Richard,
As you have well explained below the difficulties inherent in the idea of the bridge
physically moving the bridge and hence the soundboard are substantial. We could spend much
time analyzing such claimed motion only always, I think, to arrive at a point of throwing
up our hands and saying that it is, as you say, fantastic in nature to think such could
explain the energy transfer between string and bridge/soundboard due to the enormous
complexities that should trouble any analysis.
The Ripple Theorists and their 'notion of motion" would have us believe of course,
that just so happens, and that this enormously complicated motion, laden with complexity of
every kind and degree then moves the soundboard thereby radiating sound away from the
system, a sound I might add, that is periodic, and, therefore, relatively simpler than that
suggested by the behavior of a chaotic bridge. Argument being, apparently, inadequate,
let us look for a moment at a certain piano.
In my shop I have a a piano I have owned for some three years now. It is a
Chickering 123, I believe, it is the "B" model. Perhaps, it may be the "C". (Where are
you? Jack Wyatt). The piano was built around 1919. It is about 6'6'' long. Admittedly,
some will say this was during the period of the decline of Chickering. That it was a period
of change I would not argue with but I would not necessarily characterize this period as
one of decline, although it is true they had begun the gradualization capitulation to the
tenents of the Steinway style of design which eventually rendered them just another piano.
. The piano is a round tail piano and although substantially similar to, demonstrates
some differences, from the 123 of 1900 or so.
Almost anyone hearing this piano, even unrebuilt as it is, is struck by its unusually
powerful, musical tone, particularly in the bass. Having the typical 25 note bass, it has
the usual Chickering superiority of the period as regards the transition problems normally
found on Steinway and Steinway-style pianos. While the reader who only sees words and must
rely upon them to conceive of the tone of this instrument is limited by their inadequacy in
such things, the vast majority of people who in fact hear this piano are greatly
impressed and moved by its tone. They spontaneously comment upon it. The transition
region through the bass and tenor is very much substantially better than the competition,
as one would expect of a Chickering of this period, although, for what it's worth, in 30
years of working on pianos and 45 years of playing them, encountering a complaint as to
transition problems from pianists is an extremely unusual event. This is, of course,
another subject.
This piano exihibits most pertinent and unusual characteristics. The long bridge on
this piano is glued to the soundboard for about 3/5ths of its length in the usual fashion.
At this point the underside of the bridge has been relieved completely, apparently before
installation. A gap exists between soundboard and bridge. The bridge FLOATS in three
sections, suspended above the soundboard for a distance until each section reaches a small
platform from whence it repeats this configuration until reaching the end of the bridge.
The bridge root itself is a vertically laminated structure with a somewhat larger than
ordinary cap. Both laminae and cap are maple. In comparison to the methods of Steinway
who bent and continue to do so, their bridge root to shape, Chickering apparently laid up a
panel of vertically laminated material and then cut from this panel the shape of the root,
imposing curvature by bending mostly at the tenor end. This is evident from the runout
of laminations visible at curves on the side of the bridge, a characteristic feature noted
on Chickerings from this and prior periods.
Where the bridge ceases to contact the soundboard a gap exists between the bottom of
the bridge and the soundboard. This gap is about 3/16 of an inch. THERE IS NO CONTACT OF
BRIDGE AND SOUNDBOARD IN THESE REGIONS. The bridge continues, suspended above the
soundboard for c. 6 1/4 inches and carries four trichord unisons above it, at this point
the relieving ends and a platform has been left in which is contact with the soundboard.
The footprint of this platform is c.1 and 5/8 inches wide; its shape is not normal to the
long axis of the bridge but, rather, curves towards the tail end of the piano. The area
of this footprint appears to be a section of a radius of curvature of approximately 2 1/2
inches and crosses from one side of the bridge to the other. It is not added material,
but, rather, the remaining part of the root itself, that is part of the bridge root that
the relieving had not cut away. These footprints carry at least one trichord unison and
part of another themselves.
The bridge is similarly suspended again in a repeating section; again NO CONTACT for
c. 6 1/4 inches as a void exists between the bridge and soundboard which is, again,
carrying four unisons above it; the configuration of the unisons to the end supports of the
section are essentially the same as in the first section although slight differences can be
detected in placements; once again the relieving ends; a footprint appears as described
above. It carries a unison, or depending upon perspective can be said to support one and a
part of the next unison, as had the first platform. .
The relieving resumes; for now the third time the bridge is suspended but it now
begins to curve at a greater rate to the left where under the third unison, counting from
the beginning of the relieving on the treble side of the piano, it once again comes in
contact with the board. Contact resumes. The end of the bridge per se is found here
although the root, now reduced to a little over a quarter of an inch in height, runs on up
under the plate for approximately 3 and 1/2 inches or so. It is possible to inspect here
the laminae of the root itself; these are, as I said before, maple. Five are approx.
5/32'' in width, the sixth and seventh appear to be c. 1/4, and the last is but 1/16. A
cursory measurement indicates downbearing is adequate throughout the scale. There is
virtually no cracking in the board. The width of the bridge is 1 1/4 inches, its height 1
1/8 inches. A Steinway 0 sitting nearby measured exactly the same, as did a Steinway A
from the 1890's.
I would suggest that those believing the bridge motion/soundboard ripple theory
would be well served by contemplation of this entire structure. Particularly pertinent
are several facts - there is no difference in the sound of the unison where the gluing
stops, that is, the one contacting the soundboard in the conventional fashion and its
neighbor, or the others. The one is in contact with the bridge which is glued directly
beneath to the soundboard, the other no longer has any contact with the board beneath it
and in this case, and others there is no possiblity of the bridge moving the board
directly. That is, it must move a point of contact with the soundboard which is removed
from it and separated by an intervening set of strings, yet the sounds are the same. This
applies to all of the unisons whether supported or not. Other than great richness and
beauty of sound, this piano appears to be just another instrument. There are no jagged
discontinuities in sound where the unisons are spaced - some now directly in contact with
bridge, itself in contact with the board underneath, or left floating attached to a bridge
suspended at some greater or lesser distance from a point of contact, as would necessarily
have to exist if the ripple theory were correct.
Regards, Robin Hufford
Richard Brekne wrote:
> Robin, JD, Phil, etc...
>
> I Have wanted to find time to write down a few thoughts on this thread for a while, but
> Christmas and other concerns have prevented me from doing so until now.
>
> Any ways... this rocking bridge tangent has really caused a lot of trouble relative to
> the original discussion. We were really talking about the mechanisms that govern the
> transfer of energy from the strings to the rest of the system and how that results in
> the generation of the sound we hear. We had two basic ideas presented about that in
> general.
>
> One was a rather straight forward view of the bridge being physically moved, resulting
> in the sound board being moved and I have to re-read these posts from Ron on the
> "ripples" to make sure I have understood him rightly. I believe however the idea was
> that the strings movement resulted in the propagation of transverse waves within the
> system and it was these that were primarily responsible for the generation these
> "ripples" which in in turn generated the compression waves we hear as sound.
>
> The other "theory" was a bit more difficult to grasp on the surface of things, though I
> still fail to see what about it makes it so easy for some to write off without further
> ado, unless it is exactly because it is difficult and perhaps also because none of this
> is so necessarily relevant to us above and beyond being interesting and stimulating.
>
> In any case I would like to look for a moment at the first of these two "theories".
> Partially because it has been described as "simple Newtonian physics" in nature,
> partially because I have some unanswered questions in my mind about it.
>
> One problem with this is the actual movement itself, whether up and down or forward and
> back at some point such movement will become significant enough to affect the tension
> of the strings while they are vibrating. This may seem insignificant at first glance
> but it can hardly be so. Either the movement of the bridge is so small that no
> measurable frequency change can be effected, or whatever movement there is must occur
> in some other fashion which results in a stable frequency for the string. In the first
> case one needs to ask then if the bridge movement is so small, then how can it at the
> same time be enough to "cause" all the system movement that results in sound ? In the
> second case we have a really interesting mechanism going on that somehow allows the
> vibral amplitudes of both bridge and string to be large enough to affect one anothers
> pitch, yet functions in such a way as these are stable. Neither of these eventualities
> has been explained or satisfactorily dealt with throughout this thread as far as I can
> see.
>
> Another problem is the whole idea (and premise for further reasoning) that the bridge
> will move up and down 440 times a second for a string tuned at that frequency. There
> are a number of reasons why this idea should be suspect, and these require adequate
> attention shall they be resolved. As previously stated, there is a certain tendency for
> coupled strings to counter act each others motion. Secondly a single string does not
> just vibrate up and down to begin with. It vibrates on many planes both up and down,
> sideways and all around so the effect on the bridge cannot possibly be as described to
> begin with. Thirdly you have the matter of partials. They originate in the string, and
> are determined by the strings inharmonicity. At the exact point of stress exertion on
> the bridge, all of these string segments are moving in their own paths and frequencies
> and thereby exerting force on the bridge in their own way. If we accept then without
> further consideration the basic premise of this "theory" and relate it to this last
> fact, we have to explain how a bridge can be moving both up and down at the exact same
> time. For that matter we have to explain how the bridge can move in all the
> conflicting directions the strings segments move in at the exact same time. One could
> be tempted to write this off by explaining that this is exactly what the string does so
> why shouldn't the bridge do it. But the bridge is not stretched to any particular
> tension and has nothing akin to the strings inharmonicity in this regard. And if it
> did, well we would have a problem with all the other string frequencies.
>
> In fact... the more one really starts to consider the implications of accepting the
> idea that it is transverse like movement of the bridge which drives the board into the
> movement necessary to create the sound waves we hear.... the more fantastic the whole
> thing becomes. In any case it removes itself completely from some concept of simple
> Newtonian physics. No matter what way you look at it we have some very complex
> mechanics to explain if we are to stand up and say "This is how the sound board works"
>
> Another point to be considered is how to define transverse wave movement in the case of
> the bridge to begin with. Transvers wave movement is defined as wave movement
> perpendicular to the vibrating medium. Does this "up and down" movement satisfy this
> definition relative to the bridge really ? The bridge is then "defined" as a medium
> which is physically and at all times in every sense perpendicular to the wave movement,
> by reverse implication.
>
> None of which means that this model is wrong. It's just that we haven't explained these
> and other issues yet, and until they are explained we remain as much in the realm of
> speculation as we are in the realm of theory by my understanding of the terms. Nor does
> any of this necessarily mean much to the actual process of building pianos. I think it
> was Ron N who said straight out that he (and others) do not think about the issue of
> how sound is actually created, transmitted, transmuted, transduced...whatever..... from
> the strings to the board to our ears when designing a board. Further sound boards have
> been produced with similar results for quite a long time indeed, despite widely
> differing views on this issue.
>
> Still, it remains an interesting topic for anyone who is fascinated by such things and
> the fact that no one has yet managed to truly explain these things beyond reasonable
> doubt does not change that fact.
>
> I plan on re-reading much of this thread as there are some similar things about the
> other so called "theory" I have questions about as well... but this is more then enough
> for this time around.
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no
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