[pianotech] --Centering the bridge--was S&S something

[Dale Erwin]

comments below


Dale Erwin... RPT
 Mason & Hamlin/Steinway/U.S pianos
www.Erwinspiano.com
209-577-8397

 
  





-----Original Message-----
From: Ron Nossaman <rnossaman at cox.net>
To: pianotech <pianotech at ptg.org>
Sent: Tue, May 29, 2012 2:57 pm
Subject: Re: [pianotech] --Centering the bridge--was	S&S	something


On 5/29/2012 11:46 AM, Dale Erwin wrote:
Dale- Mass and stiffness in assemblies are one thing
> from a weight point of view, but what weight?
What I meant was how much physical gravity induced weight are we talking about as a
variable or as something that might have a goldilocks scale to work with.
  Weight  *is* mass, under gravity, measured with a scale.
> Also Factor in that probably no two Techs who routinely build soundboard
> systems or seem to set down bearing in the same way or even agree or
> think it all that necessary to the final outcome.

Ron- That's because no two of them are talking about the same soundboard, 
whether they realize it or not.
 Dale- Good point and that was mine. We do talk about different recipes relevant to impedance
 and this is mine and the things I factor in regarding impedance was what I was trying to share
 with Gene. Thanks for chiming in.

 Dale- So to some real extent the empirical tonal outcome is what folks say wow
> to... or not.

Ron-And the subject impression of what constitutes tone, whatever the actual 
piano sounds like.
Dale-Well a person in bad mood might condemn all piano sounds no matter how glorious on a given day. 
 I agree... its subjective. Is that a bad thing? or jsut one to take into account when dealing
  with the human factor

 Dale- We desire to create a sound our own ears intuitively have
> been pursuing on the tonal road less traveled by.

Ron-If we didn't like the result, we wouldn't have spent all those months 
and years chasing them, and wouldn't continue to build them. CC with 
flat ribs is the easiest way to build a soundboard if that's all we wanted.
D.--I agree accept If we did... we'd still have the weaknesses we subjectively object to.

  Dale- My tone described
> ___I personally like a tone that can be described as power without
> noise,

 Ron-Sounds like what you wrote about my Rochester B.
 D.-I believe it is and would enjoy hearing it again as I would other design concepts. 
 David Love and I are trying to do this when we can. 
 Its a disadvantage not to have more access to each others work. That said I think the resultant 
 sound we get from our different recipes may be different.


 Dale- I have designs that are repeatable, dependably musical and that I can
> build with confidence. I am certain many of the regular contributors to
> this subject who weigh in here can attest to the same confidence, and I
> think they would all agree that its come with lots of trial and error on
> a steep, steep learning curve.

 Ron-Yep.


Dale- We usually install a bass cut-off bar to shorten those monstrously
> long ribs and prevent energy losses in the bass corner.

Ron-I do it to center the bridge and make the ribs there stiff enough 
without having to be 50mm deep and heavy as logs. Killing the energy 
wasting open bass corner as well is a freeby.
 Understood. I don't like anything over 40 inches long and that's stretching it.
Dale- As I have listened to countless Compression crowned systems I have
> realized that so many sound fantastic. Yes, they have design
> shortcomings I do not wish to repeat, but they can sound awesome for
> some period of time and under the right conditions, a very long time.

Ron-Absolutely. They can also sound thoroughly wretched. Where RC&S systems 
are controllable to a vastly narrower range of variability that 
*averages* well above the average sound of the CC board spectrum.
 Dale-The choir should be informed by now. I remember a rebuilt A in Rochester we both 
inspected as we were leaving. Dreadful flat or oil caned board and it just came from 
 the Restoration center. If we showcased something pathetic like that,
 would anyone here take us seriously? 
Ron- control is what the CC board builders find offensive. Not enough 
"variation", too predictable. I've heard descriptions like "cookie 
cutter boards". I say I'll gladly take it.
D.-AS will the clients.  That's why they come. They want a sure thing.
Our small shops can't even have one failure.

 Dale- What I have taken a way from the C.C. model is that these boards have a
> non linear compression response when pre-loading them for stringing...
> when built right.

Ron-Which makes them much more sensitive to bearing setup than RC&S.
D.On the ones built healthy find that there is a good deal of latitude when setting bearing.
 I don't find it to be a problem using the pre-stressing method


 D.-Pre-loaded means what the board does as it is strung
> providing the bridge height was cut high enough to allow them to be
> loaded/compressed in an adequately. Meaning that the more they are
> compressed the stiffer they get till they won't deflect anymore. This is
> what makes this model work and when its dialed in to closely watched
> parameters they can sound amazing.

Ron-Indeed they can. The balance is to compress them to the point of maximum 
compression, therefor maximum stiffness, without going too far on the 
bearing and restricting what movement they are capable of at full 
compression. I think that's largely the difference in the efficiency and 
tolerance of the RC&S boards. Even built as stiff as a CC board, they 
still gave spring both up and down, where the CC board is bottomed out 
on the panel compression and is getting essentially half a spring cycle.
 Dale-I'll agree on that. When done right both Rib crowned & the RC & S models
  have more use of the springy diaphragm model I described. I still pre-stress them the same.
   I believe it accounts for the impressive tonal projection I'm hearing in these boards get. >

 Dale-So, I still see the board in my own design as the springy diaphragm
> model based on non linearity. I do make quite a stiff board, stiff set
> of ribs & I do pre-load it much the way the factories have done for
> decades.

R.-I don't because I can't. Mine don't act like CC boards at all.
D.-See these are different recipes we have chosen and thats ok. That is part of what I was sharing.
 
R.- They don't have a soft top to the deflection, and no bottoming out, and 
they're really too stiff to pre-load, even if doing so told me anything.

D.-For me, in my recipe, it tells me that at about 3 mm of pre-compression at the central strut
 the board gets really stiff. 2 mm at the next strut up and barely anything at the top one. The low tenor is
 gently loaded.
If my unloaded bearing was 8 mm I'm going to only load it to roughly half its spring 
 rate which in my opinion is good middle ground.
 D.-The other factor is how much crown is enough 
 and what are we going to do
> with it once we have it.?

 D.- In my recipe, it came to me over time, that what ever the unloaded
> upward deflection of the board was after the board was glued to the rim,
> that I wanted to compress that amount of crown by roughly half with
> string bearing. ie the board has 10 mm of crown on the longest rib. I
> want it to deflect 4-6 mm. and I want it to be strongly pushing back. I
> want it to be reactive.

 Ron-I started with the premise that I wanted a crown height at least as high 
as the bearing offset, so it was geometrically impossible under any 
circumstances for the bearing to force the crown flat or concave.
 D.-Right and its not going to happen here either
 > If I'm using tight grain Sitka spruce I will want to thin the entire
> panel to 8 ish mm and the thin it at the rib scoops/perimeter and
> further into the panel.

I haven't used anything but a constant thickness panel for some time.
I saw that David responded to this

 Dale- Gene, as to panel compression I dry to 5.5 to 6 % depending on where its
> going. I'm not concerned about a certain amount panel compression and
> consider it as a piece of the equation but a much smaller piece than a
> C.C. board. Also remember that I am using Sitka spruce in the 20 to 28
> grains an inch range and it can easily handle this amount of compression
> in many climates but especially in our western region climate and this
> is where most of our restorations end up.

Ron-I like low density panels, in the 8-12 GPI range. Since panel 
compression isn't providing much of anything to stiffness, I don't need 
high grain densities.
D.-I know that the ribs on my design are providing at least 75% of the stiffness support if not 
 higher depending on whether its rib crowned or RC&S 

 Ron-It's always been my experience that if there wasn't a fairly huge range 
of acceptability in building these things, we wouldn't be able to do it 
at all by any method.
 D.-Isn't that the salient truth of the matter
 What we're after now is more understanding of what 
does what, and a refinement of control that gets us past the crap shoot 
of soundboard building and survival that has been the state of the art 
for way too long in the CC world.-- Ron N
Well said-
Dale

 Ron N

 
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