Unstable Yamaha C7

[Ron Nossaman]

>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