Active noise control for double glazing

Abstract

Implementation of ANC on double glazing windows has been investigated through controlling the volume of the air gap between the two window panes. In past work, the major problem was the location (generally in the middle of the glass plane) and/or efficiency of the transducer generating the counter noise. A new transducer (called strip-transducer) overcomes this problem by locating the loudspeaker system in the window frame. The transducer consists of a beam like rigid membrane (less than 20 mm width and 500 mm length) attached to a longitudinal voice coil suspended in the magnetic field generated by a set of magnets located in a metallic U-shaped profile. These strip-transducers are driven by a local ANC control loop, the reference sensor being either a microphone or an accelerometer located in the emitting side and the error microphone being located on the receiving side. The control loop algorithm is based on TechnoFirsts patented cloverleaf filter, allowing a faster response than traditional X-LMS algorithms. The transducer design uses the concept of tuned membrane resonator (TMR) to reduce the drive energy needed. A prototype using this new concept is under experimentation and has shown very encouraging results.