Call for scaling spreadsheets

[John Delacour]

At 10:45 am -0500 30/9/06, Ron Nossaman wrote:

>>The covered string scale can be greatly changed with advantage on 
>>many existing scales but the only way to "rescale" the plain steel 
>>is to rip off the bridge and fit a new one of the best shape and in 
>>the best position, and if the piano was so ill-designed in the 
>>first place it's not going to be worth the expense of the exercise.
>
>Not in my experience. Replacing bridges and redesigned string scales 
>with new soundboards with added cutoffs and new rib scales, longer 
>back scales, transition bridges, log progressions across breaks, and 
>silent and functional front duplexes is becoming more common every 
>year. Just as action geometry analysis and correction has become 
>commonplace as we became aware of the need (in ill-designed 
>high-to-mid value pianos), we who do this work are finding it well 
>worth the trouble and expense in performance enhancement. The folks 
>for whom we do it agree.

Well, if you have created a market for such work and can make it pay 
an acceptable hourly rate, well and good.  But perhaps I should also 
have suggested that to make a proper job of it, one ought also to 
have new metal frame cast and a new keyboard.  Without that surely 
the job will be a compromise, won't it?  In the design of a piano the 
first line that is drawn is the strike line, and every other 
significant point in the design is drawn in relation to this line. 
Perhaps you can give more detail as to how you go about it.  Suppose 
you have a piano whose bridge shape is roughly acceptable from note 
45 to the top but from there down gives tensions rising to say 200 or 
220lbs and you want to shorten the lengths there.  Suppose, more 
precisely, you have note 40 as follows (and I should add that this is 
not fanciful, but a not uncommon case) :

Speaking length: 76.0 cm
Wire gauge 17.5: 0.1 cm
Strike point:  76/8 = 9.5 cm.

This will produce a tension of roughly 218lbs.


Suppose you now redraw your bridge to produce a tension on this note 
(assuming for argument's sake the same gauge of wire) of about 
160lbs, then you will need to reduce the length of the string by 11 
cm to 65 cm.  You will thereby achieve, nay even over-achieve, your 
desired back-length, but what of the strike point?  This will have 
moved nearly 14 mm. nearer the front bridge.  Surely the only ideal 
solution then is to move the whole string back 14 mm in order to 
bring the strike point back to the strike line.  In other words you 
need to reposition the stud (agraffe) in the metal frame unless the 
hammer is to strike the string at a less than ideal point and produce 
less than ideal harmonics.

I'd be interested to hear how you do in fact deal with this case or a 
similar case.  I don't ask this in a contentious spirit but simply 
because I'm curious to know how you proceed.  There's a lot of 
non-specific chat on this list about all sorts of hifalutin things 
and it would be nice to hear something a bit more specific and down 
to earth.  I think you'll find my figures are as exact as they need 
to be.

JD