Acoustic foam versus glass wool (fiberglass) panels
There is much misinformation in the market regarding acoustic panels. Please allow me to clarify some bits. First and foremost, if it can be made to vibrate, it will absorb sound energy. When sound penetrates the membranes in foam or the minute strands in glass wool, they vibrate and convert sound energy into heat. The science is known as thermodynamics. The absorption coefficient or ability of a product to absorb energy is rated using a simple scale with 1 being 100% at a given frequency - and 0.8 being 80%. As a general rule, the thicker the absorber, the lower the frequency. This is why bass traps are bigger. You can estimate the absorption of a given panel using quarter wavelength calculations, but this is very inaccurate. The only way to accurately measure the performance of an absorber is to place a number of these it inside a test chamber such as the ones employed by Riverbank Labs and run tests. Unless you can get a copy of the actual independent tests, do not believe what you are reading. Anyone can buy convoluted mattress foam and put it up for sale on a web site.
The absorption coefficient is also related to the density of the material. Higher density materials will absorb more bass while low density materials only absorb high frequencies. High frequency absorption is easily done with foam or even carpet. However, this causes a worse problem whereby the room will be bass heavy. So when you mix and listen back on another system, you will find that your mixes will likely sound harsh in order to compensate for the uneven response. Acoustic foam is typically cut from blocks of 1 lb per square foot foam buns. These are shaped in a zigzag to look pretty and give the impression that sound is being diffused. This is not the case. Foam is too soft to diffuse energy. Because half the foam is being cut away, you are only getting half the density - thus much less low frequency performance. Vocal booths are often plagued with a problem that is known as chest hump. This is caused by two factors: the first, since the size of the room is often 4'x4'x7' high, the room will have resonant frequencies at 157Hz and 275Hz (bumps or standing waves). Second, because the low density foam will do absolutely nothing to absorb energy below 500Hz, it will sound dead in the high end. You will end up with a muffled yet pronounced low end response that sounds awful. A viable fix is to add tri-corner traps up high in the corners.
Higher density materials such as 6lb per square foot glass wool will absorb low frequencies down to 100Hz, depending on the thickness. It is available from Owens-Corning for do it your-selfers or pre-made from companies like Primacoustic. These panels absorb audio frequencies more evenly - and can be compared to a microphone or speaker that produces a flat response. In a studio, you want your room be ne neutral. This is the type of material that professional studios employ. You hang it up on the wall like a picture. No more messy glue to contend with during installation or drywall to repair and clean up when you move.
There are a few other things to consider which got me onto this thread. The first is dusting: Foam like any plastic is affected by ultra violet rays and oxidisation. So over time, the foam will change and begin to dust. The foam itself may or may not be harmful to your health, but the fire retardant that is embedded is listed as a carcinogenic. Don't eat your foam! On the other hand, glass wool was recently removed from the list of potential hazards by the American Cancer Society. Glass is considered to be inert. But this does not mean care should not be taken when handling it. If you intend to cut and build your own glass wool panels, wear a long sleeve shirt, gloves a mask to avoid inhaling the minute fibers. At Primacoustic, each panel is surfaced with micromesh and the edges are resin treated to harden them so that the fibers are fully encapsulated. If making your own panels, you may consider doing the same. This eliminates dusting.
The second concern is fire: We all heard about the fire in the New-England night club that was caused by pyro-techniques and acoustic foam. Foam - even when treated - is not fire safe. The treatment inside the foam will only slow the onset of a fire, giving you more time to escape. This is why foam is not approved for use in construction anywhere in America or anywhere else in the world. This is particularly important for those living in apartments or high density residential areas. You can certainly use whatever you want in your home as you are your own master, but only class-A rated materials should be used in public or commercial spaces. This will not only work better, you will not be held liable if a fire happens to break out and your studio foam is blamed for being a transmitter. The owners of the night club were charge a $1million in fines and they went to jail for several years. Considering a starter London 8 acoustic kit with proper panels only costs about $250 - this seems to me as a better and safer route to go.
Peter Janis - Primacoustic
