Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner

<table>Variation of overall fan noise reduction by adaptive duct liner II of AAC technology II model with duct liner porosity change. Fan rotational speed 4000 rpm; acoustic measuring point 60 deg.; fixed perforated  plate hole dia. = 1.0; pitch = 2.0 acoustic absorbent material stuck on plate; poal + acousticel.</table>

Advances in Acoustics and Vibration

fig14

Figure 14

Figure 14: Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner 