Microphone arrays use a plurality of microphone capsules, and combine output signals of the microphone capsules in order to obtain a specific directivity of the microphone array in a particular direction. The direction of an audio source can be detected mainly by analyzing delays between audio signals arriving at each microphone capsule. Correspondingly, a directivity of the microphone array can be implemented by combining delayed microphone output signals, and the direction can be controlled by modifying the respective delays.
Microphone arrays may use automatic beam focusing in order to automatically adjust their directivity towards a speaker. For example, the microphone array may determine a direction of the speaker by determining a direction of maximum sound input. In a practical approach, the microphone array may scan sound signals from different pre-determined directions of a given scan area. It may pick up and compare energies of sound signals from these directions, determine a direction of maximum sound energy and adjust the delays for its microphone capsules so as to adjust its directivity into the determined direction. Such microphone array is described e.g. in US 2017/0164101 A1.
However, this may lead to a problem if there is a sound source within the scanned area which is not intended to be picked-up by the microphone array. For example, disturbing sound may be heard through an open window or open door. For microphone arrays that are installed e.g. in conference rooms, the disturbing sound sources may be electronic devices, such as a beamer, a loudspeaker or an air conditioner. Particularly if the disturbing sound source is near the microphone array, or in moments of silence when no person is speaking, the audio signal emitted by the disturbing sound source may irritate the microphone array. The disturbing sound may be the signal of maximum energy within the scan area, so that the microphone array focuses on the disturbing sound source. The microphone array will then refocus very often, which may decrease its signal quality, and may even pick up the sound emitted by the disturbing sound source and amplify it.