Detection of Secondary-Path Irregularities in Active Noise Control Headphones

Headphones with adaptive feedback ANC show a good performance if the secondary-path is well known. The secondary-path however changes considerably if the headphones are lifted. In this paper, it is shown that these changes mainly affect the low frequencies of the secondary-path and that the resulting low-frequency poles of the system cause instabilities. However, the changes in the secondary-path can be detected via low-frequency changes of the adaptive filter. A cost-efficient algorithm in the time-domain is developed to detect and react to these changes in order to keep the ANC system stable. Experimental results show that the algorithm yields the desired ANC performance in the regular use case and still avoids instabilities even during sudden changes in the secondary-path.