Thai classical music uses approximately 7-tet because Thai instruments have bar-like spectra whose dissonance curves have minima near 7-tet steps

Thai pi phat music (featuring renat, ranaat, and similar bar instruments) uses a tuning close to 7 equal divisions of the octave (~171 cents per step). Sethares shows that the spectra of ideal bar instruments have partials at ratios approximately 1 : 2.76 : 5.40 : 8.93 (the modes of a free-free bar). Computing the dissonance curve for these partials reveals minima near 7-tet step intervals. Thai music thus follows the same principle as gamelan: the scale is related to the spectrum of the instruments. The polyphonic structure of Thai pi phat music (using stratified melodic layers at different speeds) also creates dissonance patterns that ebb and flow with the structural hierarchy of the music.

Examples

Renat (Thai xylophone) bars produce an ideal-bar-like spectrum. Dissonance curve of this spectrum shows minima close to 171, 343, 514, 686, 857, 1029, 1200 cents — near 7-tet. Thai music avoids Western intervals because those would be dissonant with bar spectra. The same spectrum also produces minima near certain steps of the pelog scale, explaining compatibility between Thai and Balinese musical systems.

Assessment

Explain why a Western musician playing a renat in 12-tet produces dissonant results. What property of bar instruments causes this? How does Sethares’ framework predict which scale a new instrument type would ‘naturally’ want?