Extension system. Every Stop on the organ labeled Tibia, for example, comes from the same rank of pipes. Stops at 16', 8', 4', 2' plus mutations (stops which play at another pitch) all come from the same pipe rank. This means that if an octave is held down with 16 + 8 + 4 ft stops only four pipes are speaking and not six as you would expect. (two per rank).
A properly extended rank of pipes should have the pipe-work to cover the extra pitches demanded of that rank. If the stops go up to 2ft pitch then there should be two more octaves of pipe-work going upwards. If that same stop is available at 16ft pitch then the pipe-work should be extended downwards an octave. Often cheating occurs with lower pipe-work being shared between stops. The 16ft Tibia for the bottom octave of the keyboard may use the same pipes as the Bourdon on the pedals.
The main thing about the Theater Organ is that the Pipe-work should blend together to give a sound where everything can be used to good effect. The registration skill is to blend together various ranks at various footage's to give contrasting and ever changing tonal colours. It can take years of thought and experiment to thoroughly understand how to get the best out of a particular instrument. Wurlitzer Organs, for example, are voiced to give the organist endless variety of tonal blends from the loud and raucous to the quiet and ethereal.
In addition to the pipe-work there are vibraphones and glockenspiels - yes, the real thing - hidden away, plus a 'toy shop' of drums and cymbals that can be mixed in to give that additional sound which adds to the interest of the instrument.
All of the pipes and extra items are behind movable shutters which the organist controls with his feet. There may be more than one set of shutters
and boxes containing pipes; only very simple organs have one while larger instruments may have four of five. Some item may be outside such a 'Swell Box'. The grand piano on the stage of the Blackpool Tower can be played from the organ console.
The traveling organist playing organs at many venues was assisted by the fact that a standard stop layout was adhered to. While the pipe ranks on each instrument may not be the same every rank included would have it stop tabs in the same place in the horseshoe layout which is virtually standard for the Theater Organ Console.
The console shown above is the Paramount Wurlitzer - I'm sure they wont mind the use of the picture - and I recommend CD Pro Arte CDD 339 'Give My Regards' where the Paramount Organ is played by Lyn Larsen.
Many Classical/Church organists decry the Theater Organ but, in my opinion, and I play both, the Theater Organ is an instrument in its own right and good performers deserve as much credit for their musicianship as their fellow classical
I discovered a long time ago that if you put a Church Organist in front of a Theater Organ most of them do not know what to do with it.
There were exceptions and I remember Dennis Tidmarsh, a very proficient church organist who played at 'St. Michael at the North Gate', Oxford, who was also an excellent Theater Organist.
There are two main streams of Church Organ. They became known as Church Organs as that is usually where they were found. As that is no longer the case I will desist from calling them Church Organs.
The Classical organ is mainly found on the Continent. The Classical style instrument is appearing more in the UK replacing original Romantic Organs where the 'chiff'
found in the voicing of many flutes of Classical organs was removed. A new pipe rank was added called the Open Diapason. This was more suited to the style of music performed in English Churches where a loud fundamental sound was thought better rather than the more lightly pitched classical style based on the Principle.
Basically the Diapason is a large scale Principle. The Principle rank is used on Romantic organs but at 4ft (octave higher) pitch.
Scale is pipe length to pipe diameter. The smaller the diameter the more the upper harmonics become apparent as the fundamental pitch diminishes in volume.
If you used a spectrum analyzer to 'see' the various pitches coming from an organ pipe many mutations (not in unison) appear in the upper frequencies. The idea of the Mixtures and Mutation stops is to emphasise these various frequencies existing in the basic 8ft sound. Adding mutation stops and mixtures adds brightness to the sound not necessarily intensity.
A lot of music was transcribed for the organ and various composers wrote for the Romantic Organ; Reinberger comes to mind. I have played Elgar transcriptions for the organ in the past.
The music of Bach sounds much better on a Classical organ where you can hear every note played. To hear all the various parts in Fugues, for example, you need to be aware of every time the theme comes in and the development of each part which may be going on underneath the top line. The small, but audible, chiff, which the Romantic builders voiced out of English Organs, enables each part to be followed as each note played can be clearly heard.
Each type of organ has its place and is suitable for a certain type of music.
The difference is:
A Romantic Organ played loud is like being hit by a sledge hammer.
A Classical Organ played loud is like being cut with a knife.
Whatever your taste in organ music - is there anything else - I believe each type should be enjoyed and played with love.
While Meditating I entered a building like St. Pauls Cathedral in London. I looked around for the organ but could not find it. A man came up to me and I asked him where it was. He said there wasn't one. I replied that there must be in a place this size. By now we were standing underneath the dome and, looking up, it was full of light. I looked at him and he repeated "There isn't one here, this is only the doorway!"
If that is only the doorway I look forward to playing the organs waiting somewhere there.