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Niels Henrik Pontoppidan

Research Area Manager/ Research Engineer

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mail@eriksholm.com

Designing a microphone array for a headset is different from traditional free-field array design with a far-field target. This is because the headset array will be located next to a large sound-scattering object (the user’s head), and because the target source (the user’s mouth) is in the near-field of the array.
the-challenges

The challenges

This investigation was based on the development of the handheld Lexis array microphone. From that study, the routines for optimising the array processing were readily available.

The two main challenges were:

1. To replace the simple free-field model of sound propagation with a model that included the head (modelled as a rigid sphere) and which allowed for a sound source on the sphere, in order to model the target sound source (the user’s mouth).

2. To replace the standard Directivity Index and the noise sensitivity metric with measures relevant for the headset case.

Results

The array design based on the computational model was evaluated with measurements which showed excellent conformity. The results revealed that compared to the standard free-field array, the headset array yielded better low-frequency performance. This is because of the near-field (proximity) effect. At higher frequencies, the headset array’s performance level was below that of the free-field array.


Further reading

Laugesen S, Rasmussen KB, Christiansen T (2003). Design of a microphone array for headsets. Proceedings of the IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, NY, USA.