On Dec 16, 2009, at 5:32 AM, Ron Nossaman wrote: > Immediate and short term pitch change is temperature related. > Humidity changes take much longer. Absolutely correct. Harpsichords move faster and farther, but the same principles apply. I am going to describe a bit of recent harpsichord experience I had this week, partly to illustrate this point, but also for practical purposes for those without much experience. The first experience is essentially just about temperature. The instrument was provided by the presenter. It had been tuned the night before for a concert in Santa Fe. I am safe in assuming a competent tuning at pitch, at a temp around 70F. It was driven next day to Albuquerque, which means probably at least 1.5 hours in the van. Small van with the drivers seat and cargo area undivided, so heat moved freely, but the back probably got colder. I was there when it was unloaded. I felt the case, and guessed about 50F. When it was set up, I checked pitch. Quite sharp, about 8 cents for steel (5-11 range), but 25 - 50 for the bass (brass). WILD octaves. I did not get out the tuning hammer. Instead I got a clean cloth and began rubbing the strings vigorously, for frictional heat. After five minutes or so, pitch was fairly close, still a bit sharp, so I went at it again. Boring work, but much less frustrating that tuning a moving target. It ended up reasonably stable at pitch. (I told them it should be on location at least 2 hours, but the best I got was that they did move it in a heated van as I suggested. Time was short, so you do what you can do. I had 45 minutes, and spent 10 of it rubbing strings). The second experience is more complex, since it has both temp and RH involved, and longer time. My instrument this time, moved from my house at about 65F and 40% to their rehearsal space at 72F/20% at 9 am. It was at pitch at home, and still at pitch when set up. I tuned it. 8 hours later, 5 pm, I tuned it again for the second rehearsal. I found it an average 10 cents flat, to 20 cents in the bass (brass strings). I deduced a combination of higher temp and drying out. I tuned it. 16 hours later, 9 am next day, I loaded it out to take it to the performance space for the next four days. Now temp was 67F, RH still about 20% (I didn't wait around for my hygrometer to stabilize its reading fully, but RH hadn't changed a lot). I checked the tuning before packing it up. Steel strings were right around pitch, but brass were 10-15 cents sharp. I deduce that the temp drop caused the rise in pitch (what else could have?) and in the steel strings, temp induced rise cancelled going flat due to dry. But in the brass strings, the temp change was a stronger effect. I loaded it into the performance space, at 72F/10%. 8 hours later, 5 pm, I found temp had risen to 76F. Pitch was a fairly even 10-12 cents flat, including those brass strings that had been sharp earlier (and that I hadn't touched). I've been doing this for 30 years (15 of those I have dealt with a similar Messiah schedule), and based on my experience, I will see it 5-8 cents flat in 24 hours, then within a very few cents flat for each of the next three days. Then I'll move it home and it will go 25 cents sharp over a few days (but I won't be monitoring it, so I won't notice until the next time I have occasion to rent it). Some of this is temperature, some is RH. I can literally see the RH effect in the expanding crack at the treble end of the SB (it's a very rare harpsichord that doesn't have at least one). I am going to guess that over half is RH, gradually over the course of hours and days. The temperature effect, though, is nearly instantaneous, as the first story showed. And it is exaggerated on the brass strings. Regards, Fred Sturm University of New Mexico fssturm at unm.edu
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