Sound amplitude is measured as root mean square pressure because ears sense pressure

Evidence

Because human ears are sensitive to pressure, which will be described in Chapter 2, and, because it is easier to measure, pressure is used as a measure of the amplitude of the sound wave. This gives a quantity that is known as the “sound pressure,” which is the root mean square (rms) pressure of a sound wave at a particular point. The sound pressure for real sound sources can vary from less than 20 micropascals (20 µPa or 20 × 10–6 Pa) to greater than 20 pascals (20 Pa). Note that 1 Pa equals a pressure of 1 newton per square meter (1 N m−2). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 190

Categorization

• DEFINE: Defines sound pressure as the rms pressure at a point and anchors the range of real sound sources.