Phenomena and measurement
A reminder of physical acoustics

When an air particle is displaced from its equilibrium position, a temporary local increase in pressure Δp relative to atmospheric pressure P₀ occurs. Before returning to its equilibrium position, this particle transmits the disturbance to adjacent particles. The propagation of this cycle of compression and depression constitutes the sound wave.

The wide variety of sounds we can detect as humans or with measuring devices means that we need to be able to describe a wide range of sound pressures, particle velocities, frequencies and intensities. Assuming that perceptible frequencies range from 20 Hz to 20,000 Hz, we have a multiplication factor of 10³. For their part, the difference between the minimum perceptible sound pressure and the pain threshold is in a ratio of 10⁷, which represents a ratio between energies or intensities of 10¹⁴. For this reason,...