Listed only by Irwin, who says: A String stop of mild tone, at 5-1/3' on the manuals, and 10-2/3' on the pedals, either voiced with the orchestral timbre of the small-scale pipes or as a sort of Violone. This is the �Twelfth� of the sub-unison series of stop-pitches. It should be combined with a heavy-toned 16' on the manuals, or a 32' stop on the pedals, to keep from unbalancing the tone. The organist should remember that all of its extensive series of harmonics duplicate none of those heard from a 32', 16', or 8' rank. If of the proper loudness with the other stops, it makes the tone cleaner and the pitches more obvious; if too loud, it will make the tone too �quinty,� and the listened will lose all sense of balance between harmony and melody. It is usually heard from a large String organ. Irwin is incorrect. If properly tuned as a separate rank (not borrowed from an octave-sounding rank), all of the harmonics of a 5-1/3' stop will duplicate harmonics of an open 16' stop. Since harmonics are integer multiples of the fundamental, and the fundamental of a 5-1/3' stop corresponds to the 2nd harmonic of an open 16' stop, it takes little math to see that integer multiples of the 5-1/3's frequency must also be integer multiples of the 16's.
Viol Quint 5-1/3', 2-2/3', Orchestral; Cadet Chapel, United States Military Academy, West Point, New York, USA; Moller.