Rayl

A Rayl,rayl or Rayleigh is one of two units of specific acoustic impedance or, equivalently, characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. The units are named after John William Strutt, 3rd Baron Rayleigh, and not to be confused with the rayleigh unit of photon flux, used to measure airglow, and named after his son, Robert John Strutt, 4th Baron Rayleigh. It has the same dimensions as momentum per volume.

When sound waves pass through any physical substance the pressure of the waves causes the particles of the substance to move. The sound specific impedance is the ratio between the sound pressure and the particle velocity it produces.

Specific acoustic impedance is defined as:

where ${\displaystyle {\underline {Z}},{\underline {p}}}$ and ${\displaystyle {\underline {v}}}$ are the specific acoustic impedance, pressure and particle velocity phasors, ${\displaystyle \mathbf {r} }$ is the position and ${\displaystyle \omega }$ is the frequency.

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