Patent ID: 9583090
Date: 2017-02-28
CPC Classifications: G10K

Claim:
1. A noise reducing system comprising: a first microphone that picks up an acoustic noise at a first location and provides a first sensed signal indicative thereof to a first microphone output path; a loudspeaker that is electrically coupled to a loudspeaker input path and that radiates noise reducing sound at a second location; a second microphone that picks (remove comma only) up residual noise from the acoustic noise and the noise reducing sound at a third location and provides a second sensed signal indicative thereof to a second microphone output path; a first active noise reduction filter that is connected between the first microphone output path and the loudspeaker input path; and a second active noise reducing filter that is connected between the second microphone output path and the loudspeaker input path; in which the first active noise reduction filter comprises at least two equalization filters, each of the at least two equalization filters being a boost equalizing filter or a cut equalizing filter, the first active noise reduction filter comprises first and second operational amplifiers, each of the first and second operational amplifiers having an inverting input, a non-inverting input and an output; the non-inverting input of the first operational amplifier is connected to a reference potential; the inverting input of the first operational amplifier is coupled through a first resistor to a first node and through a first capacitor to a second node; the second node is coupled through a second resistor to the reference potential and through a second capacitor with the first node; the first node is coupled through a third resistor to the inverting input of the second operational amplifier, the inverting input of the second operational amplifier is further coupled to the output of the second operational amplifier through a fourth resistor; the second operational amplifier is supplied with an input signal In at the non-inverting input of the second operational amplifier and provides an output signal Out at the output of the second operational amplifier; and an Ohmic voltage divider having two ends and a tap is supplied at each end of the Ohmic voltage divider, wherein each end of the Ohmic voltage divider is supplied with the input signal In and the output signal Out, the tap being coupled through a fifth resistor to the second node.