Ron,
This incidence device, although lacking obviously a level of resolution of
others, is quite useful when used properly. It clearly shows substantial motion of
the bridge when the string has been struck and at the same time shows plainly that
deflecting the string mechanically by applying pressure and causing it to be
displaced statically, does not have an effect of any similarity to that when the
string is struck and vibrates harmonically. It should go without saying that a
device with greater resolution is likely to detect effects at some point which the
incidence meter does not show. Sure, but it is the fact that the incidence meter
does not show a deflection that is even remotely similar, or even one that is
detectable in most cases, to that produced by the flexing string that is the
salient point. A deflection of the string similar to that occuring in the maximum
excursion of the vibrating string during its fundamental, for example, should
register on the meter, similarly. It does not and furthermore, a pressure placed
upon the strings of a unison that is greatly in excess of that experienced by the
string on the most fortissimo blow, that is a deflection far greater than seen in
the vibrating string, does not induce any kind of similar results. Nor does
flexing the strings up and down, and neither does pressing upon the neighboring
unisons with the entire hand.
The model you and others uphold suggests that the string should induce a
deflection in the bridge/soundboard when it is stretched in a fashion similar to
that which occurs when the string is at excursion. This device, which is by no
means crude, as you would suggest, shows plainly pronouncedly different effects or
resulting degrees of motion from the two methods of loading. If you say, a point I
would not disagree with, that the string when stretched is at a slightly higher
tension, then a similar or much higher increment of increase in tension can be had
simply by displacing it in the middle with a finger. Doing so, to both degrees,
and observing the device one will find virtually no indication of displacement.
Please don't waste the time of both of us by pointing out that this is due to the
its level of resolution, something I have noted in the previous post on this
subject. The critical thing to note is that the same instrument, when testing one
and the same unison has a level of resolution sufficient to indicate substantial
motion in response to the vibrating string. It should exhibit markedly greater
motion when the force applied to displace the string by the finger is made to be so
very much greater than that occurring on a similar blow given the string by the
hammer. One should try this and observe the results; they at least suggest
analysis should proceed further and judgement reserved, at least to my mind, as to
the ability of the string to physically move the bridge. .
Additionally, one can mute the strings of a unison with stringing braid
thereby eliminating the effect of the standing waves upon the bridge. After having
done this when the hammer be made to strike a test blow similar to one given by
the hammer upon the strings when unmuted, once again, virtually no response will be
indicated by the meter. The cyclic pressure model, would suggest that, at a
minimum, the response should at least be similar. The discrepancy of results
occurs, regardless of whether the string is braided, or muted behind the strike
point, that is closer to the cape or agraffe, or between the strike point and
hammer in all cases.
Coming again to the main point: a comparison made of the effects of loading
in a fashion, whose magnitude, is similar or greater than that which you suggest is
happening with the effects of the string when struck by the hammer indicates a
substantial discrepancy which can only be explained away, at least as far as I can
see, by concluding that the bridge is being moved by the standing waves developing
in the board. 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.
If oriented along the axis of the strings as they cross the bridge, the
incidence meter will show rocking of the bridge; by orienting it roughly at 90
degrees to the strings it indicates a vertical motion.
Regards, Robin Hufford
Ron Nossaman wrote:
>
>
>
>
> >Well, let us test this point. We have seen the
> >Incidence Meter
> >indicates motion when the string is struck and is vibrating BUT it indicates
> >virtually NO
> >MOTION when the string is pressed down or lifted up by a finger or tool.
> -------------------------------------------------
>
> I dealt with this quite early on in this discussion, with a dial indicator
> showing that string deflection does indeed deflect the bridge and
> soundboard, and with the laser and mirror, showing that some very small but
> observable rocking motion is also evident. The fact that your device
> registers movement with strings and soundboard vibrating isn't surprising,
> since no one but John early on claimed that bridges - etc - don't move. He
> changed his mind when he learned differently. A pendulum system like this
> will pick up vibrations, that is cyclic movement, in multiples of it's
> fundamental resonant frequency and will oscillate. Clock makers have for
> many years been aware that a number of clocks of the same design hanging on
> the same wall will synchronize pendulum swing from the slight vibrations
> each imparts in the wall by it's movement. The fact that your device
> doesn't register "movement" when you press or pull on the strings means
> that the bridge doesn't rock far enough for the relatively crude device to
> register. I noted with my demonstration that the rocking motion was very
> slight compared to the vertical displacement, very likely below the
> resolution of your device. What did your incidence meter show in vertical
> displacement with your experiment, and how could it have possibly shown it?
> Stating that no movement occurs by consulting a tool that isn't capable of
> indicating the movement doesn't strike me as even minimal science, much
> less proof of anything. I trust you read my earlier post on the
> demonstration that deflecting strings up and down does both vertically
> displace and rock the bridge. Try it yourself, as I described it, and
> explain to me the fallacy of my observations in that experiment.
>
> Ron N
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