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#1125865 - 12/10/04 09:27 AM Re: Fascinating Steinway Phenomena
Steve Ramirez Offline
1000 Post Club Member

Registered: 08/08/01
Posts: 1098
Loc: El Cajon, California
 Quote:
Originally posted by JCS:
Question:

Assuming crown is retained over time, why would newer wood vibrate better i.e. with more sound and sustain than older drier wood?

Seems to me the reverse would be true... i.e. stiffer drier wood would seem to vibrate stronger. [/b]
New versus old wood has nothing to do with moisture content. New soundboards are made from seasoned lumber that has, or should have, the precise moisture content required by the soundboard maker. Soundboard makers have the capability of adding or removing moisture from lumber according to their requirements.

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#1125866 - 12/10/04 10:09 AM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by JCS:
Question:

Assuming crown is retained over time, why would newer wood vibrate better i.e. with more sound and sustain than older drier wood?

Seems to me the reverse would be true... i.e. stiffer drier wood would seem to vibrate stronger.

[/b]
This debate has gone on in the industry for almost as long as the piano has been in existence. For some reason we continue trying to ascribe some magical function to the age of a piece of wood.

In part, I think, this has persisted because of the difficulty — at least until recently — of precisely defining just how the piano soundboard works.

It might help to stop thinking in terms of wood as an individual element vibrating and start thinking of the piano soundboard assembly as an integral whole, a system made up of one or more bridges to transfer vibrating energy from the strings to a large panel or diaphragm having some controlled amount of mass and stiffness that takes this vibrating energy and changes it into sound energy. As long as the mass and stiffness of this diaphragm is controlled in a way that gives us our desired results it does not matter what materials go into its construction.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125867 - 12/10/04 10:27 AM Re: Fascinating Steinway Phenomena
Ron L. Offline
Junior Member

Registered: 11/20/04
Posts: 9
Loc: US
I'm not a tech and this is my first reply, but I've been reading and learning on this matter, as I was considering having an old Steinway rebuilt. The question of the soundboard and the associated costs came up to almost 20K for a total rebuild so I just bought a new piano. It seems that the primary argument about replacing a dead soundboard with a new one could be settled by actually measuring and plotting the sound wave of the initial attack and the subsequent sustain against a known good piano. No doubt that most of you techs on this site are able to hear the difference, but is this not an area that could be tested scientifically to settle these arguments?

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#1125868 - 12/10/04 11:24 AM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by Ron L.:
I'm not a tech and this is my first reply, but I've been reading and learning on this matter, as I was considering having an old Steinway rebuilt. The question of the soundboard and the associated costs came up to almost 20K for a total rebuild so I just bought a new piano. It seems that the primary argument about replacing a dead soundboard with a new one could be settled by actually measuring and plotting the sound wave of the initial attack and the subsequent sustain against a known good piano. No doubt that most of you techs on this site are able to hear the difference, but is this not an area that could be tested scientifically to settle these arguments? [/b]
It can be and it has been. But the equipment with which this can be done accurately is quite expensive. Somewhat beyond the budgets of most technicians.

In general piano technicians don’t go out looking for pianos that need new soundboards. At least I don’t know of any that do this. When the discussion of whether or not to replace the soundboard assembly comes up it is usually a result of the piano owner not being satisfied with the sound of the piano. The fact that the piano has a problem is accepted and the issue becomes one of identifying just what that problem is. Once the obvious is taken care of — proper tuning, adequate and appropriate hammers, good voicing, etc. — the question will eventually get around to rebuilding and/or replacing the soundboard. These are pianos with known tonal problems and through a process of elimination the question ultimately gets to the soundboard assembly.

The tonal characteristics related to soundboard problems are fairly well known, fairly consistent from one piano to the next and can be easily described. Since comparisons with pianos of known quality and performance are usually not difficult to arrange this has become a common way to help the client understand and identify what to listen for.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125869 - 12/10/04 12:11 PM Re: Fascinating Steinway Phenomena
JPM Offline
1000 Post Club Member

Registered: 02/24/03
Posts: 1010
Loc: NM, GE & Wash. DC
Del said --

 Quote:
As to your last question -- it depends on the rebuilder. Some do use a relatively authentic compression-crowning system (as is described elsewhere). We do not. Our ribs are crowned and the soundboard panel is held to a somewhat higher moisture content when it is all glued up. We believe our system has certain acoustical advantages and fewer inherent structural drawbacks. Obviously, others disagree. It is a matter of choice, experience and technological background.
Del, this would be an interesting topic to pursue -- one perhaps better suited for the Piano Tuner-Technician's Forum. I am interested in learning more about the relative merits/demerits of the two techniques in terms of the sonic qualities or characteristics they produce. I would also like to know which piano makers use the crowned rib method. This might help me better understand why certain pianos have the tonal qualities they do.

Much of what has been stated here has been corroborated, at least for me personally, through side-by-side comparisons of new and rebuilt pianos. My experience has been rebuilt pianos that retain the original shimmed soundboard often (but not always) lack power and sustain in the treble. They often lack a full-bodied rounded sound too.

It is interesting to note that when certain piano manufacturers rebuild their old pianos, they often, if not always, replace the old SB with a new one. That's the case, at least, with a certain piano maker whose piano's I'm rather partial to. I assume they do so for a reasons other than convenience and economy.

JP
_________________________
"Piano music should only be written for the Bechstein."
-- Claude Debussy

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#1125870 - 12/10/04 01:47 PM Re: Fascinating Steinway Phenomena
JCS Offline
Full Member

Registered: 07/02/04
Posts: 75
Loc: Aurora, Colorado
Is there any real statistical evidence that the Mason & Hamlin tension resonator actually works as intended?

i.e Does the M&H really hold crown better than other pianos over time in general?

Fluff or stuff?

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#1125871 - 12/10/04 01:59 PM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by JCS:


Is there any real statistical evidence that the Mason & Hamlin tension resonator actually works as intended?

[/b]
No. There is, however, evidence that it does not and can not work as advertised. This subject has been discussed in detail under previous topics.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125872 - 12/10/04 02:04 PM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by JPM:
Del said --

Del, this would be an interesting topic to pursue -- one perhaps better suited for the Piano Tuner-Technician's Forum. I am interested in learning more about the relative merits/demerits of the two techniques in terms of the sonic qualities or characteristics they produce. I would also like to know which piano makers use the crowned rib method. This might help me better understand why certain pianos have the tonal qualities they do.

Much of what has been stated here has been corroborated, at least for me personally, through side-by-side comparisons of new and rebuilt pianos. My experience has been rebuilt pianos that retain the original shimmed soundboard often (but not always) lack power and sustain in the treble. They often lack a full-bodied rounded sound too.

It is interesting to note that when certain piano manufacturers rebuild their old pianos, they often, if not always, replace the old SB with a new one. That's the case, at least, with a certain piano maker whose piano's I'm rather partial to. I assume they do so for a reasons other than convenience and economy.

JP [/b]
I do not have a list of which manufacturers use which processes. Unfortunately the representatives of these companies often do not themselves know.

As far as tonal performance is concerned you really shouldn't be able to tell much of any difference assuming both soundboards are in good condition. The differences would show up after 20 or 40 or whatever years. Tone performance is determined by a number of disparate factors ranging from scale length and tensions, bridge construction, plate design, rim and belly structure, soundboard shape and on and on. It is impossible to select out one attribute such as how the soundboard assembly is constructed and determine that the piano sounds a certain way because of that one factor.

When pianos are rebuilt by the manufacturers that originally built them they tend to use the same processes and materials that are used to construct the original. I don't know of any exceptions to this. It is what they know how to do and I’m sure they would consider it some odd if they were asked to do anything other than this.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125873 - 12/10/04 03:11 PM Re: Fascinating Steinway Phenomena
JCS Offline
Full Member

Registered: 07/02/04
Posts: 75
Loc: Aurora, Colorado
Hey Del, I went back to the thread where you discussed the tension resonator and well, the discussion was a bit over my head.

Can you dumb down your explanation a bit on why the tension resonator doesn't work as advertised by M&H?

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#1125874 - 12/10/04 09:48 PM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by JCS:
Hey Del, I went back to the thread where you discussed the tension resonator and well, the discussion was a bit over my head.

Can you dumb down your explanation a bit on why the tension resonator doesn't work as advertised by M&H? [/b]
I'm not sure how. The shape of the ribs is such that they don't push out against the rim as they are forced flat. They are pretty close to neutral, that is, if you start with a crowned soundboard assembly, glue it into a piano and physically force all of the crown out of the system the rim will not be forced outward. It will actually be pulled in very slightly.

Even if this were not the case there are a number of false claims made for how the system works. In their web site presentation they seriously exaggerate the crown radii involved making it look more like a roman arch. It is not. They make the claim that wood, longitudinal to grain is non-compressible. It is compressible. Not as much as across-grain but still compressible.

There are other problems with their claims but these are the biggies as related to the soundboard assembly. It is unfortunate this story goes on. The M&H grands are excellent pianos and inaccurate claims such as this are really unnecessary.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125875 - 12/11/04 08:23 AM Re: Fascinating Steinway Phenomena
HammerHead Offline
Full Member

Registered: 03/17/03
Posts: 354
Loc: Metro Atlanta
Del said...
"The M&H grands are excellent pianos and inaccurate claims such as this are really unnecessary."

One last thing--would it be your opinion that without the flux capacitor, sorry, I mean tension resonator, M&H grands would be just as excellent, minus the extra weight and expense?
_________________________
HH
Completely and forever out of the music business (but still full of opinions)

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#1125876 - 12/11/04 08:45 AM Re: Fascinating Steinway Phenomena
Rick Clark Offline
1000 Post Club Member

Registered: 01/04/03
Posts: 1810
Loc: North County San Diego CA
I would like to put in my 2 cents that strictly from anecdotal observation I have found that on average, old M&H soundboards do seem to hold up better. I base this not only on 30 years of observation, but also 30 years of talking to other techs whose observations agree.

This is not to say they are bulletproof, never crack or suffer any problems. I'm saying that on *average* they seem to hold up better.

What I have stated in the past here is that while I cannot say for certain whether this is due to the tension resonator or some other factor, since the mfgr's claim seems to agree with the field observation I take it as a matter of faith that the resonator is doing something good.

(OTOH I also note that their bridges seem to hold up better too, and they have nothing to do with the resonator- so there is a question mark)

And I put my money where my mouth is. I am now on my third pre-1930 M&H grand, and am quite happy with the existing board, as I was in the other 2.

Regards,

Rick Clark
_________________________
Rick Clark

Piano tuner-technician

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#1125877 - 12/11/04 09:41 AM Re: Fascinating Steinway Phenomena
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 21925
Loc: Oakland
You take a day off, and see what happens!

 Quote:
The other way is to shape the ribs so they have the right amount of curvature, and with the % moisture in the ribs and soundboard the same, glue the soundboard to the ribs. Before the strings are installed, there is no compression on the board, unlike a compression-crowned board, which starts out with a very large compression stress. Even considering the downbearing force from the strings, a rib-crowned board has much lower compressive stress on it.
Perhaps. If you start with a flat board and bend it freely, there is a difference in stress from one side to the other, depending on whether the material is stronger under tension or under compression. Since spruce is about twice as strong under compression as it is under tension, one would expect that the bottom third of a board crowned this way would be compressed, and the other two thirds would tensed. The amount of stress imparted in this board is perhaps not as great as the total compression stress in a compressioned-crowned soundboard, but since 2/3 of it is tension, and the wood can only stand half as much tension as compression without failure, it may be that the board is more likely to be stress-damaged with age if it is rib-crowned. The top of the board will be ripped apart by the tension, while the bottom will be crushed by the compression. That is, if these tensions amounted to much.

As for compression due to the downbearing of the strings on the bridge, cross-grain to the soundboard, that is withstood by the long grain of the ribs, while the pressure parallel to the grain is, of course, withstood by the long grain of the soundboard. Wood is real strong parallel to the grain, enough so that the pressure of the strings is no problem.


 Quote:
I'm not sure how. The shape of the ribs is such that they don't push out against the rim as they are forced flat. They are pretty close to neutral, that is, if you start with a crowned soundboard assembly, glue it into a piano and physically force all of the crown out of the system the rim will not be forced outward. It will actually be pulled in very slightly.
There are a few things wrong with this statement. First of all, the ribs have no effect on the pressure along the grain of the soundboard. They don't go that direction. If the stress along the ribs were the issue, the TR on the M & H 50 would probably go from top to bottom, or diagonally, but it doesn't.

In the direction of the ribs, the role of the soundboard in providing rigidity at the top of the ribs was entirely discounted. Even though thickness adds a lot of rigidity, there's enough more width to counteract that.

Of course, all this proves nothing. What I say may not be true, nor what Del says. Certainly the people at M & H would disagree with Del, as would all those companies that use compression-crowned soundboards.

Some of claims can be tested. For instance, it would be pretty easy to cut a piece of wood to the shape of a rib, fasten it to a couple of uprights, press down on it until it is flat on the top, and see if the uprights bend in or bend out. (I would bet on bending out, scoring one for M & H.)
_________________________
Semipro Tech

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#1125878 - 12/11/04 10:08 AM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by BDB:


Of course, all this proves nothing. What I say may not be true, nor what Del says. Certainly the people at M & H would disagree with Del, as would all those companies that use compression-crowned soundboards.

Some of claims can be tested. For instance, it would be pretty easy to cut a piece of wood to the shape of a rib, fasten it to a couple of uprights, press down on it until it is flat on the top, and see if the uprights bend in or bend out. (I would bet on bending out, scoring one for M & H.)

[/b]
BDB, you really need to get out in the shop and start doing some of your own hands-on experimenting and testing. Actually try to crown a soundboard assembly in the way you describe. When it doesn’t crown figure out for yourself why it didn’t. Actually measure the stresses involved. See for yourself how much a soundboard panel physically contracts when it is taken from 12% or 14% moisture content down to a verified 4% moisture content. Glue up a soundboard assembly with the panel at a 4% moisture content for yourself and watch what happens as it takes on moisture. Compare its final across-grain dimension with a sample test panel. And then try to explain the difference without acknowledging that the panel is, in fact, under some 1% to 2% compression. Doing these things for yourself will help immensely when you start speculating about things like wood tension and compression in the various types of soundboard construction.

As it is your explanations simply make no sense. They do not accurately describe the forces that are created and that exist within the various types of soundboard assemblies.

As to the M&H rib, this has been verified through actual experiment by a number of technicians (including myself). It works as I’ve described. The Centripital Tension Resonator neither helps nor hinders the creation of, or maintenance of, soundboard crown. While it may contribute to the overall performance of the piano in other ways, that is the subject for another time.

Del
_________________________
Delwin D Fandrich
Piano Research, Design & Manufacturing Consultant
ddfandrich@gmail.com
(To contact me privately please use this e-mail address.)

Stupidity is a rare condition, ignorance is a common choice. --Anon

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#1125879 - 12/11/04 11:10 PM Re: Fascinating Steinway Phenomena
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 21925
Loc: Oakland
Now I don't get you. You said:

 Quote:
The other way is to shape the ribs so they have the right amount of curvature, and with the % moisture in the ribs and soundboard the same, glue the soundboard to the ribs. Before the strings are installed, there is no compression on the board, unlike a compression-crowned board, which starts out with a very large compression stress. Even considering the downbearing force from the strings, a rib-crowned board has much lower compressive stress on it.
There's no mention of shaping the soundboard with the right amount of curvature, too. Do you do that? If so, you've never mentioned it, only that you shape the ribs.

Incidentally, I went down in my junkpile, and it struck me how to put a really huge amount of stress in a piece of soundboard wood. I grabbed a scrap of it and twisted. I found that I could twist a piece approximately 2" x 24" so that one end was 45 degrees from the other. That's a lot more stress than you would get from forming a soundboard, but it wasn't enough to make any difference in the wood. It sprang right back, even though this was a hunk of ancient probably compression-crowned soundboard wood which should have lost all of its elasticity from being in a piano under stress from strings for umpteen years.

Incidentally, some of the soundboard wood among the scraps did show some signs of stress. However, it was tension stress, rather than compression stress: Tiny cracks in the finish of the top of the board, just as one might predict from my description of stress in a soundboard.

But in the long run, I guess that all that matters is that my customers are happy with what I do, and other people's customers are happy with what they do.
_________________________
Semipro Tech

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#1125880 - 12/12/04 08:56 AM Re: Fascinating Steinway Phenomena
Calin Offline
Full Member

Registered: 09/11/03
Posts: 418
Loc: Bucharest
BDB, cracks in the finish don't necessarily mean that the wood cracked the same way.

Calin
_________________________
Calin

The Bechstein piano discussion group: http://launch.groups.yahoo.com/group/bechstein/
The Schweighofer piano site: http://schweighofer.tripod.com

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#1125881 - 12/12/04 08:58 AM Re: Fascinating Steinway Phenomena
Calin Offline
Full Member

Registered: 09/11/03
Posts: 418
Loc: Bucharest
_________________________
Calin

The Bechstein piano discussion group: http://launch.groups.yahoo.com/group/bechstein/
The Schweighofer piano site: http://schweighofer.tripod.com

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#1125882 - 12/12/04 09:05 AM Re: Fascinating Steinway Phenomena
Calin Offline
Full Member

Registered: 09/11/03
Posts: 418
Loc: Bucharest
_________________________
Calin

The Bechstein piano discussion group: http://launch.groups.yahoo.com/group/bechstein/
The Schweighofer piano site: http://schweighofer.tripod.com

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#1125883 - 12/12/04 04:19 PM Re: Fascinating Steinway Phenomena
Roy123 Offline
1000 Post Club Member

Registered: 09/20/04
Posts: 1725
Loc: Massachusetts
 Quote:
Originally posted by BDB:
You take a day off, and see what happens!

 Quote:
The other way is to shape the ribs so they have the right amount of curvature, and with the % moisture in the ribs and soundboard the same, glue the soundboard to the ribs. Before the strings are installed, there is no compression on the board, unlike a compression-crowned board, which starts out with a very large compression stress. Even considering the downbearing force from the strings, a rib-crowned board has much lower compressive stress on it.
Perhaps. If you start with a flat board and bend it freely, there is a difference in stress from one side to the other, depending on whether the material is stronger under tension or under compression. Since spruce is about twice as strong under compression as it is under tension, one would expect that the bottom third of a board crowned this way would be compressed, and the other two thirds would tensed. The amount of stress imparted in this board is perhaps not as great as the total compression stress in a compressioned-crowned soundboard, but since 2/3 of it is tension, and the wood can only stand half as much tension as compression without failure, it may be that the board is more likely to be stress-damaged with age if it is rib-crowned. The top of the board will be ripped apart by the tension, while the bottom will be crushed by the compression. That is, if these tensions amounted to much.

As for compression due to the downbearing of the strings on the bridge, cross-grain to the soundboard, that is withstood by the long grain of the ribs, while the pressure parallel to the grain is, of course, withstood by the long grain of the soundboard. Wood is real strong parallel to the grain, enough so that the pressure of the strings is no problem.


 Quote:
I'm not sure how. The shape of the ribs is such that they don't push out against the rim as they are forced flat. They are pretty close to neutral, that is, if you start with a crowned soundboard assembly, glue it into a piano and physically force all of the crown out of the system the rim will not be forced outward. It will actually be pulled in very slightly.
There are a few things wrong with this statement. First of all, the ribs have no effect on the pressure along the grain of the soundboard. They don't go that direction. If the stress along the ribs were the issue, the TR on the M & H 50 would probably go from top to bottom, or diagonally, but it doesn't.

In the direction of the ribs, the role of the soundboard in providing rigidity at the top of the ribs was entirely discounted. Even though thickness adds a lot of rigidity, there's enough more width to counteract that.

Of course, all this proves nothing. What I say may not be true, nor what Del says. Certainly the people at M & H would disagree with Del, as would all those companies that use compression-crowned soundboards.

Some of claims can be tested. For instance, it would be pretty easy to cut a piece of wood to the shape of a rib, fasten it to a couple of uprights, press down on it until it is flat on the top, and see if the uprights bend in or bend out. (I would bet on bending out, scoring one for M & H.) [/b]
The stress in the board from just bending it over curved ribs is very small--that's because the board is thin, and the rib curvature is large. However, the compressive force required to bend the ribs is quite large. Remember that the ribs are stiff, and the lever arm (the distance between the center of the board and the center of the ribs measured normal to the plane of the board) is small. Both parameters dictate high compressive forces in the board.

Take Del's word for it--he understands the physics and is telling you the truth. Forces in a compression-crowned board are much higher than in a rib-crowned board, and compression-crowned boards will lose their crown much more readily.

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#1125884 - 12/12/04 10:21 PM Re: Fascinating Steinway Phenomena
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 21925
Loc: Oakland
No, the pressure required to bend ribs isn't that much. Again, I can do it with my hands.

Besides, just compression doesn't damage the wood. The wood compresses all by itself just due to changes in humidity. You can see the situation on page 114 of Hoadley.

Standard woodworking practice for glueing crossgrain members is to use the very method of lowering the moisture content before glueing. If you don't you increase the chances that the wood will be damaged by changes in humidity. You will get cracks. The most damage that you could get from compression set, whether by compression-crowning or by glueing to shaped ribs, no matter how long it is done for, is that the soundboard would take on the arch of the soundboard permanently, even if you remove the ribs. But I don't believe that happens.
_________________________
Semipro Tech

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#1125885 - 12/12/04 11:32 PM Re: Fascinating Steinway Phenomena
Del Offline
5000 Post Club Member

Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by BDB:
No, the pressure required to bend ribs isn't that much. Again, I can do it with my hands.

Besides, just compression doesn't damage the wood. The wood compresses all by itself just due to changes in humidity. You can see the situation on page 114 of Hoadley.

Standard woodworking practice for glueing crossgrain members is to use the very method of lowering the moisture content before glueing. If you don't you increase the chances that the wood will be damaged by changes in humidity. You will get cracks. The most damage that you could get from compression set, whether by compression-crowning or by glueing to shaped ribs, no matter how long it is done for, is that the soundboard would take on the arch of the soundboard permanently, even if you remove the ribs. But I don't believe that happens. [/b]
Yes, compression can and does damage wood. The most extreme and visually dramatic occurrence of this damage in the piano soundboard are the compression ridges that often show up in soundboard panels crowned in this way. As the name implies internal compression is literally forcing the latewood layers up or down as the earlywood fibers fail in shear as the force from internal compression becomes greater than they can withstand.

Even without exhibiting this kind of dramatic failure a wood member held in cross-grain compression over a period of time will physically change shape. In other words a panel that is held in compression across grain will gradually lose some of its overall width. If you were at all inclined toward experimentation I would suggest the following:

Cut a 250 mm long (i.e., with the grain) by 1025 mm wide (across-grain) panel of nice new spruce. Dry this panel to 4% moisture content. (You’ll have to determine this by weighing samples, wood moisture content meters do not read accurately below 6%.) With the panel at 4% quickly cut it to exactly 1,000 mm and put it into a prepared frame that will hold it flat but which will not put any pressure on it at 1,000 mm but which will not allow it to expand beyond that initial 1,000 mm. Now set the whole thing aside in a normal atmosphere for a year.

When you take your panel out of the frame and dry it back down to 4% moisture content you will find it is no longer 1,000 mm wide but somewhat less that that. Just how much less will depend on the specific characteristics of the wood you used and the extent of the humidity swings to which it has been exposed. If you leave it in your frame long enough you will eventually see it actually coming away from the ends during moderately dry periods. This is the effect of compression-set.

This is the piano version of the illustration Hoadley gives on page 114 of his book, Understanding Wood. This illustration shows how constrained wood samples are damaged through the mechanism of compression-set after being exposed to varying amounts of humidity. The experiment I've described above is roughly equilivent to the middle sample. What has happened to the sample on the left is exactly the same as what happens to a compression-crowned soundboard panel over time. The soundboard panel is physically constrained by being solidly glued to all those perpendicular-to-grain ribs on one side of the panel. Those ribs don’t allow the panel to freely expand and the resulting stress-interface between the compressed (trying to expand) soundboard panel and the ribs forms the crown. Without that compression there is no crown.

A free piece of wood like a soundboard panel (or the sample on the right in Hoadley’s illustration) will not develop any internal compression or tension due to changes in humidity. It will simply expand or contract depending on whether it is absorbing or desorbing moisture. It is only when the wood is constrained and not allowed to move that it will develop either internal compression or tension.

Standard woodworking practice calls for wood to be at a minimum of 7% moisture content at glue up. To go below this can lead to starved glue joints as the wood will very readily draw the glue solvent (usually water) out of the glue. This is well above the 4% moisture content called for in the process of gluing up a compression-crowned soundboard assembly.

Gluing up a soundboard panel at the 4% moisture content required to end up with a compression-crowned soundboard assembly is abnormal to the woodworking industry. Several of the wood technologists I have consulted on the subject expressed mild shock and something bordering on disbelief when the process was explained to them.

Like it or not the soundboard panel in a compression-crowned soundboard assembly is under long-term compression and it remains under compression until compression-set has relieved that compression by physically altering the shape of the wood fibers. It is a gradual but certain process.

Del
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#1125886 - 12/13/04 05:07 AM Re: Fascinating Steinway Phenomena
Roy123 Offline
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Registered: 09/20/04
Posts: 1725
Loc: Massachusetts
 Quote:
Originally posted by BDB:
No, the pressure required to bend ribs isn't that much. Again, I can do it with my hands.

Besides, just compression doesn't damage the wood. The wood compresses all by itself just due to changes in humidity. You can see the situation on page 114 of Hoadley.

Standard woodworking practice for glueing crossgrain members is to use the very method of lowering the moisture content before glueing. If you don't you increase the chances that the wood will be damaged by changes in humidity. You will get cracks. The most damage that you could get from compression set, whether by compression-crowning or by glueing to shaped ribs, no matter how long it is done for, is that the soundboard would take on the arch of the soundboard permanently, even if you remove the ribs. But I don't believe that happens. [/b]
The force to bend a rib doesn't seem high to you because you are bending the ribs differently. I assume you are grabbing a rib in two spots with each of your hands and then torquing it or maybe bending over your knee (or whatever). BUT, the soundboard isn't doing that. The soundboard is pushing on the rib longitudinally, very close to its centerline. As I mentioned in my previous post, that's what causes the high forces. If you refuse to believe Del, here is a quote from Ron Overs, a piano guru from Australia.

"CC [compression-crowned] rib sound board panels typically are grossly overloaded in compression, even before they are subjected to the downbearing force of the strings. It is not unusual for CC boards to exhibit significant signs of collapse within twenty years, and often much earlier (some overstressed sound boards can exhibit signs of collapse even before the instrument is sold from new). Overs Pianos is currently (2004) replacing a CC concert grand sound board (circ. 1962) from a 'leading' manufacturer, with reverse crown between the bridge and the belly rail in the second top string section (colloquially known as the killer octave)."

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#1125887 - 12/13/04 08:42 AM Re: Fascinating Steinway Phenomena
Del Offline
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Registered: 09/04/03
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Loc: Olympia, Washington
Sorry for the duplicate post. Del
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#1125888 - 12/13/04 08:44 AM Re: Fascinating Steinway Phenomena
Del Offline
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Registered: 09/04/03
Posts: 5327
Loc: Olympia, Washington
 Quote:
Originally posted by Roy123:
The stress in the board from just bending it over curved ribs is very small--that's because the board is thin, and the rib curvature is large. However, the compressive force required to bend the ribs is quite large. Remember that the ribs are stiff, and the lever arm (the distance between the center of the board and the center of the ribs measured normal to the plane of the board) is small. Both parameters dictate high compressive forces in the board.

Take Del's word for it--he understands the physics and is telling you the truth. Forces in a compression-crowned board are much higher than in a rib-crowned board, and compression-crowned boards will lose their crown much more readily. [/b]
The peak compressive forces that can build up in a soundboard panel that is crowned this way is between 1% and 2% depending on the specific wood samples and the atmosphere the soundboard assembly is exposed to.

It is generally accepted within the woodworking industry that to avoid rapid compression stress failure wood should not be under any more than 1% compression (perpendicular-to-grain) for even relatively short periods of time. Significant long-term compression set will occur at much lower levels of compression than this.

Del
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#1125889 - 12/13/04 10:26 AM Re: Fascinating Steinway Phenomena
BDB Offline
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Registered: 06/07/03
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Force is measure in Newtons, not percentage.

At any rate, it doesn't make any difference. As far as I know, I've had only two pianos fail after restringing, and the reason that they failed is because they were subjected to excessive heat. That was in the Oakland firestorm, when it got up to a couple thousand degrees. Nothing was left of them except the strings, so I hear. I doubt anyone else's pianos would do any better under those circumstances.
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#1125890 - 12/13/04 01:40 PM Re: Fascinating Steinway Phenomena
Roy123 Offline
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Registered: 09/20/04
Posts: 1725
Loc: Massachusetts
Del was referrring to how much the wood was compressed in distance. For example, if a piece of wood measuring 100 cm was compressed 1%, its compressed dimension would be 99 cm.

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#1125891 - 12/13/04 05:30 PM Re: Fascinating Steinway Phenomena
Jeanne W Offline
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Registered: 01/28/04
Posts: 1240
Loc: New England
Should have done this earlier. Just want to thank you, Del, for responding to my question earlier in this thread and for continuing to visit PianoWorld. We piano people appreciate your willingness to share your knowledge. \:\)

Jeanne W
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#1125892 - 12/13/04 10:14 PM Re: Fascinating Steinway Phenomena
tritone Offline
Full Member

Registered: 08/16/04
Posts: 189
Loc: Alberta
I second that emotion Jeanne W.

Thank you to all you contributors - Educating us all. Taking the time to write thoughtful insights from your years of experience. None of this shill-baiting nonsense that drives my crazy. Threads like this remind me why I love Piano Forum. And why I will start subscribing to keep it going. Thank you all.

I've sent this one into Frank B. to have this thread join the FAQ page. Hopefully he'll listen.

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#1125893 - 03/18/05 06:21 AM Re: Fascinating Steinway Phenomena
RPD Offline
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Registered: 03/07/05
Posts: 961
Loc: Kalamazoo Michigan
 Quote:
Originally posted by Ori:
Translation: The owners/buyers finally figured out they had been “stiffed”.
And...

No, I could take people's money too, if I was a crook.
Hmmmmmm.....pretty harsh. I've been restoring, and rebuilding pianos since 1977. I've never replaced a soundboard. When I come across old Steinways, irrespective of how the SB looks or sounds, I ALWAYS tell the customers that restoring Steinways is a specialized art, and that the SB may need, and probably should, be replaced. I refer them to a shop that does that. I don't offer that service directly, although I am willing to sub that out if necessary to accomodate a complete rebuilding.

Many customers don't want, no matter what, a soundboard replaced. There is the family heirloom factor to consider. It comes up all the time in the field. Some clients simply want THEIR piano rebuilt...If, after properly advising a client as to their options, they want me to rebuild their piano, and assuming I can do a good job for them, we will take in the contract.

You run a factory, where you have a different onus. However, I have two people besides myself in my shop. We do beautiful restoration work on old pianos here. No corners cut. And, I ALWAYS advise customers to consider buying a new piano instead of rebuilding their older one...new pianos are immediately available (whereas we are 1-2 yrs. backlogged) and the results are predictable in purchasing a new (or newer) piano.

That said, if I were to refuse work on pianos that might be improved by replacing SB's, I would be virtually guaranteeing that many old, quality, pieces of family history would be basically thrown out.

I think we've found a great balance in how we bid on work. I am brutally honest with my customers about their old Brazilian Rosewood Chickering grands that need restoration. In all cases so far, those customers have wanted their pianos restored, rather than tossed. Those customers, having the option described to them, chose NOT to have the SB's replaced.

Would their pianos be better with new SB's installed?? Yes, in most cases. But I have generally found that neither the will, nor the budget, to get that done exists with the pianos I restore.

Somewhere within this issue there IS a fine art to making a piano with an original SB a beautiful restoration.

BTW, we replace virtually ALL action parts, and purchase high quality strings and hammers for our restorations...we don't cut corners...

...but neither am I a "crook" for being willing to assist my customer in bringing their fine, old, family heirloom piano back to life...

You run a factory and obviously keep high standards. If I were spec-ing on Steinways or MH and offering them for sale, replacing a SB would be no contest...it would happen virtually every time.

We live in different worlds. There are hack shops out here, to be sure...it drives me nuts too...but my clients are my best source of rebuilding referrals...they know I bring to the table a very discriminating ear, a willingness to assist them at their level, and a standard that frankly costs more than the competition last time I checked. None of our restorations have ever left a client feeling "stiffed". Never happened, never will. They get the whole picture before we start the work, and make their informed choices.

I think we come from two different worlds. I respect yours, and if you were here in Michigan I would probably refer certain rebuilding customers to you...especially those who have pianos that deserve new SB's....er, that is, if you could quit implying that anybody who does what I do is a crook.... ;\)

RD
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#1269102 - 09/16/09 02:06 AM Re: Fascinating Steinway Phenomena [Re: RPD]
Inlanding Offline
1000 Post Club Member

Registered: 08/05/09
Posts: 1744
Loc: Colorado
The sound coming from this 1917 O Steinway is from a 92 year-old sound board with 92 year old treble strings and new GC bass strings.

This piano only required proper voicing and action regulation. The sound board has no cracks. I was told that cracks only mattered if they caused a buzzing sound and that it can be corrected with shims.

Action and voicing were the main concerns for the expert Steinway tech that brought it to life.

Recorded with a DM-10 and a cheap condenser mic. The humidity over the past few months this summer knocks some of the unisons out of whack after about a week, but it's still acceptable. You will notice the bass is a bit stretched because they are recent replacements and I only bring them back into alignment once every ten days or so when they get too far off.

Glen

Snippet of Moonlight Sonata Mvt 1
http://www.box.net/shared/zv6h8ej07a

C-min Improv
http://www.box.net/shared/elyyhcuzsb

F-min Improv
http://www.box.net/shared/v70msif9xr

Schumann Warum
http://www.box.net/shared/g70giix57h







Edited by Inlanding (09/16/09 02:16 AM)
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