Inharmonicity Factors

[Farrell]

Hi List. What piano/wire/scale characteristics determine string
inharmonicity? I guess I just don't know too much about that. I tuned a 1924
McPhail 5' 10" grand (decently made instrument) recently. I measured my FAC
values with my SAT III and got very low values for inharmonicity: F - 6.5,
A - 3.2,   C - 3.5.  The F value is not soooo terribly low, but the others
are half or less than commonly found on most pianos. I checked at least
three strings for each value just to be sure and the SAT response was very
clear (no jumpy lights or anything like that - real clear instrument
response) and values were very consistent. I tested a bunch of octaves per
the SAT calculated tuning and beat rates were great. Tuned piano (after
pitch raising 30 cents) and piano sounded great (or as good as any 77 year
old worn out decent piano can sound). Both professional musician clients
(husband & wife just inherited piano - husband: jazz guitarist and wife:
cello & violin) loved the tuning.

So, clearly the piano truly has relatively very low inharmonicity. WHY? And
what are any advantages/disadvantages of designing a piano with higher
inharmonicity (as most any other piano is)?

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com