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

[Sarah Fox]

Hi Ric,

It took me quite a while to wrap my brain around what you were suggesting. 
OK, I think I get you -- sort of a footing to each rib, made up of SB 
material.  The additional stiffness would come from the additional 
mechanical advantage of the panel on the rib.  Of course with this 
arrangement, the total amount of crowning would be less dramatic, but on the 
other hand, it would take greater downbearing to flatten the thing.  I agree 
that the concept of having wood compression and rib deformation fighting 
each other is on the surface a bit counterproductive!  Of course if these 
were perfect springs, it wouldn't really matter.

Perhaps what is *really* important is that the mechanical properties of the 
wood differ according to the magnitude of compression.  A panel indeed 
undergoes compression as an RC/S board deflects towards the floor, and the 
increment in compression is even greater than that for a CC board, assuming 
the ribs are taller.  However, this compression may be more in the "elastic" 
range of the wood, while the compression increment in the CC board ventures 
even further into inelasticity.  It is in the more inelastic zone that 
hysteresis would be more evident.  In fact it is in this zone that 
distortion might be more of a factor.  Is distortion a bad thing?  Well, yes 
and/or no.  Ask any electric guitarist about distortion, and you'll get a 
very long discourse on the merits of tubes vs. transistors, soft clipping 
vs. hard clipping, clipping vs. no clipping, etc., etc.   They're after a 
sound, and distortion of a particular flavor is how they get it.  Anyway, I 
bet someone on this list has done some testing of the in/elastic properties 
of RC/S vs. CC board designs.

I also wonder whether a CC board that has lost its crown starts to take on 
some of the acoustic properties of a really lousy RC/S board -- one with no 
crown and inadequate stiffness.  Perhaps when the crown is lost, the 
inelasticities of the highly compressed panel are also lost, and so the 
distortion, hysteresis, temporal variation in tone, etc. (perhaps 
"desirable" properties) would be lost.

What I was thinking when I suggested a hybrid board was literally two panels 
fitted together.  Imagine a CC board from, say, the lower treble downwards, 
ending at a half-rib (split lengthwise, that is).  Join that half-rib to the 
half rib at the edge of a RC/S board for the lower treble and upwards.  That 
would give the longevity of crown and higher sustain in the problem areas, 
with acoustic coupling that would give the entire board some 
damping/hysteresis/distortion properties of the CC board, if only by virtue 
of the fact that vibrations would bleed back and forth across the board 
joint.  It might yield a classic CC sound with most of the benefits of RC/S. 
Perhaps???

Peace,
Sarah




----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Newtonburg" <pianotech@ptg.org>
Sent: Monday, February 14, 2005 3:19 PM
Subject: More CC vs RC questions was RE: Killer Octave & Pitch Raise


> Hi Sarah
>
> Intersting post as usual. I find much that harmonizes with my own thinking 
> in it. Especially this last paragraph which I include below. It is indeed 
> hard to argue the fact that there are quite obviously several different 
> ways of going about this whole SB problem, and equally difficult to argue 
> the fact that in the hands of a competant builder, each can perform 
> wonderfully... each in their own distinctive way.  I enjoy the heck out of 
> all the enlightening discussion that describes some of the mechanics, or 
> at least some of what is thought to be the mechanics of the different 
> approaches. But, like David Love, I am far less interested in hearing 
> about who thinks this or that method is best.  Pros and Cons there are... 
> which means just that. There is always a trade off.
>
> Hybrid ??... I suggested something of a hybrid some while back...and got 
> promptly scoffed at for it here... but to repeat just for your 
> edification, I suggested inserting a strip of soundboard material, cut to 
> match the upper flange of each rib, between the rib and soundboard... as a 
> kind of compression buffer.  One would dry the panel out as usual in a CC 
> board, and dry out the buffer material to only about 6 % MC.  Glue the 
> ribs and buffer material together (grain in buffer material in the same 
> direction as the soundboard) and then the assembled buffered ribs to the 
> panel and let the whole thing take on moisture.   Seemed like a reasonable 
> enough idea to at least try out.  I did exactly this with a few peices of 
> left over material from the old Knudsen Piano factory... and it crowned 
> nicely enough.  Tho I susppose I should have glued the thing to some kind 
> of a simulated rim and put the thing under compression to see what would 
> happen... maybe next time.
>
> The idea was simply to provide a bit more longitudinal elastisicity in the 
> ribs themselves.  I still beleive there is some, which you seem to aggree 
> with, and that the tension that must be present in the rib strains against 
> any increase in compression from the panel... effectively supporting 
> crown.  I find no real conflict between this and the point that the ribs 
> actually do resist being bent... essentially fighting crown in a completly 
> different sense.
>
> Cheers
> RicB
>
>
>
> Personally, I'm a big fan of the expressiveness of the American Golden Age 
> pianos, and perhaps some of the expressiveness in these pianos derives 
> from the inefficiencies of the CC board.  On the other hand, it's hard to 
> argue against the longevity, stability, and treble response properties of 
> an RC/S board.  It's equally hard to argue against the smooth, brooding 
> qualities of one of Ron Overs' beautiful pianos!  It would be very 
> interesting if someone were to experiment with a hybrid board, combining 
> the properties of CC and RC/S.  (Would that even be possible? Perhaps RC/S 
> in the treble end and CC elsewhere?  Perhaps a split board, joined at the 
> rib???)  Or how about a different sort of board entirely?  How about a 
> violin-like board that has its crown milled/sculpted into the wood like a 
> very shallow bowl, lightly supported/stabilized with smaller, shaped ribs? 
> How about a RC/S board with an electromagnetic low-pass damping device 
> that would slowly dissipate higher partials?  So many fun possibilities! 
> Fascinating stuff!  :-)
>
> Peace,
> Sarah
>
>
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