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From: JJTHAD~ife.uams.edu
Date: Tue, 19 Mar 1996 22:32:37 -0500 (CDT)
Subject: Re: question on bending the same note on different key harps.

Mike Curtis writes,

>Bending is caused by overcoupling a second resonant device tuned to a pitch
>close to that of the first reed.

If this explanation were sufficient, then a second resonant device tuned to a
pitch just sharp of the reed should cause that reed to bend up. To my
knowledge, this does not occur. A second observation that is not explained
by this statement is that there is remarkably little effect of blocking the
higher-pitched of two reeds in a hole on the pitch, clarity, facility, or
loudness of a bend already initiated. Block the draw reed on diatonic hole
6 while doing a draw bend. The bend continues, nice as you please. This
is true for blow bends too, when the blow reed is blocked.

The latter observation suggests that the explanation may not only be insuf-
ficient, but wrong. An alternative explanation for two-reed bends is that
the lower-pitched of the two reeds -- the one which is being played with air
streaming in the "wrong" direction -- is really the major player in two-reed
bends, and when played in this way, can vary over a wide range of pitches
depending on other variables in the airway.

So are those "other variables" some kind of overcoupling of a second resonant
device? In other words, is the overcoupling hypothesis still correct, but now
with the second resonator being the performer? I seriously doubt it. The
reason for my doubt is that I can control the pitch of an "opening" reed (the
term coined by R. Johnston for a reed played in the "wrong" direction) with
changes only in air pressure while maintaining the geometry of my mouth and
throat as fixed as I can.

Mike quotes Robert Johnston from a private communication:

> In my paper you will find that the reed with the other hole blocked do
> bend a bit. The reason that they dont bend further in the experiment
> is that the as the tube is extend the reed hooks onto the next pipe
> resonance rather than continuing to bend. This doesn't happen in the
> mouth because the upper resonances are not harmonic and are weaker.

I do wish he had expanded upon this, because it is not evident to me why weaker
and nonharmonic upper resonances in the mouth, if indeed so, can explain the
failure of the reed to "hook" onto the next mouth resonance, as RJ says it does
with the adjustable-length tube. His explanation for the limited bending of
isolated reeds with his apparatus seems to gain support from the fact that
those reeds do succeed in bending slightly further when the tube length is
right for the second bending cycle compared to the first, presumably because
the second and third tube resonances are further apart than are the first and
second. This can be seen in Figure 4, for example.

- John Thaden