[pianotech] Soundboard Analysis

[Ron Nossaman]

On 6/22/2011 11:49 PM, David Love wrote:
> All true.  I posted it as a bit of an exercise in the process I usually go
> through when analyzing whether a board needs to be changed (better than
> tapping or plucking or whistling).

Astrology might be good too. I can understand load analysis as a means 
of determining the current condition and future longevity of an existing 
board, so I think I'll stick with that.


>This was a bit of an extreme example
> where it was fairly clear early on but I thought I'd post it anyway.  Often
> the data is more borderline than this.

In my experience, most pianos out there get restrung with no data 
analysis at all other than perhaps a couple of bearing measurements.


> You're right, there isn't much point in measuring negative crown although I
> can imagine a situation in which someone set the downbearing excessively
> high by mistake (or ignorance) pushing the board negative when it might well
> have held up under a normal load.  Not sure I've ever encountered that so I
> can't really say what happens once the board gets pushed through.  Does it
> spring back when you take the load off and will it respond normally when you
> put a normal load back on it?

I'd say not. Most of the pianos we rebuild were built with compression 
crowned, or rib crowned but panel compression supported assemblies. The 
traditional method of setting bearing by wedging the board down until it 
gets hard puts the panel at it's compression limit when it's strung. At 
less than the panel compression limit, the assembly isn't stiff enough. 
So if a high compression panel which was pushed past flat by excessive 
bearing (over time) is reloaded at a lesser bearing, I wouldn't expect 
the panel to have enough internal compression strength to support even 
reduced bearing with positive crown. Or if it seemed to for now, I sure 
wouldn't count on it to do so for long.



>In this case with negative
> bearing and negative crown there wasn't really anywhere to go.

Yes, In this case one look at the right rib with the string, and one 
bearing measurement at that point in the scale, would write the ticket. 
More measurements are desirable to round out the picture, but dead is dead.
Ron N