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TEOMCAL^SUPPIY DEPARTMENT
William BraidWlute,7ee/imcalEditor
Experience and Experiment in the
Investigation of Acoustic Practice
Some Considerations on the General Methods to Be Followed in Developing the Fur-
ther Scientific Investigation of the Tone Quality of Pianos
T
HERE has recently been completed and
installed in my laboratory a simple but
very useful type of monochord especially
intended for investigating the behavior of piano
.strings. The instrument was built by the
(iaertner Scientific Corp., of Chicago, after my
own designs.
Essentially, this monochord may be called a
one-string piano with a movable bridge. It
consists simply of a channel steel base-plate
six feet long and about eight inches broad, at
either end of which is a steel angle plate ris-
ing some six inches, and a strip of resonant
pine wood, also six feet long and as wide as
the base plate, fastened to the two angle plates.
Above this "sound board," on beds fastened
to the angle plates, are arrangements for
fastening the two ends of a piece of piano wire
or a bass string. One of these fastening
damps is directly attached to a dynamometer
which shows by direct reading the amount of
pull exerted on the string. The other clamp
is attached to a threaded* shaft, whereby the
string may be stretched, and so tuned, at will.
A slot is cut in the sound board, through
which may strike upwards at the string a one-
key grand piano action model resting upon
the bass plate. This slot is long enough to
permit the stroke to take place at any point
from one-half the length upwards of a string
as long as seventy-two inches. A sliding
bridge, with staggered pins giving side-bearing,
enables the experimenter to set off any
vibrating length from one-fifth inch to seventy-
two inches.
The object of this monochord is to facilitate
investigation of the effect of changes in length,
in loading, in tension and in striking point
upon the quality of sound given out by strings.
Experience and Experiment
Hitherto, as we all know, the existing data j
on these matters have been obtained as the'
result of slowly accumulated experience in the
best shops. These experiences have in some
cases been reinforced by means of definite ex-
periments undertaken for the purpose of es-
tablishing data from which practice may be
built up. It is, however, correct to say that
most shops have been content' to follow the
lead of their more enterprising competitors and
to accept the general practice of the industry
as binding upon themselves. It is the purpose
of the laboratory in which this new instrument
has been installed to initiate the substitution
of direct and definitely established facts ap-
plicable to all cases, for the necessarily incom-
plete and imperfect data which alone can be
expected from experiments under a single set
of shop conditions. In other words, it is the
purpose of the laboratory, among other things,
to do what can be done to provide the piano
industry with reliable and basic engineering
data from which a wise, practical, scientific
system of design ran be worked out.
Punching!
Washers
Bridle Straps
5814-37th Ave.
Everyone, I suppose, is aware that the
acoustic practices of the piano industry show
very wide variations in almost all details. In
>o far as these variations are based upon
definite conceptions of tonal quality and quan-
tity, and so represent positive and deliberate
attempts at realizing these conceptions, they
are admirable; and it would be presumptuous
as it would be absurd to interfere with them.
In so far, however, as variations in acoustic
practice are based merely upon insufficient
knowledge, backed up by insufficient and one-
sided experience, badly co-ordinated and im-
perfectly digested, in so far, that is, as these
practices are the results of imperfect knowledge
and understanding, they are fit objects of
criticism, and one of the tasks of a research
laboratory should be to lay bare their pre-
tensions and discover just what mixture of
truth and "of error they contain. So much, I
think, will be admitted by all.
Two Routes Open
For the investigation of acoustic practice
'wo routes are open. We may begin by going
straight at the motions of the separate (as-
sumed) mathematical particles of which a string
may be considered to consist. The mathe-
matical methods of Rayleigh or the experi-
,mental mathematico-electro-physical methods of
the new acousticians such as Crandall of the
Bell Telephone Laboratories may be followed.
In any such case we shall obtain formulae
embodying to a close degree of accuracy the
precise factors which together make up the
behavior of a string, of a sound board or of
both, in any given set of conditions. The re-
sults obtained, however, will at once be found
to involve refinements which, at file present
stage of piano Construction, are simply beyojjjjj
our ability tb~*]j(se. To take a simple example:
any question o"f striking paint must take into
consideration the length of,, wire which is cov-
ered at the place of contact -by the striking
instrument when the blow i<* struck. Mathe-
matically we shall find that the -1-en-gth of the
fraction of the surface which is Struck by the
hammer makes all the difference in the world
to the result; and If we visualize the wave or
sound in any such case we shall obtain ocular
example • of • the fact-*.-. Yet, when wo take up
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i lie question as applying to practical piano
construction, we shall find that we cannot con-
trol the conditions closely enough to make
any practiccil use of our formulae. In other
words, a great deal of what we bring to light
in our equations must be left out of con-
sideration because the instrumental error is
too great. We can, therefore, use the more
highly refined methods of investigation and
analysis only so far as our instrumental errors,
that is, our errors of construction and our
crudities of design, permit us to use them.
And that is not far enough for all the trouble
which has to be taken in order to arrive at
the formulae.
Crude but Useful
The second route open to us is less refined;
but in the present state of the art is more
likely to give us what we arc seeking, namely,
practical improvements in existing acoustic
practice. That method is simply to take the
materials with which we have to work, ham-
mers, action, strings, sound board, etc., and
investigate the possibility of reducing to sys-
tem our knowledge of their ascertainable
variations of behavior under parallel variations
in methods of construction and design. To
put it in another way, we can investigate the
changes in behavior which can be brought
about by such changes in design and construc-
tion as are within the present-day practical
capacity and willingness of the manufacturing
end of the industry.
Such an aim is relatively narrow and ad-
mittedly crude; but it represents more than
IKIS as yet been consciously attempted or prac-
tically achieved, and to that extent, since it can
be...put into practice comparatively easily, is
probably the better one to choose and to pur-
sue.
To put the matter in still another way, we
;an choose either of two courses. One of them
will lead us slowly by recognized physical
methods of investigation to a gradual accumu-
lation of all the facts of the behavior of given
systems in given selected sets of conditions.
A great deal of the data thus slowly and ex-
pensively accumulated will, however, be prac-
tically unavailable in the -present slate of the
;irt of piano construction. This being so, we
(Continued on pmic 31)
William Braid White
Associate, American Society of Mechanical
Engineers; Chairman, Wood Industries
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
Tonal and Technical Surreys of Product
Tonal Betterment Work In Factories
References to manufacturers of unquestioned
position in industry
For particular*,
address
209 South State Street, CHICAGO
PIANO. TECHNICIANS SCHOOL,
(Under Y. M. C. A. Auspices)
Alio—Felts and
Cloths, Furnished
In Any Quantity
Practical Shop School Tuning, General Repairs,
Rebuilding
GRANDS—UPRIGHTS—PLAYERS
Woodside, L. I., N. Y.
The Y. M. C. A. Piano Technicians School
52nd and Sansoin Streets.
Philadelphia, P.i.
Direct Manufacturers of
Send for catalog
TUNERS' TRADE SOLICITED
29