Pentadacus

Pentadacus

Subgroups	5.7.11
Comma basis	831875/823543
Reduced mapping	⟨1; 3 7]
ET join	43ed5 & 14ed5
Generators (CWE)	~55/49 = 194.820 ¢
MOS scales	1L 131<5/1>, 1L 12s<5/1>, 1L 13s<5/1>, 14L 1s<5/1>, 14L 15s<5/1> , 29L 14s<5/1>/ 14L 29s<5/1>
Ploidacot	tri7cleft
Minimax error	-integer-limit:  ¢
Target scale size	-integer-limit: notes

Pentadacus is a nonoctave regular temperament in the 5.7.11 subgroup which tempers out the comma 831875/823543. It is even more exotic than Bohlen-Pierce, lacking both 2/1 and 3/1, and typically it would be used with an equave of 5/1. It is generated by a meantone-esque small whole tone interval that represents 54/49. Stacking 3 of these tones gives 7/5 and 7 of them give 11/5. Pentadacus has both low complexity (especially by the standards of the 5/1-equivalent world, where scales have lots of notes) and low error if tuned correctly, providing an efficient traversal of the 5.7.11 subgroup. It was discovered by CompactStar in 2026.

14ed5 is an inaccurate but important tuning of Pentadacus, because in 14ed5, the whole tone generator corresponds to a single step of 14ed5, although the whole tone is bigger than usual being around 9/8-sized, causing the approximations of 7/5 and 11/5 to be bad. Basically, pentadacus can be thought of as a compressed 14ed5, at least until you hit 5/1. 14ed5 is also close to 6edo, the familiar whole-tone scale with octaves, and 6 generators in pentadacus can sound like a tempered octave but it’s usually bad enough to be dissonant.

Pentadacus is connected to the octave-repeating didacus temperament as both have a small whole tone generator for which 3 stack to 7/5, and 11-limit didacus is actually a weak extension of pentadacus to include octaves.