Theatre Organ Parts – In the Organ Chambers

Experience the sound of the Theatre Pipe Organ

Most of us know that a Theatre Pipe Organ works by having wind from an electric blower pass through organ pipes which are actuated by selecting stop tabs, and then playing keys on the keyboards/pedalboard.  But for those of us who have never experienced playing at the console, or who have never examined the inner workings of one of these complex instruments, some of the parts we read about can be a mystery.  We have thus compiled some brief definitions of typical organ components:

In the organ chambers:

Pipe Ranks

Rank of Pipes  -  A set of pipes which produce the same sound up and down the musical scale. ie Flute, Diapason, Violin, Tuba, Trumpet, Clarinet, Saxophone, Post Horn,  Kinura, etc.  Some pipes are made of metal, others of wood.

Chest - A long, winded (air pressurized) wooden box with holes in the top for a rank or ranks of pipes to sit into. Under each pipe is a valve that opens when the pipe is to speak. Under the chest is an electromagnet that is turned on when the pipe (or note) is played at the console. This magnet, through a series of pneumatics (small air bags), opens the valve. Air is thus supplied to the pipe, and the note sounds. A unit chest usually holds 61 or more notes of one particular rank of pipes. (Organ keyboards encompass 61 notes).

Chests in foreground, awaiting installation of pipes.

Offset – An offset chest is usually a 12 note chest that holds pipes that will not fit on the main 61 note chest. It extends the rank with 12 higher or 12 lower notes, and it is “set away” from the rest of the rank, hence the term “offset”.

Offset chest with 12 Pipes.

Regulator / Reservoir – A unit designed to regulate the wind pressure from the organ blower before it enters the various chests. The regulator portion holds the wind at a steady rate. The reservoir portion comes into play when there is a heavy demand on the wind supply because many pipes are playing at the same time. It serves as a backup to keep the wind pressure up.  Different ranks of pipes can operate on different air pressures in the same organ, hence the need for a number of regulators.

Six Regulators, 3 in back, 3 in foreground.

Winker or Equalizer-- A small regulator that is usually used to regulate the air pressure to operate tuned percussion instruments (xylophone, chimes, etc) or air driven swell shade motors, but not pipes.  Wurlitzer used Equalizers (their term for them) on consoles and swell shades.

Swell Shade Winker

Dice Box – A small regulator without a reservoir. Placed between the regulator and the chest, it was used by the Robert Morton Company to “fine tune” the wind pressure supplied to the chest.  Our Wonder Morton crew chief says that he has never seen the device used on other than a Morton Vox Humana rank. 

Tremulant or Tremolo or Trem -- A very important item in the theatre organ. It is the unit that causes wind pressure to change upwards and downwards from the normal “regulated” pressure in a steady beat or time sequence.  The result is that the pitch of the pipes on the chest is varied sharp and flat from the normal pitch, creating the distinctive vibrato that we associate with a human voice.  The variance in pitch, or excursion in pitch, plus the change in volume (amplitude of the sound wave) spread among all the pipes in the organ creates a very full, throbbing, dynamic sound that is distinctive to the Theatre Pipe Organ.  The tremulant works with a valve to exhaust the air from the source (either the chest or regulator) and can either be self-powered with a bellows that inflates and then collapses to open and close the valve, or electrically with a magnet that operates the valve.

Wurlitzer Tremulant  (Note bellows on bottom)

Wurlitzer Tremulant with cover removed

Dump Box – The term for an electrically powered tremulant.

Swell Shades/Shutters – A unit resembling a set of fixed vertical window blinds which cover the opening from the organ chamber to the listening space. They control the volume of sound escaping the chamber. The shades are operated from an expression pedal (swell shoe) at the console. The fixed wooden slats can rotate from a fully closed to a fully open position.

A set of partially open swell shades viewed from the listening space.

Partial view of closed swell shades from inside the organ chamber.

Cipher – An organ pipe which continually speaks when it shouldn’t.  Once the blower is turned on, the entire organ is under pressure. Each pipe speaks when the valve beneath it opens allowing air in. If a valve malfunctions due to a speck of dirt, or deterioration of its leather components, air leaks into the pipe causing it to continually speak. When this happens during a concert, the quick fix is for someone to go into the chamber and remove the offending pipe from its chest. The air then leaks harmlessly into the chamber until the valve can be repaired.