Term applied to sound frequencies above 20,000 hertz, the normal upper limit of human hearing.
Natural Frequency
A frequency at which an 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.
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.
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.
Beats
A periodic variation in the loudness of sound caused by interference when two tones of slightly different frequencies are sounded together.
Rarefaction
A disturbance in air (or matter) in which the pressure is lowered. Opposite of compression.
Infrasonic
Term applied to sound pitch too high to be heard by the human ear, that is, below 20 hertz.
Compression
In sound, a pulse of compressed air (or other matter); opposite of rarefaction.
Ultrasonic
Term applied to sound frequencies above 20,000 hertz, the normal upper limit of human hearing.
