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TECHNICALANOSUPPIY
DEPARTMENT
William Braid White, Technical Editor
Relation of the Soundboard With the
Fundamentally Correct Design in Scales
Faults in the Latter Section of the Piano Cannot Be Corrected in the Bellying De-
partment—Some Problems of the Tuners
ANY years ago ingenious persons tried
building soundboards for pianos without
ribs, by the process of putting together
two boards, the wood of one of which had
been matched at right angles to that of the
other. Frederick Mathushek, one of the most
remarkable minds ever bent to the art of piano
making, worked out such a plan with consider-
able success. For many years the Mathushek
piano has been built in this manner.
The Two Functions
The argument for a double soundboard is
strong. The ribs of the ordinary board act in
two ways, as girders and as transmitters of
vibrations. Owing to their slight curvature they
are able to act as girders to the board by sup-
porting and holding it up against the down
pressure inflicted by the strings, thus maintain-
ing its crown and its integrity of form. As
transmitters, they act to carry vibratory motions
across the grain of the board, thus partly over-
coming the difficulty of transmitting such mo-
tions, wherever arising on the surface, to all
other parts thereof. It is well known that the
rapidity of transmission across the grain is only
about one-fourth of the rapidity along the grain.
Now it should seem that if one were to take
two boards, and build them with grains run-
ning at right angles one to the other, the neces-
sity for ribbing would disappear. This, in fact,
is probably the case, but what is not clear is
whether the transmissive power is any greater
with this construction than it is with a single
board and ribs. It probably is not greater, how-
ever, because the motion must travel from each
of the two boards to the other across a film of
glue and through a 90° change of direction of
grain. It is evident that the two boards must
then be doweled together if this transmission
is to take place at all freely. And, that com-
plicates matters.
Ply-Wood
On the other hand I have recently seen a
piece of soundboard work which appears to
have some considerable promise. It consists of
a three-ply construction, being in effect three
thin boards, about % inch thick each, cross
banded and glued, with the usual ribbing added.
The vibratory powers of this experimental piece
of work are apparently very good, although it
is possible that they are not quite equal to those
of an ordinary board designed and constructed
in the best possible manner. On the other hand,
there can be no doubt whatever that such a
construction should pretty nearly settle, for good
the question of splits and cracks.
The ordinary soundboard is especially liable
to splitting and cracking, qji account of its
physical properties and the peculiar texture of
the wood, which together render it most suscep-
tible to the rather powerful forces of expansion
and contraction to which it is alternately sub-
jected. The ply-wood construction should have
the effect of diminishing this liability by very
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considerably increasing the resisting power
without, at the same time, spoiling the vibratory
capacity. The piece of work which I have seen
appears to satisfy these hopes to a considerable
extent.
A Fallacy
It would please me very much indeed to see
some good work done upon the improvement of
the soundboard, because, although a piano does
not depend for its acoustic value mainly upon its
belly work, it certainly can be spoiled quite
easily and quickly by any break down at the
belly. It is, of course, rather lamentably true
that many piano makers suppose the goodness
of a piano to be completely measured by the
kind of the work done at the soundboard, so
that other acoustical points may be safely
neglected. This delusion, for that is what alone
it can be properly called, is disastrously preva-
lent throughout the industry.
Now, as a matter of fact, a good scale will
in part atone for poor belly work, but not the
best belly work will make a fundamentally bad
scale give even nearly perfect results. No ap-
proach to perfection is even possible unless the
fundamental string design be correct. Given
such correctness, everything else will be easier,
everything will more readily fit into its place,
everything will be more efficiently done. For
the string is the originator of sound, and when
the string is well designed, the sound impulses
will reach the soundboard in the best possible
shape. If then the board he unable to transmit
them properly, it will at least have received
them as they should be, and its subsequent
feebleness of treatment will show rather as an
imperfect approach to a well ascertained goal
than as a brave attempt to reach a result by
impossible means. For if the string plan is
wrong, no combination skill and construction in
the belly work can possibly give us results
comparable with what we should certainly get
if it be right. The string plan is the founda-
tion, and must be right if the piano is to be
right, and not merely nearly so.
These experiments on soundboards would be
more frequent and more fruitful if what I have
been saying above were more generally under-
stood than it is. If we could all come to an
agreement on known acoustic facts, instead of
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TUNERS' TRADE SOLICITED
Kansas City, Mo.
William Braid White
Associate, American Society of Mechanical
Engineers; Chairman, Wood Industrie?
Division. A. S. M. E.; Member. American
Physical Society; Member, National Piano
Technicians' Association.
Consulting Engineer to
the Piano Industry
Tonally and Mechanically Correct Scales
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33
obstinately pretending that these do not apply
in this or that particular case, we should all be
better off. Then we could go on rationally with
our soundboard improvements, because we
should know that the true function of the board
is amplificatory. The business of the board is
to amplify, and that is all it is. If once we
could all see that, we should also sec that our
scale must first be right, and we should de-
vote ourselves to making tone through the im-
provement of the scale, leaving the board to
its proper function, and then too we should be
able to experiment upon a clearly defined work-
ing hypothesis as to the function, the nature and
the objectives of the soundboard. That, lastly,
is why I am interested in any soundboard ex-
periments which show that workers understood
these things and are proceeding in the right
direction.
Just Intonation and Ratios
"I note in the issue of October 1
Mr. Waugh's letter about diminished fifths
and augmented fourths, together with your
answer thereto.
"The ratio of a diminished fifth is 36/25, be-!
ing lower than the perfect fifth by the ratio
25/24.
An augmented fourth should be just
this amount higher than perfect, making the
interval 25/18, which is an inversion of 36/25.
The interval 10/7 comes only where use is made
of the true seventh, or from the seventh partial
or its multiples. Taking, for example a seventh
chord such as C, D, F sharp, A, in just intona-
tion, the relation of F sharp to C equals 10/7
which is easily proved by figuring up the partial
tones. Jumping up or down half an octave to
Ab, C, Eb, Gb, the relation of Gb to C is found
to be 7/5, which is an inversion of the other
10/7, although between them is a difference
equaling 50/49. In the equal tempered scale
no such difference exists, for the interval is the
same wherever found, and is expressed by the
decimal fraction 1.414213.
I hardlv agree with you in saying that the
difference between 36/25 and 10/7 is negligible.
This difference is best expressed to my mind
by the ratio 126/125, which at middle C would
bring a difference of over two vibrations per
second, rather more than we fin^l in the major
third of the tempered scale.
"Your further comment was most interesting.
(Continued on fa()c 35)
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