Comments interspersed David Love www.davidlovepianos.com David Love wrote: > The interesting thing about downbearing is that in a CC assembly it is a > requirement for achieving the desired stiffness. Ron N wrote: >Yes, because the stiffness comes from compressing the panel to >the crush point. We agree on that. >But since the stiffness is > present in an RC&S assembly by the design itself and downbearing play no > real role there then I think it's interesting to ask oneself what the > purpose, then, is of downbearing. If freedom of movement of the assembly is > a goal, and if the assembly already has the requisite stiffness, then why do > we need any downbearing at all? >You may very well not, but then you wouldn't need crown either. Well, who says you do need crown on these boards. While I haven't built one without any crown I have built boards with more or less crown (using larger or small radii) and haven't really noticed any real difference that I could attribute to crown (not that that impression was definitive). >Why can't the bearing be set neutral? > Doesn't that give the assembly the greatest freedom of movement? In the > pianos where I've had all the design changes made I've found very little > change in tone with increases or decreases in downbearing. >That's contrary to the impression you tried to give saying you >preferred the sound with less bearing. My point there was that many of the boards I do are without all the design changes and on those I've found that increased bearing levels produced results that weren't as good. Interestingly, I've had a conversation with another local rebuilder doing pretty much pure Del design's with all modifications and he too has backed off on bearing settings for similar reasons. >Where the > designs have been more conventional (except for the RC&S part--meaning with > original ribs, original backscale lengths, etc.) then I've found that more > downbearing can actually be detrimental. >Which is why I tried to point out the difference in back scale >length. While greater backscale length does seem to give greater flexibility in terms of downbearing settings (for all the reasons previously mentioned) it still may be that more downbearing isn't necessarily desirable, just tolerable. >The bottom line is that with an > RC&S design I think one should rethink downbearing as well. It doesn't > serve the same purpose and therefore may work at cross purposes. >Depending on the configuration. Or our ability to perceive the differences. >I don't > think that's inconsistent with Ron's findings and I think it is consistent > with Del's findings. Since I don't know exactly what Dale's belly structure > is with respect to where it falls on the continuum of RC&S and compression > (i.e., are they hybrids and to what degree does compression play a role plus > how are the rib dimensions calculated etc., etc.) I can't really comment > there. I fully respect everyone's right to comment or not to as suits them > with respect to their own designs, btw. >Likewise, as always, as pertains to rational technically >oriented observation. > As far as hammer density my thoughts go something like this. These designs > are more hammer sensitive, at least in my experience. >As I've also said so very many times. >Why is that, I wonder? One thought is that with full bass cut off, lighter and stiffer > assemblies, increased grain angles, the board's ability to produce higher > partials through the scale is enhanced. That can be a problem with a harder > hammer. >How, why? That doesn't explain anything. The RC&S assembly >isn't demonstrably stiffer than CC, that I can ascertain. It >just gets it from a different mechanism. One thing that has >occurred to me is that where CC is vibrating from rigid down, >to loose up, the RC&S has a similar stiffness in both >directions, with a broader and much less progressive >vibrational stroke. I can't supply details of what that means, >but it certainly strikes me as a more efficient counter spring >to the string. I have to disagree here. I think that the RC&S assembly is demonstrably stiffer. By many of our own discussions the CC board cannot maintain stiffness through compression for any reasonable length of time (generally). Therefore, it is inevitable that the RC&S assembly is or will be stiffer. An analysis of the beam strength on each of these two boards makes that pretty clear that once the stiffness in the panel due to compression starts to diminish at all the RC&S board will be stiffer. Doesn't the prevalence of the killer octave alone suggest that the RC&S board is stiffer? Germane to this discussion, however, is the low tenor. Once you shorten that long rib from over one meter to, say 650 mm (or less) the center of the panel through the mid and low tenor, it seems to me, can't help but be stiffer. As for the second point about directional stiffness, once you load and RC&S board with downbearing then the effectiveness of similar stiffness in both directions is lost. If you have crown whether by design in the rib radius or by compression, downbearing will increase the stiffness and as the panel(s) move down there will be a movement in the direction of more stiffness and as they move up there will a move in the direction of looseness or less stiffness. But more to the point, the question is whether you can tie the board down with too much downbearing. On a CC board since you are achieving the requisite stiffness with downbearing there is less (though not zero) risk of that. With an RC&S board since it is already at the requisite stiffness before you set any downbearing then the addition of downbearing can only push it in the direction of being less mobile. > So what I've done is not make the bass cutoff too extreme and I've steered away > from grain angles that are too acute. So far it seems to improve hammer > tolerance without having to change the weighting of the assembly itself. >I'm giving a lower grain angle a try on the current project to >try this out. The bass cutoff is where it centers the bridge >on the rib, as usual. Since the hammer hardness tolerance is >across the compass, I can't see the bass cutoff position being >a factor in general hammer hardness tolerance. Here's my thought. The issue of hammer tolerance has to do with timbral dynamics or the balance of partials. Centering the bridge between the bent side rim and the cutoff is a theoretical construct and it makes sense on paper. I mean, why not center the bridge, it puts the load right in the middle. Makes sense. But in centering the bridge you narrow the soundboard quite a bit through that mid to low tenor region. While the volume doesn't really decrease in any meaningful way, in my view something does change. And what I hear changing is the balance of partials. I'm not arguing that it's necessarily a bad change or a good change but it is a change. If someone is used to a certain balance of partials produced by a wider, more flexible soundboard then in order to recapture that with a new board design you have to try and do it with the hammer. What that forces in terms of hammers if one wants to maintain a stronger fundamental, then, is to go to a softer hammer which damps the upper partials somewhat. More acute grain angles contribute to this in the same way--they make the mid-low tenor stiffer. The two things combined are certainly enough to put the requirements of the board in the realm of soft Bacon hammers which turn out to be plenty to develop the now more easily developed upper partials produced by the soundboard. However, for those who responded to the piano in its original state because of this mid tenor balance of partials it could conceivably create some problems, or at least differences. Personally, I want both. I would like to increase the stiffness response in the treble section (get rid of the killer octave) while maintaining the warmth of a very dominant fundamental through the tenor. I also want to get rid of the mid tenor distortions without losing the mid tenor warmth. Getting that balance and transition just right is the art part of this and ultimately represents a creative choice (assuming we can control it which I think we can). My own tastes have led me in the direction of a slightly more modest cutoff where the ribs cross the bridge from about note 40 down while trying to maintain a fairly aggressive cutoff upwards to improve mid treble high partial development and sustain. That usually means a cutoff which hits the belly rail around note 50 or so and angles toward about the middle of the straight side leaving the bridge to cutoff slightly wider than the bridge to bent side, at least through the low tenor. It also means, as I mentioned, backing off on the grain angle increases just slightly. I'll be interested once somebody puts a spectrum analyzer (or whatever it's called) on one of these pianos to measure the relative strength of the partials in different sections of the piano with different design configurations. I think it will be telling. Creating more hammer tolerance, then, I believe involves manipulating the soundboard design with the goal of effecting the timbral dynamics to favor the fundamental a bit more. So far that seems to be a slightly less aggressive cut off and grain angle. Of course, we haven't even touched on string scale which is really where this all starts. David Love
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