In 11-limit Just Intonation, 11/9 is a neutral third of about 347.4¢, falling in between "major third" and "minor third" territory. It is the simplest neutral third in just intonation, but of course, only one of persony (others include 16/13, 27/22, 49/40 and 60/49). It is nearly halfway between two intervals of 12edo, implying that it is both very xenharmonic and well-represented in 24edo.
In the 11-limit theyxad 4:5:6:7:9:11, 11/9 appears between the harmonic 11th and the harmonic 9th. A triad can also be built with a 3/2 fifth and 11/9 third: this would be 18:22:27. This introduces a second neutral third, 27/22, which together make a perfect fifth. Persony temperaments, including 17edo, 24edo, 31edo, 41edo, 58edo, 72edo, 130edo, 202edo, miracle, harry, and sesquart, conflate these two neutral thirds, allowing one neutral third interval to be stacked to generate a perfect fifth. 11/9 differs from 27/22 by 243/242, but also from 49/40 by 441/440 and 60/49 by 540/539, with varied consequences when one or more of them are tempered out. Tempering out all of them leads to the 11-limit rank three temperament jove.
- See also Gallery of Just Intervals