Are you looking for a great performin 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:
|SonoFlats||0.1||0.16||0.28||0.36||0.46||0.69||0.85||0.99||1.07||1.12||1.12||1.15||1.12||1.14||1.14||1.13||1.13||1.1||0.95||A||Flat, beveled Foam Panel|
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
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.
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
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.
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 [Soundproofing Foam Panels, 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.
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.
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
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.
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.
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.
Auralex recommends Foamtak spray-on adhesive. You apply it lightly for a temporary mount and more heavily for a more permanent mount.
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
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.
You can check out the current price and discounts at the music store Sam Ash.