Acoustics

The acoustics of a room are important to the success of a church organ for two reasons: 1. Congregational singing flourishes if the room is "live" (has no carpet or other absorbent material). A church organ is successful if it is associated with a singing congregation. 2. An organ depends on the room in which it is placed to supply resonance.

Chest

A wooden box, containing wind, on which the pipes stand. Types of chests are differentiated according to the type of valves and stop action controlling admission of wind to the pipes. Each type of chest has its advantages and disadvantages. There are three main types of chests:

Slider chest: The usual tracker-action chest in which valves are connected directly to the keys with mechanical linkage (trackers) and stop action drawknobs are connected to sliders, which are thin boards extending the length of the chest and which must be in a certain position to allow wind to pass from the valves to the pipes. Slider chests in electric action organs use electromagnets or electro-pneumatic mechanisms to operate the key valves and sliders.

All-electric (electro-mechanical) chest: A type of chest in which electromagnets move the valves which admit wind to the pipes.

Electro-pneumatic chest: The type most frequently used from about 1900 until the present except for mechanical-action instruments. Each pipe, except for Mixtures, has an individual valve operated by a small leather-covered pneumatic motor, called a "pneumatic". Operation of the pneumatic is regulated by a small valve operated by a small electromagnet. Stop action is achieved by controlling current to the magnet or by controlling wind between the small valve and the pneumatic.

Console

A cabinet which looks like an upright piano on steroids, typically containing 2 or more keyboards, foot pedals, and all stop controls to operate the groups of pipes.

Couplers

Console devices, similar to stop controls, of two types: An Intermanual coupler allows a keyboard to play the pipes of a second division. Example: Great to Pedal coupler allows the Pedal keyboard to play the stops of the Great division. An Intramanual coupler allows the stops on a keyboard to be played at a second pitch. Example: Swell to Swell 16' allows the stops on the Swell to be played from the Swell keyboard at a pitch one octave lower than normal. Swell to Swell 4' allows them to be played an octave higher than normal. Swell Unison Off, or Swell Original Pitch Off, keeps the stops from playing at their normal pitch.

Divisions

A pipe organ is often built in large semi-independent sections as if they were separate musical instruments controlled from the same keyboard and console. The standard divisions of a pipe organ are called Great, Swell, Positif, Choir and Pedal. Not all pipe organs have all of these divisions.

Leather

Three main functions:

1. heavy fixed leather for valve facings;

2. heavy flexible leather for airtight joints in bellows;

3. thin flexible leather for small pneumatic motors.

All organs, including those with tracker action, use leather in some way. The thin leather used on small pneumatic motors has a poor reputation for longevity. The life span depends on the tanning process and on the way the leather is employed by the organbuilder. Leather tanned before World War II is likely to last 50-100 years. Longevity is increased by coating the leather with silicone preservative. Plastic substitutes for leather are inferior.

Pipes

Made of metal or wood, pipes are best often placed in a free-standing wooden case or in a chamber, which is a separate room located outside the main listening room. Most pipes are made of metal. Wood is used for some large pipes because of its stiffness and for a few small pipes because of its mellow tonal qualities.

Rank, Stop, and Voice

A rank is a set of pipes, one for each note on the keyboard, all speaking with the same tone color. A rank of pipes produces one voice. The number of ranks, stops, and voices is the same except where there are multirank voices, such as Mixtures, in which one stop controls several ranks which play together to produce one voice. The Roman numeral with the name of a Mixture tells the number of ranks in that voice or stop. The word "Stop" may be used to indicate either a voice itself or the console device used to turn the voice on and off. The term has an interesting history. The first organs did not have stop controls. That is, all of the ranks played all of the time, and there was no means of varying loudness or tone color. In about the 14th century, as organs grew larger, mechanical devices were introduced to turn off -- to "stop" -- some of the voices.

Rectifier

The electrical unit which supplies 12-volt d.c. for the organ action.

Reverberation

The lingering sound or “echo” effect or resonance of large spaces with hard surfaces. Reverberation gives a grand sound to pipe organs, but can be terrible for the spoken word (readings and sermons). The acoustics of the entire church space affects the reverberation of sound, and is usually optimized to allow reverberation of low frequencies.

Voicing

1. The techniques by which the parts of a pipe are adjusted to cause the pipe to speak. 2. The art of deciding the proper musical character (loudness, tone color, attack) of each rank of pipes and of adjusting the pipes to achieve the desired character.

Wind

The compressed air used to blow pipes. Wind is generated by a motor-driven centrifugal blower. Most church organs have a blower of from 1/4 to 3 horsepower. The wind pressure is regulated by one or more wind pressure regulators (reservoirs, bellows). Constant wind pressure is required for pipes, as the pitch and loudness of each pipe is proportional to the wind pressure.