Ron,
On Dec 15th, 2001 in the first post I offered on this subject, and in
anticipation of the relevance of the nature of motion, I addressed this issue
with some implications arising from to the nature of a collision of a mosquito
and an aircraft carrier. You stated that the metaphor would best be expressed
in terms of the impact of an airliner, and this better expressed the
relations between string and bridge. Subsequently, and I won't take the
trouble to find and quote your post you said that the motion was substantially
above the molecular level, always adhering to the idea that the behavior of
the soundboard was a consequence of this motion. Yet it would seem you now
have progressively diminished you claims of motion to the level indicated by
that of the mosquito, if not smaller.
You implied that this motion was in some way confirmed, not wishing to put
words in your mouth, by a level of deflection detected in your test with
weights on the plate and the rim; measuring, if memory serves me, a value of
0.001 of an inch in deflection; later you find pressure on the string to move
the board by about 0.0005; you take no notice of my repeated comments that the
purported motion appears to decreasing in magnitude. What is the level of
insignificant motion to which you wish to proceed?
I have repeatedly stated, as I did in the first post, that the answer to
this question is to be found in the analysis of motion itself, referring to
the nature of translation, rotation and stress wave, another point you, Del and
others took no pains to comment upon. This in the context of an overall
discussion of what sound in fact is; therefore I take by this that you too
were concerned with sound and its evolution from a piano. I doubt very
seriously that we, all of us, have been concerned with the motion of the stars
and planets. And now you say that you don't know what the effect is, if any,
on the sound and claim that "rocking" of the bridge, however small and,
apparently, however insignificant to the sound, is the point at issue and claim
the point conceded. Preposterous! I don't think is so. If this is what you
reduce your argument to then you and your co-thinkers have in fact conceded,
which, of course, I don't think you do.
The first post overall was in response to the earlier claims made that
rippling, flexing and rocking of the bridge was occuring; that these motions
were transmitted across the soundboard surface as" ripples in a pond" and that
this was the mechanism of energizing the soundboard, so to speak. I include
a fragment of that post quoted below. The claim had also been made that this
energization was in fact similar to a that undergone by a "diaphragm in a
loudspeaker" to uses Del's words -who, to be fair, did say that it was not an
exact representation but a useful analogy. So, there is substantially more at
issue than mere rocking of the bridge were this even so which I think not the
case. Were it so, it would be as I have always maintained, essentially
insignificant and, let me now be categorical; : this is by no means the
prinicipal mechanism of transfer of energy from string to soundboard. Should
such motion exist in any appreciable degree markedly deleterious effects would
then be incurred in the sound.
Excursion of the bridge and
soundboard at this point is neglible if extant at all. One could, I suppose,
call this a ripple but this is misleading and of little significance.
Now you appear to have reduced the entire question to the extent of the
ripple("rocking" and that would be truly insignificant.
Both I and J Delacour have been very explicit on numerous occasions that
the issue was in fact transduction of the energy of the vibrating string at the
string/bridge interface: In an attempt to clarify this several posts have
been proffered addressing the nature of motion itself and, in particular,
addressing the question of suppression by some sort of clamp or other source
of pressure, this purported motion, and its effect on the vibrating string.
Examples have been offered. All have elicited little commentary other than
blase generalizations for the most part. I asked what is the magnitude of such
motion, if it exists, and how does it contribute to the sound. Your answer is
apparently, I don't know. The relevance of the effect on the board and
therefore sound has always been the issue in the context of how sound itself
arises from these processes.
Ron, you, at least insofar as I am concerned, to your credit, have been
willing to get in the trenches and debate these issues, while your
co-proponents are apparently busy elsewhere, this being the holidays perhaps
that is understandable, perhaps not. There is far more than merely the
"tension difference" inhibiting your rocking motion. The forces exerted on
the bridge which itself is stiff expressed as the downbearing load or to use
Del's term "downforce" are counterbalanced by the resisting forces provided by
the soundboard assemply including the ribs, the strain of crownd, the rim, and
so forth.
Regards, Robin Hufford
> >I have said from the outset and have been forced to repeat numerous
> >times, in response to suggestions that I have denied it, that the
> >movement of the bridge occurs. By the same token the bridge in
> >rocking will obey the same physical laws. How can you still pretend
> >that there is any argument about this.
>
> The only persistent confusion I've seen here is a disagreement of what
> moves when and what moves it, not whether or not anything moves at all.
> We've already dealt with that and, I had assumed, corrected any
> misunderstandings. Yes, everything still moves. If we're not talking about
> the same thing here and haven't been through this whole thread, I'd like to
> know that now please. If we are talking about the same thing, then we have
> been far beyond that point for some time. To bring you up to date, the
> current question I'm dealing with is whether a string displacement in the
> speaking length of a piano can rock the bridge. On that question, on 12/19,
> you wrote this.
>
> >>You are asking the list and me to accept that a variation in tension
> >>of a few pounds at most due to the trasverse vibrations of two
> >>strings is sufficient to cause a rocking of a long bridge firmly
> >>glued to a soundboard and held in position at its top by over ten
> >>tons force? You'd have the bridge in smithereens before you could
> >>rock it with a crowbar let alone such a minute force.
>
> This was up to today, as nearly as I can tell, your stated opinion. If you
> had reversed this opinion prior to your most recent post, I missed it
> altogether. Since you have apparently reversed it in the current post,
> saying it has been obvious all along, I presume pending any contrary
> revelations, that the point is conceded.
>
> >My model was designed so that those unfortunate people without lasers
> >and mirrors could see for themselves what it is not possible to see
> >with the naked eye and furthermore carry out tests that would be
> >impossible on a strung grand without highly sophisticated measuring
> >equipment:
>
> You must not have a cat. Anyone with a cat needs a $6 laser pointer. I
> think it might be a rule. In any case, there likely aren't three people on
> the planet who will actually try what I've suggested, so the potential
> global hardship imposed in exotic hardware expenditure and broken mirrors
> is negligible. As to your model, the less like a piano these models are,
> the less use they are to this thread. Your demonstration illustrates, as
> did mine, the principal that your quote above denies is even possible. So
> far so good. But you then ask how it can affect tone???? By moving the
> soundboard! How many times have I said this? Glue your bridge to a piece of
> card stock supported by a perimeter frame and try it again. The string
> moves the bridge, the bridge moves (deflects and bends) the soundboard.
> Into what shape in your model? In a piano, when the bridge is either rocked
> or deflected, or bent (it bends some along it's length too), the movement
> affects the tensions and termination position in space of all of the
> strings attached to it as well as deforming the soundboard. Once the
> soundboard is moving there is obviously feedback to the strings from then
> on. Don't stop now. You've almost proven my point.
>
> Also, contrary to your observation that the bridge is held in place at the
> top by over ten tons of string force, you might note that if a
> conscientious tuner that carefully equalized string segment tensions on
> both sides of the bridge has done his job correctly, there is only the
> tension difference (resulting from attempted movement) between segments on
> opposite sides of the bridge inhibiting the rocking. I don't know what this
> tension difference is, but it can be approximately calculated if anyone
> wants to take the time, and it isn't going to be much compared to half the
> total string tension. This makes the bridge a lot easier to rock than it
> might first appear. The soundboard stiffness will obviously inhibit string
> deflection induced rocking too, in this case.
>
> Ron N
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