Mechanical waves

As both items are of the same nature it boils down to attenuation properties of the barrier. In mechanical (acustic) matters there is NO such thing as perfect reflection. Make your measurements sensitive few orders of magnitude more and the results will be VERY instructive.

Good luck.

Stanislaw.

I don't know much about sound wave but all waves can be described by a set of partial differential equations (PDE). when wave passes a boundary between

2 medium (air and wall), the PDE must be satisfied at the boundary. this usually yields 2 products -- the transmitted wave, and the reflected wave. This is relatively easy to imagine if you think of a traveling EM wave entering a dielectric medium from free space, at the boundary, the E&M fields must satisfied the Maxwell's Equations. The result is frequency and medium dependent. For some condition, the transmitted wave is much greater than the reflected (S21>>S11), for other conditions, it's the other way (S11>>S21).

By solving your PDE, it shoul tell how much energy got reflected vs transmitted. hth, Calvin

A thin, flexible wall, exposed to low-frequency sound, will move with the pressure waves and act like a piston on the far side, so will be almost transparent to sound. An infinitely stiff wall of any thickness, or a wall of very high density, will reflect most of the sound.

At high frequencies, as the mass of the wall becomes harder to move at the sound frequency, the wall becomes essentially immobile and classic "optical" reflection/transmission rules start to apply. Since the wall's density is generally a lot higher than air's, in "optical" situations most of the sound will be reflected.

That's why you hear mostly the bass of your neighbor's terrible, loud music. It's shaking your walls.

In optics, the incoming wave doesn't cause a wall to move, so the behavior is simpler.

There's probably some formal math, probably googl'able, on sound transmission through thin, flexible walls.

John

Have a look at

There's a whole range of magnificent physics demonstrations done as Java 'applets'. Enormous fun!. Play with the '2D ripple tank' and use your mouse to add a couple of walls and slots etc. It's then clear as to what happens to the reflections when the frequency is taken up and down. Seems to me that the long waves can't cleanly reflect, as they are simple too diffuse wrt the obstacles. I.e they've gone round/slid along the obstacle before the wave reverses.

"Adam"

** Your facts are cockeyed.

For 10kHz to pass through a wall, it would have to be made from thin paper.

All solid walls refect sound pressure waves and only to the extent they can be made to vibrate (at the frequency concerned ) will that sound wave pass to the opposite side.

A solid, smooth wall reflects all sound and supersonic frequencies.

...... Phil

Le Wed, 26 Sep 2007 00:40:21 +0100, john jardine a écrit:

Great link! Thanks.

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Thanks,
Fred.