Klarinet Archive - Posting 000263.txt from 2010/08

From: Diego Casadei <casadei.diego@-----.com>
Subj: Re: [kl] About clarinet acoustics
Date: Sat, 21 Aug 2010 12:01:19 -0400

Dear Nitai,

many thanks for your important cross check. It seems that your
measurement shows indeed that the difference between the quarter of
wavelength and the total length of the instrument is quite small, in
particular significantly smaller than my estimate of 8 cm. This means
that, indeed, the approximation in which the clarinet is seen as a
closed pipe at the reed end is quite good.

Apparently, I was wrong in neglecting the effects of the bell on the
velocity: wave refraction must play an important role there so that,
though there is a pressure max at the vibrating reed (as also found by
Benade), it appears that the position of the node is very near to such
maximum.

Best regards,
Diego

Nitai Levi wrote:
>>> Before doing more measurements it's sensible to see what has already been
>>> done! Please see my long email about Vanderveen's book.
>
> I used to have that book but for some reason can't find it anymore.
> Unfortunately I also remember next to nothing from acoustics and instruments'
> acoustics classes in university. I might read that email but I'm writing here
> more to offer measuring what others were interested in and no so much to find
> out myself.
>
>>> The half-clarinet measurement would be interesting, though. Measure the
>>> bore diameter as well to do the end correction.
>
>>> Oh and you need to measure temperature inside the bore. And until the
>>> clarinet warms up, there will be a big temperature gradient inside it.
>
> OK, I assembled the mouthpiece (with reed), barrel and upper joint. I let it sit
> outside in the room and put a thermomoter next to it. I don't have a better
> method to measure the temp. It's approx 27.5c. The length is approx 341mm (with
> I think +/-0.5mm is about right). The frequency is just a tiny bit over 257.8
> hertz.
>
> The bore of this clarinet is (as accuate as I can measure): 14.76mm at the
> bottom of the upper joint, 15.10mm at the top of the upper joint.
>
> So doing the same calculation as Diego, the (1/4) wavelength for this is almost
> 337mm. That's only 4mm less than the length of the clarinet upper joint
> including barreland mouthpiece. If also doing "plus 0.6 times the radius of the
> end" (which I'm not sure what this is at all) then it's about 8.5mm difference.
>
> Nitai
>
>
>
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--

Diego Casadei
__________________________________________________________
Physics Department, CERN
New York University bld. 32, S-A19
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