Klarinet Archive - Posting 000676.txt from 2000/08

From: Bilwright@-----.net (William Wright)
Subj: Re: [kl] Plastic, wood and the G hole
Date: Wed, 23 Aug 2000 10:11:48 -0400

<><> Bill Wright wrote:
Since a standing wave involves reflection of colliding masses, and since
every action produces an equal and opposite reaction, I believe that the
mass (weight, if you wish) of the tube must affect the distance
travelled by the tube during its 'recoil'.

<><> Roger Shillcock wrote:
I don't think I understand this. The standing wave is in the air inside
the
tube, not the material of the tube.

I agree. I was thinking about the fact that the tube must absorb
some energy during each collision between the tube and an air molecule.
This introduces two effects:

(1) The tube must recoil a tiny distance and therefore the _closed
end_ of the tube (mouthpiece, where the wave begins) won't be at exactly
the same location when the next collision occurs. [Perhaps all the
collisions against the sides of the tube cancel out, but only if you
assume absolute non-compressibility and absolute rigidity and no tone
holes, which is a big leap in itself.] Therefore the starting location
of the next iteration of the vibration does not match the previous
location exactly, and the resultant (purely geometrical) phase
difference will affect the standing wave in the air column somehow.

(2) When considering whether this effect will be large enough to be
noticed by the human ear, keep in mind that there is a tremendous
difference between the total mass of the air vs the total mass of the
tube. Even the slightest transfer of energy is going to have much more
effect on the motion of air molecules than on the perceivable motion of
the tube. I include the word 'perceivable' because, except in a base
clarinet, I'm not sure if my hands 'feel' any vibration as I hold the
clarinet. This doesn't mean that the motion of air molecules inside
aren't being affected mightily by the slight energy that they give up to
the tube.

But probably the most important concept is that several "machine
mouths" already exist, complete with extensive photographic and
recording equipment. I would've thought that somebody had done this
experiment already, and that someone on this List would have replied to
me: "Bill, it's already been done, see the following article:
www.whatever.whatever."

Also, I am still caught by the G hole chimney question. If
manufacturers have found that the difference is wall thickness is
acoustically significant, then the entire question is answered already,
isn't it? (Not so if some machine tool problem encourages a different
wall thickness just for manufacturing efficiency.)

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