At 4:02 pm +1000 8/10/06, Overs Pianos wrote: >This would be a dangerously high tension as you say, if the length >was actually 197 cm on note A25, which it is not. This concert grand >has two extra bass notes... Silly me!!! -- and I actually had a good look to see what note you started on. Obviously should have worn different glasses! I'll take a new look at it in the light of this information. >>As for the covered strings, I have mentioned elsewhere that I never >>design bass strings to exceed 70% of the breaking strain, for the >>simple reason that sooner or later they will snap, and often sooner. > >I agree. In fact I prefer not to go over 60%. Mind you, there does >seem to be some variation in our calculations, which could account >for some differences in our estimated breaking strain percentages. Yes, in designing a scale from scratch I too aim for 60%. Making replacement sets for all and sundry means, of course, this is often not possible. With a good grand of about 6'9" and above it is sometimes possible to get near to 60% throughout the covered string scale, and I like to do that. So far as I recall, the S&S old B you were asking about the other day is an example of a scale where this is possible, and almost adhered to by the original designer (Theodore?) As to the calculations, yes they were on the rough side, and especially so since I realized after posting that I was using a wrong divisor -- not horribly wrong but wrong enough. What value do you use for the relative density of steel wire? I keep meaning to get access to a precise electronic scientific balance to measure this with real wire. I had a beautiful "chain dial" balance but it was stolen. The value bandied about on the WWW is 7.85, but I don't trust it. I've also never understood why Wolfenden used 7.60. As to breaking strains, I use figures my supplier provided over 20 years ago, and I don't trust them much either, but at least they are on the safe side and way below the figures Poehlmann achieved 120 years ago. >As a final comment on scaling tensions, I wouldn't trust calculated >scale tensions for a new instrument without first testing them on a >tension bench for safety margin, prior to building production >tooling. Calculated tensions are fine provided the values are obtained from exhaustive tests of real life strings, which I suppose comes to the same thing. JD
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