Klarinet Archive - Posting 000506.txt from 1995/09

From: Jonathan Cohler <cohler@-----.NET>
Subj: Re: undertones controversy
Date: Mon, 25 Sep 1995 11:54:14 -0400

Everett J. Austin said:

>Beware of clarinetists bearing equations. I would like to point out an a
>single inaccuracy in Mr Cohler's recent communication in which he refers to
>Benade's Fundamentals of Musical Acoustics and also to work done by Backus
>described therein:
>
>"They also noted (and this is key) that as you reduce the pressure of the
>embouchure against the reed, the airflow reaches its maximum at a lower
>pressure P-p, and the reed finally closes off at a lower pressure. Also,
>the maximum airflow reached is lower."

Oops! You're right, Everett. In my haste, I reversed the two. Tighter
embouchure lowers the curve. Which in turn brings the operating point
closer to zero pressure.

Nonetheless what I said still applies. For example,the discussion of the
other parameters such as lowering the pressure point on the reed (by moving
the jaw forward) to get rid of the unwanted partials is very important.
This has the desired effect of lowering the operating point and increasing
the downward slope of the curve.

I believe the reason you need to simultaneously reduce the pressure on the
reed (even though this would raise the operating point back up somewhat),
is that when you make the motion of pushing your jaw forward, the natural
tendency is to increase the pressure on the reed (try it you'll see what I
mean), because you are pushing forward against the reed. By supplying a
compensating force with your left thumb against your top teeth, it allows
you to keep the pressure constant at an optimal point.

The other motion I mentioned was lifting the tongue higher in the back.
This has the effect of slightly changing the angle at which the airstream
impinges on the reed, which, I believe, effects the reed resonance (this is
the kind of subtle change that Bonade mentions in passing). Also, the
exact "focus" of your embouchure (i.e. precise distribution of pressure
across the reed by your lower lip) has a subtle effect on reed resonance.

All of these reed resonance adjustments are what help to get rid of the
undertones, which arise when the notes you are playing get close in
frequency to the natural reed resonance (which is 2000 to 4000 Hz). For
example, at the B just above the staff the frequency is 880Hz. It's third
harmonic, which is the first strong overtone, is 2640Hz which falls right
into the range of the reed resonance, and hence the problems begin right
around there.

Sorry for all the physics. But I think it is helpful to undertanding
what's going on.

And thanks for the correction.

-----------------------------

Jonathan Cohler
cohler@-----.net