This paper presents a theoretical investigation on actively controlling the low frequency sound absorption of large-sized micro-perforated panel absorber (MPPA) on oblique incidence condition. The existing small sized hybrid passive-active MPPA consisted of a piston source (usually loudspeaker) in place of the back wall and the micro-perforated panel (MPP) is complicated and inapplicable. Placing the loudspeaker in a large sized MPPA is a more easily implemented and cost-effective scheme for realizing the improvement of low frequency sound absorption in large area. The loudspeaker can be viewed as a point source for the large sized MPPA. The modal analysis approach is developed for such active MPPA to calculate sound absorption coefficient before and after control for the oblique incidence plane wave excitation. The sound absorption is significantly improved in a wide low frequency range after control, which demonstrates the feasibility of the approach. The physical nature of active control of low frequency sound absorption is also analyzed for the oblique incidence condition, which can provide guidance for engineering application of this technic.

large sized micro-perforated panel absorber, oblique incidence plane wave, low frequency sound absorption, active control