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some comments interposed:
Terry wrote:
> Personally, I think Terry is right when he makes the point that rib
> crowning and compression crowning are just two extremes on a
> continuum of possibilities. Although it may indeed be a trivial
> distinction, the feathering at the ends of a rib on a compression
> crowned board, where such exists, means, functionally at least, an
> element of similarity to a crowned rib.
>
> Appears to me you are pointing out a similarity rather than a
> distinction. Yes, both designs are commonly made to be more flexible
> around its perimeter.
Whether it is a similarity or a distinction, occasionally, one sees a
board with no feathering at the ends of the ribs. I have never thought
much of the sound of these pianos, for what it is worth. The point,
though, was that the feathering at the ends of the ribs, in flexural
terms, has a similar effect to a crowned rib. Personally, I believe
feathering functions as a means of control of energy resistance, as I
have said before.
>
> As far as I can see, the only truly compression crowned boards would
> be those with unfeathered ribs, which I have seen on just a few
> pianos, one of which was a small Mehlin, if memory serves.
>
> One could easily build a "truly compression crowned board" with either
> tapered or untapered ribs. One could easily build a rib crowned board
> with both types of ribs. Rib tapering does not determine soundboard
> construction.
>
> If one's measure of rib crowning is a rib which has a variable
> thickness along the unfeathered area and is taller than wide,
>
> That is not a measure of rib crowning. Rib crowning is a product of
> shaping the panel side of a rib into an arc. Rib taper does not
> necessarily have nothing to do it, nor does rib cross section.
Although I did say above variable thickness along the unfeathered area,
what was intended was variable height, as the following text
suggests. This is, to me an indicator of rib crowning and is what I
intended. I give no consideration to taper, per se.
>
> then there are any number of older pianos out there with this
> characteristic. Particularly noteworthy, are the pianos of Chickering
> from about 1900 where, in their production they explored the use of
> various radii, altered rib scaling, shorter or longer ribs, larger or
> small average cross sections, larger or smaller treble sections,
> etc. The late 123 has one rib, again if my memory is correct, which
> varies in thickness by almost a quarter of an inch. Much of what is
> represented here as novel, again with all due respect to those who
> think so, appears to have been anticipated a century or so earlier
> through the efforts of this firm and the present "new" school of
> design now clamorously present as "modern" seems, in amazingly similar
> ways, to recapitulate the technical evolution of this firm.
>
> I have read repeatedly on this list how pretty much all of what is
> being done with rib crowned soundboard designs and rim modifications,
> etc. have all been done before. These have been discussed ad-naseum.
Equally ad-nauseum are the chronic claims of dysfunctionality of all
other methods, never long absent, although, this has somewhat moderated
over the last several years.
> Certainly some new thining is also going on here, but the nuts and
> bolts of it are clearly recognised as having been used again and again
> in the past. I think what might be novel here, at least considering
> the last 80 years or so, is that anything different from what that
> famous NY manufacturer does could possibly be worthy of consideration.
It is a complete source of amazement to me that any could consider me to
be a defender of the status-quo with Steinway, or any other
manufacturer, for that matter. Yes, the redesigners must climb an
unfair, unrealistic and determined obstacle should they wish to place
their pianos on a par with Steinway, or in the concert world. They have
my sympathies and encouragement. Still, so must any other rebuilder who
may wish simply to bring the pianos to a level they once exhibited, by
the simple expedient of using different actions and hammers, for an
example, instead of the disgraceful junk masquerading itself as high
quality actions and hammers, both on pianos out of the factory and those
rebuilt using the factory methodology at local dealerships. The
burden is the same for both.
>
> This may, or, may not, be fortuitous but it is certainly useful as a
> counterpoise to the "standard" approach typified by Steinway.
> The Boston school, as it were, of piano manufacturing, versus,
> say, that of New York, as a whole displays a greater similarity in
> this regard to English pianos while that of New York appears somewhat
> more similar to those of German ones, although, of course, Mason &
> Hamlin, in some aspects, at least in their independent production, is
> an exception to this generalization. Broadwood's ribbing, at least on
> the four or five mid 19th century pianos I have observed appears very
> similar to that of Chickering, even though I did not measure the rib
> heights looking for variations there. Nevertheless, I feel fairly
> comfortable asserting that rib crowning has a long history, predating
> even 1900 and would be more associated with English pianos in this
> regard; German pianos may well have favored the thinner, wide rib
> used in compression crowning.
> It may well be that, in the United States, the collapse of the
> piano industry in the third and fourth decade of the last century and
> the subsequent unchallenged preeminence of the New York school has led
> to the illustion that there has been no alternative to the crowning
> methods used there, which I think is markedly incorrect. Rib crowning
> has a long history and appears to have been well explored.
>
> I would agree with this, however, I might suggest that whereas "rib
> crowning has a long history and appears to have been well explored",
> it has perhaps not been thoroughly explored in the past.
I agree that it may well have much in the way of possiblities yet to be
developed. Particularly, as I am, as most no doubt are aware, a big fan
of Chickering pianos many of which are rib-crowned and which I consider
at least the equal of any Steinway.
It is the condemnation of the CC methodology as being virtually
dysfunctional which I disagree with and consider completely unrealistic,
inappropriate, and unfair, and will continue to consider so.
>
> There is no doubt that Chickering pianos exhibit substantially
> less cracking than those of Steinway. This appears to be consistent
> with the claims of the RC advocates. It is interesting to note that
> cracks in Steinways, in general, are significantly wider at the top
> surface of the board, as most know, than they are at the bottom which
> seems in keeping with the compression crowning view of tension on the
> top of the board and compression on the bottom; cracks found on
> Chickerings show dramatically less widening through the section of the
> board.
> Although I am not sure they qualify as RC&S boards, perhaps or
> perhaps not, these boards certainly appear to be RC.
> I have urged the view before that it is inappropriate to apply
> simple elastic moduli indiscriminately as is done here when using them
> to make a few modest calculations which are then generalized to the
> conclusion that damaging levels of compression are inevitable, much
> less, even achievable in ordinary soundboards, be they RC or CC.
> First and foremost as the intrinsic condition of every soundboard is
> one of a very complicated, idiosyncratic, triaxial stress distribution
> and not one of uniaxial or plane stress, plane stress moduli are
> inappropriate to the facts, yet these very moduli are used by those
> urging the validity of compression damage.
> What is the Fiber stress at proportional limit which is what is
> quoted for disabling cross grain compression? It is simply the point
> at which elastic action ceases and the material will be incapable of
> achieving, when freed of compression across the grain, its previous
> dimensions. This by no means is a point of "cellular crushing" or
> destruction which is so often claimed here. The net result of such
> an effect, should it occur, as Richard Breckne has just pointed out in
> a recent post is, simply an increasing density and increasing strength
> which, no doubt, increases the acoustic velocity somewhat, and, again,
> may allow an actual improvement in the perceptual aspect of tone
> quality or have other beneficial effects absent other structural
> failures in the soundboard panel.
Here, again as frequently happens, a thunderous silence when
inconvenient and contrary facts are presented.
>
> As I urged last year those interested in such things should take
> the various manuals which, at one time, were suggested to contain the
> material upon which such a claim of damage could be based and
> familiarize themselves with them. One will find, should one do so,
> for example, that the coefficient of variation were this simple
> property, that of cross grain compression strenth, applicable,
> according to The Encyclopedia of Wood is 28% which means that
> attempting to make any kind of precise extrapolation from the results
> of such a calculation is unreliable and inappropriate. As for an
> empircal indicator, I have never seen, in thousands of pianos a
> significant change in the circularity of nosebolt holes found here and
> there in soundboards, which, were such a level of damaging
> "compression set" as is frequently assumed here, underway, would be
> likely to develop a significant eccentricity and become elliptical
> with a major axis parallel to the grain.
> In my opinion, crack formation in older, high quality soundboards
> is, in most cases, the result of shear failure and stress
> concentration, and not an indication of previous compression ridging,
> followed by drying and the opening of a crack. Compression failure,
> per se, in my opinion, is more likely to be found in more modern
> boards that have been ribbed at too low a moisture content.
> Loading of a crowned, or even uncrowned, soundboard along both
> sides the bridges asymmetrically by the downbearing pressure, and
> their interactions, inevitably introduces additional significant
> shear on both sides of the bridges, in every case, which ranges with
> moisture fluctuations and downbearing load. Stress relief over time
> results in the very commonly found long crack or two or three or four,
> etc. running sometimes as a chord between the ends of the bridge or,
> sometimes, parallel to it a few inches away. Where the shear is
> greater, for example boards with a tenor bridge, a characteristic
> field of cracks may well develop. According to the selfsame
> Encyclopedia indicated above shear parallel to the grain is virtually
> the weakest property of wood. Combine the high shear levels in this
> area of the board with the weakness of the material in this regard,
> high moisture levels, the possiblity of detached ribs and throw in an
> additional factor: the stress concentrating effect of nosebolt holes
> that are found commonly in this area and you have an efficient
> mechanism for crack formation. It is this shear field that accounts
> for the non-random placement of cracks in boards and their association
> with nosebolt holes as it is extremely common to find a crack
> originating in a nosebolt hole and, sometimes, even the screw holes
> used for screws attaching the guide rail . These are not random
> events.
> A second mechanism for crack formation exists in the classic
> interaction of the differences of radial and tangential shrinkage and
> expansion along with the effects of grain angle which produces
> warping in free boards. Even though the flitches are laid up with
> grain angles aligned to minimize this, these efforts are only
> partially effective and differential stresses, unique to each
> individual flitch are still present in the completed panel which work
> their effects over time. These effects are to separate the individual
> flitches along the joint. I would argue that most cracks fall into
> either of these two categories and are not, themselves, the results of
> "cellular crushing or compression set", although a lot of newish
> pianos nowadays very plainly show compression ridges.
> I don't mean to imply that soundboards cannot undergo significant
> functional failures; of course, they can and do, but these are not
> failures of the wood material itself but, rather, structural failures
> of aspects of the panel assembly: the most important of which, in my
> opinion, is detachment of the soundboard from the ribs, bridges or rim.
>
> Build a few panel models and expose them to humidity extremes. Measure
> changes in crown. Observe crown/shape recovery. Such an activity is a
> good way to learn about "compression set". Soundboards can get
> squished with enough compression and enough time and do not recover to
> their origninal shape.
I don't have to build a soundboard; I can look at one in my shop, out of
a piano, to see such things. Plentiful observations can be made on other
boards as well. Some of these are that, in general, creep found in
most of these boards does not dramatically, others factors being equal,
degrade their acoustic capability over time, nor is the material in the
boards ruined. The dictum that the so-called "compression set" used
here equals damage does not seem at all realistic to me. At one point
for example, repeated arguments were made that boards easily exceeded
the c. 580 lbs rating for Fiber stress at proportional limit for spruce
undergoing cross grain compression, people were unwares of this, hence,
they were not aware of "compression set" and should educate themselves
by understanding wood technology. This "set" is taken as a given and
as being synonymous with and a demonstration of failure on the part of
nearly all older pianos.
Well, I am, in fact aware of these data, and others, and this
generalization is, in fact, incorrect for any number of reasons, a
simple one being the one given above which was disregarded. I have
pointed out others. Another, for example, creep, that is time-dependent
distortion, is not simply a function of compressive stress by any
means, nor is it synynomous with either cellular compression or damage,
nor is it a given that is suggests any failure of acoustic properties
whatsoever. And another, among the many: the effect of ring angle in
which the relationship of load to ring angle is an additional factor in
determining cross grain strength. Completely disregarded here, when
taken into account properly, this will result in the fiber stress
proportional limit being increased by approximately a third under
conditions found in a piano. So when generalizations, and, as I said
before, simplistic calculations, themselves frequently contrary to the
experience of many, based upon what appear to be simple
misconceptions are used to condemn virtually all older soundboards it
should be no surprise that controversy results.
I am, myself, astonished that offense is taken when such is
pointed out, as the great difficulty inherent in contending with the
established companies in the industry, loudly lamented over and over
again, a valid complaint indeed, would suggest a better course: using
the list for what it is and should be: a treasure trove of information
to be mined by all and from which can be sifted a continually
improving understanding of facts and techniques, at the pleasure of the
reader, rather than the source of disruptive antagonisms provoked by
mere disagreements, the fact of which, whether agreement or
disagreement is of no significance whatsoever.
Regards, Robin Hufford
>
> Regards, Robin Hufford
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