Sound Waves

• Sound waves are longitudinal disturbances that travel in a fluid.

• Sound involves time-dependent changes of density, with which are associated time-dependent changes of pressure, temperature and positions of the fluid particles (Fahy, 2001).

• Sound is generally associated with sound pressure variations in air within a frequency range from about 20 Hz to 20 kHz, which corresponds to the general range of the human auditory system. Vibrations of fluids outside this range are referred to as infrasound or ultrasound.

• Sound is often transmitted from one volume of fluid to another by means of audio-frequency waves in solid media (often referred to as structure-borne sound.

• In musical acoustics, sounds often result from the transmission of mechanical vibrations in solids into air pressure fluctuations (such as in stringed instruments).

• The speed of sound in air is approximately given by $c = 331.3 + 0.6 t$ (meters / second), where $t$ is the temperature of the air in degrees Celsius. A value of 345 meters / second is a good estimate at room temperature.