It was, however, through the successful development of mechanism for the automatic operation of organs that the true principles for piano-player construction began to come to light. Two leading manufacturers had both produced reed organs of a very superior kind, equipped with mechanical playing devices. The principle was pneumatic, and was applied through the medium of compressed air. The organs themselves were also operated on this principle, this being a return to the old force bellows system, adopted in the European harmonium, and always used in connection with the pipe organ. When developed to their highest point, these pneumatic self-playing organs produced superior musical effects, so that they became, and still are, well known and popular. The latest styles, indeed, rival the orchestra in their versatility and coloring, especially when operated by a skillful musician.
The pneumatic principle thus applied, and the success of the attempts to adapt it to the organ, led experimenters to emulate, and if possible improve upon, the early attempts at the practical manufacture of pianoforte-playing mechanism. Without going too much into details, it may be recorded that the two concerns previously referred to were nearly ready in 1896 to come out with such an instrument, and patents were granted in 1897 for a complete piano-player of the cabinet style, attachable to any piano, and easily detachable therefrom. Other patents soon followed, and other manufacturers fell into line, with the result that the great piano-player movement had soon begun in earnest. The productions of the different firms, of course, varied in details, but only two widely separated schools have developed, and inasmuch as both of these employ the pneumatic principle, which has triumphed over all others, and is now adapted unanimously by manufacturers who desire to render possible an approximation to artistic rendition of pianoforte music, it will be unnecessary to treat of any instruments constructed on other lines.
In the meantime it will be well to note that the above short sketch of the preliminary skirmishing, as it were, is intended to be nothing more than an outline, as the policy adopted throughout this entire work has been to avoid the historical view-point, as much as possible, and to confine ourselves strictly to the business in hand; namely, constructional principles and their application.
The pneumatic principle has been adopted in all the piano-players that we have occasion to survey, and its application has been in all cases essentially similar. Indeed, the two schools of construction differ, not in the application of the pneumatic principle, but in certain details of construction, which are important but not vital. One general description will be quite sufficient to acquaint the reader with the make-up of these instruments, and it will be easy to undertake any further explanations of important variations.
The underlying idea, upon which the whole player is built, may be described as arising from the knowledge that a bag or bellows of suitable material will collapse whenever the air is exhausted from it, and become inflated again when the air is permitted to rush into it, which happens as soon as the vacuum is destroyed. Now it is obvious that here, in these two processes, we have the possibility of producing a reciprocating motion, and the value of this is evident when it is remembered that the process of pianoforte playing, when reduced to its lowest terms, is essentially the combination of the alternate manual motions required to depress and release a key. Consequently, the matter of designing a pianoforte-playing machine is reduced to the problem of placing a bellows over a key, or in mechanical connection with it, in such a way that the inflation and deflation of the bellows will operate levers to depress and release the key. Thus far, it may be understood, we are dealing with elementary mechanical principles. But the questions arising from consideration of the control of these bellows are far more delicate, and require for their solution a high degree of mechanical talent. Let us see how the problem has been worked out.
A musical composition which is to be performed on the pianoforte by means of one of these “players,” as they are called colloquially, is first reduced to a series of perforations on a long sheet, the perforations being of uniform width, but varying in length according to the duration of the musical tone for which each stands. The sheet is then wound upon a spool and is connected with motor mechanism which is adapted to draw it across a “tracker-board” pierced with holes, each of which corresponds to some hole in the sheet. The latter, when so drawn across the plane of the “tracker-board,” is wound up on another spool, and the motor mechanism of the player is so arranged that the sheet can be re-wound on to its own spool when the whole composition has been played, so that it may be withdrawn from the “player,” and another substituted in its place. The actual process of operation is as follows: The “player” is provided with foot pedals, which operate exhaust bellows, and thus maintain a reservoir bellows in a state of exhaust, on the same principle as in the reed organ. As long as the exhaust bellows are operated, and the reservoir is kept in a state of vacuum, it is possible to maintain an “exhaust chamber” within the “player” also in a state of vacuum. This exhaust chamber communicates with a “diaphragm chamber,” in connection with the “tracker-board” hole, and with an “inflation and deflation channel” in connection with the striking pneumatic or bellows which depresses the pianoforte key. The connection with the “diaphragm chamber” is by means of a very small hole pierced in a leather diaphragm which is stretched between the “exhaust chamber” and the “diaphragm chamber,” so that the latter will be in a state of partial vacuum. Resting on the leather diaphragm is a button, attached to an upright spindle which stretches through an orifice into the inflation and deflation chamber, and there operates a poppett valve which, in one position of the spindle, will close the chamber against the exhaust chest, while opening itself and therefore also the pneumatic to the outer air, and in another position will reverse the process, opening the chamber to the power of the vacuum in the exhaust and simultaneously closing itself and therefore the pneumatic to the vacuum, which will cause the latter to collapse, and thus bring down the key. Now, when a hole in the perforated sheet comes opposite a hole in the “tracker-board,” an atmospheric communication is opened with the “diaphragm chamber,” and air will immediately rush down into the “diaphragm chamber” and at once destroy the partial vacuum which existed there. As a consequence of this, the leather diaphragm will immediately rise to its fullest extent, influenced by the vacuum in the chamber above it, and will therefore push up the poppett valve. This action will open communication between the exhaust and inflation and deflation chambers and will expose the latter to the vacuum, while shutting off the outer air which has kept the pneumatic inflated. Thus the pneumatic will collapse, and the piano key will be held down until the closing of the “tracker-board” hole once more restores the partial vacuum in the “diaphragm chamber,” thus permitting the poppett valve to sink, and reopening the connection between the pneumatic and the outer air, which re-inflates it and releases the key.
As will have been anticipated, there are endless small variations of detail in the construction of different “players,” but they all work on the same principle, and the above description will be sufficient to give an idea of what goes on inside the “player” when the perforated sheet is put into position and drawn over the “tracker-board.” Variations on the mechanical carrying out of these principles are dependent upon the ideas of the different makers. It can easily be understood that there is plenty of room for endless changes in details, and that every maker of “players” has his own special notions on the subject.
We have spoken above of the motor mechanism designed to move the perforated sheet across the “tracker-board,” and to rewind it when required. It is clear that such a motor device must be very sensitive to changes in speed control, very light and very easily operated. In the search for the ideal device manufacturers have gradually separated themselves into two schools of practice, each being champions of one particular type of motor. These two schools of opinion and practice have adopted respectively the pneumatic and the clock-work motors. Both have virtues; neither are free from vices. It is no part of our plan to enter into didactic discussion of the relative merits and demerits of the two styles, but we shall confine ourselves to an exposition of the method whereby each is adapted to its required work, and shall point out the more obvious of the good and bad features of both.
The pneumatic motor has the initial advantage of simplicity and lightness. It consists of a number of bellows, usually three or five, which are arranged in series on a board and connected by passages with the exhaust chest. They are adapted to be collapsed and inflated alternately by means of the exhaust from the bellows of the “player,” and are governed by valves so arranged as to cause one bellows to be open to the atmospheric air, and therefore inflated, while the next to it is simultaneously closed to the atmospheric air and exposed to the vacuum from the wind-chest, and therefore collapsed. This alternate process produces a motion which can, of course, easily be transferred by means of connecting rods to a crank-shaft, which by reciprocation produces a rotary motion, and also permits the take-up spool of the “player” to be connected with it by suitable gearing. The controlling valves are generally connected with the crank-shaft somewhat after the manner of the valves of a steam cylinder, and are operated by the motion of the shaft through suitable connecting rods. The reverse motion of the spool, for rewinding, is accomplished by gearing between the motor and spool, and the reversing lever, while operating this gear, also closes the valve between the exhaust reservoir bellows and exhaust chamber so as to permit the full power of the exhaust to be exercised on the motor when the rewinding is required. The speed control of the pneumatic motor is governed by another finger lever adapted to operate a valve which can entirely close the passage between the exhaust chest and motor board, the gradual opening or closing of which increases or diminishes the power of the exhaust upon the motor bellows and hence the rapidity with which they collapse and reinflate. This speed control combines simplicity and effectiveness.
In considering the less agreeable qualities of the pneumatic motor we have to note that a great deal of the alleged deficiency of the type arises from the fact that its operation depends upon the same agency as is employed for the striking pneumatics; namely, the exhaustion of air from the exhaust bellows reservoir. This means, of course, that the striking pneumatics and the motor are artificially brought into relations which would never naturally subsist between them. In consequence, there is a continual tendency on the part of one of the elements to monopolize the power reserve, to the detriment of the other. Thus, a fortissimo passage will tend to use up so much power that the motor will be slowed down; while, contrariwise, the latter, when driven at its highest speed, will take too much power from the pneumatics and prevent the expression of their highest dynamic forces. Here we touch upon the most serious defect of the pneumatic motor, and while we find the practical workings of these devices quite excellent, there is no doubt that they would be far more responsive and far lighter in operation if these fundamental defects did not exist.