Klarinet Archive - Posting 000203.txt from 2010/08

From: "Keith Bowen" <keith.bowen@-----.com>
Subj: Re: [kl] About clarinet acoustics
Date: Tue, 17 Aug 2010 06:52:29 -0400

Jennifer

One some of your points (snipping your original chain out, to show mercy to
Digest readers)

On waves inside the bore: Vanderveen shows that they are plane waves apart
from the boundary layer, which is only about 0.05 mm. These will slow down
the waves, but mean that one can use plane wave maths (hurrah). The speed
varies with bore flare (curvature), as I said before.

On turbulence: there is indeed turbulence around tone holes, though this has
little effect on the standing waves but a lot of influence on speaking of
the notes.

My first attempts at playing the bass clarinet, decades ago, was for
Britten's Albert Herring, a formidable part with prominent solos. I had the
University of Warwick cheap student plastic bass clarinet to use and was
having dire trouble getting notes to speak properly. After reading Benade on
turbulence, with my heart in my mouth, I dismantled the clarinet, found
extremely sharp edges to the inside of the tone holes, and rounded these off
a little with abrasive paper. No, I did not tell anyone I was doing this :).
The result was magic! The bass clarinet responded quite easily and I was
able to manage the part quite acceptably. (This is one effect in
undercutting holes, also, but that is a bigger change that affects tuning).

On amplification: no, a passive component such as a clarinet cannot possibly
add any energy to a sound. (That would contradict the Second Law, which as
we know is a hanging offence). Energy is all supplied by the player. What it
does is to take frequencies present in the sound generator (the reed
vibrations), and by means of the standing waves inside the clarinet, filter
these and allow some of them to build up over (a short) time till the volume
of those frequencies is relatively high.

Think of playing in a huge, resonant space such as a big church. Even a big
wind band cannot do a fast, very loud attack. It takes a few seconds for the
sound level to build up. But if they play a loud sustained note, within a
few seconds the sound level in the hall is deafening.

Your mouthpiece on its own will not contain low frequencies. But the reed
vibrates differently when it is up again a long air column (the vibrations
are coupled).

On fluid mechanics: I recall Einstein's advice to his son : "Don't go into
fluid mechanics. It's too hard." Compared to fluid mechanics, wave equations
and acoustics are dead simple. I'm not going down there...

Keith

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