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characteristic acoustical impedance

Sound characteristic impedance is a characteristic quantity for the sound resistance that a medium

opposes to the propagation of sound. The sound characteristic impedance is also referred to as the acoustic field impedance. In the far field, this begins at a distance of several wavelengths from the sound source

, and wherethe sound pressure and the sound velocity are in phase. The sound characteristic impedance (Z) is the ratio of the sound pressure and the sound velocity or the product of the density of the medium (kg/cbm) and the sound velocity

(m/s). It is a material-dependent characteristic value expressed in Newton-seconds per cubic meter (Ns/m3).

Sound characteristic impedance of various media

Sound characteristic impedance of various media

The sound characteristic impedance is directly dependent on the speed of sound or reciprocally dependent on the sound velocity. These values are directly dependent on the air density. This means that the sound characteristic impedance for air is lower at high temperatures than at low temperatures, since the air density falls with high temperatures and increases at low temperatures. The sound characteristic impedance is thus strongly dependent on temperature, changing from about 407 Ns/cbm at 30 °C to 445 Ns/m3 at -20 °C.

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Englisch: characteristic acoustical impedance
Updated at: 26.08.2020
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