From the Greek, ‘through all’, the Diapason is the main chorus flue stop of the classical organ, and is found in almost all theatre organs as well.

Open, metal*. Larger scale examples (eg Diaphonic Diapason) may have a leathered upper lip, and narrower scale examples (eg Horn Diapason) may have a bridge.

Broad, warm sound midway between flute and string. May voiced as a powerful, dull stop (esp. Diaphonic Diapason) or more lightly with more overtones (esp. Horn Diapason, Violin Diapason).

Open Diapason
Open Diapason
Diaphonic Diapason
Diaphonic Diapason


Diaphonic Diapason

Diaphonic Diapason with the 16′ extension of diaphonic pipes. Usually a heavy, large-scale stop with leathered upper lips.

Open Diapason

Standard name for stop – confusingly, may also have a diaphonic 16′ octave. Generally, less heavily voiced/of narrower scale than the Diaphonic Diapason.

Horn Diapason

Smaller scale stop, often but not exclusively used by Wurlitzer as a second Diapason on larger organs when the 16′ octave will be diaphonic (metal) and labelled ‘Bass’ on the stopkeys. May also be termed Violin Diapason. Usually with a tuning slot and, in some cases, roller across the mouth.


A very quiet member of the Diapason family (often, incorrectly, considered a string stop). May be partnered with a celeste, Unda Maris in Wurlitzer nomenclature.


4′ Diapason stop. Horn Diapason 4′ may be labelled Octave Horn on Wurlitzers.


2′ Diapason stop. On many theatre organs is derived from a string rank rather than the Diapason itself, in order to give a more balanced ensemble.

* The Stopped Diapason, usually wooden, is closer to the flute family in tonality and rarely appears on the theatre organ.