Acoustic foam sound deadening treatment: what sets it apart from conventional open cell foam
One of the first things to consider when creating a space designed for optimal sound, whether it be a dedicated home theater, recording studio, or vocal booth, is how that sound is managed. As a useful component of acoustical treatment, soundproofing foam is one of the first materials people turn to to correct flutter echoes, standing waves, and mid-high frequency issues in a room. But because foam is found in so many places and used in so many ways, the question often arises, “What’s the difference between acoustic foam and everyday stuff?”
This is a valid question, and one that should not be dismissed. After all, conventional and acoustic foams look the same, and generally feel the same, too. However, acoustic foam treatment is a specially designed material with many unique characteristics that set it apart from the foam in your sofa cushions or bed mattress. These traits combine to create a special product that is designed for a singular purpose. What follows is a list of the differences between conventional and acoustic foam, and why close enough isn’t good enough when it comes to sound treatment.
fire retardant – While not necessarily a performance characteristic, the fire resistance of acoustic foam may be its most important characteristic due to safety. In studios and home theaters, acoustical treatment is often implemented in open areas where potential sources of ignition such as cigarettes, candles, and extensive wiring and electronic devices may exist. Proper sound foam must have an acceptable fire resistance rating that meets all applicable local building and safety codes. The test method for fire retardancy of foam is evaluated by ASTM E84. That fire resistance makes true acoustic foam much safer than conventional foam when used in the same way.
Sustainability – Because acoustic foam will be used in environments where it will be in direct contact with people, it must be manufactured to handle accidental contact. Acoustic foam is made “dust free” so it resists crumbling over time. In a place where the foam would never be touched, it wouldn’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 get bumped, brushed, punctured, and scratched. Acoustic foam is designed to withstand this type of abuse longer than traditional foam if it were used in the same way.
Firmness – Like comfort foam, the firmness of acoustic foam is also an important consideration. But while the user’s personal comfort preference dictates the firmness needed for traditional foams, the firmness in acoustic foam plays a significant role in its ability to handle sound. Low-firmness foam works best at handling high-frequency sound waves, while firmer foam is better at handling low-frequency sound waves. Placing non-acoustic foam of unknown firmness in a room can leave gaps in a soundscape, while allowing other sound frequencies to run amok. Acoustic foam features a firmness that strikes a balance between absorption and diffusion at high and low frequencies for the best overall treatment.
Cell structure – A physical feature of acoustical treatment that separates it from sofa foam is the way the foam is manufactured. One way to assess cell structure is an analysis of cell size, which is measured as a pore per inch rating, or PPI. That’s exactly what it sounds like: the count of foam cells within one linear inch of the material. Conventional furniture and comfort foam has a PPI of 60-70 cells, while some specialty porous foams, such as dryfast foam, have a PPI as low as 25 or 30. Acoustic foam typically has a PPI of 80. A PPI higher makes the product more sound absorbent. . To see an example of the difference a few PPIs can make, a 12″ x 12″ x 3″ tile of 80 PPI foam would have over 127 million additional cells compared to a 60 PPI foam of the same dimensions. .
Appearance – It may seem trivial, but the appearance of the foam is another big difference between acoustic and conventional foam. Acoustic foam is manufactured to be much more consistent and uniform than conventional foam. A few air bubbles in a mattress won’t affect performance one bit and will never be seen, but in a studio, those same air bubbles would look unsightly on a wall diffuser. Due to the care that was taken in manufacturing, you can be confident that foam purchased months later will match previously purchased materials. And of course, the patterns cut into the foam, whether they be wedges, spirals, pyramids, or egg crate, have an impact on the way the material handles 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 anything like it. So if you need to treat sound in a space, make the right choice with real acoustic foam and don’t choose a bad apple.