consistent downbearing measurements

[David Skolnik]

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At 02:13 PM 6/3/2004 -0500, RonN wrote:

>>The "angle" of deflection is a hypothetical construct.  If the profile of 
>>the bridge surface was the peak of a triangle, you could speak of an 
>>"angle" of deflection, however, distortions in the bridge surface 
>>(curvature or string held to bridge contact by pins) can alter the 
>>angular perception of deflection.
>
>Not really. That's the whole purpose of using a bubble gage instead of a 
>dial or rocker type gage. With the bubble gage, overall bearing is overall 
>bearing, regardless of what the bridge top looks like. Overall bearing is 
>what you're interested in when you want to know how much load the strings 
>are putting straight down on the soundboard. Overall bearing is what you 
>are comparing against remaining soundboard crown. Front and back bearing 
>relative to the bridge top are termination concerns.

The dreaded BLUE
Ron - Maybe I should engage the lawyer I suggested for Joe Goss.  You're 
correct, I think, about the angle.  I have continued, out of habit, to mix 
my concerns about termination with those of soundboard loading.  However, 
there are still some components of your comments that I would like to 
respond to, in turn.

As I understood it, listening to Tom Lowell describe the proverbial drawing 
on the napkin, the purpose of the gauge was as much to be able to isolate 
the front and rear components constituting net bearing.  Maybe I 
misunderstood.  Whether or not it makes a difference whether we achieve a 
given net bearing with a front and rear positive or with a mixture of 
positive and negative, is a sub-question of soundboard loading, apart from 
the issues relating to termination.  This, apropos your statement 
above  "... (the) load the strings are putting straight down on the 
soundboard".  Do you have any thoughts regarding possible acoustic 
differences (effect on SB impedance) between a (basically) neutral load 
(positive front and rear bearing) and one which introduces distortive 
potential ( positive / negative)?  This would be another reason for 
measuring the individual components.

>>Still, the challenge of accurately measuring and conveying  the nature of 
>>a particular piano's string deflection, including the bridge, is, to me, 
>>a separate question from how much or little there should be or how it 
>>does or doesn't affect the instrument's qualities.
>
>You'll never get an absolute answer to that one.

This wasn't meant as a question.

>Get five techs to evaluate a piano with a flat soundboard and 
>zero-to-negative overall bearing at some point in the scale.. One will say 
>the piano sounds terrible, and indicate the bearing and crown as likely 
>causes. One will say the piano needs new hammers and voicing, and that the 
>crown and bearing aren't indicative of anything at all. One will say that 
>this is the most beautiful sounding piano he's ever heard, and you 
>shouldn't change a thing. One will say the action needs bedding. One will 
>say the piano is perfect without even lifting the lid or playing a key, 
>just from the name on the fallboard.

I wasn't speaking of evaluating the piano, or, for that matter, the 
bearing.  I'm talking about being able to take consistant, repeatable, 
duplicatable measurements, which can be accurately communicated, and which 
could be correlated with any other method of measurement which purported to 
accurately measure the same components.  In other words, I should be able 
to relate the net downbearing I measure with a bubble gauge with what I 
would get using a Hartman stick.

As for the casters, that can only be determined with a marble, placed 
carefully on the...

David Skolnik

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