One of the first things to consider when creating a space designed for optimal sound, whether it’s a dedicated home theater, recording studio or vocal booth, is how that sound will be managed. A useful component of acoustic treatment, Acoustic Foam is one of the first materials people turn to to correct flutter echoes, standing waves, and mid- and high-frequency problems in a room. But because foam is so versatile and has so many uses, the question often arises, “What is the difference between acoustic foam and everyday things?”

This is a legitimate question that cannot be dismissed out of hand. After all, acoustic and traditional foams look and usually feel the same. However, the acoustic foam treatment is a specially engineered material with many unique properties that set it apart from the foam in your couch cushions or the mattress on your bed. These qualities combine to create a special product designed for a single purpose. What follows is a breakdown of the differences between traditional and acoustic foam and why close enough isn’t good enough when it comes to sound treatment.

Fire Retardancy

While not necessarily a performance attribute, fire retardancy can be the most important property of acoustic foam for safety reasons. In studios and home theaters, acoustic treatment is often performed in open areas where there may be potential ignition sources such as cigarettes, candles, and extensive wiring and electronics. Proper acoustic foam should have an acceptable fire retardancy rating that meets all relevant local safety and building codes. The test method for fire retardancy of the foam is evaluated according to ASTM E84. This fire retardancy makes real acoustic foam much safer than traditional foam when used in the same way.

Durability

Because acoustic foam is intended to be used in environments where it will be in direct human contact, it must be manufactured to withstand accidental contact. Acoustic foam is “non-dusting” so it won’t crumble over time. In a place where the foam would never be touched this wouldn’t be a problem, but in places like studios where multiple people can fill a tiny space, or home theaters with kids or friends, foam can be bumped, brushed, bumped and bumped scratched. Acoustic foam is designed to withstand this type of abuse longer than traditional foam when used in the same way.

Firmness

Just like comfort foam, the firmness of acoustic foam is an important consideration. But while a user’s personal comfort preference dictates the firmness required for traditional foams, with acoustic foam, firmness plays a role in its ability to handle sound. Low-firm foam is better suited to dealing with high-frequency sound waves, while firmer foam is better suited to dealing with low-frequency waves. Introducing non-acoustic foam of unknown strength into a space can leave voids in a soundscape , while other sound frequencies are unbridled. Acoustic foam exhibits a strength that balances absorption and diffusion at both high and low frequencies for the best overall treatment.

Cell

Structure – A physical feature of acoustic treatment that sets it apart from sofa foam is the way the foam is made. One way to assess cell structure is by analyzing cell size, which is measured as the Pores Per Inch Rating (PPI). That’s what it sounds like: the number of foam cells within a linear inch of the material. Traditional furnishing and comfort foam has a PPI of 60-70 cells, while some porous specialty foams like Dry Fast Foam have a PPI as low as 25 or 30. Acoustic foam typically has a PPI of 80. A higher PPI makes for a better sound absorption product. An example of the difference a few PPIs can make: a 12 x 12 x 3 inch tile made of 80 PPI foam would have over 127 million extra cells compared to a 60 PPI foam of the same dimensions.

Appearance

It may seem trivial, but the appearance of the foam is another major difference between acoustic and traditional foam. Acoustic foam is manufactured to be much more consistent and uniform than traditional foam. A few air bubbles in a mattress don’t affect performance one bit and are never seen, but in a studio those same air bubbles in a wall diffuser would look unsightly . Because of the care taken in manufacturing, you can be confident that the foam purchased months later will match the materials previously purchased. And of course the patterns cut into the foam, whether wedge, spiral, pyramid or egg crate , also have an effect on the sound of the material handles.

On the surface, it seems like all foam is the same. In reality, conventional foam and acoustic foam are like apples and pears. They’re both fruits, but they don’t taste the same. So if you need to treat sound in a room, make the right choice with real acoustic foam and don’t pick a bad apple.

Acoustic foam: flat or profiled?

When choosing the best acoustic foam for your soundproofing needs, it is important whether you are using a flat , smooth foam or a profiled one. As we will see below, there are pros and cons to each.

What frequency?

One of the main differences between smooth and profiled foams is how they handle different frequencies. Low-frequency waves are longer and stronger, so they require thicker , more resilient foam. Smooth foam has no foam removed and therefore their absorbent properties are much better than their profiled counterparts. Accordingly, flat, smooth foam is better suited to absorbing low frequencies.

Think of acoustic foam as a sponge and sound waves as water; a larger sponge absorbs more water!

On the other hand, sound waves incident at shallow angles and medium to high frequency waves have a tendency to bounce off smooth foams, meaning the sound is not absorbed, just reflected. Proper placement of your acoustic foam can mitigate this effect, although a profiled foam will help capture and capture those pesky low-angle and high-frequency waves.

Beware of a common myth that prevails when choosing a profiled acoustic foam; there is no difference in sound insulation between pyramidal and wedge-shaped profiles!

Which room?

We looked at the frequency of the sound waves you want to treat. The room you want to soundproof will also affect what type of foam is best for your needs.

As mentioned above, proper placement of acoustic foam can help mitigate low-angle waves that “bounce” off your foam and reflect around the room. The natural acoustics of the room must also be taken into account. If the natural acoustics are reasonably good, you might want to use profiled acoustic foam to tighten the mid-to-high frequency treatment and fine-tune the room’s acoustic response, although you’ll also need a solution to deal with long, powerful bass notes .

On the other hand, if your room’s natural Acoustic Foam is pretty poor, a smooth foam gives you that extra bit of power to properly deal with the treatment and absorption of incident acoustic waves for the desired soundproofing effect. Think about the sponge again; a thicker sponge absorbs more water!

So which foam?

When it comes to cosmetics, some people prefer profiled foam to the bare, homogeneous, smooth variety. In terms of performance, however, a mix of smooth and profiled acoustic foams is probably the best solution. With installation advice from an experienced soundproofing professional, you can fine-tune your solution with a mix of flat, smooth and profiled foams to handle a range of frequencies for a wide variety of applications.