PLAYER-PIANO, a piano equipped with a mechanical de vice for automatically playing written music or for reproducing the playing of a pianist. All types of player-piano mechanism are operated by utilizing the difference between external and internal air pressures. In fig. r, the tracker-bar, T, with its 88 holes, is represented as being closed by the paper roll, R, which lies closely against it. Some of the air has been extracted from the duct, D, and from the chamber, C, by means of an air exhaust to which they are connected. There is a very tiny vent, V, which allows air from the tracker duct to leak into the cham ber. A disk, K, closes the chamber from the outer air, being held down because the air in C, is at a lower pressure than normal. The pneumatic, B, is full of air at normal atmospheric pressure and is open to the external air by means of the port, A.
Should a hole in the paper come into line with any hole in the tracker-bar, the external air rushes into the duct and lifts the pouch, P, which is simply a circular piece of soft kid about in diameter, and bigger than K. Hence it lifts K, connecting the pneumatic with the partial vacuum, C, and disconnecting it from the external air by closing the port A. The air in B spreads to C and, the external pressure on the surface, S, being greater than the reduced pressure inside, the pneumatic collapses suddenly, the movable leaf rising and lifting with it the pilot, L, which operates the piano action.
The pneumatic remains collapsed until paper again blocks the hole in the tracker-bar. The air in D then leaks through into C and can no longer hold up the pouch, which falls back into position and allows K to close the chamber C again, at the same time opening the pneumatic to the external air at A. The external and internal pressure on S now being the same, the pneumatic re inflates and allows the pilot to drop back into position.
In the days of heavy and clumsy valves it was difficult to provide the necessary power to lift them rapidly without hard pedalling and consequent loud tone. To overcome this defect
the more expensive player action was provided with an additional (or primary) valve of light construction, easily lifted by the inrush of air when a hole was opened on the tracker-bar. Its lifting admitted air to the other and heavier valve, through the port 0, operating the striking pneumatic as previously described. Both single and double valve systems are still in use.
The interior of the player action is maintained in a steady state of reduced pressure by forcing the pedal, F, to open the exhaust, X (fig. 2). This allows all the interior air to spread itself into X past L, a flat strip of well-tanned leather, lying over holes. A fan spring, G (about 121b. in strength), then closes the exhaust, expelling the air via another flap valve, Z. A strong spring, A, is always trying to open the equalizer, E, but is pre vented from so doing when the external air pressure is much greater than the reduced pressure inside. When, however, there is not much difference between the external and internal pressures, the spring can open and in so doing allows air to spread into it from the interior. The effect is to reduce the internal pressure once more to such an extent that the equalizer begins to collapse. Its constant to-and-fro motion enables a steady amount of re duced pressure to be maintained in the interior channels, despite unsteady working of the pedals.
Controls.—The simplest method of operating the "soft" and "sustaining" pedals is to connect the ordinary mechanism of the piano, by suitable levers, to finger controls in front of the key board. Many manufacturers prefer to control the distance from the hammers from the strings as shown in fig. 3. A button, B, opens a gate, G, when pressed down. This admits air to a pouch, P, which lifts the valve lying above it, and puts the pneu matic, N, into communication with a partial vacuum, V, thus collapsing it and causing it to lift the hammer rail, H, which softens the tone by giving the hammerhead less distance to travel towards the string, S.