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TECHNICAL^SUPPLY DEPARTMENT
William BraidWlnte,TecAmcalEditor
Advantages and Disadvantages of the
Capo d'Astro and Agraffe Construction
The Object of Each Type of Construction Is to Furnish Secure Bearing for the String at Its
Upper End Near the Tuning Pins—Effect of Each Device on the Tone Quality—
Disadvantages of the Capo d'Astro—Do Agraffes Pull Out—Tension and Tone
A
T the October meeting of the Western
Division, National Piano Technicians'
Association, a question was asked that
involves problems of very considerable impor-
tance. The questioner wanted to know what
are the respective advantages and disadvantages
of capo d'astro and agraffe construction for
grand pianos. There is so much to be said on
this question and yet so little accurate knowl-
edge that any discussion is very apt, especially
now when readers are engaged in going with
me through a sort of course in scale drafting
and design.
What follows is based on my own notes
of the debate which followed the putting of this
question. A number of us contributed to the
sum total of information and the result was
interesting enough to be presented in the fol-
lowing concentrated form:
The Two Compared
The object of either construction mentioned
is to furnish a secure bearing for the string at
its upper end, near to the tuning pins. The
agraffe consists in principle of a stud pierced
with the required number of holes, through
which the string passes, and its object is effec-
tively to delimit the string's length, furnish a
firm and rigid bearing for the wire, so that there
may be no rattling of either the speaking or
the waste lengths and, lastly, to facilitate tuning
by permitting the string to pull through it easily
and without undue strain.
The agraffe is an old device, having been used
for more than one hundred years. Grand pianos
for many years used agraffes from end to end of
the scale, but about fifty years ago the practice
began in this country—borrowing from European
makers—of casting a solid iron ledge or bar in
the plate, against which the strings should be
drawn and from which they might pass to an-
other bearing behind it, leaving a short space of
waste wire between the two bearing points.
In some small grand pianos these "capo d'astro''
bars (the name appears to be a corruption of
Capo Tasto, as used in fretted instruments)
extend over the whole scale from end to end.
Other grand pianos have the capo d'astro bar
running through the whole of the treble sec-
tions. The most frequently encountered prac-
tice, however, is that of a capo d'astro bar run-
ning from unison No. 88 downwards to the first
compression member of the plate, which may
be anywhere between No. 70 and No. 55.
Now it must be evident that each of these
devices has its own peculiar effect upon tone
quality. Let us consider that point.
Effects on Tone
The longer strings of the piano are less rigid
naturally than the shorter ones, and even
though their rigidity is intensified by increased
tension, they form easily those many partial
tones which are essential to an adequately rich
tone quality. On the other hand, the shorter
strings, being more rigid, are less readily able
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to break themselves up into a rich segmentation,
and therefore need stimulation, which is fur-
nished by the device of advancing the striking
point of the hammer until, in the case of the
very highest and shortest string, this comes to
within one-eighth of an Inch of the bearing.
Even then, however, it is found that the high
treble regions can stand further stimulation in
order to produce a sufficiently ringing and pow-
erful sound. To this end, it has long since been
discovered that a heavy bar of iron, placed
above 'these strings so as to bear down upon
them, constitutes an auxiliary resonator which
facilitates the production of the higher partial
tones and enriches the quality of the sound
given out. For this reason, if for no other, the
capo d'astro bar is very effective in the right
place.
There is still another feature of the capo
d'astro which is worth consideration. With this
device the hammer on the grand piano may be
brought right up to the very edge of the bearing
without hindrance. On the other hand, when
agraffes are used on the very short strings there
is always difficulty in manipulation of the strik-
ing distances. Everywhere between there must be
a sufficient width of iron to give a firm bearing
for the agraffe, which is tapped into a threaded
hole drilled into the iron. Naturally, the agraffe
cannot be exactly at the very edge of this iron
plate, and if it be used on the highest strings
must be set in the iron slantways, which is
rather a ticklish and often not a satisfactory
way of doing things. Thus again, the capo
d'astro bar has many advantages in the upper
regions of the scale.
Disadvantages of Capo d'Astro
On the other hand, when we come to the
middle and lower regions these advantages no
longer operate, and the issue between capo
d'astro and agraffe is reduced to the bare ques-
tion of which one is better mechanically. Now
there are two sides to this. The first relates to
the tuning. When a long string has to be pulled
through a capo d'astro bar, then evidently there
must be difficulty in dealing with that short
length of string which lies between the front
and the rear bearings. If the difference of level
between the two is considerable, the slope of
this short length will be steep, and the strain
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 Surveys of Product
Tonal Betterment Work in Factories
References
to manufacturers of unquestioned
position in industry
For particulars, address
209 South State Street, CHICAGO
39
on the wire at these points simply terrific. I
think that every tuner will agree with me on
this point. Tuning is not so easy with a capo
d'astro over the longer strings. Moreover, it is
not merely more difficult but less secure. The
constant tendency, of course, is for the tension
to equalize itself as between the speaking length
of the string at relatively low, and the short
length between the bearings are relatively high,
tensions. And that means difficulty in keeping
the piano in tune.
Do Agraffes Pull Out?
It has been said that agraffes have a tendency
to pull out of the plate. In all my experience I
have not seen this happen more than perhaps
three times. When it does happen one may be
sure that there is some very considerable trou-
ble with the scale. During the debate at the
Chicago N. P. T. A., from which I am quoting,
one member told the story of a distinguished
piano manufacturer, well known as a practical
man and the designer of his own scales, who
once complained that he had been obliged to
put on a capo d'astro over the bass section
in one of his pianos because the agraffes con-
stantly pulled out. He was asked why they
pulled out, and he answered that he could not
get his plates thick enough to hold them. He
was then asked whether perhaps there was some
error in the scale. And he at once replied in-
dignantly that there could not be any mistake
in the scale.
Now precisely that sort of spirit is what is
wrong with our industry. The gentleman in
question was a distinguished piano maker and
a very able man, but it is safe to say that if he
had been a manufacturer of almost anything
else he would not have insisted that his work
must be without fault. He would have been
willing to admit that there might have been a
mistake in his work; that is, if he had been the
maker of almost anything else save a piano.
Which is one explanation of the utter technical
stagnation that has reigned in our industry dur-
ing so many years, a stagnation only now being
stirred by the introduction of new ideas and
new principles.
Agraffes, Tension and Tone
An agraffe which pulls out of the plate is an
agraffe which is carrying a load far too heavy
for it. If it were not dreadfully overloaded it
would not pull out of the plate, as any one can
see by examination. The agraffe itself is a
sturdy brass shaft, threaded with a machine
thread which screws into the plate, and before
it can be pulled out of the plate the pull upon
it must be sufficient to strip those brass threads
as they lie close packed in their iron hole. A
scale may be overloaded, however, enough to
make the agraffes pull out, and still retain its
strings without breaking.
It is not often
realized that the breaking strain of wires to-day
runs from 350 pounds to nearly 600 pounds and
that astring will respond richly up to a tension
well above one-half of its breaking strain. There
has always been a school of piano making com-
mitted to the principle of the highest possible
tension, but no one who has seriously studied the
acoustics of the string will be inclined to-day
to support it. If we consider the highest strings
we shall see that the effect of very high tension
on them is to intensify the difficulty they already
(Continued
on page 40)
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