Patent ID: 9613612
Date: 2017-04-04
CPC Classifications: G10K

Claim:
1. A noise reducing sound reproduction system comprising: a loudspeaker that is connected to a loudspeaker input path; a microphone that is acoustically coupled to the loudspeaker via a secondary path and connected to a first end of a microphone output path; a first subtractor that is connected to a second end of the microphone output path and via a first end of a first useful-signal path to a useful-signal input, the useful-signal input configured to receive a useful signal to be reproduced by the loudspeaker; an active noise reduction filter that is connected downstream of the first subtractor; and a second subtractor that is connected between the active noise reduction filter and the loudspeaker input path, the second subtractor further connected directly to the useful-signal input via a first end of a second useful-signal path; wherein a second end of the first useful-signal path and a second end of the second useful-signal path are connected with each other; the second end of the second useful-signal path connected directly to the first end of the second useful-signal path; the first useful-signal path comprises a low-pass filter configured to filter the useful signal upstream of the first subtractor, the low-pass filter comprising a transfer function that is an approximation of the secondary path between the loudspeaker and the microphone so that the useful-signal input at the microphone is roughly identical to the useful-signal output at the loudspeaker; and a filter input signal is supplied to the active noise reduction filter by the first subtractor.