Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner

Table 1

Comparison of property and method between AAC technology and ANC technology.

	AAC technology	ANC technology
(1) Technology name	Adaptive acoustic impedance control technology	Active noise control technology
(2) Noise reduction method	Adaptively controlled sound absorption	Actively controlled sound cancellation
(3) Reduced noise contents	Both tones and broadband noise	Tones or broadband noise
(4) Control target	Maximum noise reduction in overall sound pressure level	Maximum tone reduction in sound pressure level
(5) Extension to low frequency noise region reduction	Usage of acoustic resonance and absorption in acoustic resonant chamber space	Usage of low frequency sound generated by speakers
(6) Control method and procedure	(i) Large peak frequency shift and peak level increase in acoustic absorption spectra of duct liner for tones and broadband reduction, by adjusting reactance and resistance parts of acoustic impedance of liner with mobile reflective plate apparatus and tunable perforated plate apparatus	(i) Determination of acoustic spinning modes of tones with microphone array measuring systems and acoustic modal analyzer.; (ii) Generation of spinning modes with secondary noise source array, amplifiers, noise generator, and multichannel synthesizer.; (iii) Matching and cancelling spinning modes of tones with phase shifter
(7) Feedback control system of technology	Simple and plain feedback control system	Complicated feedback control for multi-channel system
(8) Available range of technology	Low-high intensive sound (Max. 170 dB)	Low-medium intensive sound (Max. 120 dB)
	Low-high temperature (Max. 900 K)	Low temperature (Max. 350 K)