The electro-pneumatic action is a control system by the mean of air pressure for

pipe organ The pipe organ is a musical instrument that produces sound by driving pressurized air (called ''wind'') through the organ pipes selected from a keyboard. Because each pipe produces a single pitch, the pipes are provided in sets called ''ranks' ...

s, whereby air

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

, controlled by an

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movi ...

and operated by the keys of an

organ console The pipe organ is played from an area called the console or keydesk, which holds the manuals (keyboards), pedals, and stop controls. In electric-action organs, the console is often movable. This allows for greater flexibility in placement of the ...

, opens and closes valves within wind chests, allowing the

pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...

to speak. This system also allows the console to be physically detached from the organ itself. The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.

Invention

Although early experiments with Barker lever, tubular-pneumatic and electro-pneumatic actions date as far back as the 1850s, credit for a feasible design is generally given to the English

organist An organist is a musician who plays any type of organ. An organist may play solo organ works, play with an ensemble or orchestra, or accompany one or more singers or instrumental soloists. In addition, an organist may accompany congregational ...

and

inventor An invention is a unique or novel device, method, composition, idea or process. An invention may be an improvement upon a machine, product, or process for increasing efficiency or lowering cost. It may also be an entirely new concept. If an ...

Robert Hope-Jones Robert Hope-Jones (9 February 1859 – 13 September 1914) was an English musician who is considered to be the inventor of the theatre organ in the early 20th century. He thought that a pipe organ should be able to imitate the instruments of ...

.George Laing Miller (1909).
The Recent Revolution in Organ Building
'. (also a

He overcame the difficulties inherent in earlier designs by including a rotating centrifugal air blower and replacing banks of batteries with a DC generator, which provided electrical power to the organ. This allowed the construction of new pipe organs without any physical linkages whatsoever. Previous organs used

tracker action Tracker action is a term used in reference to pipe organs and steam calliopes to indicate a mechanical linkage between keys or pedals pressed by the organist and the valve that allows air to flow into pipe(s) of the corresponding note. This is ...

, which requires a mechanical linkage between the console and the organ windchests, or

tubular-pneumatic action "Tubular-pneumatic action" refers to an apparatus used in many pipe organs built during the late 19th and early 20th centuries. The term "tubular" refers to the extensive use of lead tubing to connect the organ's console to the valves that control ...

, which linked the console and windchests with a large bundle of lead tubing.

Operation

When an organ key is depressed, an electric circuit is completed by means of a switch connected to that key. This causes a low-voltage current to flow through a cable to the windchest, upon which a rank, or multiple ranks of pipes are set. Within the chest, a small

electro-magnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...

associated with the key that is pressed becomes energized. This causes a very small valve to open. This, in turn, allows wind pressure to activate a bellows or "pneumatic" which operates a larger valve. This valve causes a change of air pressure within a channel that leads to all pipes of that note. A separate "stop action" system is used to control the admittance of air or "wind" into the pipes of the rank or ranks selected by the organist's selection of stops, while other ranks are "stopped" from playing. The stop action can also be an electro-pneumatic action, or may be another type of action This pneumatically assisted valve action is in contrast to a direct electric action in which each pipe's valve is opened directly by an electric solenoid which is attached to the valve. As this is the operation of an electro pnematic system

Advantages and disadvantages

The console of an organ which uses either type of electric action is connected to the other mechanisms by an electrical cable. This makes it possible for the console to be placed in any desirable location. It also permits the console to be movable, or to be installed on a "lift", as was the practice with

theater organ A theatre organ (also known as a theater organ, or, especially in the United Kingdom, a cinema organ) is a type of pipe organ developed to accompany silent films, from the 1900s to the 1920s. Theatre organs have horseshoe-shaped arrangements o ...

s. While many consider tracker action organs to be more sensitive to the player's control, others find some tracker organs heavy to play and tubular-pneumatic organs to be sluggish, and so prefer electro-pneumatic or direct electric actions. An electro-pneumatic action requires less current to operate than a direct electric action. This causes less demand on switch contacts. An organ using electro-pneumatic action was more reliable in operation than early direct electric organs until improvements were made in direct electric components.William H. Barnes (1959).
The Contemporary American Organ
'. A disadvantage of an electro-pneumatic organ is its use of large quantities of thin perishable leather, usually lambskin. This requires an extensive "re-leathering" of the windchests every twenty-five to forty years depending upon the quality of the material used, the atmospheric conditions and the use of the organ. Like tracker and tubular action, electro-pneumatic action—when employing the commonly used pitman-style windchests—is less flexible in operation than direct electric action . When electro-pneumatic action uses unit windchests (as does the electro-pneumatic action constructed by organ builder Schoenstein & Co.), then it works similarly to direct electric action, in which each rank operates independently, allowing "unification", where each individual rank on a windchest can be played at various octave ranges. A drawback to older electric action organs was the large amount of wiring required for operation. With each stop tab and key being wired, the transmission cable could easily contain several hundred wires. The great number of wires required between the keyboards, the banks of relays and the organ itself, with each solenoid requiring its own signal wire, made the situation worse, especially if a wire was broken (this was particularly true with consoles located on lifts and/or turntables), which made tracing the break very difficult. These problems increased with the size of the instrument, and it would not be unusual for a particular organ to contain over a hundred miles of wiring. The largest pipe organ in the world, the

Boardwalk Hall Auditorium Organ The Boardwalk Hall Auditorium Organ is the pipe organ in the Main Auditorium of the Boardwalk Hall (formerly known as the Atlantic City Convention Hall) in Atlantic City, New Jersey, built by the Midmer-Losh Organ Company. It is the largest orga ...

, is said to contain more than of wire.Foort, Reginald (1970). ''The Cinema Organ'', pp 74–78. Second Edition, New York: The Vestral Press. Modern electronic switching has largely overcome these physical problems.

Modern methods

In the years after the advent of the

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

, and later,

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s and

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

s, miles of wiring and electro-pneumatic relays have given way to electronic and computerized control and relay systems, which have made the control of pipe organs much more efficient. But for its time, the electro-pneumatic action was considered a great success, and even today modernized versions of this action are used in many new pipe organs, especially in the United States and the United Kingdom.

Invention

Operation

Advantages and disadvantages

Modern methods

References

Further reading