impedance measurement?

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rory - 19 Oct 2005 10:56 GMT

Hi everyone, I am just figuring out some impedance related problems
using the formula Z = pc in free space where p=density of the medium
and c is the velocity of the sound. It's no problem to work and the
result I get is in kg m-2 s-1, where the -2 and -1 are exponents. How
do I read this? Is it kilograms in metres squared a second? That
doesn't sound right to me, can anyone clarify? Cheers,
Rory.

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liamovmanc - 19 Oct 2005 14:23 GMT

p = density = kg/m^3
c = speed of sound = m/s^2
p*c = kg/m^3 * m/s^2 = kg/(m^2 s) = m-2 s-1

> Hi everyone, I am just figuring out some impedance related problems
> using the formula Z = pc in free space where p=density of the medium
[quoted text clipped - 3 lines]
> doesn't sound right to me, can anyone clarify? Cheers,
> Rory.

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Jens Rodrigo - 19 Oct 2005 14:25 GMT

> Hi everyone, I am just figuring out some impedance related problems
> using the formula Z = pc in free space where p=density of the medium
> and c is the velocity of the sound. It's no problem to work and the
> result I get is in kg m-2 s-1, where the -2 and -1 are exponents. How
> do I read this? Is it kilograms in metres squared a second? That
> doesn't sound right to me, can anyone clarify?

Try here:

http://en.wikipedia.org/wiki/Acoustic_impedance

The letter p is not good for density rho,
because p means pressure in pascals.

Acoustic impedance is measured in N·s/m3

Pa is N/m² and N is kg m / s²

Jens

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Natural Science Forum / Physics / Acoustics / October 2005

impedance measurement?