Sound waves(The behavior of soundboards)

[Robin Hufford]

Don,

     I don't believe he has suggested any of these things.  My reading
of
Richards well expressed post is that the counterarugment offered to the
position expressed by JD and also by myself, is rather inadequate, a
point I
agree with wholeheartedly except I would say that this observation
should be
extended to the postings of some others.    Instead, of reasoned
refutation,
as I asked for at the beginning of my posting on this subject , which I
would
happily entertain and not be the least offended by, and in fact I have
not
been offended by any of the statements posted in this discussion, ,  we
have
had, for the most part, generalities of questionable relevance - where
there
is mass there is acceleration; weighty statements of the obvious - a
damper is
a mass absorber; the force on the bridge is a function of the sin of the
downbearing angle and the speaking length; a plate or a case will
deflect when
ten pounds are placed upon it, etc. .    None of these things do I
disagree
with but the issue at hand is subtantially different and how they shed
much
light upon it I am at some difficulty to say.

     Although I have not done to a  piano the test you propose using a
strobe
light,  I have done recently such  a test using a strobe and a rotating
ceiling fan.  The result is as expected:  as the period of the light
flash is
adjusted and becomes closer to that of the fan  the perceived motion of
the
fan eerily begins to slow and is eliminated.   By adjusting the period
of the
flash one can make the fan seem to be still and even appear to move in
reverse.  This, of course, happens as the flash illuminates  the blades
coming
around at the same point in their rotation:  even though the illuminated
blades may be  different they are all filling slots that are at the same
place
at the time of the flash  thereby appearing to be the same  and not
moving ;
should  the period of the light be varied but maintained close in
frequency to
the rotation of the fan,  then the timing of the flash relative to the
position of the blades at the moment they are illuminated creates the
illusion
they are actually moving backward, or forward.  This is a kind of
phasing
effect and I think were there "definite, physical motion" at the
string/bridge
interface, the light would have similar effects, it being necessary
therefore
to adjust the frequency of the light if one were trying to detect motion
with
a period of 440 herz.
Regard Robin Hufford


Hi Richard,

>
> Are you suggesting that the energy does not tranduce through the bridge to
> the soundboard, or that the bridge is initially an immoveable object?
> Energy is always conserved unless Mr. Einstein was wrong.
>
> Time for someone to borrow a strobe light and set it to 440 hertz and have
> a good look at the bridge while playing A4. This *should* be doeable.
>
> Regards,
> Don Rose, B.Mus., A.M.U.S., A.MUS., R.M.T., R.P.T.
>
> Tuner for the Saskatchewan Centre of the Arts
>
> mailto:drpt@sk.sympatico.ca
> http://us.geocities.com/drpt1948/
>
> 3004 Grant Rd.
> REGINA, SK
> S4S 5G7
> 306-352-3620 or 1-888-29t-uner