Humidity Change and Unisons

[Roger Jolly]

Hi Don,
           Of coarse the humidity effects the plate. As the crown rises,so
does the pitch. This in turn increases the loading on the plate.   The
whole reason for nose bolts, is to minimize the flex of the plate due to
changing moisture conditions. Most pianos have  a nose bolt fairly close to
killer octave range and tenor break, to minimize this effect.  In some
cases the plate web will be increased in height, and or, it's T
construction design is used to compensate. Depending on the ductility of
plate material. it will influence the shape of design, and what extra
support will be required.  Further to this, many grands will have an added
support structure that is under tension to help stabilize movement of the
whole  system.   In the case of Steinway, the horn is under compression,
the thin slats that fit across the beams tension.
Many factors come in to play. due to torsional stresses. How much force is
supported by the plate, beams, rim, integration of pin block to whole
structure, and trapezium distortion of the rim. This is just to name a few.
You have opened a real can of worms, that is extremely complex. 
No black and white answers, only case by case study will yield a few answers.
  
Regards roger


At 08:22 PM 17/08/00 -0600, you wrote:
>Hi John,
>
>I can see temperature affecting the plate but not humidity. I am still
>having trouble visualizing what you are trying to tell me. Interesting
>suggestion that the duplex is a stability device. More worms anyone?
>
>At 09:46 PM 08/17/2000 -0400, you wrote:
>>At 08:36 PM 08/17/2000 Don Rose stated
>>
>>Throw away the soundboard and bridge and just have your strings and plate.
>If the plate doesn't swell with humidity, although I think it might, it
>will at least be tilted somewhat through expansion of that upon which it
>rests. The plate edge beyond the bridge keeps getting longer, not by note
>but by string. This is on both grands and uprights and that's why your
>right string is found to be at a greater tension than the left.
>>
>>This may not be as extreme where you have those "adjustable" duplux
>doohickeys on some grands though.
>>
>>John Lillico, RPT
>>Oakville, Ontario
>>
>>
>>
>>
>>
>Regards,
>Don Rose, B.Mus., A.M.U.S., A.MUS., R.M.T., R.P.T.
>
>Tuner for the Saskatchewan Centre of the Arts
>
>drose@dlcwest.com
>http://donrose.htmlplanet.com/
>
>3004 Grant Rd.
>REGINA, SK
>S4S 5G7
>306-352-3620 or 1-888-29t-uner
> 
Roger Jolly
Saskatoon, Canada.
306-665-0213
Fax 652-0505