Music Trade Review

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THE MUSIC TRADE REVIEW
The Subject Under Discussion Is "Tensions, High and Low"—Some Eluci-
datory Remarks in This Connection That May Serve to Augment the
Knowledge of Those Striving to Master the Study of Player Mechanism.
The word "tension" is frequently used in dis-
cussion of the design and construction of the
pneumatic piano playing mechanism without any
special understanding of what it means. We
hear talk of high and low tension players, and
sometimes we hear very loose talk along these
lines. The present article is intended to. serve as
a clarifying agent in this respect.
As should be thoroughly understood by anyone
who desires to discuss the subject, the pneumatic
piano playing mechanism is operated by the energy
exerted by the atmospheric air pressing upon mov-
able parts. This energy, however, as can be
easily seen, cannot be made available until any air
contained within the movable elements is partially
withdrawn. When this is done, the necessary dis-
turbance of the atmospheric balance is made and
the external air is able to perform work. This
partial displacement is the function of the bel-
lows, a function often improperly called "suction."
The Function of Displacement.
The function of displacement, above referred to
as performed by the bellows, is made possible by
the fact that the latter operate as a form of air
pump, a relatively inefficient form, but a true air
pump nevertheless. The thing is done by simply
opening the bellows up. The bellows themselves
are connected with a source of air supply, sudh
as the chest of a pneumatic player, and when they
are opened up the air contained in the chest ex-
pands somewhat in order to fill the new space,
since it is a function of air to fill completely any
space in which it may be contained, its density or
pressure thus depending upon the relation be-
tween the original quantity of air and the space
filled. Seeing, however, that air is a fluid, it fol-
lows that its bulk depends upon the quantity of it
forced into any given space, and thus it never can
be said to have any specific bulk, since the bulk
may at any moment be instantly changed through
change of the container.
The expansion of air or any other gas, when its
container is enlarged without its own given quan-
tity being changed, reduces the pressure exercised
by any given volume of it. Thus we say that
when the air contained in a given box is partially
removed that which remains expands to a lower
pressure. This pressure naturally is less than that
of the atmosphere, since the latter is the normal
pressure of all free air. The internal air has ex-
panded to a lower pressure in consequence of
part of its original quantity having been with-
drawn. The result is that a state of greater ten-
sion is sot up between adjacent particles of it than
before existed.
air which is so reduced in pressure that the nor-
mal free air of the atmo.sphere can exercise defi-
nite energy against it. So when we speak of a
high tension player we mean a player in which a
relatively large displacement of contained air takes
place, and in which, therefore, the tension of the
remaining contained air is relatively high.
Now, it should be observed that the tension, of
itself, is not a thing, but merely a relation between
two, things; in this case between two adjacent
particles of air. We need not go into any theories
as to the ultimate condition of these particles,
since the physicists can tell us only that they are
quite immaterial. But we point out that the stress
or stretched condition existing is the so-called
tension.
speed of all bello.ws operation may be regarded
is virtually constant.
Now a large player, that is to say, one in which
the pneumatics are large, the valves large and the
windways many, is a player which on the one hand
will require a relatively higher tension for its op-
eration, and on the other hand is one which can-
not attain to high tension without the use of rela-
tively larger bellows. Hence, seeing that the
amount of effort available through the human
performer is distinctly limited and cannot be in-
creased to any perceptible degree in practice, it
follows that the larger player, in all probability,
will be of low working tension and, from the facts
above cited in connection with the low tension, v relatively low efficiency.
Low Versus High Tension Player.
The Ideal Player Construction.
A lo.w tension player, contrariwise, is a player
in which a relatively small displacement of con-
tained air takes place and in which, therefore, the
tension of the remaining air is relatively low.
Now it does not follow from this that the high
tension player is necessarily either better or worse
than the other, for a high tensio.n means the neces-
sity for a high tension, since the player is not built
to serve as an air pump but to enable the opera-
tion of the playing mechanism at the least ex-
penditure of effort. On the other hand, the fact
that a player can develop a high tension may be
accounted for by its superior construction, its air-
tightness or the Tightness of its design. In this
case, if the development of a high tension be
parallel with ease in operation and smallness of
parts, it follows the player is an efficient one.
In the above cited comparison, of course, the
question was one of construction, mainly in air-
tightness and compactness of design, so combined
as to avoid waste, for apart from all else it must
be remembered that the amount of air that can
be displaced depends upon the relative size of the
parts affected, for the question of speed cannot be
considered as of any importance. In practice the
Thus, we submit, the ideal player stands out as
the player in which are combined smallness of
parts with relatively perfect air-tightness, smallest
number of different parts and shortest air pas-
sages. Such a player—combining not a few, but
all of these qualities—will of necessity be not
only an efficient player but will naturally be a high
tension player; not because high tension is itself
of the slightest advantage but because in connec-
tion with th/ other factors it assists in the form-
ing of a perfect whole.
In Conclusion.
In conclusion it might be instructive to remark
that the working tension of players varies from
two to eight ounces, the former being equivalent
to lowest tension and the latter to the maximum
used in fortissimo, playing. Thus it will be seen
that the talk of high and low tension may easily
be exaggerated, especially when we remember
that a tension equivalent to an effective pressure
of eight ounces per square inch is only about the
same as 3 per cent, of a perfect vacuum. In other
words, only one-thirtieth or less of the contained
air need be removed to gain the maximum power
usually required.
What Constitutes Tension.
Of course, since there is no static condition pos-
sible in any fluid, much less in a gas, it follows
that when we speak of tension being set up be-
tween the adjacent particles of air we refer only
to a tension greater than normal; that is to. say,
greater than the tension existing between adjacent
particles at normal pressure. There is always
some tension or stress between the particles, for
the simple reason that they are not continuous.
When, therefore, we speak of tension we mean
that the particles are stretched or strained further
apart than is usual in a free atmo.spheric condi-
tion. Therefore when we refer to high tension
we mean low pressure. The lower the pressure
of the air, the greater the expansion between its
particles. That is to say, the greater is the stress
between them, and so the greater is the tension.
Thus when we speak of a high tension air we
mean air at low pressure, air very much thinned.
Jipes for Automatic Pianos
for VIOLIN and FLUTE music
Furnished in both wood and metal;
made of quality materials for durability
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SAMUEL PIERCE ORGAN PIPE CO., Reading, Mass.