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some comments interposed:<br>
<br>
Terry wrote:<br>
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<div><font size="2"><font face="Arial" size="3"><em>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. </em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em></font></font> </div>
<div><font face="Arial">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.</font></div>
</blockquote>
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. <br>
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<div><font size="2"><font face="Arial" size="3"><em></em></font></font> </div>
<div><font size="2"><font face="Arial" size="3"><em>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. </em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em></font></font> </div>
<div><font size="2"><font face="Arial" size="3">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.</font></font></div>
<div><font size="2"><font face="Arial" size="3"><br>
<em> If one's measure of rib crowning is a rib which has a
variable thickness along the unfeathered area and is taller than wide,
</em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3">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.</font></font></div>
</blockquote>
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. <br>
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<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3"><em>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. </em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3">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.</font></font></div>
</blockquote>
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. <br>
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<div><font size="2"><font face="Arial" size="3"> 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.</font></font></div>
</blockquote>
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. <br>
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<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3"><em>This may, or, may
not, be fortuitous but it is certainly useful as a counterpoise to the
"standard" approach typified by Steinway. <br>
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. <br>
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. </em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3">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.</font></font></div>
</blockquote>
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.<br>
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. <br>
<br>
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<div><font size="2"><font face="Arial" size="3"> <br>
<em> 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. <br>
Although I am not sure they qualify as RC&S boards, perhaps or
perhaps not, these boards certainly appear to be RC. <br>
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. <br>
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. </em></font></font></div>
</blockquote>
Here, again as frequently happens, a thunderous silence when
inconvenient and contrary facts are presented. <br>
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<div><font size="2"><font face="Arial" size="3"><em><br>
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. <br>
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.<br>
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. <br>
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. <br>
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. </em></font></font></div>
<div><font size="2"><font face="Arial" size="3"><em></em> </font></font></div>
<div><font size="2"><font face="Arial" size="3">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.</font></font></div>
</blockquote>
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. <br>
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.<br>
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. <br>
Regards, Robin Hufford <br>
<br>
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<em>Regards, Robin Hufford</em> </font></font></div>
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