**Title: ** Implementation of a Superdirective Beamformer based on an Extended Modal Subspace Decomposition

**Authors: ** Martin Eichler, Arild Lacroix

**Abstract:**

Microphone arrays in combination with a suitable beamforming algorithm
provide means to spatially filter signals from a given sound field. One very
general beamforming approach is the method of Modal Subspace Decomposition
(MSD) which regards the array and the beamformer as an operator applied to a
coefficient vector. Based on this operator, an eigenvalue problem is considered the
solution of which yields a set of eigen-beampatterns which serve as a basis for the
series expansion of the desired beampattern (directivity). From the series expansion
coefficients, the optimum filter coefficients for the beamformer filters are calculated.
In an earlier work, an extension to MSD was presented which uses a certain
class of IIR filters instead of FIR filters, thus making the algorithm superdirective.
Hence, even with very compact arrays of arbitrary geometry, it is possible to
achieve directivity at low frequencies where the wavelength is large in comparison
to the array size. In this contribution, the underlying theory of this approach is outlined
and measurement results obtained from a real-time implementation in a real
acoustic environment are discussed.

**Year:** 2009

**In session: **Signalverarbeitung

**Pages:** 174 to 181