More CC vs RC questions was RE: Killer Octave & Pitch Raise

[David Love]

I see, so therefore a lower spring rate will result in the board moving
more easily and therefore a softer hammer would be needed to control
attack levels?  So if that's true and if the firmness of the hammer
regulates the balance of partials, say, does it follow that there is a
point where a lower spring rate might result in the requirement of too
soft a hammer to create the desired balance of partials while still
keeping the attack levels under control?  A noticeable thing about most
of the CC boards that I come across is that they not only tolerate, but
seem to require a firmer hammer yet when they work they create a nice
partial balance.  I would tend to hypothesize, then, that equivalence
between soundboard assemblies (in terms of balance between tonal attack
and partial balance) has everything to do with spring rate.  How do most
CC boards compare with RC&S boards in terms of spring rate?

I have noticed since this discussion started and I am paying attention
to these things more acutely, that the difference between pianos has
mostly to do with the sound at attack, how the tone develops over time
and the balance of partials.  It seems that these should be measurable
without great difficulty with a full spectrum analysis, no?

Maybe it's time to write a grant.     

David Love
davidlovepianos@comcast.net 

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Ron Nossaman
Sent: Friday, February 18, 2005 7:47 AM
To: Pianotech
Subject: RE: More CC vs RC questions was RE: Killer Octave & Pitch Raise


>Ron:
>
>Could I ask you to amplify a bit on what progressive and lower and
>higher spring rates mean?
>
>David Love


Board A has a 5mm crown, deflects to 3mm crown under load. Board B has a

7mm crown, deflects to 3mm under an identical load. Both are supporting 
identical loads with identical remaining crown, but A has a higher
spring 
rate, and B will move farther under a given impulse than A.

Rib (beam) deflection is linear. If 10 lbs deflects a rib x distance
then 
20 lbs will deflect is x*2 distance and 5 lbs will deflect it x/2.
That's a 
constant spring rate. Soundboard assemblies are non linear in
deflection. 
If 50 lbs deflects a board x distance, 100 lbs deflects it less than
x*2, 
but 25 lbs deflects it more than x/2. As the load increases, the spring 
rate also increases. That's a progressive spring rate, and I think the 
panel compression is responsible for this.

Ron N

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