Music Trade Review

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THE
MUSIC TRADE
PHYSICAL LAWS OF PNEUMATIC ACTION.
REVIEW
further function of this "bleed-hole," ancillary to
that of exhausting the air-duct in the first instance,
is to cause the pressure of air within, the duct to
Brief and Non-Technical Discussion of the Physical Laws and Principles That Underlie the
be reduced again rapidly when the reverse process
Operation of Pneumatic Piano-Playing Mechanisms—A Statement of Fact That Should
takes place, as described immediately following.)
Interest Everyone Connected with the Manufacturing and Selling of Player-Pianos.
Now, suppose the pneumatic "collapsed," and
the corresponding hammer of the piano thrown
CONCLUDING ARTICLE.
against the string, with the result of some ap-
In the first article of the present series we dis- and the second disc closing the exhaust che:' propriate tone being made to sound. After some
cussed the broad physical laws of the pneumatic passage.
interval, depending upon the length of the per-
mechanism so far as these might be applied tc
Now, it will also be observed that, so long as the foration in the paper sheet and the latter's speed of
the cases presented by pressure-reducing apparatus pressure of air is reduced in the exhaust chest, the travel, the paper will have advanced until that
(bellows) and striking pneumatics. But we atmospheric external air will press down on the perforation comes to an end. As soon as this hap-
stopped our investigation at an important point, head of the first disc, and hold it so that the pas- pens, the air-duct is once more sealed. The small
which must now be considered with _some care. sage to the exhaust chest, covered by the second communicating passage (bleed-hole) between the
Although we discussed the simple case of one disc, is kept shut very tightly. And it is neces- end of the air-duct and the exhaust chest affords
pneumatic controlled by one simple bellows-set, sary therefore to provide means whereby the pouch instant means for the air in the duct to rush into
we did not, in the last article, undertake to con- under the two discs and their spindle may be the exhaust chest, as above described in the case
sider the case of many pneumatics which must be caused to move up or forward, as the case may of the pneumatic. As soon as this happens, the
controlled according to some predetermined plan. be, to change the position of the discs and open force which has been holding the pouch against
This we shall now do.
the pneumatic to the influence of the exhaust chest, the external pressure on the outer disc of the
Inasmuch as the co-ordination of the piano ac- whole closing it from that of the external air.
valve ceases to be operative. At once, then, this
This is done through the tracker-bar. In this, external pressure on the outer disc pushes the
tion and the pneumatic mechanism in a player-
piano is directly affected through the medium of we all know, there is a series of air-ducts, and as latter back or down, so that the inner disc is
the striking pneumatics which have already been we also know, a moving shee.t of paper passes brought into its original position, shutting off the
described, it follows that some means must be over this bar. Now, if we suppose that each of passage between the exhaust chest and the pneu-
devised for controlling these, to the end that they the air-ducts leads down below or behind the matic. At the same time, of course, the outer
may be brought into operation—that is to say, pouch, of which we have been speaking, and if we disc is pushed down so that it opens up the pass-
caused to "collapse" in the manner before explain- also suppose that a passage-way of some kind age between the open air and the pneumatic. Obey-
ed—according to predetermined arrangements. The (very small of course) is made between the bot- ing the before-mentioned principle of its energy,
manner of bringing about this control of the pneu- tom of the pouch and the exhaust chest, it fol- the outer air at once rushes into the pneumatic un-
matics furnishes a very interesting instance of lows that, if the sheet of paper be stretched over til the balance of pressures, inside and out, is re-
the tracker-bar the openings of the ducts in the stored. The spring at the hinge of the pneumatic
applied science.
Imagine that a series of pneumatics, eighty-eight bar will be sealed, and any air that is in them then forces the movable wall away from the fixed
in number, are placed in such a position that each will be subjected to reduction in pressure; since wall, and the pneumatic is opened once more, re-
one of them may easily be brought into co-action the ducts lead to the bottom of the pouches and leasing the hammer and putting a stop, through
with a hammer-section of the piano. Imagine fur- these are connected with the exhaust chest. Hence, the damper, to the vibrations of the strings.
ther that each of these pneumatics is provided it is plain that there will be air of a reduced pres-
If we add to this description the further note
with an orifice, and that this orifice is directly sure in the ducts and under the pouches. Hence, that many pneumatic mechanisms contain an ex-
connected, by means of some sort of closed pas- again, the external pressure of the air against the tra valve, the function of which is merely to act as
sage, with the main action-box (or "exhaust-chest" outer discs of the valves will keep these seated. an intermediary between the air-duct of the track-
as it is called), the functions of which, in its sim- Hence, again, the pneumatics will be free from any er-bar and the valve which actually operates upon
interference with the pressure of the air within the pneumatic, we shall have described every type
plest form, we have already discussed.
Now, plainly, if such a series of pneumatics be them, no matter what may be the condition of of pneumatic striking mechanism. This intermedi-
so connected with such an "exhaust-box," and 'f the air in the exhaust chest as regards pressure.
ary valve is operated by the air rushing down the
Suppose now that, as the paper sheet travels air-duct from the tracker. By the pouch's conse-
the latter be then subjected to the influence of
the pressure-reducing apparatus or bellows-set, over the tracker-bar, a perforation in it comes op- quent movement a button is lifted which has been
the pressure of the atmosphere in each and every posite one of the air-ducts in the bar. By hy- held down by external atmospheric pressure, so
pneumatic will be reduced likewise, until each and pothesis, the external air will find itself admitted that air flows into a second duct and under the
every pneumatic has its movable leaf or wall at once to a duct in which the air pressure has pouch of the pneumatic-operating valve. When
forced in towards the immovable part (or, as we been reduced. Naturally, then, this external air two such valves are used, the one nearest the air-
say, is forced to "collapse") by the pressure of will force its way into the duct and so down un- duct of the tracker is called the "primary" and that
the normal external atmospheric air. Hence, every der the pouch, all the time meeting with but slight which co-acts with the pneumatic is called the "sec-
pneumatic will simultaneously "collapse" and every resistance. And since the air both below and im- ondary."
hammer of the piano will be simultaneously thrown mediately above the pouch (remember that the
We may add further that the operation of mo-
upper or disc side of the pouch is actually in the I'ors for pneumatic actions is brought about by
against its corresponding strings.
The problem, naturally, is to arrange things so exhaust chest) is reduced in pressure, the external precisely similar means to those described above.
that only those pneumatics will collapse at any air, rushing down under it, will lift it upwards Slide-valves alternately reduce the internal pres-
given moment which are required to operate ham- or push it forward, as the case may be. The force sure of the air in the motor units, and restore it
mers corresponding to tones required for the ren- of this air will be sufficient, if the duct and pouch by opening communication again with the a'mos-
dition of some given piece of music. In order to be well designed, to overcome the weight of the phere.
do this, the same force of external over internal external air on the outer disc, and thus the pouch
The various types of "governor," which are
air pressure is brought into operation. The gen- will move, the spindle will move also in obedi- placed in the bellows-sets of many pneumatic
ence, and the outer disc will close the open air mechanisms for the purpose of maintaining the
eral outline of the process is as follows :
Each pneumatic has its passage way into the from the pneumatic, while the inner disc will open partial vacuum at a steady reduced pressure, and
exhaust chest closed by means of a pair of discs the passage between the pneumatic and the exhaust eliminating fluctuation in the excess of external
on a spindle, which in turn may be moved back chest. Hence the pneumatic will "collapse." Why? over internal pressure, are merely small "equal-
Since it is the property of all gaseous matter izers" of the same type as the large units described
and forth or up and down (according to the posi-
tion.of the passage way) through the motions of completely to fill all spaces in*o which it may be urder that name in the first of these two articles.
a light leather pouch. When in one position one placed, and since the air in the pneumatic, at the
Such are the fundamental physical laws, and the
of the discs closes the passage way between the time of the movements above described, is at or- application thereof, known to the art of pneumatic
pneumatic and the exhaust chest, so that the pres- dinary atmospheric pressure, while the air in the action design.
sure reduction which is all the time going on in the exhaust chest is reduced in pressure, and since the
latter may not affect the pneumatic. When the two are now in communication with each other,
IMPROVED MUSIC ROLL HOLDER.
first is in this "shut" position, the other disc al- it follows that the air in the pneumatic will rush
lows a communicating orifice or passage between into the exhaust chest. For air moves freely in
An improved music roll holder for automatic
the pneumatic and the external air to remain open. all directions, and air at a high pressure will, by musical instrument players is the subject of patent
When, on the other hand, the pouch under the reason Of that pressure, push out of its way air No. 1,008,440 just granted to Irving B. Smith of
discs is caused to move up or forward, the pas- at a low pressure. Hence the air in the pneumatic Philadelphia and assigned to the Electrelle Co.
sage way to the external air is closed from the will rush into the exhaust chest, until the pres- This inven'ion is particularly adapted to support
pneumatic by one disc, while the passage way to sure in the pneumatic is so much reduced that the music roll and take-up roll in co eiperative re-
the exhaust chest is opened by the other disc. The the external air pressing on its outer surface will lation to the roll actuating means and correlated
two discs, it will be observed, move on the one overcome the resistance of the movable wall; whicli mechanism. It has for its object to provide a mu-
spindle, and move as the latter moves. When the latter will then move upwards or downwards, a
sic roll holder capable of combining means for
spindle is moved forward, let us say, one disc the case may be, towards the fixed wall. Thus the controlling and regulating the operation of the
is closing one passage and the other is opening pneumatic will "collapse."
music roll and take-up roll and the devices for ro-
(It may be noted that the communicating smal' tating the latter, so associated that comple'e con-
the other passage. When the spindle is moved
back, the first disc is opening the open air passage passage between the pouch of the valve and the trol of the instrumentalities is had by the use of
air-duct is what is known as the "bleed-hole." A a minimum of operating levers.