Music Trade Review

Music Trade Review -- © mbsi.org, arcade-museum.com -- digitized with support from namm.org
THE MUSIC TRADE REVIEW
11
One of the Most Serious Problems Confronting the Player Manufacturer Who
Desires Perfection in the Mechanism of His Instrument Is to Overcome the
Tendency Toward Leakage—Some Suggestions for Remedying this Trouble
The practical designer and builder of player
mechanisms is well aware that none of the prob-
lems with which he has to contend exceeds in
importance that of what is commonly called
"tightness." The longer one works in the field
of design the more one perceives that the real-
ly fundamental problem is found in the rela-
tion between power input and mechanical out-
put; between the effort put in at the bellows and
the results obtained at the speaking pneumatics.
The fact is no longer concealed that too much
of the physical effort required to run the foot-
driven player-piano manages to become ab-
sorbed in the various processes that deal with
the secondary elements in playing. The turn-
ing of the roll, its tracking, the operation of
expression devices, all these, which are not the
primary but the secondary, although necessary,
elements in the playing, are capable of absorb-
ing, and do absorb, far too much of the total
power input.
This much, of course, almost every one will
agree, although it is not likely that the agree-
ment will extend either to the causes or to the
remedies for this condition. But it is certain that
there is also another source of power waste
which is almost as important and quite as un-
fortunate; but which is even less in the way of
being remedied. We refer to leakage through
improper design of vacuum spaces.
In the design of any instrument or machine
intended to make use of what is commonly called
"vacuum," it is essential to keep in mind the
fundamental fact that the power is produced
through the disturbance of an equilibrium. The
atmospheric pressure, before the machine is set
in motion, is equal both outside and inside.
When the bellows are operated the inside pres-
sure is reduced. The difference in pressure thus
existing between the inner and the outer air
is applied to move various elements known as
pneumatics, which are the prime movers of the
machine; as well as to move when required
other secondary elements such as were men-
tioned above. The difference in question con-
stantly fluctuates, for two reasons. One rea-
son is that the "load" or power requirement
varies from moment to moment according to
the necessities of the music which is being
played. The other is that the necessity for
dynamic expression—that is, for constant risings
and fallings of the general level of loudness—
requires constant changes in the power input,
as determined by the physical effort thrown
upon the feet of the operator. Add to this the
natural inability of the human operator to main-
tain a perfectly steady level of effort, and it fol-
lows that the power level of the player mecha-
nism is necessarily and inevitably, by its very
nature, in a constant fluctuation between the
minimum which will keep it going on the slight-
est load and the maximum needed for the
heaviest momentary requirement.
tendency of the higher pressure atmospheric air
to force its way into space filled with low-pres-
sure air; a tendency depending upon the law of
gravitation and operating universally as well as
constantly. To prevent this leakage by elim-
inating all possible sources thereof is a task of
considerable practical difficulty. If, in the sec-
ondary chest of a player action, one single valve
be jammed so that the inner disc is out of con-
tact with its seat, while the outer disc does not
quite close the passage into the atmosphere, an
excellent example can be had to show how slight
is the working difference between the outer
and inner pressures; that is to say, how small
is the margin of power on which the player
operates. One such valve jammed open will
let in so much air that constant and vigorous
pumping will be required to keep up the mini-
mum working pressure necessary. Two such
valves jammed open will keep the internal pres-
sure up to atmospheric against vigorous pump-
ing; or at least will keep it so high that the
minimum difference needed to do work cannot
be reached. Now, when we consider that the
eighty-eight holes drilled through the secondary
chest do not take up more than one-third of
the superficial area of the side through which
they run, and when we remember that the num-
ber of cubic inches which represent the internal
volume of the chest is usually about equal to
the number of square inches which represent
the superficial area of the long side, it is ob-
vious that the absorptive powers of the bel-
lows are not so great that we have any margin
to spare.
made in a single piece like this, openings would
have to be left at the ends to be closed by end
pieces. But even so, the improvement would
be manifest.
In such a case as is here suggested, it would
undoubtedly be possible to build the chest in
separate sections, one to each rank of pneu-
matics with cast-on communicating passage
ways. A tubular form could be used which
would have many advantages, among them sav-
ing in space and simplicity.
Of course, the notions here set forth are not
intended to discuss the matter of price or cost,
any more than they are intended to preach at
practical manufacturers who have their own
problems to solve. The idea is to set forth
new and fresh suggestions, to make out a prima
facie case for such of them as seem to have
value and thus to stimulate practical men into
experiments with their own goods. The writer
scrupulously refrains from discussing visionary
notions, but applies to each one the test of his
own practical experience. The notions set forth
above are neither specially new nor conspicu-
ously complex; but they are useful.
Valve»
The subject of valves, apart from their rela-
tions with the chest, is also of high importance
to the general topic under discussion. At the
moment when the valve, in the course of its
travel, has reached a position exactly midway
between its two extreme positions atmospheric
air is entering the chest. The inrush of air
begins, of course, as soon as the disc has risen
from the entrance to the chest, and stops when
Packed Joints
the outer passage is completely closed. When
In these circumstances, as may likewise be this happens, the inrush of air continues for a
seen by other tests that will occur to the prac- moment from the pneumatic, but the length of
tical man, it is obvious that constructional time required for the pneumatic to close, shut-
methods should be examined with the utmost ting off this flow into the chest, is, to the action-
care for the purpose of seeing whether improve- time of the valve, as the travel of the one to
ments may be made which will have the effect the travel of the other. It is reckoned that if the
of stopping, or at least of minimizing, the ten- leakage of air during the travel of the valve
dency towards leakage.
into the vacuum chest can be lessened through
To take some" of the most obvious facts, it any change in design, a percentage up to a pos-
can at once be seen that one source of weak- sible IS per cent, of the efficiency of the bel-
ness is the long packed joint between the two lows now absorbed in this waste will then be
sides of a vacuum chest. If it were possible to saved.
make such a chest with permanent joints, or
It is indeed a question whether we should be
without any joints at all, the matter would be forever content with the pouch and disc type of
simple. But so long as valves, which need oc- valve. There is much to be said for the single
casional or frequent regulating, are placed in button, with pouch and vent built into one unit
inside chests, the walls of the latter must be directly connected with the button. There is
readily removable. Hence packed joints, and much to be said for any and every idea that
hence overdrawn screws which no longer, after tends to lessen the leakage during the travel of
a few withdrawals and replacements, can be the valve. On this very point the attention of
depended on to hold the walls tightly together. practical designers may well be concentrated,
Hence, again, leaks!
for there is no doubt that much can be done
There are two ways of getting rid of this dif- here in the way of improvement, and of prac-
ficulty. One would be to use, as in the A. B. tical efficiency.
Chase Artistano action, bolts sunk into the inner
These small points, as they would once have
wall of the chest, with butterfly thumb-nuts and been considered, are daily assuming greater im-
spring washers to close down the outer wall. portance as costs rise and competition grows
It is therefore obvious that, other things being In this way the possibility of overdrawing more intense. It is no longer to be supposed
equal, the matter of preventing leakage is of screws is excluded by eliminating the cause of that we can be satisfied with "something that
the utmost importance. A moment's reflection the trouble; and the chest will remain tight for works." We have reached the epoch of detail
will show that, as the atmospheric pressure re- an indefinite length of time, in any ordinary cir- development. The future will show how far we
mains fixed, and the very nature of the foot- cumstances.
can make this epoch one of perfection in the
driven bellows renders impossible any very high
Another method is to place the valves outside manufacture of player-pianos.
vacuum, there is no wide margin of allowance the chest, as is done in the Gulbransen and some
for error or waste; and that therefore the pre- other players of the single valve type. In this
vention of leakage is not only desirable, but case the chest can be made, if desired, as a seam-
essential to the complete success of any player less hollow box. It could even be cast in vul-
ARTo, SingA
mechanism whatever.
canite or aluminum, with no opening in the long
and
PERFECTION
Rolls
Causes of Leakage
sides save the air passages to the pneumatics.
Leakage in the player mechanism is from the Even the vents could be placed outside the
STANDARD MUSIC ROLL CO., Orange, N. J.
outside inward and depends upon the obvious chest in this case. Of course, if a casting were
Quality Music Rolls