Acoustic foam sound deadening treatment: what makes it different from conventional open cell foam

Acoustic foam sound deadening treatment: what makes it different from conventional open cell foam

Acoustic foam sound deadening treatment: what makes it different from conventional open cell foam

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 is managed. As a useful component of acoustic treatment, sound deadening foam is one of the first materials people turn to for correcting room echo oscillation, standing waves, and mid- and high-frequency problems. But because foam is present in so many places and used in so many ways, the question often arises, “What’s the difference between acoustic foam and the everyday stuff?”

This is a valid question and one that should not be dismissed. After all, acoustic and conventional foam really do look the same and generally feel the same. However, acoustic foam treatment is a specially developed material with very unique characteristics that set it apart from the foam in your sofa cushions or the mattress on your bed. These features combine to create a special product that is designed for a single purpose. What follows is a list of the differences between conventional and acoustic foam and why close enough is not good enough when it comes to sound processing.

Fire resistance – Although not necessarily a performance feature, acoustic foam’s fire resistance may be its most important feature for safety reasons. In studios and home theaters, acoustic treatment is often applied to open areas where there may be possible sources of ignition such as cigarettes, candles, and extensive wiring and electronics. Suitable rigid foam must have an acceptable fire retardancy rating that meets all relevant local safety and building codes. The test method for fire retardancy of foam is evaluated by ASTM E84. This fire resistance makes true acoustic foam much safer than conventional foam when used in the same manner.

Endurance – Because acoustic foam must be used in settings where it will be in direct contact with people, it must be made to handle accidental contact. Acoustic foam is made to be dust free so it is resistant to breaking down over time. In a place where the foam will never be touched, this won’t be a problem, but in places like studios where several people can fill a small room, or home theaters with kids or friends, the foam can be hit, brushed, poked and scratched. Acoustic foam is designed to withstand this type of abuse longer than traditional foam if used in the same way.

Hardness – Just like comfort foam, the stiffness of acoustic foam is also an important consideration. But while the user’s personal comfort preferences dictate the stiffness needed for traditional foams, the stiffness of acoustic foam plays a role in its ability to handle sound. Low-stiffness foam does a better job of handling high-frequency sound waves, while stiffer foam is better at handling low-frequency sound waves. Placing non-acoustic foam of unknown stiffness in a room can leave gaps in the soundscape while allowing other sound frequencies to propagate. Acoustic foam is characterized by a firmness that achieves a balance between absorption and diffusion at high and low frequencies for the best overall treatment.

Cell structure – A physical characteristic of acoustic treatment that separates it from sofa foam is the way the foam is made. One way to assess cell structure is through cell size analysis, which is measured as a pore-per-inch rating, or PPI. It’s exactly what it sounds like: the number of foam cells per linear inch of material. Conventional furniture and comfort foam has a PPI of 60-70 cells, while some porous, specialty foams such as dry foam have a PPI of up to 25 or 30. Acoustic foam typically has a PPI of 80. Higher PPIs make for a product with greater sound absorption. As an example of the difference a few PPIs can make, a 12″ x 12″ x 3″ tile of 80 PPI foam will have more than 127 million additional cells compared to 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 conventional foam. Acoustic foam is manufactured to be much more permanent and uniform than conventional foam. A few air bubbles in a mattress will not affect the performance in the slightest and will never be seen, but in a studio these same air bubbles would look ugly in a wall diffuser. Thanks to the care taken in manufacturing, you can trust that the foam purchased months later will match the previously purchased materials. And of course, the patterns cut into the foam, whether wedges, spirals, pyramids, or egg carton, all affect the way the material perceives sound.

On the surface, it may appear that all foam is the same. In reality, conventional foam and acoustic foam are like apples and oranges. Both are fruits, but they don’t taste similar. So if you need to improve the sound in a space, make the right choice with real acoustic foam and don’t choose a bad apple.

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