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Acoustic Intensity

Acoustic intensity may be defined by

$\displaystyle \zbox {\underline{I} \isdefs p \underline{v}} \quad \left(\frac{\... ...mall Time}} \eqsp \frac{\mbox{\small Power Flux}}{\mbox{\small Area}}\right) $

where

\begin{eqnarray*} p &=& \mbox{acoustic pressure} \quad \left(\frac{\mbox{\small ... ...ad \left(\frac{\mbox{\small Length}}{\mbox{\small Time}}\right). \end{eqnarray*}

For a plane traveling wave, we have

$\displaystyle \zbox {p = R v} $

where

$\displaystyle \zbox {R \isdefs \rho c} $

is called the wave impedance of air, and

\begin{eqnarray*} c &=& \mbox{sound speed},\\ \rho &=& \mbox{mass density of ai... ...ume}}\right),\\ v &\isdef & \left\vert\underline{v}\right\vert. \end{eqnarray*}

Therefore, in a plane wave,

$\displaystyle \zbox {I = p v = Rv^2 = \frac{p^2}{R}.} $

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