Klarinet Archive - Posting 000100.txt from 2010/08

From: Tony Pay <tony.p@-----.org>
Subj: Re: [kl] Location of antinodes of vibration in an air column
Date: Sat, 14 Aug 2010 09:48:26 -0400

On 14 Aug 2010, at 03:40, Richard Sankovich wrote, in part:

> Diego, thanks for your detailed explanation of sound production by vibrating strings and air columns. I must take issue, however, with your conclusion that there will be a vibration antinode at the energy source, or, in your words, a point of maximum amplitude.

What Richard subsequently says fits in with what 'my guy':-) Michael McIntyre writes to me. (I wrote to him asking whether in his opinion the 8cm is theoretically sustainable, not having yet checked your actual experiment.)

I quote:

> ...havoc over elementary acoustics :-[ due largely to the usual failure to follow (forgive me)
> lucidity principles, even though I see you're trying to set a good example, which of course no-one notices.
>
> I find the 8 cm plausible enough. I check the wavelength calculation even though I can't check the length of a B flat clarinet just now. The end effect adding
>
>> about half a centimeter outside the bell
>
> seems about right. But the following might repay a moment's attention, regarding bottom written E:
>
>> we have an antinode at the end of the bell,... also an antinode at the reed
>
> which is plainly wrong whether "antinode" means "pressure antinode" or "displacement antinode", as well as in failing to replace "at" by "near". That creates the double absurdity that the pipe length is not only a half instead of a quarter wavelength, but also _exactly_ a half wavelength.
>
> So, just through slight carelessness, we have a deadly combination of inexplicitness with incongruous repetition, with the one word "antinode" meaning two quite different things", namely
>
> (1) the displacement antinode near the end of the bell, and
>
> (2) the displacement near-node in the mouthpiece adjacent to the reed,
>
> which the writer calls an "antinode" perhaps because he's suddenly become amnesic about the distinction between "some displacement" and "maximal displacement" and about the fact that the reed can support a helluva pressure amplitude, even if not quite maximal unless you bite the reed down.
>
> love M
>
> PS Please urge everyone concerned to take two minutes on www.atm.damtp.cam.ac.uk/people/mem/lucidity-in-brief/

Anyway, I am very surprised about the 8 cm. It throws off most of my rule-of-thumb assumptions about where to modify bore dimensions in order to change twelfth relations. Perhaps I'll do better in future:-)

Thank you Diego; and apologies for reading you far too superficially at first.

It just goes to show, again, that being specific about criticism (as you were) is worthwhile.

Tony
--

Tony Pay
79 Southmoor Rd
Oxford OX2 6RE
tel/fax +44 1865 553339
mobile +44 7790 532980
tony.p@-----.org

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