Klarinet Archive - Posting 000093.txt from 1996/05

From: Peter Bellen <Peter.Bellen@-----.BE>
Subj: Re: A question about acoustics
Date: Mon, 6 May 1996 03:21:43 -0400

> Imagine a pulse (a very short, high pressure spike) traveling down the tube
> to the open end. As the pulse "hits" the open end, the pressure must
> always add to zero. Therefore, a negative pulse (a low pressure spike) is
> reflected back (the negative pulse and the positive pulse sum to zero at
> the node).
>
...
>
> State this mathematically and you get that the possible wave lengths are:
>
> 4L, 4L/3, 4L/5 etc.
>
> Or, in other words, the possible frequencies are:
>
> v/4L, 3v/4L, 5v/4L, etc. (only odd harmonics!)
>
> Do the same drawing excercise with a node at both ends and you will quickly
> discover that the allowed wavelengths and frequencies are respectively:
>
> 2L, L, L/2, L/3, etc. (wavelengths)
> v/2L, 2v/2L, 3v/2L, etc. (all harmonics)
>
> I hope this helps without getting too technical.
>
> ----------------------
> Jonathan Cohler
> cohler@-----.net
>

I fully agree with the above explanation (I admire the way you did it,
without the wave equation and its boundary conditions), but I've still
got one problem: how to explain the different behaviour of a soprano
saxophone and a clarinet?

Thanks,

Peter Bellen
peter.bellen@-----.be