<html> <body> Mark, All depends on what you mean by "sufficient control".  An undercover (speaker cloth) takes out air circulation as a factor in overloading the DC system.  It essentially establishes a controlled climate under the piano.  Possible to overwhelm at the extremes? yes.  By a string-cover we mean a wool-felt-cover that covers everything from the tuning-pin-field to the tail end of the piano.  We specify wool felt because it naturally buffers humidity.  We specify a complete cover because we want to establish a loosely controlled climate over the board too and as much as is possible unify that with the action cavity.  There is a little air circulation possible around the bolts through the board supporting the plate.  There is also the practical situation where humidity does breath through wood, thin wood faster.  I too have toyed with the idea of drilling some holes through the belly-rail but haven't got around to trying it. In practicality, utilizing both covers does place more of the climate under control of the DC system.  The extent or preponderance of that control has its limits.  One of my piano customers bought a limited edition Sauter along with the complete system I put on it.  The tuning is rock-solid.  The regulation is close (concert ready tight) and has not changed.  She leaves the lid up on its lowest brass stick.  She also leaves the fall-board open despite my advice to close it when not in use.  Her ivory keys will probably yellow more slowly as a result of that preference (not a whole lot of UV getting into that room).  Yet, I did have to ease the keys during a very humid time here in Laredo.  Under the described scenario, there simply was not enough climate control to protect the keys.  I have not noticed a difference in tuning pin torque over the annual seasonal changes this piano has undergone with the described system.  I have not measured torque to see if there are smaller less noticeable changes going on.  I am satisfied that this is much better then a piano without a similar system as I do have similar pianos to compare to without such a system and they do undergo noticeable changes. Ideally the room in which the piano is in would have adequate climate control but that would require closing it off to the house; not desireable or controlling the whole house which is not economically feasible.  How much control is enough?  In this case the client is satisfied with the control we have achieved. I am satisfied that the action cavity is influenced adequately as hammer mating to the strings has not noticeably deteriorated with the climate swings and Sauters will show this problem long before Steinways (high inharmonicity) will. YMMV, Andrew Anderson, Artisan Piano--Sales & Service At 07:31 PM 2/17/2007, you wrote: <blockquote type=cite class=cite cite="">Hi all,   I distribute DC in Australia – where we have a huge mix of climatic conditions, much the way you do in the US but without quite the volume of snow you guys get…! What we are talking about here is frequently brought up by techs here.   I have always pondered the ability of the DC system in a grand to really cover controlling the moisture in a pinblock. In an upright, it’s easy, everything is in the same space. I realise that you are trying to achieve this when you talk about undercovers and string covers and piano covers – unifying the DC controlled space, but how can this possibly be effective for the pinblock when it is so far removed from the system? Having sufficient ‘controlled’ air moving to and surrounding the pinblock to then permeate the block and change the EMC seems almost impossible to me. I don’t have hard numbers on this, it’s merely my bush logic being applied –so I’d value any input at this point.   I know that some years ago Bob Mair at DC played with the idea of holes in the belly rail and computer type fans to circulate air from under the piano into the action cavity and therefore assisting the pinblock too, but this was ruled out due to the extraneous noise factor – it was considered unacceptable by just about everyone who heard it.   Other than that – how can sufficient control for the pinblock be achieved short of a dual tank system in an enclosed piano cabinet?   Looking forward to your thoughts   Mark Bolsius  </blockquote> </body> </html>