Acoustic panels are a technology which shapes and lends different qualities to the sound in a space, by using panel materials to alter the way that sound reverberates. They are used in a variety of spaces, such as concert halls and theaters, classrooms, ballrooms, recording studios, lecture halls, and any place where sound quality is important, including living rooms and home theaters.
The two primary categories of wall acoustic wall panel technology are absorbers and diffusers, those which soak up sound, and those which distribute sound more evenly throughout the space. Generally, these two types of panels will both be used in some combination, so that the trick to proper wall panel acoustics is in finding the right ratio and positioning of these two types of panels to create the desired sound quality.
Naturally, this is different in each individual space, and so an experienced acoustic engineer is ideally consulted in the design of an acoustic space. However, it is possible for those who don’t specialize in this to create good sound quality using acoustic panels, and here we’ll provide some tips on how to do exactly that.
Understanding a Room Acoustically
Each room has a series of reflection points and sound dynamics which will determine how best to use absorbing and diffusing wall panels. Not unlike plotting the paths of billiard balls during a game of pool, one has to understand the paths that sound takes through a room to know how best to absorb and diffuse that sound with panels, to create the perfect sound chamber.
First Reflection Points
As one might guess, in room acoustics, these are the first points that sound hits when it travels out of speakers or whatever other sound-producing implements, in a room, other than the listener’s ears. These are the first thing you’ll need to establish in your understanding of your room’s sound dynamics, because these will be the sound reflections which interfere with your own perception of the original sound from the speakers.
There are many ways to see where the focal point of sound is first striking your walls. The easiest way is to slide a mirror placed flat against the wall that is perpendicular to the wall or imaginary horizontal line of the point where the sound is originating. As the mirror moves along the perpendicular wall from the direction of the sound source towards the listener, ask the person in the listener position to notify the mirror holder when the mirror is reflecting the center of the speaker. Mark this location on the wall, and do the same for the opposite wall, and you have your first reflection points.
This dynamic should look like a triangle, with the first reflection point on each wall forming a third angle, with the listener and the sound source being the first two.
Use of Diffusers and/or Absorbers at First Reflection Points
The task here is to overcome the natural interference which comes from the sound bouncing off of this third point hitting your ears just microseconds after the original sound from the more direct line between you and the sound source.
Using sound absorbers for this purpose muffles the sound attempting to bounce from the first reflection points, reducing the interference. However, this does not necessarily resolve the interference problem, but merely reduces it, by reducing the sound bouncing from the first reflection points. These have historically been the most popular approach, but that was before improvements to diffuser technology.
Diffusers take the sound which would normally bounce and interfere, and spreads it around the room; you can think of this as making the sound from the first reflection point into a spray rather than a stream. However, there is an additional factor to consider, which is exactly what kind of spray this diffuser creates. If it isn’t diffused enough, it creates problems, and is actually worse than absorbers.
Images of Sound and Their Clarity
The critical element here is the concept of phase in room acoustics, or the timing of the sound, and how it affects our mind’s ability to form sound images. Poor diffusion results in distorted phasing that disrupts sound quality; in other words, the sound waves just bounce around the room in such a way that they form random, chaotic interference points. This disrupts our “binocular hearing”, or how our brain forms images of what we’re hearing, based on how it strikes our two ears at slightly different timings.
The goal of diffusing sound, then, is to do it in such a way that you achieve coherence, which is accomplished by using phase-distorting diffusers. These cause the sounds bouncing around the room to be spread out or diffused enough that we don’t end up with myriad chaotic sound impact and interference points reverberating in a distorted way, but rather a single, clear, coherent sound with uniform phase, amplitude, and harmonics. You could compare this to a fine mist or spray of sound, and this is a more natural sound quality to our ears, a higher quality than what we get by using absorbers.
How to Apply Phase-Coherent Diffusers to a Room
As an example, we’ll take a standard 12 x 16 x 8 living room with an entertainment system.
On the first reflection points, we can apply a slightly concave, medium-curve diffuser, on the walls perpendicular to the sound system, after finding the points, of course. Additionally, you’ll want to apply more diffusers to the center of the back wall, and one on the front wall, above the entertainment system, horizontally. This is all assuming that the entertainment system is placed midway on the front wall.
It’s also recommended to place corner panels in all four corners of the room, and this is a great place to incorporate absorber panels. Corners are important because they’re particularly bad about diffusing sound in such a way that it distorts your sound image quality.
In some rooms, there may still be distortion, in which case you can apply special ceiling panels, which are often called “clouds”. For optimal ceiling clouds, you’ll want to perform the same exercise you did to find the wall reflection points, which is admittedly a bit more challenging on a ceiling. However, it can greatly improve the sound quality in a room. Adding yet more panels directly about the listeners’ location (probably a couch in this case) is even better.