How sound waves work. A little knowledge of the mechanics involved will help make your recording sessions successful. Because sounds are physical waveforms moving through air, they are free to intermix. In the two most extreme cases, perfectly in phase and exactly 180 degrees out of phase, a pair of sound waves will double in amplitude or completely nullify each other, resulting in no sound. Either case is a recording mess.
Sound waves have other important properties to consider when setting up a recording session.
Each waveform's compressions and rarefactions also have a strength known as the intensity. The spread of values from minimum to maximum intensity is the sound's dynamic range. When a sound wave radiates from its source, it starts with a uniform intensity pushing on a volume of air. As it continues to travel away from its source, the expansion continues, but it has to push increasingly large volumes of air to achieve the same result. Without amplification, the sound's acoustic pressure dissipates, decreasing its intensity.