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.
|2″ Studiofoam 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|
|3″ Studiofoam Wedges||0.17||0.23||0.19||0.31||0.49||0.71||0.87||1.06||1.1||1.05||1.04||1.03||0.97||0.96||0.98||1.01||1.05||1.03||0.9||A||2’x4’x3″ Foam Panel|
|4″ Studiofoam Wedges||0.24||0.31||0.36||0.62||0.85||1.09||1.21||1.25||1.17||1.16||1.14||1.08||1.06||1.06||1.11||1.09||1.09||1.1||1.1||A||2’x4’x4″ Foam Panel|
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 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 [pyramids], Narrow Wedge/Wedgies or [vertical wedge] geometries. 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.
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
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
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
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
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.
Auralex Studiofoam Wedges have A Rating for fire retardancy, based on the recent ASTM E-84 Fire Rating Test Report.
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.
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.
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.
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.
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 SamAsh.com