Most linear array beamforming consider the sound source impinging on the array at the broadside. Endfire beamforming however considers a source that is impinging the array along the axis of the linear array. Consider an N microphone array as shown in Figure 1:
Figure 1: N microphone array
The aim is to find weights such that the signals from the N microphones cam be combined to form a beam in the desired direction and nulls in the undesired directions. For two microphones, the constraints are used to form:
where is the desired beam direction and is a desired null direction. Given , the choice of will determine whether the spatial beam will be a dipole, cardioid, hypercardioid or supercardioid. Sometimes, two cardioids are formed and their difference used to perform spatial beams.
Figure 2 below illustrates these 4 spatial beams that can be obtained using two microphones.
Figure 2: Endfire beam patterns
Increasing the number of microphones helps in reducing the beamwidth.
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