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Re: Gr. 9 Sc: Linings in Air Passages

DRURY wrote:
> effect of flesh linings in airways.  If I understand correctly, flesh both
> reflects and transmits sound.  Therefore, a sound wave which strikes flesh
> with bone underneath will produce two reflections: one from the flesh and
> another from the bone.  These two reflections will be out of phase by an
> amount which depends upon the thickness of the flesh layer.  If the wave
> length is long in comparison to the thickness of the flesh, the difference
> in phase will not be important.

Note that the speed of sound in flesh is much higher than in air, so
a thin flesh layer may not make much difference. Standard laws for
reflection of light should apply, like Snell's law (?) about how
much of a wave gets transmitted and how much reflected when a wave
hits a refractive index boundary (given the much different speeds
of sound, the refractive index should change substantially, much
more than in optics, and reflection should dominate).
What happens depends on the angle of incidence too-more reflection
is encountered if the wave plows in head-on, but in a throat or nasal
passage the wave is propagating parallel to the walls and reflection
also dominates for this reason. Higher harmonics excited by the
longitudinal waves that match resonance in the lateral direction
might couple into the fleshy layer better-in fact they may be
damped some this way. But this is really hand waving.

The interesting scientific test of acoustic reconstruction would be
to reconstruct comparable LIVING animals and compare the reconstructed
sounds to the observed. If you can't get a good reconstructions from
living animals, the hopes for a fossilized one...

Russ Andersson