Klarinet Archive - Posting 000435.txt from 2002/05

From: Tony@-----.uk (Tony Pay)
Subj: [kl] Turbulence (was, "grunt")
Date: Fri, 17 May 2002 04:07:42 -0400

Audrey wrote, about her 'grunt':

> Being an amateur, I probably can't help much with how it works, though
> Morrie can.....HEEEEEELLLLP, MORRIE! I can describe what it looks
> like, though: it looks like a long, sharpened pencil lead with the
> thicker end attached to the middle of the register key pad. It goes
> in and out as the register key is opened and closed. Why it works I
> don't know, but it does, and I'm delighted with it.

One of the things that gets in the way of efficient operation of a wind
instrument is turbulence. Turbulence is very often characterised by the
simultaneous presence in the system of many frequencies of vibration;
energy that would otherwise emerge as musical sound emerges instead as
'noise'.

Aircraft, too, have to minimise turbulence in order not to waste energy;
that can sometimes be achieved by making slight changes to the geometry
of the wing. These changes help the airflow to be smooth, instead of
broken up.

A good, everyday example of turbulence is the flow of water from a
simple tap (faucet). If you turn on a tap to medium flow, then the
water exits in a smooth cylinder. Increasing the flow rate, you can
observe that at a certain critical point the smooth surface of the water
breaks up, and the flow becomes turbulent.

You can delay the onset of this turbulence by rounding the edge of the
inside of the tap, where the water exits. Sharp 'corners' tend to
encourage turbulence.

Analogously, you can improve the 'ring' of a clarinet at louder dynamics
by rounding the sharp edges that the airflow encounters, both inside and
outside the instrument. (We're talking about a very tiny amount of
rounding here, almost invisible to the naked eye. It's nothing that
could possibly affect intonation.) The effect is that you can get to a
higher dynamic before the sound starts to break up -- just as you can
get to a higher flow rate in the tap before the smooth stream of water
starts to break up.

Remember, in the case of the clarinet, we're not just talking about
turbulence in the passage of air down the instrument. It's turbulence
in the forwards and backwards flow of air implicit in the *vibration* of
the whole aircolumn that has the sound 'break up' at higher dynamics.
So, actually, the quality of the instrument at lower dynamics can be
affected too.

It's been suggested that one of the differences between the response of
wood clarinets in general and the response of metal clarinets in general
can be traced to the different degree of 'rounding' that different
manufacturing techniques tend to produce.

It's also why instruments 'go' better when they're warm than when
they're cold. The onset of turbulence is temperature-dependent (it
occurs earlier at lower temperatures), so the 'dull' response of your
instrument on a cold day has a physical basis.

Much of this is covered in Benade, pp 500/501.

So finally, I imagine that the 'grunt' is one of those small alterations
of geometry that help the airflow round the pad not to be turbulent. In
this case it isn't a question of the turbulence interfering with the
vibration of the instrument; it's just that it makes a noise that you
don't want.

Tony
--
_________ Tony Pay
|ony:-) 79 Southmoor Rd Tony@-----.uk
| |ay Oxford OX2 6RE http://classicalplus.gmn.com/artists
tel/fax 01865 553339

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