Listed only by Irwin, who says:

A large-scale, loud solo Diapason of 8' manual pitch, sounding less dull in tone than the average large-scale Diapason. It is somewhat against the logic inherent in the Diapason's harmonic structure to say that a solo Diapason can be voiced. Diapason means a firm fundamental and only a modicum of harmonics, usually fewer than twenty.
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The brilliant tone (many harmonics) of a solo flue, if given to a Diapason, at once classes it as a kind of Stentorphone or loud open Tibia.
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This stop is less bright than the Diapason Sonora and Stentorphone (classified as a Flute), nor is it so loud as they are. Any of these Diapasons or the Stentorphone can be flared outward towards their tops to build up even-numbered components - that is, a fuller tonality. Slotting has been seen also in this type of flue, particularly in very large organs. It provides additional components, giving either the Diapason-Horn or the Diapason-String approach.

Examples

Bibliography