Klarinet Archive - Posting 000191.txt from 2002/03

From: w6w@-----. Wright)
Subj: Re: [kl] Re: "Choking" the bore
Date: Tue, 12 Mar 2002 15:31:31 -0500

<><> Dave=A0Spiegelthal wrote:
Bill Edinger wrote about the bore mismatch between the bodies and bells
of two of his clarinets

I can offer a data point. I have two bells for my Bb. One bell is the
normal flared shape, and the other is spherical (an adaptation of
Stadler's much-discussed basset). The bore IDs of both bells match my
clarinet's lower joint bore ID very closely. If I use a wooden dowel
as a 'feeler' inside the assembled horn, I can (just barely) feel where
the bell and joint bores meet, but only just barely.

<><> As I understand it, both approaches [both mismatches of bore ID]
should have the same effect, namely, to create an impedance mismatch at
the bottom of the clarinet to promote reflection of the pressure wave
travelling down the instrument

I believe it is more accurate to say that the wave is reflected by a
_very large_ change in impedance, namely the change where (thanks to
whichever holes are currently open) the walls of the horn effectively
'disappear'. By comparison, the change in impedance caused by a
comparatively slight amount of bore mismatch is not enough to be useful
(that is, the change is slight compared to the change where the walls
effectively disappear).

By the way, impedance is measured as a ratio between pressure and volume
of flow, not between two pressures or two flow volumes.

Many things 'perturb' the air column in a clarinet, not the least of
which is the holes themselves. One model of clarinet now has a bulge
in its bore in order to improve the tuning. But it is my understanding
that a discontinuous change, such as a mismatch between two sections of
bore, is generally considered to be a "bad thing", even though (as in
tone holes) it is unavoidable.

<><> from having read Benade's book

Benade wrote two books (at least?) which discuss horn physics. His
more conversational book --- Horns, Strings and Harmony, $10 in
paperback --- doesn't mention the word "impedance" in the index, but it
does explain what bells really do and how they affect the horn's entire
sound (high notes as well as low notes). You may find this book is an
interesting and more 'friendly' read.

Cheers,
Bill

---------------------------------------------------------------------
It's Sneezy.Org Pledge time again. Please visit
http://www.sneezy.org/Pledge.html for more information.