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From: WVE~ol.com
Date: Mon, 1 Jan 1996 16:26:45 -0500
Subject: Re: Bending & Resonant Material

In response to Bobbie;

I have a new (to me) book by Hermann Helmholtz and a new (to me) partial
theory about bending. The column of air resonance that occurs with sound
waves traveling along a cavity like an organ pipe cannot occur in the mouth
because the "pipes" are too short at low pitches. In the organ pipe, the
resonant frequency is a function only of the length of the pipe, if we
disregard secondary effects like temperature. Diameter of the pipe affects
"voice" but not pitch.

In a helmholtz resonator (like a jug), the resonant frequency is a function
of the volume and the area of the hole.(the neck of the jug) It is
independent of wavelengths! The embouchure acting as a helmholtz resonator
could have a resonant frequency at the pitch of bent notes. Mystery...where
is the hole? Is it the reed slot in the coverplate, is it at the harmonica
mouthpiece, or is it somewhere in the throat? Do we bend by changing the
volume, the hole area, or both.????

>
>While I'm on this resonance kick, I might as well make this reeaalllly
>obnoxiously long and add my dime's worth on the materials thread. If there
>is no difference between the sounds coming from harps of different
materials,
>then I guess a wood guitar and a steel guitar sound alike, too. Same for a
>nylon string and a steel string acoustic. And a percussionist shouldn't
>fret over whether to knock on a metal or wood block. And a bronze bell will
>no doubt ring the same as silver one. It seems to me that since the density

>of a material determines how sound interacts with it, the particular sort
>of materials utilized in a harmonica WILL affect it's sound because of the
>distinct vibrational, resonant properties of those materials.
>

Nice pitch, lets see if I can hit it back:

All of the instruments you mention have features that the harmonica does
not...large internal volumes or large surfaces or high-Q mechanical parts
(like a bell or a string) capable of storing energy. They also depend on
these features to couple sound stored in a vibrating part to the atmosphere.
In a harmonica, the reed modulates the air directly. Reach in with a pin
and (gently) pluck a harmonica reed and listen to the almost imperceptable
sound produced by the vibration of the reed and its mechanical coupling to
the other parts. The tiny reed stores hardly any energy and the small, stiff
parts of the harmonica do not mechanically couple it efficiently to the
atmosphere. That is the only sound that can come from the vibration of harp
parts and is easily overwhelmed by the much louder sound coming from the
modulated airstream.

Interesting argument, is it not?

Vern