Klarinet Archive - Posting 001435.txt from 1999/01

From: Tony@-----.uk (Tony Pay)
Subj: [kl] Leaky pads good??!!
Date: Fri, 29 Jan 1999 04:28:58 -0500

On Thu, 28 Jan 1999 21:13:03 PST, scottdmorrow@-----.com said:

[snip description of 'bodged up' instrument]

> Then someone will write for this "period instrument", and future
> generations will be in a quandary over how to play the piece on
> "modern" clarinets while still attaining the "sound" the composer had
> in mind!

Though Scott is taking the p*ss here, there is a fact about the
acoustics of actual period instruments, related to their leather pads,
that is not very well known. I personally try to make my instruments as
airtight as possible for reasons of security, but I was surprised to
hear that that may not be how they sound at their best. And I found it
interesting and illuminating to learn why, even if I don't take
advantage of the phenomenon.

Instruments with flat leather pads, even properly adjusted ones,
often aren't quite as airtight as modern instruments. When the
adjustment isn't optimum, there is a significant probability of
disaster, in fact; and this was at least part of the reason for the
initial resistance to clarinets with keys, until the technology matured
a bit more.

But a slight failure to be airtight has another effect on the
instrument. The effect is to flatten and broaden the resonance peaks of
the tube.

As has been explained here before, the clarinet tube for a given
fingering has resonance peaks that correspond only approximately to the
harmonics of the fundamental pitch that is being sounded. When these
resonance peaks correspond well, the sound is richer in harmonics; and
when they correspond less well, the harmonics are not so strong.

So if the tube is very slightly leaky, the effect is that the resonance
curve, rather than having very steep high peaks, as it would if the tube
were completely airtight, instead has lower peaks that are approached
more gently. The summits of the peaks are in the same place, but lower
than the 'airtight' ones, and on either side of them the tube is
actually *more* resonant than before.

(Just to be clearer about what is meant by this picture I'm describing:
the tube resonates differently to different frequencies. If you draw a
picture of how resonant the tube is for varying frequencies, you get
a curve that looks like a mountain range, with the high peaks at
frequencies where the tube is more resonant, and valleys at frequencies
where it's less resonant. In the picture, the height at a given
frequency is a measure of how much resonance you get from the tube at
that frequency.)

But what this means is that a harmonic that was 'off-peak' when the
instrument is airtight can actually be amplified *more* if it's slightly
leaky. So the sound is actually richer in harmonics, which is what you
mostly want, even though you have to work harder to get it. The
response of the instrument is also more even.

I'm told that some horn players use a similar technique to make 'tricky'
notes more secure: they allow a bit of air to escape at the embouchure,
thus broadening the resonance peaks of the instrument so that it gives
more 'help' to the pitch that they want.

Tony
--
_________ Tony Pay
|ony:-) 79 Southmoor Rd Tony@-----.uk
| |ay Oxford OX2 6RE GMN family artist: www.gmn.com
tel/fax 01865 553339

.... I don't steal taglines -- I replicate them.
.

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