Acoustic impedance
| Sound measurements | |
|---|---|
|
Characteristic
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Symbols
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| Sound pressure | p, SPL |
| Particle velocity | v, SVL |
| Particle displacement | δ |
| Sound intensity | I, SIL |
| Sound power | P, SWL |
| Sound energy | W |
| Sound energy density | w |
| Sound exposure | E, SEL |
| Acoustic impedance | Z |
| Speed of sound | c |
| Audio frequency | AF |
| Transmission loss | TL |
|
|
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Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting of an acoustic pressure applied to the system. The SI unit of acoustic impedance is the pascal second per cubic metre (Pa·s/m3) or the rayl per square metre (rayl/m2), while that of specific acoustic impedance is the pascal second per metre (Pa·s/m) or the rayl. In this article the symbol rayl denotes the MKS rayl. There is a close analogy with electrical impedance, which measures the opposition that a system presents to the electrical flow resulting of an electrical voltage applied to the system.
For a linear time-invariant system, the relationship between the acoustic pressure applied to the system and the resulting acoustic volume flow rate through a surface perpendicular to the direction of that pressure at its point of application is given by
or equivalently by
where
Acoustic impedance, denoted Z, is the Laplace transform, or the Fourier transform, or the analytic representation of time domain acoustic resistance:
where
Acoustic resistance, denoted R, and acoustic reactance, denoted X, are the real part and imaginary part of acoustic impedance respectively:
where
Inductive acoustic reactance, denoted XL, and capacitive acoustic reactance, denoted XC, are the positive part and negative part of acoustic reactance respectively:
Acoustic admittance, denoted Y, is the Laplace transform, or the Fourier transform, or the analytic representation of time domain acoustic conductance:
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