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THE
JULY 19, 1919
MUSIC
TRADE
13
REVIEW
OurTECHNICAL DEPARIMENT
CONDUCTED BY WILLIAM BRAID WHITE
of the bass bridge will come always so close to
the edge of the sound board that the motion
transmitted to the board will impinge at the
worst possible place for good results. The very
Written for Piano Makers, Technicians and Tuners by William Braid White—Twelfth Article
woody tone noticeable in some pianos towards
I have mentioned the bridges before now, but imposing a load on the sound board quite out the lower end of the scale and the extremely
only in a very light manner. It, however, will of all proportion to the acoustic results ob- dead tone at the last few strings may be ex-
plained in this way principally. The remedy is
be worth while to say a few words in further tained from it.
to
cut out the bridge so that its lower end does
detail. Let it be understood that in writing
Now, in order to put the bridge in the best
these articles I am stressing throughout the possible condition to conduct motion from string not contact the board directly and to build out
fundamental elements of tone and am trying to board it would seem evident that the weight a supporting apron which shall touch the board
constantly to keep the reader's attention fas- of the structure itself ought to be reduced as further up towards its middle.
tened upon these elements. No matter what much as possible. This can be done in two The same procedure, of course, is implied in
part of piano construction we are discussing, I ways. It can be done by substituting metal what was said above about stepping out the
have been careful to consider it in the light of for wood. It can also be done by cutting down bridge at the break. If this is done the ex-
its physical functions, as these may be ex- the size and weight of the wood in every way tremity of the bridge will be left in the air
and it will be necessary to use a supporting
pressed in terms of acoustics. Thus, in speak- possible.
apro
l also. Excellent results wilt then surely
ing of the sound board, it has been necessary
Some years ago no metallic structure would
to consider the element of the p:aio in terms have been practical, but to-day, with the im- be attained.
The general problem of the sound board is,
of harmonic motion. In precisc'y the same way provements which have been made in the alloy-
we can best, for our purposes, consider the ing of aluminum and with the invention of the of course, to provide a tone amplifying apparatus
function and construction of the bridges by ex- piocess known as die casting, it seems prob- whose motions are determined by the motions
pressing them in terms of the conduction of able that a bridge could be produced of this of a battery of strings forming a tone-selecting
motion from string to bridge.
nature which would be lighter than wood. If it apparatus. This tone-amplifying apparatus will
The function of the bridge, whether it be on were made in hollowed-out, arched form it have a certain period of vibration proper to
the sound board or on the plate duplex, is to would combine lightness with strength. Such itself, but this must be as little powerful as may
The vibratory capacity must be high,
support and conduct alike. It must support a bridge could be built with the bearing for be.
and.
above all, the natural wave-form of
the
strings
cast
right
into
its
surface
and
might
the strings between their tuning and hitch
pins, while determining also their lengths, and be considerably narrower than the wooden the resultant pf any number of string-vibration
at the same time conduct their vibratory motion structure. A great deal might be promised forms must be preserved free from the intrusion
to both sound board and plate. The motion of of such a bridge. It would be a better con- of extraneous forms induced by peculiarities in
the plate constitutes an element in the general ductor, it would load the board less than the the structure of the apparatus. The board, in
tonal complex which must not be overlooked, wooden bridge now does and it would distribute a word, must reproduce, but not originate;
although it frequently obtains much less recog- the motion better over the surface of the sound must amplify, but not modify.
A board such as we have described, then, must
board.
nition than it deserves.
have
the greatest possible freedom of vibra-
The great and crucial question here, however,
Now, the bridge being obviously and function-
ally a conductor it follows that its construction is not one of design, but of expense, and must tion, be loaded by ribs and stiffening bars as
little as possible and have to carry the smallest
ought to be considered from this standpoint be settled by trial and experiment.
mainly. But we know that in the past the bridge
However, much has been done, and very suc- possible load of bridge. It must be highly ten-
has not been so considered. Of course, during cessfully, too, in the way of lightening the sioned and in order to give and maintain a good
the formative period of piano construction the wooden bridge by the process of "stepping" out, down-bearing for- the strings it must be arched.
The sort of board I should recommend is one
many false hypotheses which from time to time as it is called. According to this idea a bridge
sprang from fertile brains and flourished till is not laid flat along the board, but is scooped which is built up of spruce evenly grown, in
their falsity was exposed were responsible for out along its lower surface so that it meets the which the rings of hard and soft texture suc-
producing all sorts of freak ideas in regard board only at a number of determined places. ceed each other at nearly equal distances. This
alike to the bridge and to the sound board. It is, in effect, set on the board much as a board should be quite lightly ribbed if the piano
The general notion of bridge construction has bridge is set on piers which rest on the bottom be a low-tension instrument and should have a
been bound up, naturally enough, with the no- of a river. This method of setting the bridge stepped-out bridge. It should be well arched
tion of wood as the only possible material and on the board has special advantages at the and fastened to the edges of the back upon lin-
in consequence the structure evolved after many break where the treble bridge ends and the ings made as wide as possible. Other details
years of experiment is both clumsy and heavy, bass bridge, begins. By stepping out at the will suggest themselves to the practical piano
break the disagreeable tone quality at this point man at once.
Very little has yet been said as to the influ-
is often entirely eliminated. The reason, of
course, is found in the fact that the bridge ence of the plate and the back upon the ele-
at the break is often, or usually, too heavy for ments of tone. But it is surely evident that the
It makes varnish appear new and prevents cracking. the tension of the shortened strings, and in con- vibration of the plate must be more intense than
Hundreds of American dealers use and indorse it.
SOLD ON A MONEY BACK GUARANTEE.
sequence does not transmit rightly in response that of the back, due to the greater rigidity of its
Price, 1 doz. 7oz. bttle. $2., 1 gal. $1.75, % gal. $1.,
to
them the motion they originate. The bridge, material, and that, on the contrary, the great
1 qt., .70. LESLEY'S CHEMICAL CO., Indianapolis, Ind-
too, is thus loaded excessively and needs to be weight and extreme massiveness of the back
relieved at this point especially. "Stepping out" h;ive a deadening effect.
I do not think that a full iron plate has any
the bridge does relieve this load with the hap-
effect on tone worth considering. The plate
piest results.
is a supporting structure and its effect upon
In exactly the same way the bass end of the
(Continued on page 14)
Individual pneumatic stacks, roll
piano needs special treatment. The lower end
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Old style bridle strap
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