主题：How to understand acoustic radiaton impedance in the case of infinite baffle?

The acoustic impedance Z (or sound impedance) is a frequency f dependent parameter and is very useful, for example, for describing the behaviour of musical wind instruments. Mathematically, it is the sound pressure p divided by the particle velocity v and the surface area S, through which an acoustic wave of frequency f propagates. If the impedance is calculated for a range of excitation frequencies the result is an impedance curve. Plane, single-frequency traveling waves have acoustic impedance equal to the characteristic impedance divided by the surface area, where the characteristic impedance is the product of longitudinal wave velocity and density of the medium . Acoustic impedance can be expressed in either its constituent units (pressure per velocity per area) or in rayls.

Note that sometimes vS is referred to as the volume velocity.

The specific acoustic impedance z is the ratio of sound pressure p to particle velocity v at a single frequency. Therefore

Distinction has to be made between:

• the characteristic acoustic impedance Z₀ of a medium, usually air (compare with characteristic impedance in transmission lines).
• the impedance Z of an acoustic component, like a wave conductor, a resonance chamber, a muffler or an organ pipe.