Beats- a throbbing variation in the loudness of sound caused by interference when two tone of slightly different frequencies are sounded together.
compression- A pulse of compressed air (or other matter); opposite of rarefaction.
forced vibration - The vibration of an object that is made to vibrate by another vibrating object that is nearby. The sounding board in a musical instrument amplifies the sound through forced vibration.
infrasonic - Term applied to sound pitch too low to be heard by the human ear, that is, below 20 hertz.
natural frequency - A frequency at which en elastic object, once energized, will vibrate. Minimum energy is required to continue vibration at that frequency. Also called resonant frequency.
pitch - Term that refers to how high or low sound frequencies appear to be.
rarefaction - A disturbance in air (or matter) in which the pressure is lowered. Opposite of compression.
resonance - A phenomenon that occurs when the frequency of forced vibrations on an object matches the object's natural frequency, and a dramatic increase in amplitude results.
ultrasonic - Term applied to sound frequencies above 20,000 hertz, the normal upper limit of human hearing,