At 5:18 PM +0100 11/23/01, Richard Brekne wrote: >Outside of the fact that the results of this experiement fit >point in the exact same direction that Conklins research points to, my initial >feelings would be to think this does indeed apply. So.... my next step is to >build a monochord variation of this apparatus to run the experiment in a more >piano like set of circumstances. > >I suspect actually that the same results will show themselves, but >we will see. >I dont really see any reason to think that the double bearing point clamp no >matter how massive will act as an inhibitant to longitudindal waves continuing >through the medium (string). After all, these are internal to the >string and the >clamps are on the outside. I carried out a similar test with a Ø 9.5 brass-sleeved steel stair rod about 78 cm long clamped in a vice precisely in the middle for about 8 cm. Provided the rod was gripped centrally, a clear ring of ca. 3000 cps was obtained. Otherwise it was impossible to obtain any tone, including the case where the rod was firmly clamped at each end. The frequency of a piano string removed from one of the bridges and pulled taut by hand, is of a quite different order from its frequency when held, even at quite low tension between two hard terminating bridges. By the very nature of the oscillating medium (molecules of steel in a certain configuration) some disturbance of at least the central part of the rod or string is likely to continue past any clamping mechanism. I would visualize a far greater impedance to the wave in a 1 mm wire than in a 10 mm rod, though this would need to be tested. I did the test just out of curiosity but saw no use in it for the purposes of our discussion since the conditions in the Kundt experiment are so far removed from piano technology. We are concerned with compression waves in taut steel wire, their undoubted existence as audible tones, their undoubted exchange of energy with the transverse waves, and the means and quantity of their continuance past simple and compound bearings such as are either commonly used or such as might be conceived of. Beyond these considerations, except as an aid to understanding basic principles, more generalized experimentation is pointless. The compression wave is generally represented as a series of vertical lines oscillating like the coils of a 'Slinky'. That's fine for elementary school but a picture of the relative position of millions of molecules in a steel wire, in close contact at numerous points with other metallic objects would be very different. It is almost certain that the hardened shell of the drawn steel reacts to the shock in a different way from the more crystalline interior of the wire and that Young's modulus for the two is different. I for one need to have a far clearer picture in my mind of the internal forces at work, and I think the answer to questions such as this might go some way to explaining the speaking length problem. All that is very interesting, and personally I believe in understanding my materials to the nth degree so far as I'm able, but a line needs to be drawn between scientific knowledge as an aid to design and that knowledge for its own sake, which has no more to do with piano technology than the last words from the cross. I have just build a nice little 60 mm trichord with sufficient front and back lengths to allow of a good range of tuning. It is quite possible that Duplex Scaling started life in the same way. Thoeodore S. talks of longitudinal vibrations at a time when he would probably have had only Lord Rayleigh's work as a reference. In view of the base length of the waves in the upper part of the scale, it is hard to see they could have any effect, and yet the tuning and detuning of the partials in the duplex scale, not to speak of the damping or not of the free wire between hitchpin and brass bridge, have a considerable effect on the ringing quality of the heard tone, and to dismiss compression waves as beyond range might be simplistic -- a reading of Jim Ellis' patent might give some credence to Steinway. One last unreported fact: During the few tests I carried out on the stringmaking machine, I wondered what would happen if I loosened the copper coils to get a buzzing or rattling string. With the coils loose, it was quite impossible to get any semblance of an audible compression wave. This suggests to me initially not that the loose coils prevent the disturbance of the molecules along the steel wire but that this disturbance, in order to be audible MUST be converted into transverse waves. Our hearing of a sound is enabled only by compression waves in the air acting on the diaphragm of the ear. A wave moving through a steel rod or wire cannot conceivably be audible unless it causes a significant movement of air molecules and this it will not do, any more than light waves will escape from an optical fibre. The audibility of the compression wave must therefore be due to its conversion to transverse movement of the wire which does set up compression waves in the air. My explanation of the loose coil effect is that the normal movement of the wire excited by the compression wave is totally absorbed by the loose coils. JD
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