Introduction to Computer Music: Volume One

10. What is reflection?

Sound waves reflect off of objects the same way billiard balls bounce off the bumpers of a pool table—the angle of incidence equals the angle of reflection. A sound wave hitting a flat wall at 45° will reflect off it at 45°.

The reflected wave can interfere with the incident (original) wave, producing the constructive and destructive interference mentioned above—it can increase its amplitude or, with phase cancellation, decrease its amplitude. In a typical listening environment, we are hearing sounds that have reflected off numerous objects and surfaces, with the reflections themselves interfering with other reflections. Just as color is determined by which frequencies of light are reflected or not, the "color", or acoustic characteristics, of a particular listening environment is determined by the angles and materials the sound may reflect off. Different materials reflect some frequencies more efficiently than others, due to their roughness or absorbancy characteristics. The acoustic foam at the end of our studio, for example, does not reflect higher frequencies very efficiently, but has little effect on particularly low frequencies. (We need a bass trap for that.) The distance both the incident sound and the reflected sounds must travel is another key element in the characteristics of an acoustic environment, since the incident sound typically reflects off many surfaces at differing distances from the listener, thereby striking the ears at differing times.

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