A low-frequency feedback-controlled audio system

A novel closed-loop low-frequency speaker system has been designed, built, and tested which provides the control signal through the use of a single pressure-sensitive sensor internal to the speaker enclosure. This technique allows the use of one or more passive radiators in the same radiating system while ensuring that the control signal accurately reflects the total radiation from all elements. The nature of the sensor used also tends to correct for nonlinear distortion caused by finite cabinet volume, and the use of a passive radiator allows the production of a power level well beyond that produced by the same speaker in a sealed-box alignment. Feedback factors of 30 to 50 dB have been achieved using conventional speaker elements and active analog correcting networks. The effects of acoustical delay, placement of speaker and sensor, and direct acoustical radiation on the sensor are discussed, and results described. For purposes of subjective evaluation, conventional mid-range and high-frequency elements have been added re the system, and a stereo pair has been constructed and measured acoustically. (C) 1999 Acoustical Society of America. [S0001-4966(99)01308-9].