Two other interesting percussion instruments that we find in theater organs are a glockenspiel and a xylophone. These both consist of tuned bars that are struck by hammers. The glockenspiel has steel bars that are struck by steel hammers, and the xylophone has wood bars that are struck by hard rubber mallets. In both instruments, the hammers are carried on bellows-like actuators called pneumatics.
     When compressed air is admitted quickly, the pneumatics inflate almost instantly and cause their respective attached hammers to strike the tuned bars to create the tones of these two instruments. Pressing appropriate keys on the keyboard of the console operates small electro-magnetic pilot valves which in turn power larger, pneumatically operated valves, or primary valves. The primary valves admit the air to the power pneumatics which strike the bars.
    When the musician releases a key, the pilot valve gets de-energized which causes the primary valve to close off the supply of air to the power pneumatics and exhaust them to atmosphere. The power pneumatics quickly deflate and collapse, which actions are aided by a return spring on each power pneumatic. In picture one, we are winding these return springs from lengths of spring steel wire, using a small motor powering a mandrel. Figure two is a close-up of some of the spring coils, which we subsequently cut to length and then attach to small hooks on the power pneumatics, figure three.

Fig. 1. Left. Winding small springs. Here we use a small electric motor to turn a wire mandrel. The motor is sup- plied through a transformer at 45 volts so that it develops less than normal torque and speed which makes controlling the spring winding process easy. Notice the spring steel wire being guided by hand.

Figure 3, left. Attaching the return springs to hooks on the pneumatics, a number of which are piled up in the background. These will subsequently be attached to the primary valve action boxes of the glockenspiel and xylo-phone units for the pipe organ.

Figure 4, Right. Assembling the Glock-enspiel and Xylophone. The main frame of this dual percussion unit has been installed on the wood support rails and the sets of tuned bars have been mounted. Below, we have just installed the concert flute rank.

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