The first question you need to ask yourself before installing any type of acoustic treatment is: What am I trying to achieve? Generally speaking, there are two broad categories of acoustic treatment. The first is reducing the volume of harsh reflections and reverberation which are annoying to the ear in a wide range of situations. For example, harsh reverberation caused by cymbals, snare drums, guitars in a rehearsal room, or in a restaurant, the clatter of cutlery and chatter (due to hard floors and walls). The second category is the specific application of acoustic treatment, in order to create a more accurate listening environment, such as a recording studio, home theatre or audiophile room.
For the first category, any acoustic material that absorbs high frequencies is suitable. This can be standard acoustic panels*, carpet, drapes, or soft furnishings. Roughly speaking, all these materials will absorb 500hz and higher, reducing harsh higher frequency reflections. To put this into perspective, middle C on the piano is 261 Hz.
Acoustic treatment for the second category requires are different approach. To create an accurate listening environment, the acoustic treatment needs to be effective over a wide frequency range. This requires bass trapping for low frequencies (usually mounted in corners) and broadband acoustic panels (best at first reflection points). Most importantly, if you are on a budget, start with bass trapping first. Low frequency reverberation interferes with your ability to accurately assess the volume of low frequencies when mixing and listening to music. The most common symptom of an unbalanced room, in a recording studio, is a mix which translates poorly to other playback systems.
In an audiophile room or home theatre, it is low frequencies that ‘jump out’ or conversely, disappear.
*Most acoustic panels on the market (such as our own AT600/40) are only ‘mid/high’ frequency absorbing panels. For example, eggshell foam or similar. The ability of acoustic foam to absorb lower frequencies is directly related to thickness. For example, the SA600-75 (75mm thick) broadband panel absorbs affectively down to 200Hz, where as the AT600-40 (40mm thick) absorbs down to 400hz. Which is virtually an octave difference.