Soundboard Evaluation

[Farrell]

Well, let's push the board up 1mm. At note E4, the back scale would go from a  -2/3° angle to a +2/3° angle, and the front angle would go from a +1/6° angle to about +1/4° (I'm just guessing at a 2-inch back scale and a 20-inch front scale). I hope I have done my math correctly (I actually had quite a bit of advanced math in college, but, well, er, a, some of it has slipped on by). That seems like a lot of change for a tiny bit of soundboard movement. But I do see your point. It doesn't have to roll to produce negative back bearing with positive front bearing. Interesting. Thanks.

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: Saturday, June 01, 2002 10:13 PM
Subject: Re: Soundboard Evaluation


>Hmmmm. I agree three measurements will give you more info, but I should 
>think with the two you could conclude positive or negative bearing. 

Right, but not necessarily positive front bearing.


>- when the piano was new, presumably both 
>the front and rear string segments were angled upward toward the bridge.)

Hopefully, but again, not necessarily.


>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?

That's 0.003" per inch, I believe, or 1/6° per line. That's why I like
measurements stated in degrees, so it will mean the same thing to everyone
everywhere - except maybe Elbonia.
 


>I can see how this bridge is apparently rolled toward the piano rear in the 
>tenor, and overall bearing is negative in this area. 

Again, not necessarily. The back scale is considerably shorter than the
speaking length, so the back angle changes much more for a given bridge
height change than does the front angle. Assuming the bridge went straight
down without any "roll" whatsoever, taking the speaking length and "duplex"
length of say, F5 or C6, at what bridge top height above string plane would
there be a positive back angle?

 What's the resulting front angle, and the
difference in bridge heights between this computed one and what's there in
the piano now? I seriously doubt that it's physically possible for a solid
bridge to "roll" backward here.


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

Agreed.

Ron N