Table 1: Comparison of property and method between AAC technology and ANC technology.

AAC technologyANC technology

(1) Technology nameAdaptive acoustic impedance control technologyActive noise control technology

(2) Noise reduction methodAdaptively controlled sound absorptionActively controlled sound cancellation

(3) Reduced noise contentsBoth tones and broadband noiseTones or broadband noise

(4) Control targetMaximum noise reduction in overall sound pressure levelMaximum tone reduction in sound pressure level

(5) Extension to low frequency noise region reductionUsage of acoustic resonance and absorption in acoustic resonant chamber spaceUsage 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 technologySimple and plain feedback control systemComplicated feedback control for multi-channel system

(8) Available range of technologyLow-high intensive sound (Max. 170 dB)Low-medium intensive sound (Max. 120 dB)
Low-high temperature (Max. 900 K)Low temperature (Max. 350 K)