Design of Remote Quiet Zones Using Spot-Type Sound Reducers

Abstract

SummaryThis paper presents a local control approach to generate remote quiet zones. To deal with situations where global control can hardly be achieved, it is proposed to use an arrangement of spot-type sound reducers as originally suggested by Olson and May. Assuming that cross-coupling between control units is weak, each can be controlled independently and a decentralised feedback controller is implemented without the need for direct monitoring of the primary source. Active noise attenuation in the remote target region is achieved using a linear quadratic optimization based on prior knowledge of the transfer path of the system. The performance of a particular configuration comprising three control units is examined by numerical simulation and experimentally evaluated for a tonal noise source in a free-field environment. An average noise reduction of about 6 dB was measured in a target region of volume 0.25 × 0.25 × 0.25 m 3 for a 160 Hz tonal primary source distant more than one wavelength from the secondary sources. The performance of the control system in relation to changes in the primary field is also considered with a view to extending the concept to more realistic enclosed sound field conditions in future work.

Dual-Zone Active Noise Control Algorithm

“…Active noise control (ANC) is widely used as it reduces noise at low frequencies. Global ANC can achieve a larger-space noise reduction in the control zone [1][2][3], while local ANC can realize multi-zone noise reduction [4][5][6]. However, under some special circumstances, such as anti-detection and noise reduction between seats where the sound field is distributed over multiple zones, it is necessary to decrease the increase of sound power outside the control zone when a large noise reduction is required in the control zone to prevent the detection and disturbance of others.…”