Chris, just a point of interest. Running the different radii through my spread sheet program here's what I find. Assuming that the goal is deflection of 50% of crown (as you stated) then with two ribs of equal length, width, height but one has a radius of 9M and one of, say, 17M (30' and 56'), the 9M rib will produce 16.8 mm of crown and the 15 mm board 8.9 mm of crown (half as much). To deflect each rib 50% you would have to load the 9M rib with 65 lbs and the 17M rib with 34 lbs. So by tightening the radius and maintaining a 50% deflection goal the tighter radius would need nearly twice the load. That certainly has impedance implications. That might well explain your ability to remove mass.
FYI the rib dimensions I used were L 1100mm, W 24 mm, H 23 mm. White spruce with MOE of 1340000 and FSPL of 6500. Fixed ends formula.
Original Message:
Sent: 08-02-2021 01:06
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
Chris
I don't use impedance formulas in the design of boards either. But the impedance characteristics are a
result whether you do or don't.
if your boards have a 30' radius (9M) then the long rib on the average piano, which is about 43" (1100mm) would have 16.8 mm of crown or .66". That's at least double the crown on most new boards (8mm is pretty typical), and probably 3-4 times the crown on many old boards that get reused. I'm surprised you don't have strut clearance problems on a Steinway. But if you squash that board to half the crown I would say that board is stiffening up quite a bit.
I know some people are designing with very tight radii. I've wondered how that impacts the stiffness when compressed: Is a board that has 16 mm of crown squashed to 8 mm stiffer than one that is 8 mm squashed to 4 mm, all other things being equal? I don't know the answer but if I had to hazard a guess I would say the 16 mm crown board would be stiffer. That might well allow you to substitute stiffness for mass in this case, depending on where you take the mass from and your rib scale. However, I wouldn't recommend just removing mass on a more conventionally crowned system.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 08-01-2021 19:04
From: Chris Chernobieff
Subject: Apparent Down Bearing on what turns out to be a flat board
I would describe the tone of compression boards as full and lively, and rib crowned boards as small and thin.
Approaching my 300th board i recently measured the crown of a new board, it was at a 30 ft radius in bass, in mid range, and treble. I aim for a DB load that takes up half the deflection gap i have.
I pay no attention to any such talk as impedance as it has no practical use in a shop setting. How does the talk of impedance help you taper the board around the perimeter? Or explain the transition Steinway went through from 1935 to 1936? Same models, different types of boards.
I do use a practical weight model. I just removed 2 lbs off of the Steinway B I am working on. I found that reducing unnecessary weight, only has advantages which manifests itself as a wider range of dynamics and a powerful projection. Nothing like a percussive tone that theorists toss around.
A couple pianos back i worked on a Mason and Hamlin which had the thickest heaviest board i ever saw. A half inch thick, i wouldn't copy that. I installed a new board that was 8 lbs lighter than the original,I used Ronsen Wurzen felt hammers, and the treble was so crystal clear and the tone was robust. It still sounded like a Mason and Hamlin but just better. I don't buy the theory either that states CC crowned ribs want to go flat again. I've removed too many "flat" boards that crowned back up after removal. I think in those cases the board was just overloaded too long.
-chris
------------------------------
Chernobieff Piano Restorations
"Where Tone is Key"
chernobieffpiano.com
grandpianoman@protonmail.com
Lenoir City, TN
865-986-7720
Original Message:
Sent: 08-01-2021 15:43
From: David Skolnik
Subject: Apparent Down Bearing on what turns out to be a flat board
David , Jim
can you the potential differences (theoretical if not tonal, but tonal would be good) between a traditional compression crowned board and rib crowning?
- differences in emc
- when does 're-hydrating' occur? ( I know that's not the correct term)
- please correct:
-- compression method uses
- bellied table; flat ribs; low emc; what are forces on ribs and board when 'rehydrated' (rib wants to return to flat; board wants to crown but has to fight with rib stiffness.)
-- rib crown uses:
- bellied table; shaped ribs; higher emc; Ribs seem more neutral, rehydrating board not fighting counter forces from ribs.
question(s) would be - tonal differences? stress differences? stability and longevity?
This question is still looking at nuances within impedence model.
------------------------------
David Skolnik [RPT]
Hastings-on-Hudson NY
917-589-2625
Original Message:
Sent: 08-01-2021 13:00
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
I'm not sure what you mean by "success". All impedance refers to is the rate of transfer of energy. I'm not sure how the impedance model can be rejected. Whether the board has zero, negative or positive downbearing there will always be some rate of transfer and some desirable rate of transfer. Too fast, the tone is percussive, too slow the piano lacks power. Controlling impedance can happen several different ways; by the stiffness (and mass) of the assembly by design or by design plus downbearing settings that serve to compress the board and raise the impedance. But there is no question but that controlling impedance is the goal no matter what.
The older model is crown and downbearing with an assembly that without downbearing falls just short of the impedance level you are after. However, you can build a more rigid structure, and/or one without any crown or downbearing at all that seeks to control impedance by the weight and stiffness of the structure alone. That isn't to say that achieving a comparable impedance level will result in the same tonal output. It won't. There are other factors that affect tone and loading the board and compressing a dome shaped soundboard spring has other ramifications besides impedance.
I've not seen too many alternative models. Maybe Stuart's design with bridge agraffes and a lattice structure for ribs is probably the biggest deviation that I've seen. But I don't know if those boards are crowned or if downbearing even plays a role in the set up. They are good sounding pianos but they sound different than the standard crowned, rib supported and compressed via DB structure. Not sure how to describe that difference but it is a bit different, to my ears.
The point though is that you can't reject the impedance model, you can simply try other methods of controlling impedance. It's always a factor.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 08-01-2021 09:14
From: Jim Ialeggio
Subject: Apparent Down Bearing on what turns out to be a flat board
David L <But what you said was that the only purpose of DB was to insure strong front terminations. I don't agree with that.
In relation to this statement, how do you explain the success of zero DB agraffe boards, three versions of which are currently in production in high end instruments? One may say that the sound profile is different than a bridge pin/bearing profile, with the zero DB versions offering high(maybe too high) sustain, but all exhibit exceptional fundamental presence, without either requiring a load, or in one case without requiring ribs at all.
The no-ribs version really challenges the impedance model as it is usually applied to soundboard design.
------------------------------
Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
Original Message:
Sent: 07-31-2021 17:10
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
Sort of. What I'm saying is that increases in bearing change the stiffness of the assembly which has tonal implications in terms of impedance. There is a point of diminishing returns, of course. I don't think the change goes to zero but graphically it looks something like this with increases in downbearing on the x axis and stiffness (and deflection) on the Y axis.
Initial additions of DB make the most difference, subsequent additions have less effect until there is little perceived difference with added units. But what you said was that the only purpose of DB was to insure strong front terminations. I don't agree with that. Certainly in the case you're describing where you start farther out on the X axis where the curve is leveling off and then add more DB load, the rate of change has already diminished considerably and added units of DB will make much less difference than if you start reducing the load from that point. But if you start close to the origin then adding downbearing makes a much greater tonal difference with each increment added.
Most soundboard assemblies are designed such that DB is part of the formula for achieving the desired stiffness and impedance. Also loading the board creates potential energy in the system as the spring is compressed, that too makes a difference. Of course you can go too far where you are not getting any real added benefit and perhaps even deleterious effects like "choking" the system or as you say "catastrophic failure", though I'm not sure what that is or if I've ever seen it. I've never seen a cracked rib from too much downbearing but I have seen choked assemblies either from too much bearing or, more often, from rescaling in which the string gauges and overall tension was increased on a board designed for a lower load.
There is a tonal and dynamic difference between building a board that is stiff enough purely on the merits of the rib scale and one that achieves the requisite stiffness through the addition of DB. I've seen this in some designs where a heavier rib scale has necessitated very light bearing settings but that tonal signature is different than a lighter rib scale with adequate bearing to achieve the requisite stiffness and the impedance levels that go along with that. So while solid front terminations are important. I also agree that positive front bearing is much more important that positive rear bearing. given the sum is still positive or achieves the desired level of DB. But DB also provides other benefits, or, at least other dynamic factors that affect tone either positively or negatively.
Changing DB settings can be a very useful ability on an assembly and I've done that (and many others do this routinely) either through nose bolt adjustments or with WNG adjustable perimeter bolts with noticeable effects.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 07-31-2021 16:06
From: Jim Ialeggio
Subject: Apparent Down Bearing on what turns out to be a flat board
Let's try that again...
David L< But if you notice that reducing downbearing has an effect that means that increasing it does too.
This statement and needs clarification, which is the point of my post. It implies, as stated, DB changes spring function...true...and that changes in spring rate are thus responsible for tonal changes...partially disagree.
At the point where the spring is no longer a spring, that is, at compression limit, tonal change is catastrophic...highly perceptible. The so-called spring is, to be clear, no longer a spring, so it has no spring rate. It is not appropriate to even call it a spring at this point, because it is not a spring. Your comment implies simply that spring rate changes are responsible for tonal changes. What I am saying is, that after recovering the existence of spring rate (where there is a huge tonal improvement), further changes in DB produces such tiny, hard to perceive effects, that one easily perceives changes that often cannot be verified on a second listen. I am clarifying the difference between tonal adjustments when there is no spring rate, and tonal adjustments in the bandwidth where a spring is actually functioning as a spring. In the bandwidth where the spring is actually functioning, tonal changes within that bandwidth, are so minor its easy to fool oneself as to their existence.
On the other side of this question, in a board which is dead, ie glue joint failed or semi-failed, there is, here, again, an absence of spring rate. The tonal result is catastrophic and obvious.
Give me some spring function and excellent terminations, and I will give you an excellent fun to play piano.
------------------------------
Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
Original Message:
Sent: 07-31-2021 15:03
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
Jim
That's exactly what I said. Read it again. It depends on your starting point. But the fact that you've compressed the board to it's maximum doesn't mean that the tone wasn't changing along that continuum until it wasn't changing any more.
If you ease off on the bearing and the tone changes, that means if you increase the bearing back to where it was the tone will also change. You suggested the tone only changes when you ease off on the bearing and not the other way around. That doesn't make sense.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 07-31-2021 14:46
From: Jim Ialeggio
Subject: Apparent Down Bearing on what turns out to be a flat board
David L<But if you notice that reducing downbearing has an effect that means that increasing it does too.
Not necessarily. Reducing DB most often has an effect when the linear spring has been overloaded, and the spring is no longer being allowed to function. The spring is being artificially restricted by high load. Mostly on compression boards, this compression limit, that Chris refers to, which starts out closer to the limit than rib crowned boards do, becomes tonally problematic. When the spring has been overwhelmed, it is no longer functioning as a spring,
In this case, ie spring being overloaded to non-functionality, variable loading of the spring is not the parameter that is effecting tone. Rather, removing the restriction that allows the spring to function at all, makes the tonal difference. After this recovery of spring rate has been accomplished, in my experience, variable rates of loading really does not have that much effect tonally. So, that being the case, why challenge the board structure, by asking the structure to withstand high tonally superfluous loads.
In my own experimenting with varying loads, I have gravitated to minimize DB, and address, as well as physically possible, with traditional bridge pins, efficiency of termination as a big bang for the buck next step. My move in this direction is supported by the various work of the bridge agraffe crowd; Paulello, Dain, and Stewart, who target zero downbearing, and Paullelo who has jettisoned ribs altogether. My view at this point is, that DB is an engineering requirement imposed by the inefficiency of traditional bridge pins...which I still use. I use them, but for a few years which have produced the best sounding pianos of my career, have been experimenting with ways to improve the efficiency of this rather prehistoric "bang a nail in wood and call it good" technology, and as a result, welcoming much more flexible assemblies that the more efficient termination allows.
------------------------------
Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
Original Message:
Sent: 07-31-2021 08:33
From: Peter Grey
Subject: Apparent Down Bearing on what turns out to be a flat board
If I had encountered what Jim did upon restringing, I would have simply said: "Well, I guess I was deceived again...the board's flat. So my next step is...can I improve it?"
Pwg
------------------------------
Peter Grey
Stratham NH
603-686-2395
pianodoctor57@gmail.com
Original Message:
Sent: 07-31-2021 01:57
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
I think the back posts and bracing serve mostly to stabilize the rim and belly rail, not to support upward or downward movement of the plate. The nose bolts are anchored to the bracing but the upward or downward forces are relatively small
The forces on the plate are mostly horizontal forces not vertical. The strings, however, as they rise to the bridge are pulling up on the capo bar and aggraffes and are also pulling up on the hitch pins to the degree that there is a rise from both sides to the bridge. But even with negative bearing, the strings travel downward from the tuning pins to the capo and agraffes before traveling to the bridge so there is always an upward force on that part of the plate.
The distal side is a bit more complicated because the aliquots are between the hitch pins and bridge. Still, the net forces on the plate are tending to raise the plate not lower it. Certainly on the bass bridge positive bearing on the backscale is pulling up on the plate.
But I'm ready to have that clarified if I have it wrong.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 07-31-2021 00:27
From: Blaine Hebert
Subject: Apparent Down Bearing on what turns out to be a flat board
Dave,
Important observation.
Perhaps some pianos have no deflection while others have upward or downward deflection.
The substantial back posts and beams serve some purpose.
Where is St. Fandrich when you need him?
------------------------------
Blaine Hebert
Duarte CA
626-795-5170
Original Message:
Sent: 07-30-2021 10:36
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
Not sure what that means. If you remove the cap screw and turn down the nose bolt the plate will not follow it down ( assuming the bolts are set neutral to begin with). To pull the plate down to the bolts you will have to tighten the nose bolt caps. On Steinways the nosebolt caps are quite substantial with a fitting for a wrench.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 07-30-2021 02:40
From: Blaine Hebert
Subject: Apparent Down Bearing on what turns out to be a flat board
No. The cap nut on a nose bolt is usually brass and only knurled to be installed by hand. The plate bends downward into the back or under belly beams. This should increase pressure on the soundboard.
------------------------------
Blaine Hebert
Duarte CA
626-795-5170
Original Message:
Sent: 07-30-2021 01:39
From: David Love
Subject: Apparent Down Bearing on what turns out to be a flat board
The plate doesn't deflect downward, it deflects upward. If the bridge is deflecting downward then the plate must be deflecting upward. How would you lose downbearing when taking off tension? It's just the opposite.
------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
Original Message:
Sent: 07-30-2021 01:14
From: Blaine Hebert
Subject: Apparent Down Bearing on what turns out to be a flat board
Note: I am not a rebuilder!
The function of the nose bolts and beams of a grand piano is to support the strong downward deflection of the plate. I have worked on an antique grand that did not have sufficient plate support and the plate collapsed (I installed an additional support and "saved" it).
If a piano is unstrung and loses its down bearing then you need to suspect flexing of the plate and nose bolt beams.
Yes, pianos are dynamic systems.
------------------------------
Blaine Hebert
Duarte CA
626-795-5170
Original Message:
Sent: 07-29-2021 09:20
From: Jim Ialeggio
Subject: Apparent Down Bearing on what turns out to be a flat board
Interested in input from other belly rebuilders with this experience of old boards;
Piano comes into shop for belly work. You measure down bearing (DB). It is apparently, and often, right on the money...positive, and right where you would want it to be...perfect in a suspicious way. Then measure loaded crown...flat...none. Remove strings and measure unloaded crown. Still flat, no crown appears after removing the load.
How is this physically possible? I have gone over the physical possibilities many times, and come up with limited credible explanations. In order to have DB, there must have been some unloaded crown. But how can you have a flat board, both under no load and loaded conditions, while still showing positive DB readings (composite angle)? The board can often deflect, at least on the current victim with a meer 25lbs applied from a spring loaded go bar from below, so there is plenty of give in board...its not stiff enough to create DB without deflection.
It might be possible that parts of the board which have very minor deflection even under new board scenarios (high treble) are supporting, and suspending other parts of the board, by the bridge pins. But I only see that happening from one end of the beam...the high treble. The other end of the beam doesn't seem like a good candidate to be the second support. It could be, that the Bass bridge provides that second support, as the bass is purposely very lightly loaded, and close to the rim. Maybe the bass could be supporting the mid long bridge from going negative??
------------------------------
Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
------------------------------