Tom, your harpsichord seems to have been happy at 50% relative humidity 
but the difference between 50% and 20% is fairly large. My instruments 
are in Florida where everybody air conditions in the summer and there 
are a few days in winter when heat is needed. The indoor relative 
humidity range for us here is between 40% and 50%, though it could go 
higher in the summer, depending on the level of AC. The only times I 
have had to use a dehumidifier is limited to the shop when I am drying a 
soundboard prior to installation.

The tolerance for any harpsichord to changes in humidity has to do with 
where it was built (England, Florida vs drier climes) and how the 
builder designed to increase that tolerance. The adverse effect of low 
humidity is usually a split soundboard. High humidity can result in 
bulging or sunken soundboards and the sticking of action parts (keys, 
jacks, jack tongues) as the wood swells.

Every harpsichord is different but in your case, I'd get a humidifier 
for use during the dry months and try to keep the humidity at or above 
40%. In Florida, I would worry if my ambient humidity got much lower 
than that. Your nasal tissues will also thank you for the humidity 
increase...

Best of luck.

Rob

-- 
ROBERT BROOKE HARPSICHORDS
4214 18th Ave W
Bradenton, FL 34205

www.robertbrookeharpsichords.com

941-746-6725


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