Sound intensity does not rely on distance?

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z5017731
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Joined: Sat Jun 07, 2014 8:19 am

Sound intensity does not rely on distance?

Post by z5017731 »

Probably something obvious I have misinterpereted, but I don't understand how for the equation I=(1/2)*Ro*v*omega^2*(Smax)^2, not rely on distance from the source (no distance terms), as I=Power/Area suggests. This confuses me for questions such as calculate intensity at a distance.
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joe
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Re: Sound intensity does not rely on distance?

Post by joe »

Whether or not the intensity depends on distance depends on the geometry. For sound propagating down a pipe, the intensity is approximately constant. For uniform radiation in 3D space, I goes as 1/r^2.

In both cases, the formula you quote applies.
In the (lossless) pipe, the maximum displacement (Smax) does not depend on distance.
In the 3D radiation, the maximum displacement (Smax) is proportional to 1/r, so I is proportional to 1/r^2.

Joe
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