I don't know that I can give a definitive answer, but....
With all the discussion about music wire with lower tensile strength we seem to be focusing just on that one parameter. I think it is more complicated than that. For example:
On my string test frame I've set up side-by-side comparisons of Mapes IG wire and Paulello low tensile strength wire and have found some difference in tone but not as much as I had expected given the amount of hype involved.
The parameter being left out, I think, is the aggregate resistance to motion presented by highly tensioned scales vs. lower tensioned scales. The strings being drawn across the bridge act as springs resisting the motion of the bridge. Strings with higher tensions exert a higher spring force resisting the motion of the bridge than do strings with lower tensions. With a single string, or a single note, this is not significant but when the aggregate tensions are considered it is significant.
I've tried setting up combinations of strings of the same length but using radically different tensions (i.e., strings of the same length but with one side using relatively thin wire and the other using thicker wire). Using backscale lengths common in real pianos the higher tensioned strings present more resistance to deflection and more restorative force than is seen in lower tensioned scales.
In these tests the resulting sound shows more energy in the higher harmonics in the note using the larger diameter (higher tensioned) strings while the side using smaller diameter (lower tensioned) strings show more energy in the lower harmonics. In a single note these differences are not great but when applied to a broad range -- in a real piano when we play one note we are not playing a mono-chord -- they become significant.
While this illustration is not at all definitive I will add that empirical evidence tends to back this up. An early (1882) Knabe I've just finished originally had scale tensions upwards of 200 lbf through most of the tenor and lower treble sections. The sound was "thin" and "constricted" (to use the words of pianists trying the piano in its "before" condition). To be sure, many things have been changed along the way, but one of them was to drop the tensions (by virtue of using smaller diameter wire) down to the 155 - 165 lbf range. The difference in tone quality has been dramatic.
ddf
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Delwin D Fandrich
Piano Design & Manufacturing Consultant
6939 Foothill Court SW, Olympia, Washington 98512 USA
Email
ddfandrich@gmail.comTel 360 515 0119 -- Cell 360 388 6525