Sound waves(The behavior of soundboards)

[Robin Hufford]

Richard,
     The incidence meter does in fact show motion vertically, notwithstanding the claim
otherwise, which is among a number of specious comments made regarding it recently.  I
urge all that have a real interest in evaluating this question fairly, to acquire one,
play around with it and see for themselves the discontinuity between the response at
the bridge to vibrating strings and those same strings subject to a static
deflection.   The device is  inexpensive.  The inability of the soundboard system to
respond to a static deflection on the strings which is much greater than that purported
to be imposed on it by the vibrating strings should be correctly and fairly analyzed as
to its implications.  They are substantial and must, I think, directly weaken the
accuracy of the cyclic pressure view.  Should one be able to clearly show that there is
a substantial discrepancy in these two behaviors then the suggestion must, at least,
exist that the cyclic pressure view is flawed.  This device shows this plainly the
discontinuity of the two responses.  Of course,  I do not expect a fair treatment from
some as regards this device even though it can be most useful.  Some, who cannot refute
the message prefer instead to attempt to discredit the messenger, which is a
transparent ploy and a very poor method of argument indeed.
     We see now another  distinctive notion of high school physics - the new, momentous
and trivial distinction between deflection and rocking.  Were the bridge rocking then
some part of it must be experiencing deflection - a point so superficial that I will
waste no further time on it.
     It has been complained of that I have offered no references to these subjects, or
that the ones offered have been rudimentary.  This, notwithstanding the fact that I
have offered more, I think, by far than the contrary camp have taken the trouble to
submit.  Where the quotes have been taken from a relatively rudimentary text this was
noted by myself.  Such note was avidly seized upon and great commentary repeatedly made
as to this aspect.  The quotes which were from more advanced  sources have been
ignored and continued to be so treated, evidently they represent points either not
comprehended or  inconveniently contrary to the views of the other camp.   Den Hartog
is obviously too rudimentary to be given any  credence:  he was merely the Professor of
Physics at M.I.T. for some years and is a prominent author of  numerous, well written
books on various aspects of mechanics, including the one I quoted which addresses
vibration analysis. Elmore and Heald were from the physics department of Swarthmore.
Their book, although highly technical, is, again, apparently insufficiently advanced
for the high school physicists to take note of although I can say for certain that it
is far more advanced than the text I enjoyed in my high school physics classes.  It is
readily apparent that some understand but little that which the rudimentary texts
address and dismiss at the same time the more advanced ones as being too rudimentary to
take notice of.  More on this latter.
Regards, Robin Hufford


Richard Brekne wrote:

> Ron Nossaman wrote:
>
> > > Robin wrote:
> > > The fact of deflection being indicated by your laser device,
> > >although pertinent, is not complete because you would have to be able to
> > >compare
> > >the extent of the measured deflection caused by the finger with those
> > >deflections
> > >caused by the vibrating string.
> >
> > Not deflection - rocking. The dial indicator measured deflection. And no
> > one said anything was complete. This has been addressed.
> >
>
> Just a point here... I thought it became somewhat clear that the rocking motion
> that your finger exercise was supposed to show was indeed erroneous. Askenfelt
> clearly addressed thot point and said the rocking motion the bridge experiences was
> caused by longitudinal waves.
>
> For that matter I have yet to see anyone from either camp address the frequency
> dependent speed of sound issue that results from the particular kinds of complex
> transverse waves that  he says occurs.
>
> Being more curious about all this then worried about who's right or wrong I would
> really like to hear some concrete discussion about these things as they do seem to
> conflict somewhat with the way the bridge motion model was earlier described.
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html