Reduction of Construction Machinery Noise in Multiple Dominant Frequencies Using Feedforward Type Active Control

Usually, engine sound of construction machinery has several predominant frequencies in low frequency region and that sometimes makes noise complaint from neighbors. The low frequency noise is difficult to be reduced by conventional methods such as soundproof walls, without remodeling the machine greatly. So we developed a feedforward type active noise control (in the following, ANC) system which can be operated more stable against noise of working machineries than conventional feedback control system. The ANC system estimates the predominant frequencies of the band-pass-filtered noise in time domain with an optimized filter of least mean square algorism, and calibrates amplitude and phase at the each predominant frequency in time domain, then the system outputs the same amplitude and anti-phase sound of the engine noise from a loudspeaker located in the vicinity of a noise source of engine sound such as an exhaust tube. By the numerical simulations, we confirmed the ANC could output the appropriate anti-phase sound of noise. Through the field experiments, the ANC system showed remarkable reduction effect of the engine noise from construction machinery (concrete mixer truck, etc.) about 5 to 10(dB) in 80 to 160(Hz) band.