CAUT

I have long had the impression that while a quick rise in RH (rain storm) leads to very rapid change in pitch in certain patterns, a fall in RH seems to have a slower effect. This past week I had a great opportunity to observe that.

Scenario: a series of five recording sessions, Sat through Wed, tuning before each. On Thursday before, I gave the piano a full tuning in preparation. RH was 19%, had been steady at 10 - 19% over the preceding month, had been tuned the week before. The tuning was simply a matter of polishing unisons on a stable instrument. This provided a base line.

Friday there was a short rain shower. I did not measure RH that day, but Sat when I tuned, it was 27%. Sun RH had dropped back to 18%, Mon had dropped to 12%, Tues back upward to 16%. Then there was another brief shower Tuesday afternoon. Wed RH was up to 26%. IOW, there was a rapid rise in RH, followed by just as rapid a fall, an additional fall, and then another rapid rise.

Results: Saturday the piano needed a complete tuning. There were fairly severe right/left string unison problems (right sharp, left flat or at pitch, especially G4 - G6, as I would expect from long experience), and the low tenor had risen significantly, with F2 3.5¢ sharp. I tuned to pitch throughout. 
Sunday, the piano needed very little. Just unison polishing, I guess one could say that it had gone more flat than sharp, but on the order of 0.5¢. Monday, pretty much the same, but it was a wee bit flatter, and Tuesday again the same, now with F2 dropping 1¢. This morning (Wed), after the rain yesterday, I found F2 1¢ sharp and some unison issues with left string sharp, right flat pattern, less severe than on Saturday.

I conclude that wood absorbs moisture from the air more quickly than it releases it, in response to RH change - BUT keep in mind the actual readings, in the 10 - 30% range. I have no idea whether this would hold at higher RH levels. Practically speaking, it confirms what I had thought I had observed (but without day to day readings): if there is a rain storm, I definitely need to tune afterwards. But that tuning will hold fairly well for a good while.

-------------------------------------------
Fred Sturm
University of New Mexico
http://fredsturm.net
"When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou
-------------------------------------------

Hi Fred,

My experience corroborates your findings. When pianos get as dry as they do in your environment (New Mexico) and mine (SoCal high chaparral--in the single digits for much of the school year), when moisture is in the air, the dried out wood eagerly sucks it up. And when the tables are turned, losing Equilibrium Moisture Content does seem to take longer.

-------------------------------------------
Alan Eder, RPT
Herb Alpert School of Music
California Institute of the Arts
Valencia, CA
661.904.6483
-------------------------------------------






Original Message:
Sent: 06-18-2014 10:28
From: Fred Sturm
Subject: RH and pitch change - quick rise and fall

I have long had the impression that while a quick rise in RH (rain storm) leads to very rapid change in pitch in certain patterns, a fall in RH seems to have a slower effect. This past week I had a great opportunity to observe that.

Scenario: a series of five recording sessions, Sat through Wed, tuning before each. On Thursday before, I gave the piano a full tuning in preparation. RH was 19%, had been steady at 10 - 19% over the preceding month, had been tuned the week before. The tuning was simply a matter of polishing unisons on a stable instrument. This provided a base line.

Friday there was a short rain shower. I did not measure RH that day, but Sat when I tuned, it was 27%. Sun RH had dropped back to 18%, Mon had dropped to 12%, Tues back upward to 16%. Then there was another brief shower Tuesday afternoon. Wed RH was up to 26%. IOW, there was a rapid rise in RH, followed by just as rapid a fall, an additional fall, and then another rapid rise.

Results: Saturday the piano needed a complete tuning. There were fairly severe right/left string unison problems (right sharp, left flat or at pitch, especially G4 - G6, as I would expect from long experience), and the low tenor had risen significantly, with F2 3.5¢ sharp. I tuned to pitch throughout. 
Sunday, the piano needed very little. Just unison polishing, I guess one could say that it had gone more flat than sharp, but on the order of 0.5¢. Monday, pretty much the same, but it was a wee bit flatter, and Tuesday again the same, now with F2 dropping 1¢. This morning (Wed), after the rain yesterday, I found F2 1¢ sharp and some unison issues with left string sharp, right flat pattern, less severe than on Saturday.

I conclude that wood absorbs moisture from the air more quickly than it releases it, in response to RH change - BUT keep in mind the actual readings, in the 10 - 30% range. I have no idea whether this would hold at higher RH levels. Practically speaking, it confirms what I had thought I had observed (but without day to day readings): if there is a rain storm, I definitely need to tune afterwards. But that tuning will hold fairly well for a good while.

-------------------------------------------
Fred Sturm
University of New Mexico
http://fredsturm.net
"When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou
-------------------------------------------

Fred,

Thanks for you report. It certainly rings true with my experience here in West Central Colorado. Eight years ago when I began tuning at our local university, wanting to please the piano prof, I spent a generous amount of time with her two studio pianos. It had been a dry week until that night when we got a heavy downpour. Very frustrating.

For years I've told customers:

      "Wood absorbs moisture much quicker than it releases it during drying." 

        [See last paragraph on page 7:  <http://www.fpl.fs.fed.us/documnts/pdf2002/willi02b.pdf>]

In this climate, evaporative (swamp) coolers are widely used and can easily elevate RH into the 50s & 60s (up from the typical 10-20% I measure in the winter). Even with AC, summer rains alone can be very upsetting.

-------------------------------------------
David Bauguess
Grand Junction CO
970-257-1750
-------------------------------------------






Original Message:
Sent: 06-18-2014 10:28
From: Fred Sturm
Subject: RH and pitch change - quick rise and fall

I have long had the impression that while a quick rise in RH (rain storm) leads to very rapid change in pitch in certain patterns, a fall in RH seems to have a slower effect. This past week I had a great opportunity to observe that.

Scenario: a series of five recording sessions, Sat through Wed, tuning before each. On Thursday before, I gave the piano a full tuning in preparation. RH was 19%, had been steady at 10 - 19% over the preceding month, had been tuned the week before. The tuning was simply a matter of polishing unisons on a stable instrument. This provided a base line.

Friday there was a short rain shower. I did not measure RH that day, but Sat when I tuned, it was 27%. Sun RH had dropped back to 18%, Mon had dropped to 12%, Tues back upward to 16%. Then there was another brief shower Tuesday afternoon. Wed RH was up to 26%. IOW, there was a rapid rise in RH, followed by just as rapid a fall, an additional fall, and then another rapid rise.

Results: Saturday the piano needed a complete tuning. There were fairly severe right/left string unison problems (right sharp, left flat or at pitch, especially G4 - G6, as I would expect from long experience), and the low tenor had risen significantly, with F2 3.5¢ sharp. I tuned to pitch throughout. 
Sunday, the piano needed very little. Just unison polishing, I guess one could say that it had gone more flat than sharp, but on the order of 0.5¢. Monday, pretty much the same, but it was a wee bit flatter, and Tuesday again the same, now with F2 dropping 1¢. This morning (Wed), after the rain yesterday, I found F2 1¢ sharp and some unison issues with left string sharp, right flat pattern, less severe than on Saturday.

I conclude that wood absorbs moisture from the air more quickly than it releases it, in response to RH change - BUT keep in mind the actual readings, in the 10 - 30% range. I have no idea whether this would hold at higher RH levels. Practically speaking, it confirms what I had thought I had observed (but without day to day readings): if there is a rain storm, I definitely need to tune afterwards. But that tuning will hold fairly well for a good while.

-------------------------------------------
Fred Sturm
University of New Mexico
http://fredsturm.net
"When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou
-------------------------------------------

There is a US Forest Service wood products data sheet that lists the rate of moisture intake verse moisture release of several species of wood. I am just going from memory of studying it some 30 years ago but wood takes on humidity about 5 times as fast as it releases it. That is why the Damp Chaser with Humidistat is valuable. It protects against and moderates humidity pulses. I usually put two 50 watt rods in 6' or larger pianos and I try to place them along the beams rather than under to increase the "dry island" under the soundboard. The "watering can" they sell I don't like. Too many ways things can go wrong for too little gain.

-------------------------------------------
Edward McMorrow
Edmonds WA
425-299-3431
-------------------------------------------






Original Message:
Sent: 06-18-2014 14:58
From: David Bauguess
Subject: RH and pitch change - quick rise and fall

Fred,

Thanks for you report. It certainly rings true with my experience here in West Central Colorado. Eight years ago when I began tuning at our local university, wanting to please the piano prof, I spent a generous amount of time with her two studio pianos. It had been a dry week until that night when we got a heavy downpour. Very frustrating.

For years I've told customers:

      "Wood absorbs moisture much quicker than it releases it during drying." 

        [See last paragraph on page 7:  <http://www.fpl.fs.fed.us/documnts/pdf2002/willi02b.pdf>]

In this climate, evaporative (swamp) coolers are widely used and can easily elevate RH into the 50s & 60s (up from the typical 10-20% I measure in the winter). Even with AC, summer rains alone can be very upsetting.

-------------------------------------------
David Bauguess
Grand Junction CO
970-257-1750
-------------------------------------------






Original Message:
Sent: 06-18-2014 10:28
From: Fred Sturm
Subject: RH and pitch change - quick rise and fall

I have long had the impression that while a quick rise in RH (rain storm) leads to very rapid change in pitch in certain patterns, a fall in RH seems to have a slower effect. This past week I had a great opportunity to observe that.

Scenario: a series of five recording sessions, Sat through Wed, tuning before each. On Thursday before, I gave the piano a full tuning in preparation. RH was 19%, had been steady at 10 - 19% over the preceding month, had been tuned the week before. The tuning was simply a matter of polishing unisons on a stable instrument. This provided a base line.

Friday there was a short rain shower. I did not measure RH that day, but Sat when I tuned, it was 27%. Sun RH had dropped back to 18%, Mon had dropped to 12%, Tues back upward to 16%. Then there was another brief shower Tuesday afternoon. Wed RH was up to 26%. IOW, there was a rapid rise in RH, followed by just as rapid a fall, an additional fall, and then another rapid rise.

Results: Saturday the piano needed a complete tuning. There were fairly severe right/left string unison problems (right sharp, left flat or at pitch, especially G4 - G6, as I would expect from long experience), and the low tenor had risen significantly, with F2 3.5¢ sharp. I tuned to pitch throughout. 
Sunday, the piano needed very little. Just unison polishing, I guess one could say that it had gone more flat than sharp, but on the order of 0.5¢. Monday, pretty much the same, but it was a wee bit flatter, and Tuesday again the same, now with F2 dropping 1¢. This morning (Wed), after the rain yesterday, I found F2 1¢ sharp and some unison issues with left string sharp, right flat pattern, less severe than on Saturday.

I conclude that wood absorbs moisture from the air more quickly than it releases it, in response to RH change - BUT keep in mind the actual readings, in the 10 - 30% range. I have no idea whether this would hold at higher RH levels. Practically speaking, it confirms what I had thought I had observed (but without day to day readings): if there is a rain storm, I definitely need to tune afterwards. But that tuning will hold fairly well for a good while.

-------------------------------------------
Fred Sturm
University of New Mexico
http://fredsturm.net
"When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou
-------------------------------------------