I am positive from my experience with harpsichords (especially one I have been renting out on a regular basis for over ten years) that temperature is the main factor in rapid pitch drift, and there is a tremendous difference between the two metals. During the winter, it makes no sense to tune right after moving in and setting up - if I do, I generally notice the first register I tuned has changed up to 5 cents while I am pulling in unisons on the second (even a less than half hour drive in the back of the van the strings have changed temp enough to make that happen). Half an hour to an hour of sitting is usually enough to stabilize for tuning purposes, as far as temp is concerned (assuming the hall is stable). I have also observed an upward spike in pitch of two to three cents (steel wires) to five cents (brass wires) after about ten minutes with a door opened to lower the temperature to the specifications in the symphony musicians' contract (breeze flowing over the strings). I used to attribute most of the fluctuation to humidity. That is a factor over a period of hours or days (and a major one if the change in humidity is major), but pitch drift due to temperature is almost instantaneous. It affects wind instruments about as much (and in the opposite direction), so enormous cacaphony can result. I'm glad modern pianos aren't affected so much by temperature fluctuations, though I have noticed pitch drift on bass strings while tuning when a heating vent blowing directly on them, or sunlight hitting bass strings, warm them up. Affects the bass strings more - my theory is that's only because the copper conducts the heat faster. Anyone else had experience along those lines? Fred S. Sturm, RPT University of New Mexico
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