There are many variables to room acoustic treatment. There can be even more variables to the application of the technology associated with room acoustic treatment. A step by step check list is needed. Just as a pilot goes through a pre-flight check list, we need an acoustical flight checklist before we can musically “fly”.
Choose the correct room size. Find the balance between height, width, and depth that minimizes all resonances that occur below 200 cycles. Remember, our room is a huge box of sound pressure. We need to have room size that has all room resonances spread out through the room. If you need to take an existing room and make it smaller to fit a golden ratio of room dimensions that spread resonances out, do it.
Treat all low frequency issues now. Run a room modal calculation and find out where these rascals lie within the room. One has to take a measurement, move the measuring mic. and then take another measurement. Repeat this process every three feet around the room. One can actually map the resonance’s location and its amplitude. It takes awhile and a couple people to help do it, but it will be worth it. If building new, use a resonant cavity to control low frequency energy. If using an existing room, use a resonating panel type of absorber. A diaphragmatic absorber is a good example of a resonating panel.
Isolate the room from outside noise. Insulate and isolate the rest of the world from the sound produced inside the room. Do not increase the ambient noise level of the universe. Keep all sound produced in the room where it belongs, in the room. keep all outside noises from getting into our mixes or playback musical presentations. Use barrier technologies to achieve sound transmission loss within or on existing structures.
Choose room building materials that will naturally produce a better room sound. Room energy that strikes a surface within our rooms takes on the sound of that surface. Sound strikes glass, one gets glass sound. You know that sound. That is the sound of your car stereo. Sound strikes wood, one gets wood sound which is smooth and warmer sounding. Some rooms are harder than others. A concrete room will have more reflectivity due to the harder surface of the concrete. A gypsum wall surface will flex slightly when compared to a concrete wall that will move much less and cause less reflectivity.
Decide on the room purpose and use. A monitoring room has different acoustical goals than a playback or listening room. In a monitoring room, we need to keep the room sound out of the mix. We need to hear only the music, not the music and the room. In a playback room, we want to hear the room sound and the music. Our goal is to reproduce the original recording with all its accuracies and sometimes flaws. We want to manage the amount that we hear, but we want some room sound.
Find the proper location within the room for your speakers. The distortion that occurs from the speaker/boundary is a source of acoustical distortion. Improper speaker positioning can boost some frequencies and bury others. Find the location that produces the smoothest frequency response curve. This position will be a certain distance from the front and side wall boundary surfaces.
Reflection control must compliment room usage. If one is using the room for professional monitoring of recorded signals, then we must use a near field monitoring position to minimize side wall reflections. We also must absorption technologies for side wall reflections, so they do not interfere with the direct music sound from our monitors. Our monitors must be frequency response flat. If we are using the room for playback, we want a blend of absorption and diffusion on the side walls, rear, and front walls.
The rear wall of any monitoring or listening room must have two dimensions of diffusion. This is a minimum requirement. A two dimensional diffusor can be installed or one can use quadratic diffusion. The frequency range of the diffusor must be specifically designed for. Once that is determined, one must position both vertical and horizontal quadratic diffusors to achieve a two dimensional reflection free sound field at the listening or monitoring position.
Use absorption as the ceiling treatment in a professional project studio that has lower ceiling heights. Our goal with our professional mixing environment is to keep as much as the room sound out of our mixes as we can. Ceiling reflection absorption technology employed on the ceiling will keep ceiling room sound as a minimum. Listening rooms need two dimensions of diffusion or a blend of absorption and diffusion.
There are only three things that happen with the sound energy within our rooms. Sound energy is either absorbed, diffused, or reflected. To control and manage these three energies we use sound absorption and diffusion technologies to deal with reflections within our rooms. We use absorption technologies for lower frequency control and management. Lower frequency energy is not diffused only absorbed. We do not want to encourage it by using huge diffusors.