What is Sound?

• Sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid.

• Humans have a limited range of reception for sound pressure variations of about 20 - 20,000 cycles/second or Hertz (Hz).

• Sound travels at about 345 meters/second in air at room temperature. Using the relation $\lambda = c/f$ between frequency ($f$), wave speed ($c$) and wavelength ($\lambda$), a sound at 20 Hz has a wavelength of about 17.25 meters, a sound at 1000 Hz has a wavelength of about 0.3 meters and a sound at 20 kHz has a wavelength of about 17 millimeters.