<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> JIMRPT@AOL.COM wrote: <blockquote TYPE=CITE>In a message dated 17/01/02 11:47:05 AM, RNossaman@KSCABLE.com writes: <<  Let's hear your thinking based entirely on something akin to logic, mechanics, science and physics, rather than a sideline comparison of other peoples thoughts. Put yourself on the line this time. I'd like to hear what you think.  >>  Dis ain't dat hard Ron.............  The fork transfers energy to the soundboard and the soundboard expresses that energy in the 'best' way it can. While there might be a little side to side motion of the assembly......that is the path of most resistance....The path of least resisitance to the energy transmitted by the fork would be an up/down movement of the board..........so although the energy would be traveling in all directions the most evidence of such would be up/down as opposed to any other direction................. Huh? Jim Bryant (FL)</blockquote> Im not sure I have a problem with this explanation. Remembering that the end of the fork is open (i.e. the hole holding it goes all the way through the board). Any up and down piston like motion is going to be difficult to explain methinks. But that the board itself most easily vibrates in this bending transverse wave I can buy. My problem with all this is what gets the board moving in the first place. It seems to me that Ron is saying that its just some force that yanks the damned thing around, where as I am bogged down on the idea that whatever force is exerted creates a wave front that propagates through all three dimensions of the panel and that the eventual vibration seen in the panel is the reaction that the panel has to said wave front. Beyond that I seem to be more in agreement with On then with JD at the moment. Why do I insist on the wave front being the direct source of vibration in the panel. Well, for a couple reasons. The speed of transverse bending waves is dispersive.... that is to say that the wave velocity is frequency dependent. Yet we operate with a constant when we use the formula for the speed of sound through wood. That says to me that that formula is referring to a compression wave or perhaps some form of quasi longitudinal wave, as in Rayleigh surface waves for example. Also I cant escape the fact that the panel has three dimensions, and any force acting upon that simply has to propagate though all three. I don't see this is in conflict with the 2 dimensionalilty of the panel as a vibrating plate. A tuning fork is a so called linear quadrupole source, or a bar clamped in the middle whose ends vibrate in opposite phase, and as such the output at the base is the same for a cylinder in which there is a simultaneous contraction along the vertical axis as there is expansion (this would mean elongation) along the horizontal, and of course the opposite way around on the other half of the wave. This says to me (and I might be totally misunderstanding this) and I will sort of over simplify for the sake of illustration, that the bottom alternates pumping up and down, while the sides alternate pumping in and out, in a fashion which results in two waves, one at 12 and 6, followed by one at 3 and 9 o'clock . I see nothing transverse in this action at all.  Take a look at Dan Russell's animated illustrations and watch single points moving back and forth at <a href="http://www.kettering.edu/~drussell/Demos/forkanim/latquad.gif">http://www.kettering.edu/~drussell/Demos/forkanim/latquad.gif</a><a href="http://www.kettering.edu/~drussell/Demos/forkanim/latquad.gif"></a> So given this action by the tuning fork, mounted as it I described, there is no piston like up and down motion exerted on the panel as far as I can see. Only only a piston like out and in motion exerted alternately on the north/south then east/west sides of the hole. That this should send a wave front traveling directly outwards and parallel to the plane of the panel in a non dispersive fashion which results in a transverse like action on the surface ala the quasi longitudinal wave types mentioned above seems to me a quite plausible explanation. That the panel gets further stimulated to vibrate in a more pure bending transverse fashion in addition is also covered in the texts before me. though I have a bit of a chunker figuring out the consequences of the dispersive characteristics of this type of wave relative to how sound is produced.. but then I suppose its highly possible I have totally misunderstood everything I have read so far so....well.... grin... I aint too worried about it. I suppose I will learn in the end :) The variation of the loudness of the system resulting from bending this panel between the knees is the result of altering the stiffness of this little panel and thereby its acoustic impedance... ?? At some point an optimal for sound production is reached. Ok... thats my first shot at it... I await the now er.... acoustumed slaughter...hehe. -- Richard Brekne RPT, N.P.T.F. Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A>  </html>