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Klarinet Archive - Posting 000847.txt from 2000/09

From: "Karl Krelove" <kkrelove@-----.net>
Subj: RE: [kl] Reed behavior on mouthpiece
Date: Tue, 26 Sep 2000 16:52:15 -0400

> -----Original Message-----
> From: William Wright [mailto:Bilwright@-----.net]
>
> Notice that Benade says that the sound wave's amplitude continues
> to increase after the reed begins to close completely. Thus full
> closure does not (according to Benade) limit the sound's volume.
> Elsewhere in section 21.3, Benade talks about pressure, not
> continuity of airflow or volume of airflow, as determining the sound's
> amplitude.
>
>
> Cheers,
> Bill

I've always read these acoustical discussions with fascination, even though
my physics background is much too limited to be able to contribute anything
useful. I am having trouble at an intuitive level visualizing how a reed
vibrating as it does in a periodic motion could continue to increase the
distance through which it vibrates (amplitude?) once it begins hitting the
mouthpiece rail.

If I put my hand up to interfere with a clock's pendulum, the pendulum swing
becomes erratic and doesn't (whenever I've tried it) rebound even to the
point where it had started. If I touch a finger to a vibrating string, its
volume is muted (and/or it divides into harmonics). I don't think I can make
it louder with greater bow speed or pressure once my finger begins to
interfere with its vibration.

I can't visualize the reed's motion through any greater a total distance
than twice the tip opening (equal distance in each direction from its rest
point) without it's becoming erratic and out of control. If the amplitude of
the sound is directly related to the amplitude of the reed's vibration (?),
then, I'm having trouble understanding how the sound could continue to get
louder beyond the point where the reed begins to beat against the
mouthpiece's tip rail. Unless it's actually flexing farther into the baffle
area once contact at the tip has been made.

This is, of course, assuming that the resting point is at the center of the
vibrating displacement. Maybe this doesn't need to be true?

I apologize if this is answered explicitly in Benade or Backus. I've read
bits and pieces of each but may not have recognized the answer even if I had
seen it. I'm making my lack of physics grounding very obvious, but I'm very
curious about this and am not sure I'd understand the answer if I could
indeed find it in the books. I'm taking a deep breath and reciting the
bromide "The only stupid question is the one you don't ask."

Karl Krelove

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