Absorbed and Reflected

After it is produced, sound is transmitted through a “medium”. Air is the typical medium, but sound can also be transmitted through solid or liquid materials. Generally, a sound wave will move in a straight line unless it is absorbed or reflected by physical surfaces or objects in its path. However, the transmission of the sound wave will be affected only if the size of the surface or object is large compared to the wavelength of the sound. If the surface is small (compared to the wavelength) the sound will proceed as if the object were not there. High frequencies (short wavelengths) can be reflected or absorbed by small surfaces, but low frequencies (long wavelengths) can be reflected or absorbed only by very large surfaces or objects. For this reason it is easier to control high frequencies by acoustic means, while low frequency control requires massive (and expensive) techniques.

(from Audio System Guide for Houses of Worship, Shure Educational Publication)