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#2481827 11/18/15 12:02 AM
Joined: Apr 2007
Posts: 3,287
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I dutifully write down temperature and humidity on my invoices to get a sense of how the piano is responding to climatic changes. I've been thinking lately that it would be a better idea to measure the EMC (Equilibrium Moisture Content) of the soundboard itself. That should be the real factor in climate-caused tuning drift.

There is a lot of variation in price for pinless moisture meters. This one looks pretty good:

Does anybody use one to correlate EMC with the state of the tuning? Am I just being fanatical?? It just seems to make more sense to measure the actual moisture in the wood than the air (which can fluctuate a lot more within shorter periods of time).

Ryan Sowers,
Pianova Piano Service
Olympia, WA
Piano & Music Accessories
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Hi Ryan

not sure what you are trying to pin down concerning EMC but most meters are not very accurate at the moisture contents you would normally find in a stable structure like a sound board. Anything below 10 or 12% as I recall gets fairly iffy to measure by electrical conductivity, though it is possible that there exists better tech than I am familiar with. A stable piece of wood in a 42% relative humidity environment at room temperature will be at about 8% EMC. That is fairly accurate for most species of wood.


This will take you to several graphic representations of wood EMC versus temperature and RH.

The other issue as I see it for now is that these type of pinless meters require contact with unfinished wood surfaces. This would require an unfinished sound board surface.

EMC is certainly related to piano pitch but the general/approximate EMC should be discernible from temp and RH with the understanding that EMC is a lagging indicator of environmental conditions. I doubt you could garner accurate enough EMC readings to be of any real use at the time of tuning. The bigger problem that I see here is that RH can change rapidly and vary widely in most homes and churches and do so on a daily basis. EMC will chase RH changes but it will be constantly on the move in most cases.

Now, if you are building soundboards and are establishing EMC for rib glue up purposes, you can use a good scale and determine EMC by oven drying samples for your conditioning box and then calculating EMC based on weight. There are other methods available that can give you an analog measurement that changes based on EMC. Both of these methods require time be allowed for the wood to condition long enough to negate the hysteresis lag of EMC as it follows changing RH.

Dale Fox
Registered Piano Technician

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