Irwin lists Sub Quint with the following description:

A Foundation stop, usually of Diapason tone, at 10-2/3' on the manuals, and 21-1/3' on the pedals. Flutes, both open and stopped, may be substituted for this Diapason, and are sometimes borrowed or extended from some other ranks of pipes of different name. These stop-pitches represent the third harmonics (“Twelfths”) of the sub-sub-unison series. They both speak at the notes two octaves below the true Twelfths of the unison series. They are necessary if the organist is to have available a complete choir of stop-pitches for his pedal 64' series and the manual's 32' series. The pedal's 21-1/3' Sub Quint will make a Resultant of 64' with any flue of 32'. The manual's 10-2/3' Sub Quint will make a manual Resultant with any flue 16', but this latter effect is usable in only a few large organs, perhaps in large, high-ceilinged cathedrals, as a device occasionally to deepen the 32' manual tone. Synonyms: Gross Quint, Grossquintenbass.

While Irwin lists Gross Quint as a synonym for Sub Quint, actual usage suggests that it is in fact a synonym for Fifth or Grosse Quinte. The name Grossquintenbass is not, strictly speaking, a synonym for Sub Quint, as the “bass” suffix indicates a pedal stop which would not properly appear in a manual division.

The name Double Quint is mentioned only by Audsley in his entry for Gravissima in The Art of Organ-Building, without any definition other than being a pedal stop at 21-1/3' pitch.

Examples

Sub Quint amd Double Quint are each listed only twice in Osiris:

Sub Quint 10-2/3', Great; Convention Hall, Atlantic City, New Jersey, USA; Midmer-Losh 1929-32.

Sub Quint 10-2/3', Great; John Wanamaker Store, Philadelphia, Pennsylvania, USA.

Double Quint 10-2/3', Great; Liverpool Cathedral, Liverpool, England; Willis 1923.

Double Quint 21-1/3', Pedal; Royal Albert Hall, London, England; Willis 1872.

Bibliography