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Acceptance Angle

As we saw in Section 6.1, the bandwidth of a filter is determined by the frequency band limited by the points where the signal is 3 dB lower than the maximum output of the filter. Microphones have a spatial equivalent called the acceptance angle. This is the frontal angle of the microphone where the sensitivity is within 3 dB of the on-axis response. This angle will vary with polar pattern.

In the case of an omnidirectional, all angles of incidence have a sensitivity of 0 dB relative to the on-axis response of the microphone. Consequently, the acceptance angle is $\pm180^\circ$ because the sensitivity never drops below -3 dB relative to the on-axis sensitivity.

A subcardioid, on the other hand, has a sensitivity that drops below -3 dB when the angle of incidence of the sound source is outside the acceptance angle of $\pm99.9^\circ$. A cardioid has an acceptance angle of $\pm65.5^\circ$, a hypercardioid has an acceptance angle of $\pm52.4^\circ$, and a bidirectional has an acceptance angle of $\pm45.0^\circ$.

Table 6.7: Acceptance Angles for various microphone polar patterns.

Polar Pattern (P : G)	Acceptance Angle
Omnidirectional (1 : 0)	$\pm180^\circ$
Subcardioid (0.75 : 0.25)	$\pm99.9^\circ$
Cardioid (0.5 : 0.5)	$\pm65.5^\circ$
Supercardioid (0.375 : 0.625)	$\pm57.9^\circ$
Hypercardioid (0.25 : 0.75)	$\pm52.4^\circ$
Bidirectional (0 : 1)	$\pm45.0^\circ$