Design and applications of lean active resonator silencer cassettes

Active resonator silencer cassettes (ASCs) are composed of a housed loudspeaker coupled with a microphone sensor via an analog electronic control loop. ASC-units are very efficient in attenuating low-frequency noise, especially in applications with tight constraints on the available installation space. At the Fraunhofer IBP the design of ASC-units, ASC-arrays and their practical application has been investigated for more than two decades. This paper gives a brief overview on the characteristics, the performance and some practical applications of classical ASC-units and arrays. Classical ASC-units have dimensions in the range of decimetres. More resent work on ASCs at the Fraunhofer IBP has been focused on the design of much leaner units with dimensions in the range of centimetres. Scaling the dimensions of the ASC-units down by an order of magnitude widens the range of possible applications, but also comes with a number of design challenges. In this paper, these design challenges and the characteristics of the lean ASC-units and arrays are discussed. The paper also presents results of studies where the lean ASC-units are used to build up a compact active noise control system for a partly opened sliding window, and a compact active silencer system for a domestic ventilation duct.