humidity effect

[John Lillico, RPT]

>Well I just measured another piano and guess what--I see the exact same
>effect (only less obvious).
>
>The piano in this case was an upright Heintzman from the 1920's. It was
>last tuned by me in November of 1997 with humidity at 35%. Today the pitch
>had risen 10 cents (humidity today 56%) and the tri chords all exhibited
>the bass wire flatter than the middle and the treble wire sharper than the
>middle.
>
>Regards,
>Don Rose, B.Mus., A.M.U.S., A.MUS., R.M.T., R.P.T.
>
Gee, Don. I spend more time putting them in tune than trying to figure out why some strings of a tri-chord go sharp and others go flat. But your question has me thinking. Could we consider overall string length? Hardly, because the right string is longer on the grand and shorter on the upright. Bridge roll? Nah, I doubt it for all strings would be altered in the same direction. What about the shape of the plate itself? Is it possible that it has expanded along its inner edges (behind the bridge) causing increased tension on the right strings in both the upright and the grand? Hey! Am I on to something?

One thing I have observed recently with excess humidity is extreme sharpness in those eight to ten low tenor notes (but not the wound ones). Like yourself, I started recording temperature and humidity readings in February. It's an interesting study.

John (with a longer name than titles) Lillico, RPT
Oakville, Ontario