sound pressure

sound pressure [′sau̇nd ‚presh·ər]

(acoustics)

effective sound pressure

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Sound pressure

The incremental variation in the static pressure of a medium when a sound wave is propagated through it. Sound refers to small-amplitude, propagating pressure perturbations in a compressible medium. These pressure disturbances are related to the corresponding density perturbation via the material equation of state, and the manner in which these disturbances propagate is governed by a wave equation. Since a pressure variation with time is easily observed, the science of sound is concerned with small fluctuating pressures and their spectral characteristics. The unit of pressure commonly used in acoustics is the micropascal (1 μPa = 1 μN/m² = 10^-5 dyne/cm² = 10^-5 μbar). One micropascal is approximately 10^-11 times the normal atmospheric pressure. See Pressure, Pressure measurement, Wave motion

The instantaneous sound pressure at a point can be harmonic, transient, or a random collection of waves. This pressure is usually measured with an instrument that is sensitive to a particular band of frequencies. A concept widely used in acoustics is “level,” which refers to the logarithm of the ratio of any two field quantities. When the ratio is proportional to a power ratio, the unit for measuring the logarithm of the ratio is called a bel, and the unit for measuring this logarithm multiplied by 10 is called a decibel (dB). The sound intensity, which describes the rate of flow of acoustic energy (acoustic power flow) per unit area, is given by the mean square pressure divided by the acoustic impedance, defined as the product of the medium density and compressional wave speed. See Decibel, Sound, Sound intensity