Text: From: johan.liljencrants@telia.com.geentroep (Johan Liljencrants) To: "rolls@foxtail.com" Date: Sun, 30 Apr 2000 22:31:23 +0200 Subject: Reed Voicing in Organ Pipes A few back comments remaining to the recent thread: John Nolte (MMD 00.04.24-09) mentions that 'High speed photography shows that a properly curved tongue never actually strikes the shallot'. To illustrate and verify my earlier description of the tongue 'rolling and bouncing' I might refer to a paper [1] showing among other things the time dependence of the reed aperture (optically measured) and the dependence of frequency from blowing pressure (which would not be there without the rolling). These are taken from a conventional organ reed pipe mechanism in order to verify a mathematical model. So is there a controversy? Really, I tend to say no, because of John's particular word 'properly'. No doubt you can find an operating point where everything is right, but I remain amazed at the precision required to get there, in dimensions and shape of the tongue, and in blowing pressure. In the same spirit John Page (MMD 00.04.26-08) describes the proper way to curve the tongue by banishing. Reminds me of a famous movie scene where Picasso paints a perfectly balanced bird on a glass pane, in one single draw with his brush. I have not interviewed too many persons knowledgeable in reed voicing (3), but what strikes me is they all gave me different recommendations on tools, in particular the banishing support. Whether steel or hardwood, flat or concave, and whether to lift the free end of the tongue or not. I appreciate John Page's good steel cigar, so far I have had to put up with a heavy screwdriver and a flat steel block. You may note that banishing (repeatedly) against such a flat and non yielding surface does give a curve, concave toward the banishing cylinder. Also I was once recommended to try twisting (!) the tongue toward its end, in order to soften the final part of its bouncing against the shallot. I have done so several times with a satisfactory result. To me, that is ;) I have seen mention that one could make the reed curve either circular (as would be with uniform banishing, not saying this is the right thing to do) or parabolic. But if you load the tongue with a force distributed evenly along it, like the force exerted on it by the blowing pressure, then it takes a different shape from both of these. And loading with a single force like lifting or pressing at the tongue tip yet another one. Comparing these four shapes, normalized such that the fixed ends and the tips are the same places, then the parabolic and the distributed force shapes are the most extreme - half way along the tongue they differ by 10% of the tip deviation. This tells something about the precision requirement. If the tip gap is 0.5 mm then the middle gap for all four shapes spans a range of 0.05 mm. And the difference here between the circular and the parabolic shapes are 0.008 mm. May I put a tiny question mark as to what tolerances even a skilled voicer can keep under control? Robbie suggested methods to measure the reed action. I could add a polarized PVDF (polyvinylidene fluoride) foil with a silver coating both sides which works as a piezoelectric transducer (Measurement Specialties Inc., http://www.msiusa.com/metallized_piezo_film.htm). Right now I try to locate a sample in my junk piles. Johan Liljencrants Reference: [1] Hirschberg, van de Laar, Marrou-Maurieres, Wijnands, Dane, Kruiswijk, Houtsma: A quasi-stationary model of air flow in the reed channel of single-reed woodwind instruments. Acustica, vol 70 no 2, Feb 1990, pp 146-154.

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