Sound

Sound is defined as mechanical compression waves that propagate through a medium (solid, liquid or gas). Most sounds are combinations, but a theoretical pure sound can be described as having a given speed of oscillation or frequency measured in Hertz (Hz) and "loudness" or amplitude? with various measures such as decibel level or sone? level. The range of sound audible to the human ear? falls roughly between 20 Hz and 20 kHz at typical amplitudes with wide variations and response curves. Above and below this range are ultrasound and infrasound?. Some animals make use of ultrasound and infrasound for communication and echo-location.