>From: "Bill Spurlock, RPT" <74077.3053@compuserve.com>
>
>I'm wondering if others have noticed temperature-caused pitch change
>occuring while tuning verticals equipped with Dampp Chaser rods, and
>if so how you handle it. It seems that because the heating rod is
>adjacent to the plate and strings, there is enough warming of these
>parts to cause the pitch to rise or drop several cents within about 15
>minutes whenever the rod turns on or off.
>Overall, you're trading a temperature-caused deviation of a few cents
>for moderation of perhaps a 15 - 25 cent humidity-caused variation (in
>areas where wide humidity swings occur). It's a small price to pay,
>but it would be better yet to have no temperature effect.
Yes, yes, yes! This is a very real problem. Bill, you took the
words right out of my mouth. I considered putting material on the
short term tuning effects of climate control systems in my Journal
article, The Long and the Short of Temperature and Humidity, but
basically, I didn't have the nerve.
When I come to a piano with a climate control system, I first
determine which components (dehumidifier/humidifier) are present and
which component is presently operating. If the dehumidifier rod is
operating, I use an extension cord, which I carry for just this
purpose, to plug the dehumidifier directly into the AC, bypassing the
humidistat. This insures that the rod will stay on during the entire
tuning. There is little chance of my forgetting to plug the
dehumidifier back into the hunidistat, because in doing so I would be
leaving my extension cord with the piano.
At first I thought it was a real hassle to open every piano in
order to fiddle with the plugs, but we should be checking the correct
operation of these units on a regular basis anyway. Most of the
climate-control systems in this area are complete with both
dehumidifers and humidifiers. When I find a humidifier operating, I
simply unplug the dehumidifier from the humidistat, insuring that it
cannot come on during the tuning. My assumption is that the 8-watt
dehumidifier's going off during a tuning has little effect.
Your measurements of the effect is in line with what I have
observed. I might point out that the effect is indeed measureable on
grand pianos, although obviously diminished by the interposed
soundboard. I think that on grands the effect will measure in the
area of one and two cents rather than the four and five cents that you
measured on verticals.
In the end, I believe climate-control systems are worth the
bother. I happen to have installed two systems Tuesday, and, if I
have the parts, I will install three systems Wednesday. But
technicians need to be aware of how much of a bother these
systems can really be.
My understanding of the humidistat is that it ALWAYS cycles every
two or three hours, even if for only a short time, so there isn't ever
really any time when the humidifier is always on or the dehumidifer is
always on. I believe I have heard the Dampp-Chaser people say that
this cycling provides some protection against too much of a good
thing. The point is that it is quite likely that a climate-control
system will cycle during the time it takes to do a tuning. It is
clearly worth taking some steps to avoid the temperature induced
effects caused by this cycling.
There are other implications here that are worth mentioning. I
have heard customers with good ears for tunings, tell tales of their
pianos going out of tune all at once. D-C cycling could provide an
explanation here. What if two pianos are side by side and both have
climate control systems. What happens when the pianos are being
played together and one cycles and the other one does not?
And while we're at it, when one is tuning two (or more) pianos
together and climate control systems are present, wouldn't it be a
good idea to make certain that the tunings are done with uniform
climate control systems, that is, with all the dehumidifers on, or
with all the dehumidifiers off?
Kent Swafford
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