We are stuck with 27/25 as one generator, which I put horizontally.
Vertically we have a choice, and what we choose leads to different
complexities for the most compact versions of the tetrads. Below I
give various generators, tictactoe diagrams for a utonal tetrad, and
the notes of the tetrad. Choosing either 6/5 or 5/3, or else 10/9 or 9/5,
leads to a nice compact arrangement, and it seems to me a Bosanquet
keyboard with a 10/9-/6/5-27/25 triangle might be quite practical for
someone wanting to be able to play, for example, Ennealimmal[45] in
real time. This would be, therefore, a keyboard allowing considerable
flexibility playing perceptual 7-limit JI.
5/3 [1, 3, 5, 7/2]
O X O O
O X O X
O O O O
X O O O
6/5 [1, 3/4, 5/8, 7/8]
X O O O
O O O O
O X O X
O X O O
9/5 [1, 3, 5, 7/2]
X O O O
O X O X
O O O O
O O X O
10/9 [1, 3/4, 5/8, 7/8]
O O X O
O O O O
O X O X
X O O O
10/7 [1, 3/2, 5/2, 7/4]
O O X O O
X O X O O
O O O O O
O O O O X
49/40 [1, 3/2, 5/2, 7/4]
O O O O X
X O X O O
O O O O O
X O O O O
36/35 [1, 3/4, 5/8, 7/8]
O O O O O X
O O O O O O
O O X O X O
X O O O O O
54/35 [1, 3, 5, 7/2]
O O O O X O
O O O X O X
O O O O O O
X O O O O O
21/20 [1, 3/2, 5/4, 7/4]
O X O O O O O
O O O O X O X
O O O O O O O
X O O O O O O