Hz which is important because it is the typical fundamental frequency of a male voice. At 125 Hz the absorption coefficient of 2″ Studiofoam Pyramids is 0.13, greater that the absorption coefficient of 2″ Studiofoam Wedges! How can that be?

We claim that this is due to an important difference in how sound waves at 125 Hz reflect in 3D once they enter the pyramid acoustic foam, see section on Directionality below.

Directionality Of Sound Proof Foam Panels

Second most important quality of the soundproof foam is direction of waves that are reflected from the foam, or directionality. You will not want your soundproof foam to allow the sound to reflect in highly predictable directions, such as straight back.

Such predictable reflections can support building of standing waves in the recording studio or the sound booth. Standing waves can be detrimental to a studio recording because they distort the sound by increasing the room response at certain resonant frequencies. There can be a big difference in direction of reflected waves between the pyramid foam and the wedge acoustic foam. Another important property related to directionality is diffusion. Diffusion of sound happens when a soundproof foam allows the reflected sound to be directed in multiple different directions. A greater diffusion will prevent buildup of standing waves in the recording studio.

We will treat sound as narrow sound rays for the purpose of this section. These narrow sound rays experience reflection and refraction as they hit onto the surface of the foam. We will focus our attention to the important range of 20 Hz – 500 Hz where neither the wedge foam nor the pyramid foam are absorbing the sound adequately. However, when positioned right, both such forms can absorb more.

Refraction: Breaking Of The Sound Wave Upon Transmission

For maximal absorption in the foam to occur, the sound rays must enter into the foam and preferably stay in the foam for as long as possible. The process of wave entering into the foam is called transmission. When transmission happens, the sound wave will “break”, or change its direction of propagation. This is called refraction of sound. The conceptual picture of the process of transmission of a sound wave from air to a soundproof foam is depicted in the figure below. Note the breaking of the sound wave direction as the sound ray enters the foam from air.

An important quantity that determines the breaking angle in refraction is speed of sound in air and speed of sound in foam. Speed of sound in air is independent of frequency and is about 330 m/s under normal conditions (room temperature, normal atmospheric pressure). What is interesting, however, is that, for frequencies between 20 Hz and 200 Hz, speed of sound in foam can depend on the frequency significantly. In particular, we see that speed of sound is as much as 3x slower in a foam than in air at around 100 Hz. This is important as the angle of refraction (the angle of bending of the sound ray as the sound ray enters into the foam) becomes very large.

In the figure above, the breaking of the incoming sound ray corresponds to the speed of sound in the foam of about 110 m/s.

We have used simulations assuming the speed of sound in foam equal to 140 m/s or about two times slower than speed of sound in air. We performed simulations using online simulator at PHET.

3D Directionality Difference Between The Pyramid Acoustic Foam And The Wedge Foam

Wedge Acoustic Foam

Consider normal incidence of a sound ray on a wedge acoustic foam first. Look at the figure

In the right part of the figure, normal incidence of a sound wave on the wedge acoustic foam is pictured. Sound wave (in blue) initially travels straight down, then gets bent as it crosses the boundary from air into the foam, then reflects of the bottom of the foam (assuming the foam is attached to the wall), and then takes up the symmetric path back up, hits the boundary foam-air on the other side of the wedge, refracts, and goes straight back up in the exact opposite direction where it came from. Thus it reflects back normal to the base, away from the wall.

Pyramid Acoustic Foam

Now consider a similar normal incidence onto the pyramid shaped acoustic foam. That is depicted on the left side of the figure above. The blue sound wave, or sound ray, impinges onto the right hand side surface of the pyramid. Depending on where exactly the sound wave hits the foam (specifically, close to the center of the side surface), it is still possible that it takes the same path as it would in the wedge acoustic foam. This is not pictured.

What can also happen, however, is that the ray, instead of going out on the left side panel of the wedge, it hits the front side of the pyramid first. What happens then is that, instead of the sound exiting in the exact backwards direction as in the wedge acoustic foam, it internally reflects and stays inside the pyramid. This is also known as total internal reflection. It may even internally reflect several more times after that before it exits the pyramid. A case of single internal reflection and exit toward the opposite (back) side panel of the pyramid is pictured on the left side of above figure.

This is our explanation why, even though the pyramid acoustic foam has less volume than the equally-sized wedge acoustic foam, it can still absorb more sound than the wedge foam, especially for low frequencies when the speed of sound is very low (as low as 100 m/s) and the internal reflection happens readily.

Diffusion Of Reflected Sound: Pyramid Acoustic Foam Vs Wedge Acoustic Foam

A sound ray that impinges on a surface of the acoustic foam or another substance that has the speed of sound different from the speed of sound in the air will experience reflection. Reflection of sound can either be specular or diffuse.

Specular Reflection

In specular reflection a single incoming sound ray results in a reflected ray going in a single direction as well. Specular reflection occurs in flat and smooth surfaces such as flat acoustic foam.

Diffuse Reflection

Diffuse reflection happens when a single ray impinging on an acoustic panel reflects in many different directions. Such diffuse reflection is helpful in a recording studio because it randomizes the waves reflected of the walls covered with acoustic foam, thereby reducing the chance of a buildup of distorting standing waves in the room. Diffuse reflection occurs in complex-shaped, or rough surfaces such as pyramid acoustic foam or wedge acoustic foam.

The set of directions of reflected sound rays is different in pyramid foam compared with the wedge foam. For example, a sound wave impinging in perpendicular direction (normally) onto the wedge foam whose ridge is in the up-down direction, can only be reflected left or right. This is due to symmetry. An example of a possible reflection is in the right part of the figure above. Notice how the wave bounces back and returns in the opposite direction where it came from. A sound wave directed normally toward the pyramid shaped foam can, however, reflect left, right, up, down, as well as in directions that are somewhere in-between. An example of such reflection of a sound wave impinging normally is in the left part of the figure above.

Similarly, there will be a more diffuse pattern of reflection off of the pyramid acoustic foam for incoming sound rays impinging in non-normal directions, compared with the wedge acoustic foam.

Overall we can say that the pyramid foam offers a more diffuse reflection pattern than the wedge foam. Pyramid acoustic foam is therefore preferable because it generally offers more diffuse reflections and is therefore less likely to allow resonant standing waves buildup.

Note On Speed Of Sound In Acoustic Foams

Speed of sound is measured to be as low as 110 m/s for in foams, as the report Jones illustrates. It turns out that speed of sound is strongly depending on the frequency of sound in polyurethane foam materials. Indeed, speed of sound approaches 100 m/s at the frequency of around 100 Hz. This has several important consequences for such important low frequencies. First, it bends the sound waves significantly due upon crossing the air-foam boundary, as illustrated above. Second, slow wave speeds allow for “packing” of more wavelengths into the relatively thin depth of the sound proof foam, therefore increasing overall absorption. This is mentioned here.

In figures on this page, we assumed frequency of sound of about 240 Hz, and we assumed speed of sound in such foam is about 140 m/s, about one half of the speed of sound in air. This is quite amazing. Such low speed of sound inside the foam can cause many internal reflections, which further amplify the absorption of sound inside the foam.

Note: Why Is NRC Sometimes Greater Than 1?

In the table above we observe that, for frequencies over 1,000 Hz, the measured absorption coefficient is often greater than one. The reason for absorption coefficient reported to be greater than one for some frequencies and some types of soundproof foam is diffraction.

Diffraction

What is diffraction? Diffraction is the deviation of the movement of the sound from the straight line, or from the sound ray behavior as we described it above. Even though sound is a wave, in many circumstances we can consider it to be a ray traveling through space on straight lines. This is what we did above. Often times this is a great description of the behavior of sound, and we can describe many phenomena this way. In the absorption coefficient formulas used in the experiment that measures absorption coefficient, and in the formula that gives the final value of NRC for a given frequency, diffraction is not taken into account.

Sound Bends Around The Corner

In simple terms, because of diffraction, the sound bends around the soundproof foam panel. Part of the sound is absorbed on the sides of the panel. This makes the measured absorption coefficient larger, even larger than 1. In particular, in reality, sound absorption coefficient can never be above 1, as this would imply that more than 100% of sound is absorbed. This would violate the law of conservation of energy. However, the way NRC and AAS are measured, often times, due to diffraction, the calculated absorption coefficient, NRC and AAS will be greater than 1.

Wave Diffraction At A Surfer’s Paradise

A great example of diffraction or bending of waves that approach an absorbing surface are waves hitting on the beach. Uluwatu surfing beach on the island of Bali, Indonesia, is pictured in the image below. As you can see, the breakers (in white) will bend around the corners of the beach. They will then hit the beach from many different directions. It looks as if the waves are trying to hit the beach at the right angle. Absorption of the wave energy happens even on the beaches that are not perpendicular to the original direction of the water waves. The length of the beach that absorbs the water wave energy is longer than the length visible from the perspective of waves far from the beach.

Difraction of ocean waves hitting a beach that bends. Surfing waves approach the Uluwatu beach from the west (left). They are absorbed by the west-facing part of the beach. The waves further to the north (up) turn south due to the bend in the Uluwatu beach. These waves hit the north side of the beach from the north. Effectively, both the west side of the beach and the north side of the beach contribute to wave absorption. When such effective increase of absorption due to a longer beach line is not taken into account, it appears as if more of the energy is absorbed than expected.

Advantages Of Pyramid Acoustic Foam And Wedge Acoustic Foam

So which foam to use in what circumstances? As discussed above, there are two advantages of pyramid acoustic foam: greater and more diverse diffusion of reflected waves, and higher absorption coefficient around 125 Hz compared with the wedge acoustic foam. The advantage of wedge absorption foam is greater absorption of sound in the 200 Hz to 1,000 Hz range.

Bottom line, if you are recording human voice, especially male voice, and it is important that the fundamental frequencies of it (around 100 Hz – 150 Hz) be as well absorbed as possible, then using pyramid acoustic foam makes more sense. If you are concerned with higher pitch instruments, then the wedge foam will absorb more. Another reason for using pyramid acoustic foam is to reduce the build up of standing waves. These build up readily between opposite and parallel walls in the recording studio.

However, when you know, approximately, where the sound is coming from, and you want maximal absorption for directional waves, then you can take advantage of the directionality of the wedge foam and the generally higher absorption coefficient of the wedge foam and use wedge acoustic foam.

Where To Place Pyramid Acoustic Foam Tiles and Wedge Acoustic Foam Tiles In A Recording Studio

In a separate post we describe positioning of different types of soundproof foam panels in a recording studio.

There we use computer simulation to investigate the differences in sound absorption of pyramid and wedge acoustic foam. We consider both normal sound incidence and oblique (non-normal) sound incidence. In simulations we go beyond the SAA and NRC measurement standards talked about in this post.

In the recording studio conditions, sound will indeed approach the sound proof foam at a variety of angles of incidence. Angles of incidence will depend on the location of the sound proof panels. These angles will also depend on the location of the sound source relative to the sound proof panels. We suggest to position pyramid and wedge sound proof foam panels away from the source so that the angle of incidence will not be too close to zero. For such larger angles we see that the wedge acoustic foam will absorb better.

Check out our review of the best pyramid shaped acoustic foam. You will find there details on the recommended pyramid acoustic foam which we couldn’t cover in this post.

For more information on wedge acoustic foams, check out our review of the best wedge acoustic foam.

We have also recently reviewed a special type of wedge acoustic foam that we call “vertical wedge” acoustic foam. See the review of the acoustic foam with vertical wedges here.

There is a great variety of sound dampening foam panels available in the marketplace. When you are building out a sound recording studio, you will have questions such as these: What type of sound dampening foam you want to use? Where to buy soundproof foam? Where to place sound dampening foam in your recording studio.

We have looked into some of the best acoustic dampening foams out there and investigated the differences between them as far as the sound propagation in them, sound reflection, sound refraction, and, ultimately, sound absorption and sound diffusion. Among these properties, sound absorption and sound diffusion are the most important.

Sound Absorption

When your acoustic damping foam absorbs sufficient amount of sound, you don’t have to worry about what happens with the remaining sound that  reflects back into the room. However, when insufficient sound is absorbed, it becomes important that the reflected sound reflects in a diffusive manner.

Sound Diffusion

Diffuse reflection means that the sound reflected off of the sound dampening foam reflects in many different directions. Then, before it finally reaches the microphone, it will have more opportunities to hit another sound dampening foam. The sound dampening foam will absorb it further then. When the diffusion is insufficient, it can happen in the worst case scenario that most of the sound from the sound source reflects directly into the microphone, which would cause a clear, most likely unwanted, echo.

Sound Dampening Foam Placement To Reduce External Noise And Internal Echoes

There are two aspects of sound dampening. The first, reduction of noise coming from the outside of the sound recording studio. The second, reduction of reflections from the walls to reduce echoes, reverberation, and buildup of standing waves all of which will adversely impact the recorded sound.

Placing sound dampening foam on the walls would have to be wall-to-wall in order to be completely effective. We have found that … are the best foams to reduce the intensity of the outside noise. Check out our more detailed findings in this post: Sound Absorbing Foam Panels For Reduction Of External Noises. The most important reason for placing sound dampening foam, however, is to reduce reflections off the walls of the sounds originating inside the recording studio.

Placement Of Acoustic Dampening Foam To Reduce Internal Reflections

We have simulated absorption of sound that impinges on the acoustic dampening foam at a certain angle off the normal. We simulated normal incidence, where the sound impinges at a right angle to the foam surface, as well as incidence angles of 15, 30, 45, 60 and 75 degrees. These incidence angles cover incidences between normal and grazing incidence. The important frequency in the simulations was around 240 Hz, corresponding to speed of sound in the foam of about 140 m/s.

We have found (see post Acoustic Sound Foam Placement In Recording Studio, Part 2, Oblique Incidence) that for normal incidence and 15 degree incidence, as well as for 60 and 75 degree incidences, the “vertical wedge” foam absorbs best, as long as it is oriented with the vertical side toward the source of the sound. We also found that for the 30 and 45 degree angles of incidence, the “narrow wedge” foam absorbs best.  In our simulations we found that the foams that absorb the most also diffuse the reflected sound the most.

Based on these findings we envision positioning sound dampening foam in the recording studio in positions relative to the source of sound which can either be the vocalist, the musical instrument, or a loudspeaker. We present the positioning of panels in the figure below, as an example.

The figure represents a schematic top view of the recording studio. The source of sound is toward the left, in the middle. The front wall is closer to the source, and you can see it on the left side. The side walls are on top and bottom of the picture, and the rear wall is to the right. The black lines originating at the source of the sound represent directions in which we should place vertical wedge dampening foam panels. The orange lines represent directions in which we should place the narrow wedge foam panels.

We see that for the front wall, sound only hits the wall under the normal, 15, 30, and 45 degree angles of incidence. The sound hits the rear end of the side wall under the 60 degree and 75 degree angles also. The angles under which the sound hits the rear wall are between 0 (normal incidence) and 30 degrees only.

Placement Of Sound Dampening Foams On Side Walls And Rotation Of Foam Tiles

In the figure below

we show a view of one of the side walls. Again, the position of the sound source is further on the left. The front wall is on the left, and the rear wall is on the right. The sound source is assumed to be positioned somewhere at the mid-height of the room. The black panels represent the narrow wedge panels while the orange panels represent the vertical wedge sound dampening foam panels.

In this view we can also show the optimal rotation of both types of foams. Our simulations show that in order for sound to enter the foams best, the vertical wedge foam should face the source of sound with the actual vertical side. Likewise, the narrow wedge foam should be oriented in relation to the sound source such that the ridge of the wedge is perpendicular to the direction of the incoming sound. This is shown in figure above by orienting the panels above and below the mid-height of the room, we will achieve better sound absorption.

Placement Of Sound Dampening Foams On Rear Wall And Tile Rotation

In the figure below

we show the suggested placement and rotation of sound dampening foams. This is for the rear wall. Again, the black foams are the vertical wedge foams. They are oriented toward the source of sound with their vertical side. The orange colored squares represent the narrow wedge foams. These are  oriented such as to face the source of sound with one of their sides. A similar suggestion about orienting wedge foams holds for the front wall as well.

How should acoustic sound treatment foam be placed on the walls and ceiling of the recording studio? The choice of sound treatment foam and its placement should insure the best absorption and remove the most unwanted distortions.

Sound distortions such as standing waves, echoes, reverbs, are all a direct consequence of sound reflections from the walls. To minimize reflections, we need to maximize absorption in the sound dampening foam. We place sound foam panels on the walls anyways. So, it would be great to know what type of foam to use in different places to maximize absorption. This is the purpose of our investigation in this post.

Computer Simulations Of Different Acoustic Sound Treatment Foam Types

We have simulated oblique incidence of sound for a good number of different sound treatment foams. These are: flat sound treatment foam, narrow wedge sound treatment foam, regular wedge foam, and vertical wedge foam. Let’s look at the results.

We Discussed Normal Angle Of Incidence Before

When absorption coefficients are reported in standardized measurements, they always only include predominantly normal incidence results. We presented investigations of various types of sound treatment foams under normal incidence in a previous post. Check it out here: Soundproof Foam Panels Placement, Normal Incidence. Here we go beyond normal incidence onto sound acoustic foam. We investigate a wide range of oblique angles of incidence from 15 degrees off normal to 75 degrees off normal.

Here We Discuss Oblique Angles Of Incidence

Simulations of different angles of incidence are important because the sound from a sound source hits the walls of the recording studio at different angles. The angle depends both on the location of the foam on the wall and the location of the sound source. It makes sense that we would want to position different types of sound treatment foam at different locations to maximize absorption.

We simulate reflections, refractions, including internal reflections inside several different types of sound treatment foam at different angles of incidence.

The angles include 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees off the normal. We comment on absorption and diffusion of sound. Both are important components, and both contribute to absorption and overall sound treatment.

The assumptions are as before, given here: Soundproof Foam Panels, Normal Incidence. Our simulations simulate sound with the speed of sound of 140 m/s in the foam. We assume speed of sound in air to be 330 m/s. These conditions are accurate for sound with the frequency of about 240 Hz. This is a very relevant frequency as discussed here. In acoustic sound foam, typically, the speed of sound will vary with frequency. Speed of sound will decrease with the decreasing frequency, as we explained here: Soundproof Foam Panels Placement, Normal Incidence. We expect the results at frequencies even lower than 240 Hz and speed of sound even lower than 140 m/s to possibly present additional surprises, but for now the speed of sound is fixed to 140 m/s in our simulations.

Best Sound Acoustic Foam For Incident Sound At 15 Degree Incidence

For the 15 degree sound wave incidence angle, the narrow wedge sound foam and the vertical wedge sound foam outperformed other geometries.

Narrow Wedge Sound Treatment Foam Results For 15 Degree Incidence

Figure below

 

shows a 15 degree incidence angle sound wave impinging on the right hand side of a narrow wedge sound treatment foam.

The refracted part of the ray, similar to results for normal incidence here, first internally reflects off the bottom of the foam, then internally reflects again and makes a whole up-and-down loop within the foam, then another up-and-down full loop. Effectively, the sound wave travels quite a long distance through the foam, and is therefore significantly absorbed.

The diffusion of the reflected waves from the narrow wedge sound treatment foam is excellent. There are at least 10 different directions in which the reflected wave leaves the foam and enters back into the room, as seen in our figure above.

Vertical Wedge Sound Dampening Foam Absorption And Diffusion Results For 15 Degree Incidence

Figure below

shows that a portion of the incoming wave impinging on the vertical side of the wedge refracts and travels nearly horizontally through the foam. Such long path of travel through the foam translates into higher absorption.

A part of the wave that reflects off of the vertical side of the wedge however, impinges on the inclined part of the wedge, and travels a short distance about vertically, and then exits the foam after reflecting off of the bottom. The path of the reflected part of the wave through the foam is therefore not that long.

The diffusion of the wave reflected from the vertical wedge sound dampening foam can be inferred from the above image as well. The initially refracted part of the impinging wave eventually finds its way out of the foam, but nearly straight backward. The initially reflected part of the wave is reflected back at a different angle, but that seems to be all the diffusion there is.

So at the 15 degree angle incidence, the vertical wedge sound dampening foam performs well for absorption at frequencies around 250 Hz, but not as well as the narrow wedge foam. The vertical wedge foam also exhibits lesser diffusion based on our simulations.

Best Acoustic Sound Foams For Reflection And Diffusion At 30 Degree Incidence

Vertical Wedge Acoustic Sound Foam Performance At 30 Degree Incidence

Vertical wedge acoustic sound foam performed best of all sound foam geometries in our simulations at the 30 degree incident angle. Figure below

 

shows a sound ray impinging on the vertical side of the vertical wedge sound dampening foam panel. As we can see, a good portion of the wave will refract into the foam and then internally reflect off of the right side of the wedge, then reflect off the bottom of the foam, and then hit the left side of the foam four wedges away, internally reflect back, and finally exit from the foam.

We can also see that various rays that will come out will have many different directions, as many as six or more. This indicates great diffusion of the vertical wedge acoustic sound foam panel.

Narrow Wedge Sound Treatment Foam Performance At 30 Degree Incidence

Figure below

 

shows refraction into and reflection off of the narrow wedge sound treatment foam, which performed second best of all foams simulated. We can see the path of the typical refracted wave first refract into the foam, then internally reflect off the bottom of the foam, and then exit the foam on the left in a symmetric fashion.

The initially reflected wave enters the foam through the neighboring wedge, and then internally reflects off the right wall, bottom wall, and then exits on the left at a different angle.

A significant number of reflected/refracted waves travel through the foam in various ways, even in one or more loops, and then exit at a variety of angles. We can count as many as ten different directions in which the sound waves exit the foam. However, the most prominent exit wave is the one that reflects only once off the bottom and then exits on the left. So diffusion of narrow wedge acoustic treatment foam at 30 degree incidence is significant if not perfect.

Best Sound Foam For 45 Degree Incidence

Vertical Wedge Sound Foam Shows Best Absorption And Diffusion

Figure below

 

shows why vertical wedge sound foam is the best performing foam for maximal absorption and diffusion. When the incidence is from the vertical side of the foam, the refracted wave internally reflects off of the slanted side of the wedge, then bounces off the bottom, and the internal reflection off the bottom is then reflected internally from the slanted slope to return and make one more trip down and up the foam. This significantly increases the traveling path of the wave and thus absorption.

In addition, the diffusion of the waves from the vertical foam is significant, in the figure above we can count at least six different directions in which the reflected waves are traveling back into the room.

Narrow Wedge Sound Foam Panel Is The Runner Up For 45 Degree Incidence

Figure below

 

shows why narrow wedge sound foam panel is the runner-up for the best absorption and diffusion performance among the various geometries of sound foam panels. Initially refracted wave first internally reflects off the opposite side, then internally reflects off the bottom, and finally exits the foam in a symmetric fashion. However, the initially reflected wave hits the opposite side of the wedge, refracts, and enters into the neighboring wedge at an almost normal incidence. Then, it internally reflects from the other side of the neighboring wedge, internally reflects off the bottom of the foam, and then internally reflects off of the side of a wedge, and makes another round through the foam. This causes the traveling path to be quite long and provides for high absorption.

As for the diffusion, we can count at least a dozen different directions into which reflected and refracted/reflected waves exit the foam back into the room. The narrow wedge sound foam will provide excellent sound diffusion.

Incident Angle 60 Degrees: Best Absorbing And Diffusing Sound Foam Panels

Narrow Wedge Sound Foam Panel Wins

Figure below

 

shows the 60 degree incidence of a wave onto the side of the narrow wedge sound foam. The initially refracted wave proceeds to internally reflect off of the opposite side of the wedge, then internally reflects off of the bottom of the wedge, and then makes at least one if not two or three internal loops internally reflecting/refracting through the wedges, and internally reflecting off the bottom of the sound foam panel. This provides for an extremely long path through the foam and great absorption.

Similarly, diffusion is excellent. We can count at least 14 different directions into which the reflected waves travel back into the room.

Vertical Wedge Sound Foam Panel, The Runner Up For 60 Degree Incidence

Vertical wedge sound foam panel reflections and refractions after the 60 degree incidence are shown in the figure below.

The incidence should be from the vertical side of the wedge for vertical foam panel to be effective. In the Figure we see the initially refracted wave to internally reflect off of the slanted side of the vertical wedge, then internally reflect off of the bottom of the foam, internally reflect off of the slanted side of another wedge next, internally reflects off the bottom again, and finally exits the foam. Such long path inside the sound foam panel assures good absorption.

As for diffusion, there are at least 9 different angles into which the sound reflects back in the room. That indicates solid diffusion.

Best Acoustic Sound Foams For 75 Degree Incidence

Narrow Wedge Sound Foam, Best Absorption And Diffusion At 75 Degree Incidence

Figure below

 

shows a 75 degree incidence of a sound wave onto the narrow wedge sound foam. The initially refracted wave proceeds to internally reflect off of the opposite side of the narrow wedge. It then internally reflects off the bottom of the foam. Then, that wave proceeds to internally reflect off of the wedge two removed from the original wedge. It then refracts through the wedge one removed from the original wedge. Finally, that sound wave makes one more circle through the depth of the foam. First, the wave internally reflects off of the original wedge. Then it reflects off of the bottom of the foam. Then it reflects off of the wedge one removed from original. Finally it exits the foam.

As for diffusion, we can see at least eleven directions in which the parts of the wave reflect back into the room, signifying solid sound diffusion.

Vertical Wedge Foam: Runner Up At 75 Degree Incidence Into Vertical Edge

Figure below

shows an interesting pattern of internal reflection for 75 degree incidence. This pattern occurs when the sound impinges onto the vertical edge. First, the initially refracted wave internally reflects off of the slanted side of the wedge. Then, the wave internally reflects off of the flat bottom of the foam. Then, it internally reflects off of the wedge three removed from the original wedge. Subsequently, it internally reflects off the bottom of the foam. Finally, it exits the foam. These two back-and-forth reflections cause the path of the wave to be quite long, which should assure good absorption.

In line with multiple internal reflections, the corresponding diffusion pattern shows at least 9 different directions in which the wave reflects back into the room, none of which is dominant. This warrants above average diffusion.

Conclusion: Best Acoustic Sound Foams For Different Angles Of Incidence

We simulated sound waves impinging on a variety of sound foams at different angles of incidence. Our simulations were done assuming speed of sound of 140 m/s in the foam and 330 m/s in the surrounding air. Frequencies of sound around 240 Hz propagate with such speeds in foam and air. As foams will be placed on the walls and possibly ceilings, each soundproofing foam panel will have a different angle of incidence from the sound source.

We define angle of incidence to be the angle between the incoming sound ray and the normal to the flat bottom of the acoustic sound foam.

You will have to estimate that angle of incidence of the sound. One line of the angle should go from the sound source to the point on the wall. The other line should be normal to the wall at that point. You should then pick the type of foam that absorbs and diffuses best for that angle of incidence.

We simulated here the normal incidence where angle of incidence is zero.  We also simulated oblique incidence where angle of incidence was 15, 30, 45, 60, and 75 degrees. Based on the highest absorption in the foam and best diffusion of sound reflected back, two clear winners emerge.

Vertical Wedge Sound Foam Wins At Small Angles Of Incidence

For normal incidence up to 15 degree incidence, the best performing geometry is vertical wedge acoustic foam. The vertical side must be facing toward the source of sound.

Our simulations showed that, with these geometries, the sound will make as many as two or more round trips between the shaped surface and the flat bottom of the foam. In addition, that path is not straight up and down. Instead, it involves a significant, long path, in general left-right direction parallel to the bottom of the foam. This long a path is the reason for higher absorption. See, figures above under 15 degree incidence.

Likewise, such long path in a variety of directions reflects and refracts several times, going from air to foam and back several times. Each such transmission gives rise to both reflected wave and refracted wave. This great number of reflections and refractions on multiple surfaces, in turn, contributes to high diffusion of the waves that ultimately reflect back into the room.

Narrow Wedge Sound Foam Wins For Intermediate Angles Of Incidence

Foam panel of a narrow wedge  type has a geometry with the top angle less than 60 degrees. An example of narrow wedge foam is soundproofing foam Auralex Studiofoam Wedgies.  We used the term regular wedge for foams with the top angle of 60 degrees or more.

Our simulations are based on the assumed speed of sound of 140 m/s in the foam. Speed of sound in the air is assumed to be 330 m/s. The best performing foam for the intermediate angles of incidence of 30 and 45 degrees was the narrow wedge acoustic sound foam.

For these angles of incidence, the narrow wedge foam shows the desirable effect of sound being “trapped” inside the foam. There are several back-and-forth cycles that involve several paths between the bottom of the foam and the structured part. Also, there are several trips left-and-right before the sound ray finally exits the foam and returns to the room. This should provide a long path over which the absorption of sound will be significant.

Vertical Wedge Acoustic Sound Foam Best For Large Angles Of Incidence

For angles of incidence of 60 and 75 degrees, the winner, again, is the vertical wedge acoustic soundproof foam. The foam must be facing the source of sound with the vertical side. This side allows the initial wave to predominantly enter the foam with little reflection. Then, several internal reflections later, the wave again has bounced several times from the bottom of the foam and the structured top of the foam. The wave exits after spending a significant travel path in the foam. This path is much longer than the height of the foam. This assures enhanced absorption.

Diffusion of the vertical wedge sound foam is solid as well for large angles of incidence. It is, however, not as large as under other angles of incidence. The gamut of directions in which the reflected waves ultimately reflect is surprisingly wide. It includes angles of reflection from normal to grazing, and everything in between.

We discuss best placement of acoustic sound foams further in this post: Sound Dampening Foam Panels Placement. Our findings from this post are included there.

We will discuss flat soundproof foam panels, pyramid soundproof panels, and a variety of wedge soundproof foam panels. We will find out how each of them can best contribute to the improvement of recordings in your sound recording studio by removing room-related distortions in the recordings.

By simulating a variety of angles of incidence for each of the different geometries of foam panel surfaces, we find out which foam geometry is best suited for a specific location in the room.

Reflection-based Distortions That Acoustic Soundproof Foam Can Reduce

The types of distortions that can ruin your recording discussed here include echoes, reverberation, and standing waves. Reflection of sound from the walls and other objects in the recording studio causes all of these three distortion effects.

For instance, wall-to-wall standing waves build up after several bounces of the sound from the studio walls. After several bounces, the wave begins to constructively interfere with itself. This interference creates strong standing waves at specific frequencies that are resonant in the room. These resonant frequencies become disproportionally represented in the recording. They distort the sound balance.

Echoes, as another example, are, again, caused by multiple reflections of a short sound wave from walls. Echoes cause multiple repeated pickups of the original sound signal, possibly attenuated, in the microphone.

All of these distorting effects are a consequence of sound reflection. It is therefore plausible that reducing sound reflection from walls in the recording studio will possibly reduce all of the reflection-based distortions: echoes, reverberations, and standing waves.  One of the best ways to reduce reflections is through judicious placement of soundproof foam panels.

Soundproof Foam Panel Types For Distortion Reduction Compared In This Post

Acoustic soundproof foams have been used as acoustic treatment for a long time. They have proven to be an efficient means of improving the sound of recordings both in home studios and in professional recording studios.

These are the types of acoustic soundproof foams that we will compare in this post: Pyramid Acoustic Treatment Foam, Regular Wedge Acoustic Foam, Narrow Wedge Acoustic Foam, Vertical Wedge Foam, and Flat Soundproof Acoustic Foam.

Superb Acoustic Foam Soundproofing In The Frequency Range Above 500 Hz – 800 Hz

We will focus in this post on performance and placement of various soundproof foam panels based on their absorption properties for frequencies lower than 500 Hz. These frequencies are important as the fundamental frequencies of both male and female voices. The sub-500 Hz frequencies are also fundamental frequencies of many musical instruments’ low-to-mid tones. As we can see from the table below, sound absorption in wedge-type foam and pyramid-type panels is superb for all sound frequencies above 800 Hz. This holds true for flat-type foam panel of 2 inch thickness as well.

 

Check out the above table of sound reduction coefficients. Observe that a 2 inch thick wedge acoustic damping foam will absorb over 90% of sound in normal incidence conditions for frequencies above 500 Hz. A 2 inch thick pyramid soundproof acoustic foam will absorb over 90% of sound in normal incidence conditions for frequencies above 800 Hz. A thicker, 3 or 4 inch foam will absorb over 90% at even lower frequencies.

So, as far as over 800 Hz frequencies of sound are concerned, many types of acoustic damping foams will work well, even under the normal incidence conditions. Let’s turn our attention now to sub-800 Hz frequency range.

Physical Properties Of Soundproof Foam Panels At Sub-800 Hz Frequencies: Speed Of Sound, Absorption

Check out the table above. The absorption coefficient for normal incidence is severely reduced for frequencies below 800 Hz. The absorption starts from nearly perfect 100% absorption of the sound above 800 Hz. It ends up at around 10% absorption in the 100-200 Hz frequency range. There is a great reduction in overall absorption as the sound frequency drops.

Absorption behavior in the frequency range below 800 Hz therefore becomes crucial for the distortion elimination in a sound recording studio. We will see here how the right placement of the right type of soundproof foam in the recording studio can have a big impact on noise and distortion elimination.

Speed of sound: It is interesting that acoustic foams are very peculiar when it comes to speed of sound propagating through them. Foams are made of solid frame and are filled with air, yet speed of sound in acoustic foams is lower than both speed of sound in the air and speed of sound in bulk solid frame. Furthermore, speed of sound diminishes with frequency, which is not common in solid materials, liquids or gases. Figure below shows speed of sound in acoustic soundproof foam adopted from this source.

Figure shows approximate speed of sound in foam as a function of sound frequency. For our purposes in this section we will work with a representative frequency of 240 Hz. This implies the speed of sound of 140 m/s. This is significantly lower than speed of sound in air which is approximately 340 m/s.

Refraction And Reflection Of Sound On Flat Soundproof Foam-Air Boundaries

The much lower speed of sound in soundproof foam panels has consequences. One is strong refraction of sound waves that hit the acoustic foam surface. Refraction means bending of the direction of the sound wave when the sound wave passes the air-foam boundary. The lower the speed of sound in foam, the more the sound wave will bend.

Another important behavior is sound reflection off of the air-foam boundary. In reflection, the sound bounces back into the air without entering the foam.

Both the reflection and the refraction behavior in acoustic soundproof foams can be simulated easily. We used an online simulator on PHET. This is intended for simulations of light bending upon refraction and reflection. However, the laws of refraction and reflection are similar for any type of wave. In particular, the bending angle in refraction depends on the ratio of wave speeds in air and in the acoustic foam. Likewise, the angle of reflection is the same as incident angle for reflection of both sound and light waves.

Illustration Of Sound Refraction And Reflection On An Air-Soundproof Foam Boundary

The illustration below shows a flat foam, in gray-blue. In the image, you can see refraction and reflection of a sound wave, in shades of red. The reflection happens on the boundary between air, in white color, and the flat soundproof foam. Dark red stands for high intensity of sound, while the lighter red line represents an attenuated sound wave.

 

The sound wave originates at the source on top right. The sound ray is a directed line representing the position, the direction of motion, and the trajectory of a sound wave. We assume in this picture that the sound is traveling in air with the speed of 330 m/s and in foam with the speed of 140 m/s.

Below the sound source is the flat variety acoustic soundproof foam. When the sound ray first hits the surface of the foam, it is partially reflected back into the air. This reflection obeys the law of reflection. This is represented by a fainter red line pointed back up, and still to the left. At the same time, a part of the wave is refracted into the foam, following the law of refraction. This is represented by a dark red line directed in the direction toward the bottom of the foam. Next, the sound ray hits the boundary between the bottom of the foam and the air below or the wall below. The wave is internally reflected and starts to move back up toward the room. A few more reflection/refraction occurrences happen until the entire sound wave exits the foam, either back into the room, or out through the wall.

One can clearly envision that, the longer the path of the sound ray through the foam, the more sound will be absorbed.

Investigating Reflection, Absorption, And Diffusion Of Sound For Acoustic Soundproof Foams

Given the accessible tools, we chose to investigate reflection, absorption, and diffusion of different shapes of acoustic soundproof foams. We focused on a foam that has speed of sound of 140 m/s, which, in turn, corresponds to frequency of sound of 250 Hz.

In this and in the accompanying post, we consider five different types of soundproof foam, pyramid, regular wedge, narrow wedge, vertical wedge, and flat soundproof foam. We perform computer simulations of sound waves with the intent to determine which type of foam absorbs the most sound at a given angle of incidence.

We vary the angle from 0 (normal incidence) to 15, 30, 45, 60, to 75 degrees. Then, we compare the different geometries of acoustic soundproof foams. We compare both the length of sound path inside the form, and by the diffusion of the reflected sound.

Why look at the length of the sound path inside the foam? Because, the longer the path, the more of the sound will be absorbed.

Why look at the diffusion of the reflected sound? High and random diffusion is important because it prevents the creation of prominent standing waves through back-and-forth reflections in the recording room.

Normal Incidence Results For Best Absorption And Diffusion

Based on speed of sound assumed above, we find that the best performing geometry is narrow wedge, followed by vertical wedge.

Narrow Wedge Acoustic Treatment Foam Results For Normal Incidence

Let’s look at the pattern of a sound ray entering and bouncing off a narrow wedge acoustic treatment foam in figure below.

The original sound ray impinges straight down onto the steep incline of the narrow wedge. It then splits into the refracted part, going into the wedge, to the right, and the reflected part, bouncing off the steep wedge.

The refracted part of the sound wave bounces off the side of the panel, then bounces off the bottom of the panel again, and makes a whole loop through the wedges, then another, and possibly another, before it finds its way out of the foam. The path that circles multiple times around the foam provides for significant absorption due to its length.

The reflected part of the sound wave refracts into the foam through the neighboring wedge on the left, makes one bounce off the bottom of the foam, and exits through a wedge four wedges away, at an angle. This means that the reflected wave is not reflected straight back. Instead, it contributes to diffusion of the reflected waves.

Overall, as seen in the image, the diffusion is quite significant. We see about 10 distinct directions of outgoing sound rays. This is a sign of significant diffusion of the reflected waves.

Vertical Wedge Sound Foam Results For Normal Incidence

Figure below

shows bouncing off of a sound ray off of a vertical wedge acoustic dampening foam. One of the surfaces of the wedge is vertical, thus the name “vertical wedge”. The refracted part of the sound ray is stronger than the reflected here.

The refracted part enters the foam toward the right, then bounces off the bottom of the foam, and then makes a whole loop through the wedges, another half loop bouncing off the right side, the bottom, and finally finds its way out to the left side. The length of this sound ray is significant as well, indicating good absorption under the normal incidence angle.

The diffusion of the reflected wave in this case is not very significant, but there is no ray reflected straight back.

The other acoustic dampening foam geometries, flat foam, regular wedge, and pyramid, did not perform as well in this simulation.

Conclusion: Our choice for acoustic soundproof foam with best absorption of low frequencies/best diffusion of low frequencies for normal incidence is narrow wedge type foam.

Check out our review of one of the best such narrow wedge soundproofing foams.
Our review of a runner up, vertical wedge soundproofing foam is here.

For simulations on what foam works better at incident angles other than normal incidence, see review of foam performance under oblique incidence here. Reading this part is important. You will be able to fully understand our choices for placement of different types of soundproof foam panels in different places of the recording studio.

Final Conclusion: What Soundproof Acoustic Foam To Purchase And Where To Place It

Figure below

 

shows a top view of an example recording studio. The front wall is on the left, the side walls are on top and the bottom, and the rear wall is on the right. The circle on the left represents the position of the source of sound. The thin rays originating in the circle represent the directions of sound rays originating at the source of sound such as loudspeaker. The black rays point to the positions on the walls where the wedge foam should be placed.  You should turn the vertical side of the wedge toward the source of the sound. The orange rays point to the positions of narrow wedge soundproof foams. Again, the orange lines represent the lines of the ridges of the wedges.

Positioning Soundproof Foam Panels On The Side Wall

Figure below

shows a side view of a side wall belonging to the same recording studio. Here we see the flat side of soundproof panels. We also see their recommended orientation. The black panels represent vertical wedge soundproof foam panels while the orange panels represent narrow wedge soundproof foam panels. The position of source is the same as in the top view picture, about one fifth of the way from the left (rear) wall to the right (front) wall. The panels on the side wall closest to the sound source should be the vertical wedge panels. Following them should be a layer of narrow wedge panels. This, again, is followed by the layer of vertical edge panels.

The height of the sound source is assumed to be at the middle of the height of the room in the figure. At this level, all of the ridges of both vertical edge and narrow wedge soundproof foam panels should be vertical, except for the vertical wedge panel closest to the source of sound which should be horizontal. As stated before, all vertical edge sides should be facing the source of sound.

You should turn the soundproof foam panels that are either higher or lower than the height of the sound source in the direction toward the source of sound. The side of the wedge (vertical side in case of vertical wedge panel) should be directed toward the source of sound. This means that some of the panels will be tilted as shown in the figure.

Positioning Soundproof Foam Panels On The Rear Wall

Figure below

 

shows the optimal positioning of the soundproof panels on the rear wall, behind the sound source. This is an example only. The single sound source is located in front of the rear wall, at the mid height, and at the mid width of the rear wall, approximately half of the height away from the rear wall. You should consider the typical positions of sound sources in your case. These sources include various musical instruments, loudspeakers, or vocalists.

Based on the optimal choice of soundproof foam panels, we suggest the optimal positioning of the foam panels. Optimal positioning is as follows: In the center of the rear wall you should place the vertical wedge panel, with its ridges oriented horizontally. Up, down, left and right of the central vertical wedge panel, you should place four narrow wedge panels. These should have their ridges perpendicular to the line connecting them to the center of the central panel, see the figure. This placement leaves empty space at the edges and corners of the room. There, you can place supplemental soundproofing materials. A great choice would be to use bass traps, see Project 2 Roominator Kit Review.

Auralex Studiofoam Wedgies is considered by Auralex as “a great solution for spot treatment of sound studios”. They only offer Wedgies in one color, charcoal gray, and one size, one foot by one foot. However, in our simulations, we have found that Studiofoam Wedgies come closest to what we termed “narrow wedge” soundproofing foam. In our simulations, we often found that the narrow wedge foam performs better than what we termed “regular wedge”. Regular wedge soundproofing foam would correspond to the Auralex Studiofoam Wedge soundproofing foam.

Auralex notes, correctly, that Studiofoam Wedgies have a larger surface area than Studiofoam Wedges. This is true. A larger surface are does, in certain circumstances, improve sound absorption. Studiofoam Wedgies have a larger number of wedges per foot than Studiofoam Wedges. Thus, not only is the surface area greater, but also the “wedge angle” in Wedgies is less than the “wedge angle” in Studiofoam Wedges.

Let’s go into more details of the claims of better performance, and let’s review Auralex Studiofoam Wedgies, and compare them with their counterpart Studiofoam Wedges as we go along.

Dimensions, Material, Density Of Auralex Studiofoam Wedgies

Auralex Wedgies come in 1 ft by 1 ft squares. There are 15 wedges in each. This is more than 12 wedges per two foot in Auralex Studiofoam Wedges. This means that the base of each wedge in Studiofoam Wedgies is 1.6 in. long. Each wedge’s height is 1.5 in. A relatively larger height makes Auralex Wedgies fall under the “narrow wedge” category. We will see down below that such narrow wedge foam has better acoustic properties, especially for critical lower frequency where speed of sound diminishes and the foam surface geometry, not just foam surface area, starts to play a greater role.

Wedgies are made of high density open cell polyurethane rubber material. Its surface density is 0.83 kg/m². While this is a relatively high density for a foam, Auralex Wedgies is still a featherlight material, and it is very easy to mount or glue on the walls and ceilings.

Speed Of Sound And Dispersion In Soundproofing Foam

Speed of sound in polyurethane foam actually varies with frequency of sound. This is the meaning of the word “dispersion”. This behavior is quite unusual. In general, speed of sound in acoustic foam will be lower than speed of sound in air. The speed of sound actually tends to approach zero as frequency of sound approaches zero. Practically, this means that for very relevant frequencies in the 100 Hz – 300 Hz, where fundamental frequencies of both male and female voice, as well as fundamental frequencies of many musical instruments, lie, the speed of sound can be as low as 100 m/s or less, compared with the speed of sound of 330 m/s in air.

Sound Absorption And Noise Reduction Coefficient

In the table below, we compare sound absorption coefficients of Studiofoam Wedgies and Studiofoam Wedges.

Role Of Surface Area And Shape

As Auralex states, due to 15 wedges per foot in Studiofoam Wedgies, as opposed to lesser number in regular Studiofoam Wedges, the Wedgies will have larger surface area. That is true because each wedge adds approximately equal amount of surface area. However, for absorption, it is not only the surface area that matters, but also volume, and, in particular, the angle of incidence of the sound wave onto the wedge surface. Due to the larger number of wedges per foot in Auralex Wedgies, and due to the same height of an individual wedge, the wedges in Wedgies are significantly narrower. We call this type of wedge foam a “narrow wedge” as opposed to “regular wedge” in Auralex Studiofoam Wedge soundproofing foam.

Because of the top angle of the wedge is smaller in Wedgies, the same incoming sound wave will impact under a much different incident angle, and will be sent upon transmission into the foam in a significantly different direction. Because of that, its path could be much longer or shorter inside the foam, therefore the sound could be absorbed much more or less. We will study these differences, and how they affect optimal placement of Auralex Wedgies in the recording studio, below.

Sound Absorption Of Auralex Wedgies For Various Angles Of Incidence

Absorption At Normal Incidence

Figure below shows a simulation of a normal incidence of a sound ray

onto a narrow wedge, Wedgie-like acoustic foam. We observe that it is possible at certain impact locations, that the normally impacting sound ray (in red) will be partially transmitted into the foam, then will totally internally reflect off the bottom of the foam, then totally internally reflect off the other, left, side of the narrow wedge, two wedges away. Then, it will bounce back to the right, pass two wedges in total, and do one more circle back down into the bottom of the foam, and then experience another loop before it finally exits the foam back into the room. This long, double, loop means a long path through the absorbing foam, which means high absorpti
When we compare these results with [Auralex Studiofoam Wedges review] the review of Auralex Studiofoam Wedges, we notice some of the same characteristics, and some differences. The multiple loops made by the sound ray can be observed with Studiofoam Wedges as well, though the details of the directions are different. There is no apparent clear winner when it comes to absorption at normal incidence at low frequencies. This is also seen in Table above where Wedges performs better at 100 Hz, 160 Hz and 200 Hz while Wedgies performs better at 125 Hz, for the normal incidence sound.

Absorption At 15 Degrees

In the figure below a 15 degree incidence onto a simulated Studiofoam Wedgies

geometry soundproofing foam is shown. We observe that the part of the incident wave that refracts into the foam on the right behaves similarly as the normally incident wave behaved. It bounces off of the bottom surface, hits the opposite side of the wedge on the left and partially exits at an 15 degree angle to the left, and partially internally reflects back into the wedge, and makes another loop back to the bottom of the foam and back into the wedge. This indicates good absorption for the part of the wave that makes into the foam upon initial incidence.

The part of the impinging wave that reflects off the wedge on initial approach makes it easily into the neighboring wedge on the right, and then starts a trip at a low-slope angle toward the right edge of the foam tile, where it reflects off the vertical side. This nearly horizontal, long passage through the foam makes for good absorption too.

Absorption At 30 Degrees

In the figure below we see that the effect of “looping” back and forth

between the wedge side and the bottom side of the foam is still there, but less pronounced. Instead, as compared with the 15 degree incidence and especially normal incidence, we see that, because the 30 degree incident wave is closer to being normal to the wedge side on impact, more of the wave refracts into the foam, and, likewise, more of the wave exit on the left after just one internal reflection on the bottom of the foam. This is the behavior of the flat foam, a foam with the flat surface, and is the so called specular reflection. Since a lot of the sound exits back into the room after just one reflection off the bottom, the absorption is less than that at 15 degree incidence.

Absorption At 45 Degrees

Figure below shows what happens when the angle of incidence is 45 degrees.

At this angle, it becomes very likely that the incident wave will refract into the foam (due to near-normal incidence onto the wedge surface) and then totally internally reflect off of the opposite side of the same wedge. This is shown in the figure. After that, the wave bounces off the bottom of the foam and exits out of the neighboring wedge to the right. This, again, is a typical reflection behavior in specular reflection. The path through the foam is short, thus absorption will not be great at this angle of incidence. Likewise, the dispersion is not great as the majority of the wave will reflect back obeying the law of reflection.

Absorption at 60 Degrees

Figure below shows a simulation of a 60 degree incidence onto the Studiofoam Wedgies type

foam tile. Note that the elements used did not allow to simulate the entire tip of the wedge, which makes the actual path a bit different, but the main conclusion still stands. The sound ray enters the third wedge from the left at an 60 degree angle from the normal, which is nearly normal to the surface of the side of the wedge. The wave enters the foam with little reflection, and then totally internally reflects off the other side of the wedge, the bottom of the foam, and off the neighboring wedge. It then repeats the loop, but at the next wedge.

This bodes well for absorption as the wave is trapped in the foam along a relatively long path. As seen in the figure above, the sound does exit back into the room, but at a variety of places and at a variety of angles, so the diffusion is good.

Absorption At 75 Degrees

The figure below depicts the path of the sound wave as it enters the foam at a 75 degree angle

of incidence (measured, as usual, from the normal). The incoming wave transmits under about 90 degree angle into the side of the foam on the right. The wave then totally internally reflects off of the left side of the same wedge. It continues down toward the bottom of the foam. There, it nearly totally reflects back up and completes the internal reflection loop. This loop repeats again. Due to this looping, the path of the wave will be quite long inside the foam. Therefore, the absorption will be significant. As one can see in the figure, the diffusion is looking good as well due to a great variety of angles in which the sound wave finally enters back into the room. This result compares favorably with the result for a “regular wedge”, or Auralex Studiofoam Wedge type foam.

Conclusion: Placement Of Auralex Studiofoam Wedgies

Based on the results above, we can see Auralex Wedgies being used effectively in many different situations. They show best results for angle of incidence around 15 degrees. The simulation shows Auralex Wedgies absorbing well at 60 and 75 degree angles of incidence as well. The Wedgies seem to perform well at normal incidence. They seem to do better at 60 to 75 degree incidence. Whenever possible they should be used instead of regular wedge foam at these angles. For more information on placement or soundproofing foam, see Soundproofing Foam Placement For Recording Studio.

Bottom line, we find that, Studiofoam Wedgies can be used effectively for much more than “spot treatment of sound studios”. Due to their narrow wedge structure, they have unique capacity to absorb sound at low frequencies. We have showed that for certain angles of incidence such as near normal, and for 60-75 degree incidence. Their diffusion properties for these angles of incidence are superb also.

Fire Retardancy

Studiofoam Wedgies are made of open cell, polyurethane based foam that is fire retardant. We could not confirm that they have A Rating for Fire retardancy. We suspect that they do have A Rating. After all, the Auralex Studiofoam Wedges have A Rating. See also recent ASTM E-84 Fire Rating Test report Auralex Rating).

Durability

Unlike some other soundproofing foams, Studiofoam Wedgies are not made of melanine but of polyurethane. Therefore, they will be durable and will not crumble over time.

Appearance: Colors And Look

Auralex Studiofoam Wedgies are only available in charcoal gray color. This color will match other colors that are available for other Auralex foam products.

Accessories

We recommend Foamtak spray-on adhesive to attach Wedgies directly to the wall. You apply Foamtak lightly to achieve a temporary mount. You apply it heavily for a more permanent mount.

Availability

Auralex Studiofoam Wedgies are available in single packs and four packs at SamAsh.com.

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Are you looking for a great performing acoustic foam for your home recording studio, one that is convenient, light, easy to install? Do you want a foam that absorbs a significant portion of the sound that hits it and therefore increases the sound quality of the recordings? If so, you will find Designer Series Treatment (DST) acoustic wedge foam by Auralex a serious contender.

We will investigate physical properties of Auralex DST 114 and similar foams, especially as it comes to sound absorption in a realistic situation of a sound recording studio. The results will apply to a sound booth as well.

To summarize, Auralex DST 114 is a great foam, made of a great acoustic foam wedge material, and, on top of that, shaped perfectly to be placed in multiple locations in the recording studio. We are basing these strong statements both on data presented in specification sheets, as well as on our data from simulations of sound impinging on such acoustic wedge foam, both of which are presented below.

We call this type of acoustic wedge foam a “vertical wedge” foam because one of the sides of the wedge is perpendicular to the base. If you think of base as being horizontal, then that side is vertical, thus the name.

We will investigate qualities of Auralex DST vertical wedge foam such as density and dimensions, speed of sound in the foam and dispersion, surface shape, diffusion, absorption, fire retardancy, durability, and finally, appearance. We will suggest best placement of this vertical foam in your recording studio.

Auralex DST 114 and DST 112 Acoustic Foam Material Properties And Dimensions

Auralex DST foam material is a very low density open-cell foam which assures high absorption at mid to high frequencies, and light weight for ease of installation. The reported nominal density is 2 lbs/ft³ or about 38 kg/m³. This is only about 4 percent of the density of water. The 2 inch foam is 0.5 inches thick at the valley and 2 inches thick overall. The tile comes in a single size but different number of foam wedges: DST 114 is a 1 ft by 1 ft tile, 2 in tall and has four wedges. DST 112 is a 1 ft by 1 ft tile, 2 in tall and has two wedges.

The number of wedges is the biggest difference between the two. Correspondingly, the vertical side of the wedges are about the same, but the slanted side is about twice as long in DST 112 as in DST 114. The four-wedge DST used to be available as DST 224 having 2 ft x 2 ft tiles and as DST 244 having 2 ft x 4 ft tiles but we could find no sources for DST 224 and 244 anymore.

Speed Of Sound And Dispersion In Auralex DST 114 and 112 Foam

Speed of sound in Auralex foams is one of the reasons why Auralex foams absorb so well. For the relevant range of frequencies below 2,000 Hz in the audible range, speed of sound in acoustic foam is below the speed of sound in the air. This is an unusual property of acoustic foams. Normally, both liquids such as water, and solids such as plastic, have speed of sound that is higher than speed of sound in the air. Speed of sound in air is about 330 m/s and is about constant for all audible frequencies. Speed of sound in the acoustic foam, however, is lower.

Moreover, speed of sound in acoustic foams exhibits a property of dispersion, which means that speed of sound varies with the frequency of sound. It tends to go to lower values as the frequency of sound is lowered. See the reference Jones for one example of dispersion in acoustic foam.

It is important that speed of sound is lower in the acoustic foam because the sound transmission across the air-foam boundary depends strongly on the speed of sound in the foam and in the air. Based on the data available for acoustic foams, we have assumed in our simulations, below, that speed of sound is 140 m/s at the frequency of 240 Hz, which is consistent with reference Jones.

Absorption: Experimental Sound Absorption Coefficients For DST-112 And DST-114 Acoustic Foam

Here is the table of experimentally obtained sound reduction coefficient for both DST 112 and DST 114:

 

For comparison, Auralex Studiofoam SonoFlats (flat foam) tiles’ absorption coefficients are given, too. Experimentally, under normal incidence that was measured, absorption is consistently better for DST 114 than for DST 112 at lower frequencies. At 100 Hz, both DST 112 and DST 114 have better absorption than the 2″ SonoFlats. Since both DST 112 and DST 114 contain less acoustic foam material than the wedge-free SonoFlats, this behavior can only be explained by their different shape.

Surface Shape Effects For DST 114 and DST 112

 

The main difference between Auralex DST 114 and DST 112 is in the number of wedges in a square foot tile. The DST 112 has two relatively shallow vertical wedges while the DST 114 has four more spiky vertical wedges. In DST 112 the angle of the slanted side of the wedge with the base is less than the corresponding angle in Auralex DST 114. The angle in DST 112 is about 15 degrees to the base. The angle in DST 114 is about 30 degrees to the base.

We have seen elsewhere that acoustic foam shape of DST 114 will give good absorption at normal incidence, at 15 degrees, as well as at 60 degree and 75 degree incidence. Now we want to see if there are indications that DST 112 might outperform DST 114 at any of these angles.

Which Panel Soundproofs Against External Sounds Better?

We have discussed here: Best External Sound Absorbing Foam that some acoustic foam shapes are better than the others in soundproofing the recording space. The simulations were performed for all-important frequencies around 240 Hz which are within the range of the human voice frequencies. What that means is, when the sound from the outside coming in through the wall and hitting the bottom foam surface (the one attached to the wall). We found, in particular, that the foam of the DST 114 shape is very good at absorbing external sound coming at a normal angle directly from the wall. The figure below

shows how the impinging sound ray from the bottom gets trapped in the vertical wedges because of perfect internal reflection on the wedge. In contrast, for the same frequency, figure below

shows that a lot of the sound impinging on the bottom of the foam of the DST 112 shape passes the foam and, for the largest part, refracts directly into the room. We can see in the figure that the part of the sound that internally reflects off the side of the wedge and returns into the foam indeed stays inside a foam for a while. That is a small part of the total sound, however. In conclusion, here is much less soundproofing with the flatter DST 112 than there is with the larger-wedge-angle DST 114. This is due to the shallower wedge angle of the DST 112 as compared to DST 114.

Normal Incidence From The Room To The Foam

DST 112

Figure below

 

shows a typical case of normal incidence on a DST 112-type vertical wedge acoustic foam. We see that the incoming ray refracts into the foam and then bounces off the bottom and off the top, wedged, side, several times before it finally leaves the foam. Most of the internal reflections are of the “total reflection” type. This means that none of the sound leaves the foam upon encountering the boundary from the inside. Altogether three round trips can be counted. In comparison, a similar behavior is found in the DST 114-type acoustic wedge foam.

DST 114

Figure below

 

shows an example of normal incidence of a sound wave on a DST 114-type vertical wedge acoustic foam. The incoming ray refracts into the foam and travels to the bottom and back to the top, wedged, side several times. Two round trips can be counted before the sound ray leaves the foam. Again, most of the reflections inside the foam are of the “total reflection” type, meaning that no sound leaves the foam upon encountering the boundary.

This behavior for both the DST 114 and DST 112-type foams is much unlike the behavior of a flat foam upon normal incidence. While back-and-forth internal reflections are still present, they are never 100% efficient. The wave always encounters the boundary at a right angle. A part of the wave will always leave the foam when it hits its boundary at a right angle. This could explain why, as seen in Table above, the vertical wedge acoustic foams DST 112 and DST 114 exhibit a higher sound reduction coefficient than the more massive but wedge-free SonoFlat acoustic foam.

So what might be the reason that DST 114 absorbs more for lower frequencies? The reasons are yet unclear, however, the 15 degree incidence simulations show that DST 114 indeed should have better absorption at this slightly off-normal angle.

15 Degree Angle Of Incidence From The Room Into The Foam

DST 112

Figure below

 

shows the sound ray impinging on a simulated acoustic wedge foam of the “vertical wedge” type such as DST 112. Notice that the pattern of back-and-forth internal reflection is still there. However, the first incidence from the inside of the foam toward air on top is not a total reflection anymore as it was in the case of the normal incidence. This means that lesser part of the sound stays inside the foam and gets absorbed.

DST 114

In contrast, figure below

 

shows the wave impinging on the acoustic wedge foam of the “vertical wedge” type but of type DST 114 with a larger angle between the slanted surface and the base. The wave refracts to the right, and then internally reflects on the neighboring slanted side. The reflection in this case is total, which means all of the sound is trapped and does not escape back into the room at this point.

Can these results of the simulation indicate the reason why Auralex DST 114 shows better absorption at low frequencies around 100 Hz compared with Auralex DST 112? Quite possibly. We have verified that DST 114 internally reflects for angles of incidence as little as 5 degrees while the DST 112 does not for such small angles either. Since in real life no incidence is exactly normal but includes small angles of incidence, the results presented in this subsection could explain better absorption of DST 114 at normal incidence, as measured in the absorption experiments.

Another difference between the two geometries at 15 degree angle incidence is that the chance of part of the wave hitting on the vertical side of the wedge is double in the case of the DST 114 type acoustic foam. Figure below

 

shows that such a wave immediately turns and travels laterally through the foam, therefore significantly increasing absorption. This figure applies to the DST 114 type vertical foam. However, vertical angle is vertical angle in both acoustic foams, so the travel direction inside the foam after the initial refraction into the foam is the same for both foams.

In conclusion, our simulations seem to suggest that the DST 114-type foam is superior for normal incidence, in agreement with experimental results. DST 114 is superior for 15 degree incidence as well, due to more internal reflection and larger vertical surface.

Large Angles Of Incidence: 60 Degree Angle Of Incidence

For large angles of incidence, such as 60 degree, we found the vertical wedge acoustic foams of the type of DST 114 are competitive with best performing foam geometries. Only the narrow wedge soundproofing foam was arguably better performing. This is detailed in the post Soundproof Treatment Foam Panels Placement, Oblique Incidence. We investigate now whether, for angles of incidence of 60 degrees and 75 degrees, which of the two acoustic foams, the DST 114 or DST 112 type would absorb better in simulations at these angles. We start with the angle of incidence of 60 degrees.

DST 114

Figure below

shows the sound wave impinging on a DST 114-type foam under the angle of incidence of 60 degrees. Note how the wave refracts into the foam after penetrating the vertical side of the wedge, then totally internally reflecting off of the slanted side, then internally reflecting off of the bottom, and then doing one more round trip before exiting to the room. This is a hallmark of good absorption because of the long path the sound wave travels inside the foam before exiting back into the room.

DST 112

Similar refraction pattern will persist in the DST 112-type foam as long as the wave impinges under 60 degrees onto the vertical side of the wedge. But for the DST 112-type acoustic foam, sound also impinges on the slanted side of the wedge first. Figure

shows this situation. Because of the grazing angle of incidence on the slanted side of the wedge, most of the sound will reflect off of that side, and then refract into the vertical side of the neighboring wedge. Then, the sound internally reflects and continues under about 60 degree angle through the foam toward the bottom.

Based on these simulations, we can not tell for sure which foam would absorb more. Both seem to do a good job in absorbing sound impinging under 60 degree incidence angle.

75 Degree Angle Of Incidence

DST 114

The situation changes dramatically at a 75 degree angle of incidence. Figure below

 

shows the sound wave impinging on the vertical side of the wedge of an Auralex DST 114-type foam. After the first refraction, the wave internally reflects toward the bottom of the foam. Because of the sharper angle, the sound internally reflects back from the bottom and exits the foam on the upper side in the second neighbor wedge. So there is only one round trip of the wave.

DST 112

The Auralex DST 112-type vertical wedge acoustic foam behaves quite differently at the 75 degree angle of incidence. Figure below

 

shows a typical situation. The impinging wave is nearly parallel to the slanted side of the wedge. The wave that entered through the vertical side of the wedge will not internally reflect off the slanted side. Instead, it will propagate through the foam nearly horizontally. The angle will be even greater than 75 degrees. The wave will make a long distance trip laterally through the foam. Good absorption should follow.

Conclusion, The Auralex DST 112 And DST 114 Foam Should Work Well At Largest Angles Of Incidence

Our simulations for angles of incidence from zero (normal incidence) to approximately 60 degrees, the Auralex DST 114-type vertical wedge foam is always superior or equivalent in providing good absorption to the Auralex DST 112-type vertical wedge foam. For the angle of incidence of about 75 degrees, the Auralex DST 114-type acoustic foam becomes superior. At such large angles of incidence the DST 114 provides better absorption. This is due to the sound wave propagating a long distance in the lateral direction through the acoustic foam once it has entered it through the vertical side of the vertical wedge.

When deciding on what acoustic foam to place where in your recording studio, be sure to give both Auralex DST 112 and Auralex DST 114 proper consideration. Both will work well at normal incidence. DST 114 will work better at 15 degree incidence and 60 degree incidence while DST 112 will work best at 75 degree incidence and higher. So include DST 114 and DST 112 in your design of your recording studio. Be careful however, to orient either one of them in the direction such that the ridge of the wedge is perpendicular to the direction of where the sound is generally coming from. Also, be sure to direct the vertical side of the ridge toward the sound source. Find more details on how to position acoustic sound foam in this post.

Material Used, Durability, Cellular Structure

Material used for DST 112 and DST 114 acoustic wedge foam panels is polyurethane. It has an open cell structure. Open cell structure means that the cells of the foam have numerous sides that are not covered over. These sides allow the air flow through as the sound waves hit the cell. The molecules of air then experience turbulent motion as they pass the grid of the foam. Because of that, sound energy turns into heat.

Fire Retardancy

The panels have demonstrated Class B performance when tested in accordance with ASTM E84 test for fire retardancy. ASTM E84 is the standard test method to determine surface burning characteristics of building materials. In simple terms, Class B means that on the surface of the panels, fire will propagate about as fast as it would on the surface of wood.

Polyurethane material is more durable than many other materials used in acoustic foams. It will not become brittle with time.

Appearance: Colors And Looks

Auralex DST 114 vertical wedge panels come in three colors: Purple, Burgundy, and Charcoal. You can mix and match to give your recording studio a unique look. Auralex DST 112 comes only in Charcoal Gray color.

Accessories

Auralex recommends Foamtak spray-on adhesive. You apply it lightly for a temporary mount and more heavily for a more permanent mount.

Pros

To summarize above:

These are the main pros of Auralex DST 112:

• great room sound absorption and diffusion performance for mid-high frequencies
• great room sound absorption and diffusion for angles of incidence above 75 degrees, even for lower frequencies
• lightweight, easy to install

These are the pros of Auralex DST 114:

• great room sound absorption and diffusion performance for mid-high frequencies
• great room sound absorption and diffusion for angles of incidence between normal and 15 degrees
• lightweight

Cons

As stated above, we do not recommend DST 112 for near-normal angles of incidence. We suggest DST 114 instead. We do not recommend DST 112 nor DST 114 for angles of incidence between 30 and 45 degrees. For those angles of incidence, we prefer the narrow wedge acoustic foam.

Another con of Auralex DST 112 compared with DST 114 is lesser soundproofing of external noises. These external noises are coming normally from the wall into the foam from the bottom of the foam. The reduced soundproofing is due to a slim angle of the DST 112 wedge.

Consumer Comments And Ratings

We scoured the web to find consumer ratings of Auralex DST 112 and DST 114. For the most part, buyers are recording engineers or mixing engineers, music producers, home recording studio owners. Professional vocalists, guitar player and drummers were among satisfied buyers too. Some of the buyers are music enthusiasts and hobbyists.

The buyers commend DST acoustic foam for killing echo and reverbs in the studio. They notice a more professional feel immediately after installation. Some noticed reduction of high volume high frequency ringing sounds.

Some buyers noted a better stereo imaging in the recordings.

Price And Quantity

Auralex DST 112  and DST 114 acoustic wedge foam comes in packs of 24 1 ft x 1 ft tiles. Each package contains 24 tiles that will cover 24 sq. ft in total. There have appeared numerous imitators recently. The imitators, however, do not have fifty years of tradition, experience, and quality that Auralex offers.

Currently, the best deal we could find on DST 112 and DST 114 was inside the Auralex Roominator DST D-36 which includes both DST 112 and DST 114 foams. In sound treatment of your studio, following suggestions above, you will need both for sure.

Check out the availability and pricing of DST 112 and DST 114 acoustic foam included in Auralex Roominator DST D-36 directly at Walmart.