Characteristic Impedance

The characteristic impedance of a material is the ratio of sound pressure to particle velocity for sound waves travelling inside the material. For air it is equal to the density of air times the speed of sound. Its main use is in calculating other more directly useful properties such as the absorption coefficients. It can also be defined as the product of the effective complex density and the complex speed of sound. It may also be derived from the complex compressibilty and complex density (see Beranek Noise and Vibration Control Chapter Ten).