Active noise control of an exhaust-mounted, two-fan array

Fan arrays are used to cool various types of electronic equipment. In addition to adding multiple noise sources, using two nominally identical fans with closely spaced blade passage frequencies (BPF) can create an annoying beating effect. In this work, a two-fan, exhaust-mounted array has been considered for active control of the radiation at the BPF and second harmonic of each fan. Two con¬trol con?gurations were theoretically and experimentally compared. The ?rst control con?guration consisted of one controller using six control sources and six error sensors in a fully coupled control system designed to control the noise from both fans simultaneously. The second con?guration used two independent controllers with three control sources and three error sensors, i.e., one noise con¬troller per fan. Each noise control con?guration was theoretically modeled to examine minimum radiated power and appropriate near-?eld error sensor loca¬tions. Experimental results suggest that independent controllers perform better than a single controller at lower computational cost. It is also demonstrated that active reduction of radiation at both BPFs is suf?cient to signi?cantly reduce the audible acoustic beating between the two fans.