Bridge pin angles

[David Skolnik]

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Ron, Phil, Ric, others -

At 09:05 AM 4/21/2005 -0500, Ron wrote:
(David S)
>>Phil, are you discounting, or unaware of the Wapin system of bridge=20
>>pinning?  I know Ron is aware of it, though, given his reaction to my=20
>>raising it in the context of a previous thread about downbearing, I got=20
>>the sense that he was not favorably disposed towards it, reasons unknown.
>(Ron N)
>As I've said before, I don't see a need for it, nor do I consider a poorly=
=20
>functioning soundboard to be "fixed" by it's application.

Why assume the presence of a poorly functioning soundboard?  Or that I or=20
Wapin is proposed as a "fix" for such?  There may very well be no "need"=20
for it.  That doesn't preclude the fact that someone claims to have=20
observed and measured certain phenomena, and created an experiment, albeit=
=20
in the form of a commercial enterprise, which claims to interact favorably=
=20
and predictably with said phenomena.  The claims may or may not be=20
accurate, but it seems a bit capricious to dismiss the ideas out of hand,=20
given their applicability to the topic we're discussing.

>(David S)
>>As I see it, you need to decide, from the beginning, whether your inquiry=
=20
>>is directed towards understanding the mechanical processes at work, or=20
>>the more practical aspect of building something that will continue to=20
>>function for a reasonable length of time.  For the most part, questions=20
>>of loosening bridge pins and crushing notches and caps are of the latter=
=20
>>direction.
>(Ron N)
>I disagree. I consider these concerns to be inseparable. Trade-offs can't=
=20
>be reasonably assessed without considering function, production cost, and=
=20
>longevity.

Maybe I mis-spoke, though our history suggests that my explanation will=20
likely kalso fall short.  I was trying to suggest that it might be=20
instructional to contemplate as clearly as possible the idealized, or=20
theoretical physical mechanisms operating, which could be subsequently=20
compared to the "real-world" issues of materials, unpredictable production,=
=20
etc. Separate, then synthesize.  In rereading Phil's original post, I=20
realized that I imposed a bit of my own bias in focus of my comments.  Phil=
=20
actually was contemplating both the practical AND the more theoretical.


>(David S)
>>That an angled bridge pin might be more prone to causing cap damage than=
=20
>>a vertical one is helpful to understanding piano forensics, but it=20
>>doesn't, by itself, explain the possible differences in acoustic=20
>>properties of between each.
>(Ron N)
>When the acoustic property in question is false beats. I disagree. No=20
>other acoustic property has been claimed or discussed.

First of all, in the course of most of the recent discussions, I and others=
=20
have attempted to establish that the classic "false beat" is not the only=20
acoustic phenomena that is observed as a termination anomaly.   However, in=
=20
the quote above, I was trying to pose the question whether, in purely=20
mechanical / acoustical terms, an angled bridge pin elicits a different=20
response than a straight pin.  Surly there is some merit in asking such a=20
question, especially if the answer turns out to be affirmative.

>(Ron N)
>The point is that we can't assume downbearing, so we angle and offset pins=
=20
>to provide a positive termination that's largely independent of bearing.=20
>If the above piano had 15=B0-20=B0 angled front bridge pins in that problem=
=20
>unison, the only tonal problem would have been the generally nasty=20
>distortion at higher attack levels in the killer octave that everyone is=20
>so used to hearing that they don't even notice, and everyone would have=20
>been happy. What I'm interested in is a standard of offset and pin angle=20
>that will reliably provide that termination. I'm not particularly=20
>interested in establishing minimum tolerances, because I don't wish to=20
>build to minimum tolerance, and these tolerances can't be accurately=20
>established anyway. There are too many variables.

We can't assume downbearing, and we can't assume front bearing, whether=20
caused by wood crushing, poor planing, incorrect setting of bearing,=20
etc.  You say "we angle and offset pins to provide a positive termination=20
that's largely independent of bearing".  What, precisely, IS "positive=20
termination"?  Does it mean that the reflection of waves in all three axis=
=20
(pl?) occurs at a point which is a singular distance from the opposite=20
string termination? Does it imply a certain ratio of reflected energy to=20
absorbed energy? Does it reference the actual space and surface area that=20
constitutes the termination?  And of course, does it define or quantify the=
=20
degree of sliding motion of the string along the terminating structure=20
(bridge surface or bridge pin) parallel to the direction of the wave, thus=
=20
a lateral movement along the bridge edge, or a vertical movement on the pin?

Presumably, it implies a reference to all these conditions, and probably=20
more (don't forget longitudinal waves).  Any of these conditions might be=20
less than perfectly fulfilled, possibly with some perceptible or measurable=
=20
consequence, or possibly not.  For example, how might you imagine the=20
difference in functioning between a string with negative front bearing=20
which is (temporarily or not) held in contact with the edge of the bridge=20
by the slanted pin, and that same string if or when it loses that=20
contact?  Will the vibrating string slide up and down the pin? If it=20
initially did, would it ultimately abrade a groove or otherwise create a=20
surface which precluded any movement, thus effecting a terminating point=20
for both horizontal and vertical waves?

As an attempt to understand the acoustic process more fully, I see no fault=
=20
in considering such models of inquiry, even if you choose to build your=20
product with multiple layers of insurance.

David Skolnik

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