[pianotech] Breaking bass string

[Nicholas Gravagne]

On Sun, Apr 10, 2011 at 12:44 PM, John Delacour <JD at pianomaker.co.uk> wrote:
> At 11:29 -0700 10/04/2011, David Love wrote:
>
>  Wolfenden also calculated his scales on the basis of tensions that were
> possible with the older stronger wire.
>
> JD

John:

This explains to me why, when I have run some of Wolfenden’s working
scales (steels only) the tensions and breaking %s (mostly top two
octaves) are relatively high (many values at mid 60s and as high as 70
+ or -) compared to what I usually see RE the usual rebuild candidate
here in the States.

Other than that, one scale that comes to mind in particular, where
note 88 at 54mm, and having no hook-back in the low tenor (note 27) is
practically perfect RE:

1.	remarkable evenness of tension (though avg. tension is 191 lbs.)
2.	string lengths that plot out into a perfect log scale,
3.	a near perfect BP% curve (rare: some scale BPs look wild by comparison),
4.	a near perfect progression of wire gages and unison count changes,
5.	a virtually straight inharmonicity log curve.
6.     the rate of string length change (ROG) exists in a tightly
controlled pattern.

(Spreeman's Ravenscroft scales exhibit these desiderata as well).

The above conditions are so, even given that I don’t see where any of
Wolfenden scales were based on A440. Rather, and as I loosely gather
from his book publication dates, in 1916 they were based on C 517.305
(A435), but then in 1927 were based on a few possibilities including C
522 (A438.94). I ran the scale above based on A440, which is only
0.24% higher than A438.94. Thus tensions at the slightly lower pitch
would still be high.

Granted we should expect that a scale based on note 88 at 54mm would
by design yield a high tension scale, said scale was a working scale
of Wolfenden, at least a suggested one.

Wolfenden extolled at the time the New Westphalia Gauge Wire chart,
sizes etc. I have done a better-than-cursory search on this, but
haven't yet hit on its specific history or anything technically
useful. You probably know something here. Not expecting a treatise,
but perhaps a line or two, if that is a fair request.

NG


-- 
Nick Gravagne, RPT
AST Mechanical Engineering