Rayl

A rayl (symbol Rayl ) is one of two units of specific acoustic impedance and characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. These have the same dimensions as momentum per volume. The units are named after John William Strutt, 3rd Baron Rayleigh. They are not to be confused with the unit of photon flux, the rayleigh.

A rayl (symbol Rayl ) is one of two units of specific acoustic impedance and characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. These have the same dimensions as momentum per volume. The units are named after John William Strutt, 3rd Baron Rayleigh. They are not to be confused with the unit of photon flux, the rayleigh. {\underline{Z}(\mathbf{r},\omega) = \frac{\underline{p}(\mathbf{r},\omega)}{\underline{v}(\mathbf{r},\omega)}} where \underline{Z}, \underline{p} and \underline{v} are the specific acoustic impedance, pressure and particle velocity phasors, \mathbf{r} is the position and \omega is the frequency. {Z_0= \rho_0 c_0} Here, {Z_0} is the characteristic impedance, and {\rho_0} and {c_0} are the density and speed of sound in the unperturbed medium (i.e. when there are no sound waves travelling in it). In a viscous medium, there will be a phase difference between the pressure and velocity, so the specific acoustic impedance \underline{Z} will be different from the characteristic acoustic impedance {Z_0} . The MKS unit of specific acoustic impedance is the pascal-second per meter, and is often called the rayl (MKS: 1 Rayl = 1 Pa·s·m −1 ). The MKS unit and the CGS unit confusingly have the same name, but are not the same quantity (or unit): As an MKS unit, one rayl equals one pascal-second per meter (Pa·s·m −1 ), or equivalently one newton-second per cubic meter (N·s·m −3 ). Expressed in SI base units, that is kg·s −1 ·m −2 : 1 Rayl = 1 N⋅s/m = 1 Pa⋅s/m = 1 kg/(s⋅m ) As a CGS unit, one rayl equals one barye-second per centimeter (ba·s·cm −1 ), or equivalently one dyne-second per cubic centimeter (dyn·s·cm −3 ). Expressed in CGS base units, that is g·s −1 ·cm −2 : 1 Rayl = 1 dyn⋅s/cm = 1 ba⋅s/cm = 1 g/(s⋅cm ) The CGS unit rayl is ten times larger than the MKS unit rayl: 1 Rayl = 10 Rayl

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