Hi Charles Well Thermal Expansion is 4.05×10–6 / K @ 10...50 °C So plug in some numbers and enjoy the results. The more important effect though is made clear when you look at a psyhcometric chart of the change in relative humidity when temperature is varied. It causes spikes in the R.H. That changes the absolute moisture content of the wooden parts of the piano. I don't have definitive hour by hour data on this phenomina, but I do have pianos that have become less stable when a set back thermostat was used and pianos that became more stable when the usage was stopped. As for the DC unit catching up I have measured a pitch change of 14 cents 12 hours later at A4 when a grand damppchaser was plugged in at 4% room humidity after being unplugged for an unknown amount of time on a Steinway Model A (I think--not entirely sure of model number) This was in the days before bottom covers were available and the piano did not have a floor length cover. At 11:52 AM 3/22/02 -0600, you wrote: >What would you consider to be a large temperature variation? We manually set back our thermostat at night. The temperature can change by around 12 deg F every day. That seems like a lot. > >Also, when the relative humidity in the room drops rapidly to about 25%, has anybody noticed how long it might take the D-C to catch up? I find that it takes a while to catch up when it's this low. In fact, I'm not sure it CAN bring the relative humidity from 25% to 42% if the room stays so dry. I don't have enough data yet. When the room is around 35%, it does fine with the humidifier staying on all the time. > >Charles Regards, Don Rose, B.Mus., A.M.U.S., A.MUS., R.M.T., R.P.T. mailto:pianotuna@accesscomm.ca http://us.geocities.com/drpt1948/ 3004 Grant Rd. REGINA, SK S4S 5G7 306-352-3620 or 1-888-29t-uner
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