Soundboard Evaluation

[Farrell]

Hmmmm. I agree three measurements will give you more info, but I should think with the two you could conclude positive or negative bearing. Anyway, here are six notes remeasured. I centered the bubble on the bridge top, and then measured the forward (speaking) side (the first number) and then the rear side (the second number). A positive number reflects the string angled the way it presumably was when the piano was new (both the forward and rear string lengths would have a positive number). (A positive number means the string is angled up toward the bridge, and a negative means the string is angled downward toward the bridge - when the piano was new, presumably both the front and rear string segments were angled upward toward the bridge.)

E7   +10   +1
A6    +6     +2
C6    +7     -3
F5    +5     -4
C5    +2    -5
E4    +1    -5

The instructions say to multiply these number buy 0.003 to get an answer in thousandths. Mr. Lowell sure made a neat little gauge, but it does not seen that he was a scientist. Thousandths of what? Inches? Degrees? It must be degrees? Like my chemistry professors used to say "show me you units - where are your units?"

I can see how this bridge is apparently rolled toward the piano rear in the tenor, and overall bearing is negative in this area. But even at F5, even though you can see the bridge has creaked over to a new angle (I hope Baldwin did not make it that way!), bearing is still probably positive because of the longer length of the forward (speaking section) string segment. Likely around C5 you have no bearing at all, and E4 perhaps has negative bearing. I'm not sure though how exactly to paint a physical picture of how all this relates to bearing and the board.

However, it still seems to me that these numbers on a flat board mean this board is toast. Opinions?

Terry Farrell
  
----- Original Message ----- 
From: "Baldwin Yamaha Piano Centre" <baldwin@mta-01.sk.sympatico.ca>
To: <pianotech@ptg.org>
Sent: Saturday, June 01, 2002 6:24 PM
Subject: Re: Soundboard Evaluation


> 
> 
> Hi Terry,
>               You need to take 3 measurements with the gauge, speaking length, bridge cap, and back scale.  You can easily get fooled by bridge roll.
> 
> Centre the gauge on the speaking length, then the bridge cap should be minus some, and back scale minus some more, if all is healthy.
> 
> Rolled or twisted bridges become very apparent this way.  Now you have a real idea of bearing in each section.
> 
> The crown is measured with a piece of high tech string. Available from the Jolly supply company at $90US per length.  I feel you should order at least 5 lengths <G>
> 
> Roger
> 
> 
> >I measured downbearing with my Lowell gauge. The numbers below are the difference in lines on the bubble gauge between the reading on the speaking length segment and the backscale length segment. A positive number means there is positive bearing.
> >
> >E7   +10
> >C7   +7
> >A6   +7
> >break - G/G#6
> >F#6  +6
> >E6    +5
> >C6    +4
> >A5    +2
> >F#5  +1
> >E5    -1/2
> >D#5  -2
> >break - C#5/D5
> >C5    -2
> >A4    -1
> >E4    -3
>