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Re: Question about EEb bass

On Sun, 28 Nov 1999 at 09:03:16 -0000, Mike Stevenson wrote:
> On 26th November Dave Taylor wrote:

> little modification. The standing wave set up in the instrument has a node
> at the bell end and an antinode at the mouthpiece, therefore the tube length
> will be equal to an odd multiple of half-wavelengths. In the case of the 2nd
> harmonic the length of the tube will be 3 half wavelengths. David calculates
> the wavelength of a low E natural to be 7.79m, that makes the
> half-wavelength 3.895m and the length of tube 11.685m (or approximately 38ft
> 4inches). This seems a bit long to me, perhaps we should ask Boosey &
> Hawkes.

Err, no. Brass instruments sound every harmonic. Instruments that only
do odd harmonics overblow at the 12th and 17th (e.g. clarinet family).

In a brass instrument there's a real (velocity) node at the mouthpiece,
and an effective node just outside the bell opening. Since the bell is a
hyperboloid, the node is probably near the asymptote.

So all notes have whole numbers of half-waves in the tube. The lowest
non-pedal notes therefore use a whole wave's worth of tubing. At
1100ft/sec, that's 14 feet (open) or 27 feet (4 valves down).

> I don't think it matters what length you use as long as you can justify it
> to the people who loose!

True, assuming you mean "lose".

Suggestion: get someone (e.g. local tech college metrology lecturer,
borough surveyor) to measure it for you before the contest, result in
sealed envelope. Open the envelope with great ceremony: no disputes!

Ian


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