Multipoint equalization with the condition number

Equalizing the acoustical frequency response of a room at several points, using several loudspeakers, involves taking the inverse of a matrix frequency response. An exact inverse is generally not practical because the room transfer-function matrix is often nearly singular at some frequencies, causing high-Q equalizer peaks and making the room response unacceptable at points other than those where measurements are taken. We show how to diagnose and deal with the problem. The results presented were acquired using measurements taken in a car.