Thanks, Ron. I knew that it wasn't the piano. Your reply gives me the math that will (I hope) provide the impetus for the Studio owner to deal with the root problem. Meanwhile I'll just tune octaves aurally and continue to hope that the pitch rises and falls by a similar amount across the entire scale so that when I've finished the piano will be in tune with itself. Kinda like the aural equivalent of mal de mer. - Mark -----Original Message----- From: Ron Nossaman [mailto:rnossaman@cox.net] Sent: Thursday, June 17, 2004 3:14 PM To: Pianotech Subject: Re: Unstable Yamaha C7 >I take care of an older Yamaha at a recording studio that has a tuning >instability problem that I’ve never encountered on any other piano – the >pitch fluctuates by as much as 3 or 4 cents over the course of only a few >minutes. It took me quite a while to realize that this fluctuation ran in >sync with the forced hot air heating system. If I did this right, an A-4 of #17 wire, 406mm in length, will raise or lower in pitch by 2 cents with a 4°F temperature change - give or take a tad. That's just from linear thermal expansion or contraction of the wire. I just took high and low cycle temperatures from my air conditioner of 76.4°F and 59.1°F right at the register. Some distance into the room, the temperature spread won't be nearly as broad, and the wire temperature will naturally change slower then that of the air, but a piano sitting in the breeze from an AC register or in a room where the central thermostat is not, could very easily experience enough temperature shift with normal heating or cooling cycle times and temperature differences to account for this. I'd say it ain't broke. Don't worry about it. Ron N
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