Dampp Chaser or not, that is that question!

[Woodrow, John (Parramatta)]

Ron,
Summing up what your have said in relation to temperature, RH and soundboard
moisture:

 at a constant 50% RH
moisture content of the soundboard for various temperatures will be

60 degrees F	9.4%EMC
70 degrees F	9.2%EMC
80 degrees F	8.9%EMC

So for a 20 degree F shift in temperature, there is only a 0.5%EMC change.
Contrast this to a 20% shift in RH (ok I know they are different scales, but
lets just assume both about the same significance) you get a 3.9%EMC change.
Or eight times the amout for temperature.

So in summary, your data says to me that RH range is the important driver of
EMC in line with what common sense would suggest.  Temperature range is by
comparison only a minor factor in influencing EMC.  This would support
selecting either a dry, normal, of wet DC system based solely on the spread
of RH ranges.  The effect of temperature differences between moist
sub-tropical and tropical regions on EMC may be so minor as to not be
important.    

John Woodrow.



Date: Wed, 02 Feb 2000 11:46:09 -0600
From: Ron Nossaman <RNossaman@KSCABLE.com>
Subject: Re: Dampp Chaser or not, that is that question!

>Because of the known relationship between spruce and atmospheric RH, RH in
>the soundboard environment will provide an accurate (although indirect)
>indicator of soundboard moisture content.
>
>Terry Farrell
>Piano Tuning & Service


"The Encyclopedia of Wood" (Sterling Publishing) lists a chart of EMC
related to temperature and humidity. It shows at 70 degrees F:
        
RH%    EMC 
 5         1.3   
10        2.5
15        3.5 
20        4.5    
25        5.4
30        6.2
35        6.9
40        7.7
45        8.5
50        9.2
55       10.1
60       11.0  
65       12.0
70       13.1

These numbers aren't specifically for spruce, but they're pretty close, and
good enough for general use.  At 60 degrees F, 50%RH = 9.4%EMC and at 80
degrees F, 50%RH = 8.9%EMC. 

For what it's worth.

Ron N