Sound is energy that travels in waves – sound waves. These sound waves have a frequency and a wavelength, both of which relate to pitch, to put it in musical terms. The higher the frequency (pitch), the shorter the wavelength: the lower the frequency (pitch) the longer the wavelength.

Sound waves can be reflected, which can be a good thing (echo, reverb, ambiance) or a bad thing (standing waves). Echo is when a reflection is delayed long enough to be perceived as a distinct repeat of the original sound. Reverberation is when there are many overlapping repeats of the original sound that last after the original sound has stopped.

One of the advantages of a professionally designed recording studio is the pleasing sound of the space and the lack of acoustic problems. The most common problems in semi-pro and home studios are a) keeping the sound from escaping and disturbing others (transmission) and b) the sound inside the room. In a nutshell, the way to deal with transmission is a combination of mass and airspace (isolation) in the walls, ceiling and floor. Dealing with the sound of the room is done with a combination of geometry, absorption and diffusion.

One of the basic problems to be dealt with is that of parallel surfaces – they can create an unwanted effect called ‘standing waves’ – basically the sound ping-ponging back and forth. Standing waves occur at certain frequencies related to the distance between the surfaces. The original sound and the reflected sound will combine to boost certain frequencies and to cancel others – creating a comb filter effect. The best way to deal with this is to design the room with no parallel surfaces and with enough volume (room size) to minimize standing waves. Unfortunately, this isn’t always possible, so other remedies must be considered, which leads us to absorption and diffusion. Frequencies above 500Hz are very short and are easily soaked up by using foam or rock wool type products. The sound waves bounce around inside the absorptive material and turn into heat. Frequencies below 500Hz are tougher, due to their length, and require ‘bass traps’ big enough to capture the wave and let it turn into heat. Diffusers work by reflecting the sound back into the room, but spread out, usually over a 180 degree arc.

A room with too much absorption will sound overly dead; too little will make it sound overly live. It is preferable to have a mix of absorption and diffusion to create a good sounding room. There are many great resources available to help with acoustic design. Enter “basic acoustics” into a web browser and you will find many great websites, especially those of manufacturers of absorbers, diffusers and bass traps, ready made for studio use.