Change of sound characteristics of yidaki (didgeridoo) coated with thick films of lacquer (Wajima-nuri)

Thick films of lacquers were coated by Wajima-nuri on a yidaki (didgeridoo), a woodwind instrument loved by indigenous Australians from ancient times. An investigation of frequency spectra of fast Fourier transform before and after the coating revealed a significant enhancement of sound pressure from the yidaki coated by Wajima-nuri, particularly in the low-frequency region of 500 Hz-1 kHz. All peaks of the sound pressures were shifted to higher frequencies by the Wajima-nuri. The improvement of sound characteristics was greater by Wajima-nuri both inside and outside the yidaki than by Wajima-nuri on the outside only. It might have been due to the fact that the lacquers soaked through the perforated holes and cracks inherent to the original yidaki. Urushiol in lacquers tends to solidify by oxidative polymerization, which resulted in a smooth surface that suppressed the turbulence of the air breathed. These results could be useful for other musical instruments.