Acoustic panels, bass traps, combination absorber / diffusors and pure diffusors

In my mind there are four main types of acoustic treatment, divided principally by their construction and hence their application in high end home theaters and listening rooms:

1. Absorptive acoustic panels - at their heart these are simple fabric wrapped fiberglass / rockwool / acoustic cotton. The thicker the core the lower the frequency to which the panel absorbs. Even 6" thick panels do not provide much absorption below about 80Hz. These panels can be used for a number of purposes such as control of strong early reflections, room modes and shaping of the room's overall reverberation character.
2. Bass traps - products specifically designed to provide high absorption below about 100Hz. Below 100Hz straightforward acoustic panels become ineffective and additional elements are needed to boost absorption. The additional design component in commercial products is typically some form of resonating membrane such as wood, mass loaded vinyl, felt or plastic. Sometimes this membrane is tuned to resonate at a particular frequency.
3. Combination absorper / diffusors - these products contain absorbing elements and diffusing elements. They are often employed on side walls at reflection points to shape the spectral content of the reflected sound. In heavily damped rooms such as Home Theaters they also more generally take the place of straightforward acoustic panels which, if over used, can lead to an overly 'dead' environment.
4. Pure diffusors - designed to provide diffusion across a certain part of the freqeuncy spectrum. We use these devices primarily on the rear of the side walls in two channel listening rooms to provide additional envelopment. Construction varies but the many diffusors are based on implementations of Schroeder's theories which require precise construction techniques. For this reason many commercial diffusors are formed from plastic, expanded polystyrene or CNC'd wood.

Buy or DIY?

The choice about whether to buy or DIY acoustic treatment is going to vary depending on the type of acoustic treatment. Some forms of acoustic treatment like the absorptive panels are much easier to DIY than others whereas others such as the pure diffusors are very tricky for a DIYer to make. It is important to realize that in treating a typical room a combination of all of the above acoustic treatment types is normally necessary. Just putting up absorber panels everywhere is not going to treat all of your room's acoustical issues! We'll be examining each type of treatment and its 'DIY potential' in more depth in follow up blog articles over the coming weeks. Finally - if you are interested in commercially made products be sure to take a look at the range from RPG, Primacoustic, RealTraps and Golterman & Sabo we have available in our shop!