The Rochford Compton

HOW DOES THE ORGAN WORK?

Cinema organs are pipe organs. They work on a similar principle to church organs but are controlled electrically

Key Parts of the organ
The key elements of a Cinema organ are...

• The Console, containing the "controls"
• An electric Blower to provide air for the pipes.
• Wind Regulators to stabilise air pressures.
• An electric generator to provide operating current for the electrics.
• Wind chests containing valves to allow air into the pipes.
• A Relay unit for control of the wind chest valves.
• Electro Magnets to operate wind valves.

The Console.
The Rochford/Kingsway organ is a typical example containing...

• 3 Keyboards of 61 notes.
• A pedalboard of 32 notes.
• 126 switches called "Stops" to control all the pipes and effects.
• An illuminated glass surround with colour effects.

The Generator
This is a rotary generator, belt driven from the Blower drive shaft. This produces 16 volts at 50 Amps for the technically minded. This provides "action current" to operate all of the electrical parts of the organ.

The Blower
This is a set of fans, shaft driven inside a cylindrical housing about the size of a dustbin. It rotates at 1500 rpm and produces a large volume of air at low pressure.

The Wind Regulators
There are 5 of these on the Rochford organ although 6 - 10 are not unusual depending on the size of the instrument. Air from the Blower is fed to the regulators, inside each is a set of springs and wind valves adjusted to a specific pressure. A contant pressure is necessary to keep the pipes in tune. The pressure is measured in "Inches of Water."
That is, the distance the pressure will push a column of water up a glass tube.
This is an ancient and very reliable method of measurement. Typically Cinema organs work on a pressure of between 8" to 15" of Water depending on which rank, or set of pipes, is being fed.
This picture is of the Rochford organ regulators during fitting.

The Tremulants
Have you ever wondered how that wobbling, or vibrato effect is produced. This is achieved by the Tremulants. These are boxes with oscillating tops which produce a pulsating air wave in the wind supply for the appropriate rank of pipes. There are three on the Rochford organ. Adjustment of these is a bit of an art form as no two ever react the same.

Wind Chests
In the simplest terms these are the long boxes that the pipes stand on. Inside however are complex mechanisms that allow air into each pipe when an electric current is applied to the appropriate "Magnet"

The Magnets.
The proper name for these are "Electro Magnets". Every pipe in the organ has one so this equates to several hundred. There are two types, Standard and Compound. Generally the larger pipes require a Compound magnet. The Magnet operates a small air valve which in turn opens a larger valve to admit air into the pipe.

Relay Unit
This is often referred to as the Heart of the organ. It is certainly the most complex part. It has been likened to a telephone exchange in as much as it controls which pipe will sound when a Stop is selected and a Keyboard key is pressed. The combinations are endless and a problem here is sometimes very difficult to fix.
In the Rochford organ there are 4 Relay cabinets each about the size of a large suitcase and crammed with thousands of fine contact wires and dozens of contact bars. The Rochford organ is still using it’s original Relay, a tribute to Compton craftsmanship.

Illuminated Surround
This is four glass covered cabinets containing coloured lighting units. There is one each side of the organ, one in the seat and one on top. They contain lights of the three primary colours, Red, Green and Blue. By mixing these at different intensities any colour can be produced.
Originally the Rochford organ surround was driven by an electro mechanical dimmer unit the size of a wardrobe. This has long since gone and currently the surround is controlled by a modern unit the size of a VCR.

Tonal Percussions
This is the unit mounted on the right hand side of the organ.
It consists of a Xylophone and a Glockenspiel. These are percussion instruments played by hammers. The hammers are connected to pneumatic motors operated from the keyboards. They can be set for single stroke playing or for repeating strokes known as re-iterate.

The "Traps"
These are non-tonal percussions, also sometimes called affectionally the "Toy Counter".
This unit contains devices designed to make a noise. On the Rochford organ they are mounted on the front of the organ chamber. In a theatre installation these are usually inside the chambers but at Rochford they do make an unusual display and can be better heard.
There is a set of drums, Cymbals, a Triangle, Castanets, a Tambourine, a Chinese block, a Sand Block and for those Christmas tunes, Sleigh Bells!