<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META content="text/html; charset=iso-8859-1" = http-equiv=Content-Type> <META content="MSHTML 5.00.2919.6307" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV> "This humidity thing is always fun... and dont worry... even if I am = blowing air out of my better end,,, I still enjoy the conversation.. grin." Me also!........But. Look at Dampp-Chaser marketing propaganda. All = their graphs about soundboards. Now I don't really think that they truely = represent the results of any particular experiment, but rather trends they are = trying to exemplify (although I do believe they should state that some of the data = in their brochure might be a bit idealized). Anyhow, as the RH decreases in = air in a piano, the soundboard Moisture Content also declines. Moisture content = is water in wood. Lower moisture content means less water in wood. That = means the water left the wood. It is no longer there. It does not have = anything to do with the amount of water the wood may be able to hold (like RH). This is = a central issue in wood technology - manipulating the moisture content of = wood. It really, really is true. You can trust me! I is edgeekated. I got = me a deegree in Forestry (two lives ago)! So there! Top that!   ;-) <BLOCKQUOTE TYPE="CITE"> Terry Farrell Piano Tuning & Service Tampa, Florida <A = href="mailto:mfarrel2@tampabay.rr.com">mfarrel2@tampabay.rr.com</A></BL= OCKQUOTE></DIV> <BLOCKQUOTE style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: = 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black">From: <A href="mailto:Richard.Brekne@grieg.uib.no" title=Richard.Brekne@grieg.uib.no>Richard Brekne</A> </DIV> <DIV style="FONT: 10pt arial">To: <A = href="mailto:pianotech@ptg.org" title=pianotech@ptg.org>pianotech@ptg.org</A> </DIV> <DIV style="FONT: 10pt arial">Sent: Wednesday, October 18, = 2000 6:21 PM</DIV> <DIV style="FONT: 10pt arial">Subject: Re: Different question = about heater bars</DIV> <DIV> </DIV>  Farrell wrote: <BLOCKQUOTE TYPE="CITE">Gee whizz Richard. You of course know that = it pains me to an unimaginable extent to suggest that my thoughts might = be more valid and someone else may be, er, a, less than correct, = BUT.....  </BLOCKQUOTE> You isolate the system far too much, and over simplify the = situation as such... grin... Number one.. you cannot discount the back side of the = piano.. or the exterior of the piano otherwise... Equilibrium will always take = the easiest path. And the easiest path is air ... from wherever it leaks = in... That being said..... you will have to some degree the affects as = you describe them below... But on the other hand, you will also have the = affects as I describe them. Raising the temperature does indeed also lower RH = in the interior of the wood... whats good for the goose is usually (and in = this case as well, good for the gander. Your Kiln example is a much more isolated system to begin with. And = if it was completely and totally isolated... where on earth do you think = these water molecules would migrate to ??? You put a panel into an oven that is already dry inside... thats how it draws out water.. this isnt = exactly the same process as damp chaser creates.. tho admitedly some of the = same functions are at work. I think you would aggree that takeing a panel and puting it into a = kiln which has the same moisture content in the air as the panel does in = the wood, sealing the kiln and turning it on wouldnt have exactly the same = effect.. now would it. This humidity thing is always fun... and dont worry... even if I am = blowing air out of my better end,,, I still enjoy the conversation.. grin. <BLOCKQUOTE TYPE="CITE"> Lets say the RH of air in vertical = piano interior is 70%, temperature is 70 degrees F and soundboard = moisture content is 10%. Equilibrium conditions exist (water molecules = are evaporating from the soundboard surface at the same rate that = water molecules from the air are imgrating into the soundboard = surface). Turn on heat inside piano. Raise temperature to, say, 90 degrees F. = The RH in piano interior immediately drops to perhaps 50%. Immediately, = the air inside the piano is capable of holding much more water vapor = than previously. Water molecules will then migrate from the soundboard surface from within the wood and evaporate into the air inside = the piano at a rate exceedingthe migration of water molecules migrating = from the air into the soundboard wood. Hence there will be an net decline = in the number of water molecules in the soundboard (and a net increase = in the amount of water molecules in the air within the piano - untill = it leaks out and mixes with room air). That is what is meant by = soundboard moisture content. That is the absolute amount of water "trapped" = within the wood. It is not a mere artifact of heating the wood and the = air wihin the wood pores having a lower RH. A net volume of water = will continue to escape from the soundboard until a new equilibrium = is established between the RH of the piano interior and the water = content of the soundboard. (We are or course neglecting the fact that = the soundboard is also exposed to the outside air on the backside, but = this does not change the course nor end point of this discussion.) This is why when one dries a soundboard before installing into a = piano or before shimming, the soundboard shrinks - because the board has = an lower absolute volume of water within it. You can prove this to = yourself by weighing a piece of wood before and after heating for a long = time. It is why  a freshly cut log is real heavy, but one of the same = size and species that has dried for a year is much lighter - because = water has been "drawn out" from the wood! I think. I'm having fun watching language at work. I truely hope = you are also. :-) Terry Farrell Piano Tuning & Service Tampa, Florida mfarrel2@tampabay.rr.com ----- Original Message ----- From: "Richard Brekne" <Richard.Brekne@grieg.uib.no> To: = <pianotech@ptg.org> Sent: Wednesday, October 18, 2000 2:33 PM Subject: Re: = Different question about heater bars > > > Farrell wrote: > > > > = Moisture is not exactly "drawn out" of > > > the = piano... rather the relative humidity is reduced. > > > > = No and yes. Assuming that the air inside the piano is at some elevated = > > reletive humidity and the soundboard is in equalibrium with = those > > environmental conditions. Now turn on the Dampp-Chaser = heat rod.The relative > > humididy in the interior of the = piano is indeed reduced. That sets up a > > non-equilibrium = condition between the reletive humidity in the piano > > interior = and the moisture content of the soundboard wood. Because the air = > > has less reletive humidity and can now hold more humidity, there = will be a > > net movement of water from the soundboard to the = air. So, it is reasonable > > to say that "moisture is = drawn out of the piano and into the air. > > Grin... How fun it is = to watch language at work. I'll buy your interpretation of > the = words "moisture is drawn out of the piano and into the air" in this = > connection. Its actually what I was saying. Still, from the other standpoint.. > absolute humidity remains the same within = the wood as it does within the air.. > expanding the air = surrounding air, and thereby decreasing Relative humidity does > indeed = create the non-equilibrium you describe, but as to whether or not one = > describes the equalizing of this in terms of "drawing out humidity" = or rather > that the soundboards air content also expands, = retaining the same volume of > absolute humidity is ...grin.. up = for discussion... I would choose the > latter.... for ..... clarity...hehe.. > > Keith.... sorry to be so = picky...:) > > > > > > > Terry Farrell = > > Piano Tuning & Service > > Tampa, Florida = > > mfarrel2@tampabay.rr.com > > -- > Richard = Brekne > RPT, N.P.T.F. > Bergen, Norway > > ></BLOCKQUOTE> -- Richard Brekne RPT, N.P.T.F. Bergen, Norway =   </BLOCKQUOTE></BODY></HTML>