Klarinet Archive - Posting 000455.txt from 1998/01

From: Mark Charette <charette@-----.com>
Subj: Re: tuning and articulation
Date: Fri, 9 Jan 1998 14:27:48 -0500

George Kidder wrote:

> Why this is important is said to be due to the different molecular weights
> of the two gasses. Oxygen has a molecular weight of 32, while carbon
> dioxide has a molecular weight of 44 (round numbers). Therefore, room air
> (the start of an expiration) will be less dense than main-stream air (the
> balance of the expiration), which will result in a higher vibration
> frequency (pitch) for the same resonance structure (the instrument, lips,
> reed, etc.) [Have you ever seen a demonstration of the effects of a breath
> of helium on the pitch of the voice? Same phenomenon in the extreme.] The
> difference in densities should be about 1.8% maximum.

Francl Laloe (who at least _used_ to be on this list) is a
physicist and made this comment on the list back in October
1996:
> >
> >Speed of Sound in Different Media
> >
> >"....The speed of sound in a given medium also depends on the density of
> >the material,
>
> True for liquids and solids, not for gases. As I posted before, in gases
> what counts is the velocity of the microscopic particles, their number per
> volume does not. The density is irrelevant, and this useful property is used
> in some laboratory devices.
> As for the temperature dependence, it of course exists, but it is not very
> pronounced; the velocity is proportional to the square root of t+273, so
> going from zero degree to 30 degrees changes the velocity by only 5 per cent.
>
> >will be given by the speed of sound in a gas, divided by the characteristic
> >wavelengths of the resonant vibrators. Since the speed of sound is now
> >three times larger than it was in air, the frequencies will also be three
> >times larger. The resonant vibrator is the main determinant.
>
> Yes, this is basically correct. With hydrogen, the effect would be even more
> pronounced. But please do not try!!! Beware of explosions. Helium is safer.
>
> I promise, I will not post again on physics for at least a century! Franck
> Franck Laloe, labo de physique de l'ENS, 24 rue Lhomond, F75005 Paris (France)
> tel 33 (1) 47 07 54 13, fax 45 35 00 76 -- laloe at physique.ens.fr

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