A unit of specific acoustic impedance and of characteristic impedance, based on the ratio of sound pressure to particle velocity at some point. In the centimeter-gram-second system of units, the specific acoustic impedance is 1 rayl (cgs) when a sound pressure of 1 microbar produces a linear velocity of 1 centimeter per second, = 10 pascal-seconds per meter.
Beranek (1954)1 distinguishes between the "mks rayl", defined as "newton-sec/m³" and the "rayl", which is in the cgs system and defined as "dyne-sec/cm³". In other words, in both the MKS and cgs systems, the rayl is the ratio of unit pressure to unit velocity.
Forty-eight years later, the American Institute of Physics Desk Reference2 defined the rayl only as a unit of specific acoustic impedance, with the definition first given above.
The rayl is not one of the special units approved by the CGPM for use with SI.
The unit is named for the English physicist John William Strutt, third Lord Rayleigh (1842-1919). In Britain, "Rayleigh" is pronounced ray-lee, not rawl-ee, as Americans pronounce Raleigh, the city in North Carolina. The name of the unit is also pronounced with a long a, like the "rail" in "railroad."
1. Leo L. Beranek.
Acoustics.
New York: McGraw-Hill, 1954.
Page 11.
2. E. Richard Cohen, David R. Lide, George L. Trigg, editors.
AIP Physics Desk Reference. Third Edition.
New York: Springer-Verlag, AIP Press, 2003.
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