Klarinet Archive - Posting 000873.txt from 2003/03

From: Tony@-----.uk (Tony Pay)
Subj: Re: [kl] Introduction
Date: Sat, 22 Mar 2003 10:35:34 -0500

On Sat, 22 Mar 2003 06:44:03 -0800, leeson0@-----.net said:

> Bill Hausmann wrote:
> >
> > The saxophone, having a CONICAL bore, overblows an octave, as does
> > the oboe (yes, it really is conical). The clarinet, being basically
> > cylindrical, overblows the twelth.
> >
> > Bill Hausmann
>
> Bill, I still remain a confused person with respect to a wind
> instrumnet overblowing of an octave as contrasted with a 12th. Your
> comment above suggests that it is the geometry of the bore of the
> instrument that determines the nature of the overblow; i.e., conical
> overblows an octave while cylindrical overblows a 12th.
>
> While I do not doubt that the bore geometry does have an impact on the
> overblow phenomenon (though I have no idea why), I still point out
> that a clarinet with a cork stuck in the moutpiece end of the barrel,
> and with a hole in that cork big enough to hold an oboe reed, and with
> such a reed inserted in that hole, will produce an instrument with a
> cylindrical bore that overblows an octave.

Well, I've never tried this myself, though you say later that others
have. I will organise that we try it in the orchestra tomorrow.

What I would expect is, overblowing neither an octave nor a twelfth over
most of the range; but closer to an octave with fingerings corresponding
to short tube-lengths, and closer to a twelfth with fingerings
corresponding to long tube-lengths. That's because an oboe reed itself
approximates a cone, so sticking a short cylindrical bit onto it keeps
it 'more' conical than sticking a long cylindrical bit onto it.

Still, we shall see!

Of course, real oboes and clarinets are only approximately cones and
cylinders. So the mathematics that indeed does predict octaves for
cones and twelfths for cylinders isn't accurately applicable to real
instruments -- which doesn't mean, of course, that real instruments
can't be coerced into producing octaves and twelfths by clever design.

I wrote about the cone/cylinder mathematics in a long-ago post:

http://www.woodwind.org/Databases/Logs/1998/12/000783.txt

...in the course of which I said that it's difficult to make the octave
overblowing of the oboe intuitive without quite complicated mathematics.

But I now see that the new UNSW acoustics reference page, courtesy of
Joe Wolfe, produces a version of the argument that manages to sidestep
most of the complications:

http://www.phys.unsw.edu.au/~jw/pipes.html

So I hope that's helpful.

Tony
--
_________ Tony Pay
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