Sound II Reading

One of the most common problems in acoustics, that particularly affects 'room-sized' rooms, rather than concert halls, is standing waves.

A standing wave occurs when a wave reflects between two boundaries and travels back along the incident path, interfering with the original wave and causing a waveform that appears to be stationary. In the simplest case, when the distance between two parallel walls is exactly half the wavelength of a particular frequency, then a standing wave can build up. If the losses are minimal (due to a lack of absorption), the wave will potentially resonate and cause localized peaks in volume at the specific frequency – the result being that the sound that is heard within the room is no longer a good representation of the original sound.

In the example below the blue wave is the original signal moving from left to right. The red wave is return signal from a parallel wall. The black wave is the result of the two waves combining. The resulting wave is the resonant frequency of the room.

Smaller rooms sound worse because the frequencies where standing waves are strong are well into the sensitive range of our hearing. Most people will immediately recognize common parallel walls within a room. Using a typical home studio setup as an example, the four walls of the room create two common sources of parallel walls. Another source people overlook is the floor to ceiling parallel wall.