Active Control of Environmental Noise

Active Control of Environmental Noise, Vii: Performance of Multi-Frequency, Multi-Channel, Freefield Sound Cancelling Systems

“…However, large cancellations have been obtained over considerable distances using a divergent arrangement of basic cancelling units in an electronically controlled acoustic shadow (ECAS) con"guration [1]. The paper focuses on the reduction of predictable discrete frequency noise and multiples of discrete frequencies (periodic noise), which is one of the main causes of industrial annoyance and hearing loss.…”

“…To compare the acoustic performance of real hardware implemented adaptive systems with theory, the sound pressure characteristics were computed using acoustic wave equations used to establish the acoustic properties in references [1,2]. The system dimensions were chosen so that the acoustic characteristics could be computed and then compared with the measurements made in the laboratory.…”

Active Control of a Moving Noise Source—effect of Off-Axis Source Position

“…The local-control strategy, on the other hand, is to attenuate sound pressure in certain directions or in certain desired regions. It is a more practical option when global control is not achievable [4,5]. Furthermore, in many applications, the reduction of the sound pressure over the whole space is not necessary; it is su$cient to create quiet zones in some desired areas.…”

Active Control of Environmental Noise, Vi: Performance of a Fundamental Free-Field Sound Cancelling System

“…The basic wave theory using computer modelling, and point acoustic sources in free-"eld was reported in reference [1]. The theory was extended to complex high-frequency sound from large non-compact sources in reference [2].…”