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Apparent Down Bearing on what turns out to be a flat board

  • 1.  Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 09:21
    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
    ------------------------------


  • 2.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 11:19
    Just going off of your description: can you apply downward force above the board to see what it would take to induce negative crown?  you've only tested deflection in one direction.  
    positive DB readings (composite angle)
    are you measuring positive angles on fron & back of bridge or is it a matter of some positive net angle showing through a larger front bearing + smaller negative rear angle?
    Maybe the bass could be supporting the mid long bridge from going negative??
    Do you mean the passive stiffness of the bass bridge itself or an effect of it being strung, with the attendent down force?

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 3.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 11:52
    I long ago gave up measuring DB prior to disassembly. Not only did I conclude that it is difficult to impossible to get an accurate (true) reading, I also concluded that it is irrelevant to me at that point. 

    I do make a quick diagram of crown/DB in an unstrung state simply to see if there are any massive issues that need special attention. Ultimately though I am going to do what is necessary to create a healthy situation overall throughout the rebuild process. 

    Not everyone agrees with this viewpoint but I arrived at it better than 25 years ago after being taking pains to get all this data in to my notebook, never to look at it again, or if I did, it had no relevance to me. Why bother?

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 4.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 12:10
    Hi Peter -
    Disclaimer - I'm not a bellyman.  I have no standing to challenge the procedures and conclusions you've arrived at in the course of your experience.  For the sake of the discussion, however, it would  be at least interesting to clarify aspects of what you've proposed:

    I long ago gave up measuring DB prior to disassembly. Not only did I conclude that it is difficult to impossible to get an accurate (true) reading, I also concluded that it is irrelevant to me at that point.

    Would you have measured for DB at any point in the process of determining what was needed?   
    What makes it 'difficult to impossible' to get those readings?

    I do make a quick diagram of crown/DB in an unstrung state simply to see if there are any massive issues that need special attention. Ultimately though I am going to do what is necessary to create a healthy situation overall throughout the rebuild process.
    This doesn't really tell me anything.  Why a 'quick' diagram?  You must have to take some sort of measurements to do that.  What would constitute a 'massive' issue?   "do what is necessary.."  ?  Can you elaborate?

    Thanks

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 5.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 12:25
    Jim,
    When there is crown with compression there's a  "spring" range. When too much bearing is set you bottom out (overwhelm) the spring range and enter the tensioned "tight rope" range. In that range you can add weight and more weight (and you won't see much movement either) until it fractures. Probably was a board that had a 3 degree downbearing LOL,
     I have a little soundboard jig I made a while back, I'll make a little "demonstration" with it sometime today.(There ED, I didn't use the word experiment).
    I'll post it on my youtube channel.

    -chris

    ------------------------------
    Chernobieff Piano Restorations
    "Where Tone is Key"
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Lenoir City, TN
    865-986-7720
    ------------------------------



  • 6.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 16:12
    David,

    Initially I'm more interested in crown (If it exists) in a string state. I look closely and all over using a thread and make a mental note (then write it down asap). 

    After disassembly I look at it again to see if it changed, and if so how much (a lot or a little). This gives mne an idea of what pressure may (or may not) be on the SB. Then I use the standard string process from agraffe to hitch pin to take stock of what the overall DB situation was at that time. My "diagram" simply consists of the notes at each end of the sections and maybe one in the middle. Bass top and bottom. 

    Then I try to correlate the two sets of data top and bottom. It's basically a "good thing/bad thing" worth of assessment to start thinking about where and how much I will need to mess with the plate height if necessary. I also will check to see if nosebolts were cranked up or down, plate feet well situated, etc etc. 

    A massive problem would be negative DB at the top of the bass bridge coupled with a flat board or concave at worst. Another massive problem might be the thing was rebuilt once before and they already lowered the plate...decisions, decision s.

    Hope that helps

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 7.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 17:35
    Peter,
    Assuming you mean 'strung' state.  While I'll repeat that I don't actually do bellies, I'm around them and try to take measurments when I can.  Wheh time permits, I sometimes will tape indicator strings between every other (or third) rib to observe any changes when strings are removed, or the opposite way, before board is strung, and observe what becomes of crown post-stringing.  
    You don't appear to measure downbearing of strung piano (pre de-stringing).  If this is correct, I'm wondering why.
    Is your description primarily directed towards reusing existing board, or in preparation for a new installation?
    Thanks

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 8.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 20:25
    David,

    Yes, I meant strung...autocorrect. 

    There are two basic reasons I don't attempt to measure DB in the string state: 

    1) I have dealt with too many "mis-diagnoses" due to the fact that it is a dynamic system and what "appears" to be...ain't

    2) There is nothing I can do about the matter in a strung state, so even if I COULD measure it accurately, I'm DITW on it. 

    Like I said, not everyone agrees with this so...

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 9.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 13:23
    Peter describes what I do as well. I look at crown with original load, no load and then check bearing at bridge.

    ------------------------------
    Edward McMorrow
    Edmonds WA
    425-299-3431
    ------------------------------



  • 10.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 12:54
    Peter, I get the futility of measuring something you are going to target differently anyway, especially when the measurement is noisy. I approach the redesign from my own bias, as you do your own bias, so don't fret not recording this data too much. The question I have is different. It is, why is the DB measurement often misleading unto bogus. Geometrically I don't understand how it can be this misleading....but it is often, infact, a highly misleading pre teardown measurement.

    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 11.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 14:15
    Unless thoroughly sidetracked by upcoming events in Orlando, I would anticipate only limited time before someone (not unlike myself) raises the question of how DB measurements are being taken.  On the other hand, it shouldn't distract from the primary question.

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 12.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 14:51
    Weighted Wooden Spring  Demo
    https://www.youtube.com/watch?v=s0hZ8gnQnkg

    ------------------------------
    Chernobieff Piano Restorations
    "Where Tone is Key"
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Lenoir City, TN
    865-986-7720
    ------------------------------



  • 13.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 17:39
    Entertaining mad scientist video   :)

    So one could surmise that even a flat board, or one with seemingly zero bearing, is actually still under tension.





  • 14.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 18:01
    Not sure that 'tension' is what you mean.  'stress' or 'compression' perhaps, but, even then, where would that come from without downbearing?

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 15.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 18:16
    I see it a little like a diving board: when you put pressure on it with weight (compression), its inherent elasticity is flexed and resultingly under tension.

    The SB though,  being glued on all edges, appears to have less give with zero weight or too much weight (evidenced by video).

    Suggesting a "sweet spot " range of flexibility when under tension.   Maybe this state exists even in flat boards with seemingly no bridge bearing: until a certain weight is applied?





  • 16.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 12:32
    Well, the board itself has some internal stress even without downbearing if you are using a compression system at all, meaning you're either drying the panel down before ribbing or before installation into the rim or both.  Downbearing is an additive component.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 17.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 12:47
    Not to get overly metacognitive, but isn't there 'stress' in the panal, even prior to becoming a 'board'?  If the panal has some inherent resonance, doesn't that imply presence of stress?  Response to climatic change induces some sort of internal changes, no?
    Just trying to determine where we're starting from.

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 18.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 18:58
    David S.

    An unribbed panel (that's not glued into the rim) doesn't really have any "stresses" in it.  And I think every object has it's own natural frequency, if that's what you mean by resonance.  In fact "resonances" are a tonal problem.  It means that those frequencies will be enhanced, like that note you find while singing in the shower that seems to resonate louder than all the others.  It's because the space you're in has it's own natural frequency.  Natural resonances have caused bridges to fall down, though i don't think I've ever seen a soundboard come apart because of one.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 19.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 02:01
    I use a bubble gauge.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 20.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 17:38
    Jim -

    "misleading unto bogus" - can you describe how so?

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 21.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 20:23
    <"misleading unto bogus" - can you describe how so?

    This was the content of the OP. Bogus means, when loaded there is DB, and loaded board is flat. Then when unloaded, the board remains flat...no crown recovers. This does not physically makes sense, but I have seen it numerous times before I start a belly job. 

    I am measuring composite angles front string plane plus the hitch string plane. together they form the composite angle, or the included angle between the SL and hitch length string planes over the top of the bridge. I know you measure a different method, which indicates whether the string, at the pin reverses direction or continues on an upward path...would you care to share your device. My interest in this question is DB as interpreted as the included angle between the SL and Hitch length string planes, because this indicates how much down force is being exerted on the board. Your method, as I understand it, wants to know whether the string is set up for as an efficient termination as can be had using bridge pins. Yours does not quantify, if I understand it correctly, down force. It measures efficiency of termination. Efficiency of termination is hugely important, but it is different than down force,

    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 22.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 21:45
    Hi Jim -
    Skipping over my particular obsession with front termination issues for the moment, I also use a Lowell gauge in a more semi-traditional way, comparing SL to HL segments, but relying upon my  other methods to ascertain negative relationships at those terminuses.   As it relates to understanding 'down-force',, I think what I have tended to observe with regard to the 'rear-bearing', that is, the angular relationship between the bridge surface directly in front of the rear bridge pin and the HL is very often found to be significantly negative, effectively compensating for a heavy angular loading at the front of the bridge. In these examples, which I believe I see frequently, the net bearing may end up within an acceptable range but it comes at the expense of a distortion of the load distribution: excessive front bearing and negative rear bearing.  
    I guess my two questions would be:
    a) can this sort of load distortion have tonal, or structural repercussions?
    b) can this sort of configuration distort the results of your measureing method?

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 23.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-29-2021 22:12
    The tech obsession with angular equality of the front and back segments, I find, emprically, to be spinning wheels in the sand. It has no meaning, in my experience, if it is even being accurately measured. Efficiency of front termination is very important, and can be perceived. So, in the bang of the buck department, composite angle creates a scenario where the efficiency of the front termination will not be challenged, by the string wanting to pull up and away from the bridge.

    I only fuss on things that empirically produce tangible results. I'm not interested in incremental, hard to percieve results...but tangible bang for the buck results. Fussing with the angular differences and inequalities, is first, difficult to measure, let alone target correctly on 230 strings in a non-linear structure, and second, has produced no tangible empirical results for me, ever. So I don't pay it any heed. 

    The question is whether this sort of configuration you describe can distort my measurement results of composite angle. And to this I say I am not sure. I don't think so, and don't see how, but would be very open to someone geometrically describing how that could happen, as it could answer the query of my OP..

    By the way, in terms of bang for the buck, our Steingraeber problem child is responding, in a bang of the buck kind of way...overall reduced angular bearing, and mass loading in rather creative configurations I have not done or seen before. So I go for the bang of the buck big picture configurations, because they work and give clearly tangible results.

    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 24.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-29-2021 23:06
    I don't believe I was arguing on behalf of angular equality.  Rather, wondering if a configuration that acheives a target moderate amount of NET downbearing by combining grosser amounst of positive front and negative rear is a) functionally the same as the more recognized positive / positive, and b) whether it introduces dileterious stresses.

    As to your original question, wouldn't it be possible that, without excessive downbearing, a stiff, flat board would support that  force without collapsing or going negative? (I'm not sure Chris Chernobieff's demo quite addressed it, but it was cute.)

    I'm feeling a pilgramage is increasingly overdue.

    And last: what is OP?  (original proposition?)

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 25.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 00:49

    The downside of high positive front bearing and negative back bearing is that you can cause the bridge to rotate forward (bridge roll) as it's pressed down from the front and lifted from the back. That can cause some distortion of the panel in an extreme case.  Tonal effects are unclear but I would try and avoid that.

    BTW, In theory the bearing can't be pushed negative.  You can end up with negative bearing in a section but that's only because in some adjacent section of the bridge the bearing is positive. That is usually a result of uneven bearing settings in different and adjacent sections. 



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 26.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 03:50
    OP = Original Post

    Alan

    ------------------------------
    Alan Eder, RPT
    Herb Alpert School of Music
    California Institute of the Arts
    Valencia, CA
    661.904.6483
    ------------------------------



  • 27.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-30-2021 07:17
    David S... NET DB is simply equal to the sine of the included angle (front and back added...ie the composite angle) * string tension. It doesn't matter whether the front and back are equal. Only thing that effects the actual DB force is the composite of the two angles added into a net angle.

    Whether it adds deleterious stresses, in my view, only if the system is negative behind the front pin. For me, mostly, the only point of DB is to assist the termination at the front pin. The whole bridge pin system is so prehistoric in design, it needs as much assistance as possible to avoid turning, what is already a lousy termination, into a really lousy termination. Bridge agraffes need no DB, and Paullelo has proven don't even need ribs to function.

    So my view is I have never improved tone by increasing DB. only by decreasing DB, and improving the condition of the front pin termination...empirically speaking. 

    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 28.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-30-2021 08:35
    Blaine,

    If you look under a lot of plates, you will often see a gap between the shoulder of the nose bolt and the plate bottom. Indicating the plate deflection is either neutral or upward. Pressure on the nose bolt screw can also be high, if you try and loosen a nose bolt under tension. This indicates a tendency towards upward pressure. Hand tightened machine screws are actually capable of exerting significant force. This, upward tendency is common, at least in the hitch pin field.

    The pin block webbing could be a different scenario, as the tension on the pins and block, want to rotate the top of the block near the stretcher up. This is evidenced by the tendency of Bechstein plates to fail on the underside of the front strut right next to the pinblock flange. This indicates the bottom of the strut, at that location, is under tension, not compression as you find if the plate deflected uniformly upwards. And frankly there has to be a counter force to any force. So, I think the tendency of deflection in the plate, is like everything else under this much tension, including things like the squirming board, complex.

    What was the antique grand you worked on that went south, and where?  

    I, and I think we all, tend to consider the system more uni-dimensional than it actually is, regarding my OP (original post). This mainly reflects the limitations of how hard it is to think about complex systems. We all tend to simplify complex systems, because its too hard to think about...one of my biggest beefs about physical modeling. Complex, high force systems include hard to quantify minute movements which we can only guess about. I have to add this complexity point of view into my data set, re my OP, and let my brain think on in in the background for a while.  I do get the sense that Peter experienced exactly what I am talking about, and shifted his empirical methods to reflect those noisy and inconclusive loaded measurements. 



    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 29.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 10:51
    Jim,

    I would agree with that.  I have a couple of questions though.

    1) How did the piano sound overall prior to teardown?

    2) Were there any specific "problem areas" you isolated ahead needing investigation?

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 30.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 10:31

    Jim wrote

    "the only point of DB is to assist the termination at the front pin."

    i don't agree with that. DB compresses the soundboard. Since it is a non linear spring that stiffens the assembly and affects impedance. The compression also loads the board with potential energy.  

    Whether adding or subtracting DB has a noticeable effect on tone depends on your starting point. Since board compression is non linear, adding DB to a fully loaded board may have little effect just like removing DB from a very minimally loaded board. But if you notice that reducing downbearing has an effect that means that increasing it does too. 



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 31.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 15:11
    Hi Jim

    Glad to see your comment about DB.  I wish you had been at a chapter meeting a couple of years ago that Jude did the technical on appraisals..
    He suggested the string across the underside of the board to assess crown.  I interjected that is not a reliable indicator and stated that it is impossible to know the true state of the board while under tension.  I got an immediate and strong rebuff from Crawford and Pliem that the DB reading would be sufficient to tell the customer everything they needed to know. I repeated my position quite clearly and the situation got quite heated.  Alas, I was a lone voice in the wilderness.  My point in particular , realizing how many newbies attend the meetings and suck up any amount of misinformation and carry it with them, was that it is precarious at best to offer up a job estimate based on ignorance.  So they might say the block need work but the board is OK.  So what is one to do when they destring and find the board gone negative or flat.  My approach for many years is to tell the customer that I might try to save the board if that is possible but they need to be prepared to cough up more money for a new board if that is what is required.  Otherwise, what do these guys do?  String up a bad board?  For the benefit of less experienced members, I offered at least a cautionary note.  I was once again reminded why I have lost interest in meetings.  Curiously, I was hanging out with Dave Betts and brought the subject up.  He said he agreed with me completely.  ;  Wish so bad you had been there.

    Gary Ford

    ------------------------------
    Gary Ford
    Boston MA
    617-536-0526
    ------------------------------



  • 32.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 00:57

    In this scenario did you measure the change in the downbearing with the tension off the strings?  

    When I destring a board I first measure the DB with tension. Then when I take down the tension I leave a string in each section with tension and then measure the downbearing on those strings with the tension off. If there's an increase in the DB with the tension off then the board has "crowned". I've never figured out an accurate way to measure the change in crown directly  



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 33.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-30-2021 01:35
    I've never figured out an accurate way to measure the change in crown directly
    I used to measure the free space between a bridge top and strut before and after de-stringing.
    Jim,
    I also would want to know bearing after de-stringing, did it change?
    How was crown measured before de-stringing, I'm assuming with a pulled thread between ribs, would this
    not show an oil canned board as flat, that is, a reverse crown would not be apparent by pulling a thread on the bottom?
    A plate set much to low?


    ------------------------------
    Fenton Murray, RPT

    Fenton
    ------------------------------



  • 34.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 01:15
    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
    ------------------------------



  • 35.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 01:39
    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
    ------------------------------



  • 36.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 02:26
    Like David S., I'm not any sort of belly man and may be off base or not even on the playing field, but. 

    In an earlier thread, David Love posited that the reason strings continue to go flat as one begins a pitch raise below is that the plate and cabinet absorb some of the added tension (contracts). Also Mr. Gravagne recently gave an eloquent description of how energy moves dynamically from the plate via the horn into the cabinet structure. Could it be that the dimensions of the rim change enough to be a factor in the discontinuity in these various DB measurements? Spread out around the perimeter even a minute change could be enough to skew expectations. In effect, the dynamic tension in the frame would be a rather complicated counter-lever to downward pressure on the sound board which is pushing outward on the perimeter. Yes? When the tension is removed both sides of the lever the system would return to a more neutral state, the interface between the two being the rim. Could this account for the nonlinear results of measurements taken at different stages of the process?
    This line of thought led me to immediately think about the M&H tension resonator, which it seems is designed to maintain the dynamic tension in the frame independent of the string tension. Is this so and has anyone found that M&H's are any different in regard to bearing behavior during restringing?
    Maybe I'm misunderstanding Jim's dilemma; just speculating here.


    ------------------------------
    Steven Rosenthal
    Honolulu HI
    808-521-7129
    ------------------------------



  • 37.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 02:40
    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
    ------------------------------



  • 38.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-30-2021 10:36
    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
    ------------------------------



  • 39.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-31-2021 00:28
    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
    ------------------------------



  • 40.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-31-2021 01:57

    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
    ------------------------------



  • 41.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-31-2021 08:33
    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
    ------------------------------



  • 42.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-31-2021 14:47

    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
    ------------------------------



  • 43.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-31-2021 15:03
    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
    ------------------------------



  • 44.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-31-2021 16:07
    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  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
    ------------------------------



  • 45.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 07-31-2021 17:11
    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
    ------------------------------



  • 46.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-01-2021 09:15
    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
    ------------------------------



  • 47.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 13:00

    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
    ------------------------------



  • 48.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 15:44
    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
    ------------------------------



  • 49.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-01-2021 19:05
    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
    ------------------------------



  • 50.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 01:06

    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
    ------------------------------



  • 51.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 12:49
    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.


    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 52.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-02-2021 15:46
    Thanks. The math looks correct to me. I don't normally do a 30' radius btw, playing and finessing the emc% and timing recipe, now that i have more accuracy of measurement. I'll see if the high crown causes an issue. I like the way it looks though. However, I'll most likely raise the moisture % back up half a degree at a time, and see how much that lowers the crown for educational purposes.
    -chris

    ------------------------------
    Chernobieff Piano Restorations
    "Where Tone is Key"
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Lenoir City, TN
    865-986-7720
    ------------------------------



  • 53.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-02-2021 08:42
    David L <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. 

    This is correct. But no one is rejecting the existence of impedance,. What I am saying is, that the assumptions and empirical experience of what constitutes "adequate" impedance, tonally, is drastically reduced when the termination is more efficient than the traditionally applied bridge pine configuration. Drastically meaning, ribs are not required, and compression of the panel not present....the board is passive, and in Paullelo's design, the spring is predominantly the internal recovery rates inherent in the high tension wire. The board, of course, does have impedance, but relative to a traditional ribbed board, its values have to be negligible. Certainly, if a ribless board were installed with traditional bridge pins, it would be a tonal failure. The difference is the configuration of the bridge termination.

    So zero DB does not in fact require, a very stiff board assembly be present. The board assembly can be pretty darn close to passive, if the termination is not so inefficient at the bridge. This turns the interpretation of what the impedance requirements are tonally, on its head, in my view. The impedance values we associate with good piano tone, are generated not by the need of the board/string system  to be a counterbalanced spring, but by the requirements the bridge pin termination imposes on the system. Change out the bridge pins, or redesign the configuration, and perhaps materials, and the system impedance requirements change drastically.






    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 54.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 11:49
    Would it be out of line to take a moment (or 10) to revisit termination, in general, but specifically at the bridge?  Can it be viewed a separate from impedence?  In other words, how does termination work with regard to string energy - reflecting, transmitting, distorting, absorbing.  How much of that function relies upon the characteristics and quality of the clamping function, which the traditional design nominally accomplishes with front downbearing, angled bridge pins and offset?  How many directions and types of energy are being propigated?  
    (I don't know if the question that provoked a fairly agitated to-do, some years ago, on the original pianotech list, ever got fully resolved.  It had to  do with whether the strings actively moved the bridge (thus board) up and down.  Robin Hufford from Ft. Worth Texas had some theories that were quite in oppostion to those being esposed by a majority, including RonN, RIP.  I'll try to reach out to him to see if my memory is only partly shot.

    My earlier question about negative rear bearing would seem to be relevant only to stress forces, and not termination, unless one could prove that the rear NS length is measurably affected by the same terminiation functions noted above.  But let's keep it simple.

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 55.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 12:29

    OK but something seems at odds here.  We agree that the transfer of energy to the board is necessary, unavoidable, in fact.  I mean, it's the board we're hearing driven by the string.  If better termination *lowers* the impedance, meaning that energy transfers faster, you would want a stiffer board or something that raised the impedance back to the levels you desire (assuming they were where you wanted before you installed a new bridge system).  We're not after lower impedance per se, we're after a targeted rate of transfer, one that provides adequate power with adequate sustain.  If  a modified bridge pin system lowers the impedance then you would have to adjust for that somewhere else.  I'm not convinced that it actually lowers the impedance but rather, perhaps, minimizes the energy loss at the point of termination, though I'm not even convinced of that.  Obviously if you have a system in which downbearing is not needed to insure solid bridge contact then you have other options.  For that matter, if you had bridge agraffes you could set the bearing negative so that the string is pulling up on the agraffes and by that on the panel.  That may very well change the termination dynamics but it doesn't change the fact that the impedance target still needs to be considered and, if it is as you describe, lower the impedance by virtue of the terminations would then require compensation by other means.  Or so it seems to me.  



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 56.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-01-2021 14:56
    I said "impedance model as it is usually applied to soundboard design". Maybe I should have said traditionally.instead of usually.

    In any case, If DB is, as has been proven by successful alternative belly/bridge setups, not necessary to load the board's spring, as traditionally modeled, than the amount of loading necessary is a factor imposed by the lousy bridge pin terminations, not by loading requirements. Said another way, an efficient bridge termination reduces the impedance levels required of the board by an order of magnitude.

    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 57.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 16:08
    I'm not really following that.  DB is necessary if you want to "load" the board.  That's by definition.  Loading the board means compressing the dome shaped spring.  Positive downbearing is necessary to "load the board" but it's not necessary to achieve stiffness in the assembly.  You can do that by just altering the rib scale, the amount of crown, the thickness of the panel, the grain orientation.  But that design will be dynamically different than one that is made relatively lighter or less stiff and relies on crown compression to add stiffness.  As I mentioned, there are other properties as well that spring compression achieves.  

    You said, "an efficient bridge termination reduces the impedance levels required of the board by an order of magnitude".  So you're saying that efficient bridge termination improves energy transfer.  That is probably true, or it might be true that there's some loss of energy with poor terminations.  I'm not sure if that's quite the same thing.  I agree with you that positive front bearing is important for good string terminations at the bridge, but I'm talking more about the impedance levels as dictated by the structure of the  assembly itself regardless of the method or attaching strings to the bridge. 

    It seems that the question we're asking is can you achieve the required impedance levels (can they be high enough in this case) without downbearing.  I would say the answer is yes.  You can make a structure that is stiff enough using other design features to achieve the requisite impedance levels.  The more important question might be is that desirable, what do we lose or what do we gain by not have a dome shaped spring that is compressed?  For example, If loading the board means introducing potential energy into the system and that has tonal consequences then i would say that you're trading one system for another but at what cost?  I've certainly heard boards that were designed much stiffer and required minimal downbearing--just enough to keep the speaking side of the bridge termination positive.  I didn't particularly like what I heard.  It was somewhat lifeless even though there was adequate control of energy flow, meaning that the attack/sustain relationship was fine.  

    But to the point, my main objection is that you seemed to suggest that terminations were the main reason for positive downbearing and I don't agree with that.  I think there are other considerations that are very important depending on the system you're using.  


    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 58.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 20:18
    The trouble with applying the impedence model is the equation lacks a term for the effect string coupling produces on piano tone. The standard impedance equation has two variable; stiffness and mass. They are both at equal balance in the equation, meaning a same value change of one or the other, would produce the same impedance result.

    Anyone with experience quickly learns that mass and stiffness change the perceived musical tone of a piano differently.

    My preferred axiom is: Lighter and tighter.

    ------------------------------
    Edward McMorrow
    Edmonds WA
    425-299-3431
    ------------------------------



  • 59.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 20:55
    I've never seen an impedance equation as it pertains to pianos so I can't comment. The point I was making is that controlling impedance, energy transfer, is an essential part of any design or execution whether it involves the contribution of downbearing or not. Mass and stiffness do affect tone differently and you can't substitute one for the other with impunity.  But in most systems downbearing is part of the stiffness side of the equation. If you eliminate downbearing you will have to compensate in some other way.  Further, if you have designed a system that is stiff enough without downbearing then by adding downbearing you run the risk of a system in which the impedance is too high. 

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 60.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-01-2021 23:43
    The impedance equation I am familiar with is the square root of mass times stiffness equals impedance. Impedance being a rate of change for energy moving from one system to another.

    ------------------------------
    Edward McMorrow
    Edmonds WA
    425-299-3431
    ------------------------------



  • 61.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 00:24
    OK but that means that mass and stiffness are not equal partners in the impedance equation.  Stiffness plays a bigger role.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 62.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 10:27
    Sorry my post didn't make it clear. Mass times stiffness are both under the square root sign.

    ------------------------------
    Edward McMorrow
    Edmonds WA
    425-299-3431
    ------------------------------



  • 63.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-02-2021 19:16
    Ed.

    Perhaps the problem is how we are defining "impedance model". I don't think most soundboard makers, if any, are plugging in impedance formulas and trying to find a way to measure stiffness and mass in order to produce some targeted level of impedance.  It's determined indirectly.  We use beam formulas, load bearing figures, MOE,  calculated loads via DB, etc etc, to give us a quantifiable working model.  We determine impedance characteristics by what we hear and if it doesn't comport with our goal then we change our inputs, beef up or trim down the ribs, thin the panel, change the grain orientation, whatever we decide, to alter the impedance characteristics.  In practice, at least, that's what happens.

    You don't need to take measurements on an existing board, crown or otherwise, to determine if you have an impedance problem.  You can hear it.  You may want to take measurements to determine if, say, there is any crown left in the panel that allows you to alter the downbearing and raise the impedance, if it's too low, or vice versa, or look for some other approach.  But impedance characteristics are the result of what we do in whatever manner we do it.  That includes altering the bridge pin array, having a board with or without ribs, adjusting the thickness of the panel, the rib scale, the grain orientation, panel thinning, and so on, as I've said. 

    In the end most of us, from the beginning, probably took an existing board and duplicated it as best we could.  We made some determination about how it came out and what we heard were largely those impedance characteristics: does it sound like a guitar or a banjo, does it have adequate power and adequate sustain.  Over time we came up with ways to quantify our changes, built it again and again made whatever changes we thought necessary to achieve the impedance characteristics we wanted.

    Of course there's more to tone than just the  power/sustain continuum.  Stiffness versus mass has different effects on different ranges of frequencies so we are also judging that part of.  Some of that is scale driven (higher versus lower tension scales).  Nobody said this was easy.  But over time we make small tweaks hopefully keeping all other things equal so we know what affects what.  

    The point is that impedance is a very large part of what we are trying to control.  We can pursue that goal in different ways and even radically alter traditional approaches but it's still the rate of the transfer of energy from the string to the board that will determine how successful we are.  You can't really abandon the impedance model because that's a fundamental physical property of what we are creating.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 64.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-02-2021 21:40
    David l< If better termination *lowers* the impedance.

    No...I meant to communicate, that better termination allows the board to be constructed with less stiffness built into the soundboard/rib assembly. So to be clear, I did not mean to say (and don't think I said) better termination lowers impedance. 

    So, I said ( or meant to say), better termination allows the board to be constructed with less stiffness? Why?

    I hypothesize...In a traditionally ribbed board, with a traditionally pinned bridge, there is an interaction at the front bridge pin/string/cap/bearing contact point, where the pin/string/cap/bearing clamp must not be over-driven beyond its capacity to clamp the string. If the impedance of the board assembly is too close a match to the impedance of the clamping assemble (the front pin/string/cap/bearing), the rate of energy imparted to that clamp interface simply overcomes the ability of the clamp to efficiently restrain the string.

    I have never heard anyone talk about the natural resonances of the bridge pin clamping/termination system. We always refer to board or string impedance, but never to the clamp assembly's impedance. (clamp assembly includes bearing).

    The reason we assume, in traditionally constructed compression and rib crowned structures, that a relatively stiff structure is necessary to produce tone, is that the with the traditional front pin assembly, energy transfer must be slowly exchanged between board and clamp systems, in order to avoid overwhelming the clamp assembly. It is why we try to mis-match, not match, but mis-match the two systems' impedances. Match the impedances of the two systems, and you overwhelm the clamp's ability to clamp, and we get the classic explosive tone breakup. Changing the impedance of the termination, is one way to assure mis-matched (a good thing) board and termination impedances. Stiffening up the board system is another way to assure mis- matched impedances.

    As David suggested, with a traditional pin termination, when reducing bearing, which reduces the clamp's system impedance, one way to deal with the lowered impedance of the clamp system, is to raise the impedance of the board assembly. This assures that the two system impedances are adequately mis-matched. 

    Another way to mis-match the impedances, is to raise the clamp system's impedance, while lowering the board's impedance.  By raising the clamp system's impedance, we can assure that a lower impedance board, does not transfer energy too quickly into the clamp system. And this is what I am striving to do, with success, with altered traditional pin configurations.   Agraffes do it even more efficiently, and also have higher mass, which also raises their system impedance. So that also helps to achieve the required mis-match as well. 
     





    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 65.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-03-2021 12:52
    Jim

    I see, perhaps I misread.  So what you're saying is that less efficiency in termination requires you to raise the impedance of the board, or better termination allows you to reduce the impedance.  

    I'm not sure I agree that those two are related that way.  If I read you correctly you're basing this on the idea that at some level the front termination can be compromised (decoupled in some way) resulting in a loss of energy at the termination that is compensated for by having to build, in essence, a higher impedance system.  I'm trying to wrap my head around that.  If there's energy loss at the termination, which means it's not transferring to the board, wouldn't you want to build a lower impedance system to insure that adequate string energy transfers even with some loss?  And if the front termination were modified so that the transfer of energy was more efficient (less loss) then you could build a higher impedance system because, effectively, you're not losing energy at the termination.

    Also, the impedance level that we hear, whether wrong or right, is present at every level of playing including levels that are far below stressing the front bearing in a conventional system.  If the board has a tendency toward too percussive, for example, we hear that at pianissimo as well as fortissimo.  So if the modified terminations create a more efficient system in which there is less energy loss that would make things even more percussive.  It seems to me then that by your argument with a more efficient system you would want higher impedance, not lower.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 66.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-03-2021 23:10
    Going to risk taxing some patence.   Taking fragments at a time to try to leave information truly unambiguous.
    Can we just look at the front termination at the bridge?  
    Jim, you say :  with a traditionally pinned bridge, there is an interaction at the front bridge pin/string/cap/bearing contact point,...
    How far can we go in just defining the qualities/aspects of that interaction?  As in, what do we mean?  Perhaps it would help to contrast that interaction with an assortment of alternative termination configurations.   You then introduce the specific quality of 'clamping'.  In how many directions?  vertically, horizontally, longitudinally.  

    pin/string/cap/bearing clamp must not be over-driven beyond its capacity to clamp the string.

    Finally, for now, how do you define the impedance of the clamp system?

    Start with that?


    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 67.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-04-2021 08:35
    David S< Finally, for now, how do you define the impedance of the clamp system?

    Beats me.  I just work here...

    Why do you think no one has ever tried to define or quantify it. Good luck with that...its too complex. It would probably require several doctoral dissertations, leaving us holding our collective Johnson's while we wait for definitive explanations of various phenomena...seriously. Even just defining the impedance of a pin driven into maple, is too complicated. This is why it exists on no spread sheet I have ever seen, and has never even been discussed. Analysis is all seat of the pants. If it works tonally...WOW!. If it doesn't work, mess with it some more and try again. Musical pleasure being the only arbiter of success. Even FEM modeling gets nowhere with this stuff. System modeling taken from a tonal perspective rather than just a structural perspective is astoundingly complicated. 

    The only quasi scientific approaches which are employed, are quantitative models, which relate certain parameters of the structure with empirical results, over time. And, on those models, parameters that are too hard to model are eliminated from the model. This means that the model will only be useful if the basic assumptions are always followed. Only small quantitative differences can be accomodated in these models. Change a major parameter, or assumption, as I am suggesting here, and the empirically derived quantitative model becomes non-informative, unto misleading.

    This is why all my work is empirically driven. It has to be.  I have ditched my quantitative models, and instead, over the last 5 years or so, have spent my brain bandwidth coming up with empirical ways to adjust the "in the ballpark" strung board and termination system in real time, as much as possible. 

    Here's what I know,  after 5 years of experience approaching the rebuild process this way.  You can take a dead board, reconstitute the glue joints along the entire length of the rib/panel joints, leave the board flat, with no crown along either the ribs or the long bridge whatsoever, assuming most all dried down compression long since went south on the flat board, then, improve the bridge termination by capping, and in my case, reducing front to back pin spacing, while maintaining a 13 deg offset, rescale, and end up with a gorgeous fundamental heavy bass & tenor.

    Then, in addition to using the same pin spacings as the bass & tenor, with addition of precision targeted minor mass loads, end up with a first capo that is a good as any new board I've ever heard, with sustain, power and without damping. This jettisons the blunt application Del and Ron taught, but follows a precision located, seat of the pants, see what works, application of often non-bridge centered loads. The usual damping tendency is avoided. The damping comes from the bridge centered protocol Del and Ron advocated applying the loads. Precision loading not blunt instrument loading. (Most, if not all concert violins, by the way mass loads in a precision location.)  Additionally, when mass loads are not applied to the bridge location, and sometimes way off to towards the rim, and sometimes purposely non-symmetrical, the amount of weight added and the amount of leverage added imposed by those loads is drastically reduced. Damping comes from asking the bridge to work those loads. In precision loading in small amounts, compared to the overall variation in soundboard weights from board to board, the weight differences become negligible. So, the oft stated opinion of mass damping a board, like everything else...depends.   MInd you "as good as any new board I've ever heard" means there still are some 1st capo issues, just like all new boards I have ever heard, have some first capo short-comings and occasionally wolf notes of some sort.

    Then, in the high treble, with good duplex design, strike point locations, and bridge termination protocols, end up with a lovely high sustain high treble...all on a previously dead, and still flat board...Empirical results, guided by real time adjustability, just like real time hammer voicing. 

    Explain it how you like...but the explanations will only be of very general help, in directing the empirical adjustments needed to make the board sing its best. 



      
     



    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 68.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-04-2021 09:49
      |   view attached

    David Skolnik, I am going to try to answer your questions about front terminations. albeit within the context of relationships where I think it will make the most sense when referencing the Paulello bridge agraffe design and other accompanying relationships in the overall design of the Opus 102.  All the discussions about impedance as it relates to the Paulello piano have said very little about what the design is, and what the effects are on the piano tonally.  As such, any comparative remarks are not very sensible without some further information.

    I have been struck by the radical simplicity of Palello's soundboard and bridge design.  It truly is all it needs to be and not one thing more. 

    I have seen many pictures of the bridge agraffe, a large number of patent drawings, and read Stephen Paulello's descriptions of his design goals and means of achieving that.  I have also listened extensively to many recordings over a period of a number of years to familiarize myself with its tonal characteristics and its merits in making good piano music. 

     

    As you can see from the drawing, the agraffe consists of 3 pieces – a bottom plate with a recess in it for a pin, the pin, and a top capping piece.  The string is captured at 3 points of deflection; at the front, the back, and over the pin in the center.  The agraffe is 20 cm long and the center pin is equidistant from the ends and at 10 mm. distant.  The string is deflected in the vertical plane, unlike the traditional bridge pin's horizontal deflection.  Both designs have side bearing, but in different planes.  It is critically important that Paulello's design has the 3 points of deflection as shown, in that he has arranged the forces that accompany side bearing in such a way that the forces of deflection cancel each other out.  In the traditional pinned design, the forces at the front and rear pins operate in such a way that, throughout the life of the piano, torquing forces exist always twisting the bridge counter-clockwise.  I believe that there are tonal consequences and losses that attend this, and the same is true for downbearing.  Of course, we cannot have musically sensible tone with downbearing without sidebearing in the traditional design.  I will call the two a necessary evil. 

    The 3 points of capture are closely clustered, so as to most fully capture the string.  The top piece is made of brass, and the wire self-machines the half round to achieve a good mating.

     

    Stephen Paulello comes right out and says there is no loading of the panel.  His design goal is to eliminate all forces that do not need to be there.  To wit, the string runs perfectly straight from the agraffe to the hitch pin in both the horizontal and vertical planes.  Vertical hitch pins assure that the bearing is neutral, with no positive or negative bearing.  The top of the bridge and the lay of the agraffe also reflect this neutrality, with no tilt at either end.  There is no twist in the arrangement of the agraffe to the string plane.  The only deflection from a straight line occurs within the agraffe, as seen in the drawing. 

    The result is a piano that sounds different in what I consider important ways.  I won't go into that right now, but will offer you several links to good quality recordings that can allow you to form your own impressions apart from my own.  Good headphones or a connection to your stereo are to be desired. 

    Bach Tocattas, beautifully played:  https://www.prostudiomasters.com/album/page/82312

    Beethoven, 32 variations:  https://davidbismuth.bandcamp.com/album/beethoven-et-ses-maitres

    Franz Liszt - Franz Schubert, 2. Der Atlas , (extract), track 3.  A sample near bottom of page:  https://www.musicologie.org/17/opus_102_cyril_huve_joue_le_piano_dernieres_technologies.html

    Debussy – La Cathedrale Engloutie  https://www.youtube.com/watch?v=ssSVwcjxb5U&ab_channel=EvidenceClassics  

    Franck Avitabile –  Body and Soul:   https://www.youtube.com/watch?v=JMSwiuVrUzE&ab_channel=FranckAvitabile

     

     

     

     

     



    ------------------------------
    William Truitt
    Bridgewater NH
    603-744-2277
    ------------------------------

    Attachment(s)

    docx
    Oops, Paulello drawing.docx   223 KB 1 version


  • 69.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 08-04-2021 11:30
    A very clean, but a dry and thin sound imo. It didn't seem to hold my attention, because it became rather a monotone of color to me. One could say it makes the case for the Genius of Steinway and others, that the imperfections create the interest through the little nuances in tonal character and color.

    -chris

    ------------------------------
    Chernobieff Piano Restorations
    "Where Tone is Key"
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Lenoir City, TN
    865-986-7720
    ------------------------------



  • 70.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-04-2021 12:20
    Hi Will -
    Thanks for this extensive response.  Only had a chance to read through once, but will spend more time.  I listend to the recordings (also thanks) and might concur a little with Chris C as to the sound, but, given how aware I was of the limitations of my (not inexpensive) Bower & Wilkens headphones, as well as some issues of the recordings themselves (and realizing I haven't spent enough time straight out listneing), I'm more interested, for the moment, with the concepts.  I'll do the work of blending them into Jim's ideas.
    Again, thanks.

    ------------------------------
    David Skolnik [RPT]
    Hastings-on-Hudson NY
    917-589-2625
    ------------------------------



  • 71.  RE: Apparent Down Bearing on what turns out to be a flat board

    Registered Piano Technician
    Posted 08-04-2021 13:57
    Hi David:

    Except for the limitations of fidelity of the YouTube video, the samples are from audiophile digital sites.  As for headphones, it is mostly a matter of choose the  colorations you like the most for the majority of us.  So we do the best we can.  Luckily, we have a tonal memory of what a real piano sounds like.

    I too am most interested in the concepts - the elements of design.  That is what I am presenting here.  I am least interested in whether someone likes the piano or not, that goes no deeper than f it's got a nice beat and you can dance to it, so I like it.   A waste of time and words.  We all have our preferences and prejudices, but if one opens themselves to deep and repeated listening without judgment, quite a lot can be revealed.  

    As my ears have opened up over time and I heard more and more different things, I would ask myself, what is that?  What is going on to create it?  If it is different, how is it different?  Is it important?  Do these tonal characteristics contribute to the music that the musician is trying to create?  If one is a skilled voicer servicing pianists with discrimination, one has to do this kind of listening.  And, yes, it has everything to do with the terminations.

    ------------------------------
    William Truitt
    Bridgewater NH
    603-744-2277
    ------------------------------



  • 72.  RE: Apparent Down Bearing on what turns out to be a flat board

    Posted 07-31-2021 14:51
    The plate is strong, but its also flexible. Just observe what happens before and after with the Steinway Bell. The plate flexs up. The whole point of the bell is to stop that upward thrust to provide tuning stability to the treble.  Notice the nosebolts divide the plate into shorter sections and make it more stable because it will mitigate the flexing. If its flexing up. then its also pulling in. There is a company near me that for some reason remove the nosebolts in their rebuilds and within 5 years the instrument pulls itself apart. And their attempted repair of it is even more hilarious, but that's another story.
    Here's the video:
    https://www.youtube.com/watch?v=HpXVz4wl7jk&t=388s

    -chris

    ------------------------------
    Chernobieff Piano Restorations
    "Where Tone is Key"
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Lenoir City, TN
    865-986-7720
    ------------------------------