Theatre Organ - Technical

Technical

As in a traditional pipe organ, a theatre organ uses pressurized air to produce musical tones. Five important things that distinguish a theatre organ from traditional church organs are unification and extension, the exclusive use of electric action, high wind pressures, percussion instruments, and the horseshoe console.

Unification and extension gives the theatre organ its unique flexibility. A rank is extended by adding pipes above and below the original pitch, allowing the organist to play that rank at various pitches by drawing separate stops or tabs. A simple example of unification follows:

The Tibia Clausa at 8' pitch has 61 pipes. The Tibia can be made available at 4' pitch by adding 12 pipes to the top of the Tibia 8'. Tibia 2' is similarly accomplished by adding 12 more pipes. The Tibia Clausa 16' as a pedal voice is accomplished by adding 12 pipes to the bottom of the Tibia 8'. Hence, in a unified organ, four "ranks" (really tabs or draw-stops) can be obtained from a total of 97 pipes. In a classically designed organ, four "straight" ranks would require 244 pipes. Additionally, up to five mutated stops can be drawn from this 97-pipe rank, resulting in a total of nine stops from a single unified and extended 8' Tibia Clausa.

These ranks are voiced in relation to other pipe ranks in the organ, allowing a handful of ranks in a typical theatre organ to imitate a wide range of instruments. Unification also makes it possible to play any rank of pipes from any manual and the pedals independently, unlike a traditional church organ, where a rank of pipes is playable only from one manual or the pedals, or from two manuals via couplers.

The electro-pneumatic action was invented by Robert Hope-Jones, and is considered by many to be the single most significant development in pipe organs. Up to the turn of the 20th century, all pipe organs were operated by a tracker, tubular pneumatic, or pneumatic Barker-lever action, where the keys and pedals were physically connected to the pipe valves via wooden trackers, except in the case of tubular pneumatic, where all actions were operated by air pressure. Hope-Jones' electro-pneumatic action eliminated this by using wind pressure, controlled by electric solenoids, to operate the pipe valves, and solenoids and pistons to control and operate the various stop tabs, controls, keys and pedals on the console. This action allowed the console to be physically detached from the organ. All signals from the console were transmitted by an electric cable to an electro-pneumatic relay, and from there to the pipes and effects in the organ chambers.

Hope-Jones believed that higher wind pressures would allow pipes to more accurately imitate orchestral instruments by causing the pipes to produce harmonic overtones which, when mixed with other pipe ranks, produced tones more imitative of actual instruments. The high wind pressures also led to the development of instruments that are unique in theatre organs (such as the diaphone and tibia clausa), and allowed any rank in the organ to function as a solo instrument. These higher pressures were possible due to the development of high-velocity, motor-driven blowers and wind regulators.

Another hallmark of theatre organs is the addition of chromatic (tuned) percussions. In keeping with his idea of a "unit orchestra," Hope-Jones added pneumatically- and electrically operated instruments such as xylophones, wood harps, chimes, sleigh bells, chrysoglotts and glockenspiels to reproduce the orchestral versions of these instruments.

Later, Wurlitzer added other effects, such as drums, cymbals, wood blocks and other non-chromatic percussions and effects to allow the theatre organ to accompany silent movies.

A traditional organ console was not adequate to control a theatre organ, as the large number of draw knobs required made the console so huge an organist could not possibly reach all of them while playing. Thus, the horseshoe console was born. Based on a curved French console design and using stop "tabs" instead of drawknobs, the horseshoe console now allowed the organist to reach any stop or control while playing any piece of music, eliminating the need to move around awkwardly on the bench. The smaller stop tabs also permitted the addition of many more stops on the console than could be added on a traditional console.

After the advent of unification and the electro-pneumatic action, builders of church organs started to see the advantages of these systems. As a result, several organ builders began adopting these concepts for use in their church organs. Among these were Austin, Möller, Aeolian-Skinner and Kimball, who used electro-pneumatic action in many of their organs. Today, approximately one fourth of all new or rebuilt church pipe organs use an electro-pneumatic action either exclusively, or as an augmentation to existing tracker actions. In the same vein, some amount of unification was utilized in some church organs, and even today many church pipe organs utilize some degree of unification in areas where it is not critical to the "classical" sound sought in such instruments, or in instruments where space for pipes is limited. With stops such as the 32' bourdon in the pedal division, or a 16' reed in a manual division, the basic theatre organ concept of "extension" is commonly—but discreetly—used by even the most noted organ builders.