Figure 310. Basic components of the ElectroVoice Model 642
Card line directional microphone
c. Since the ports are equally connected to the transducer unit by the
common tube, acoustic delays are introduced ahead of the transducer element.
d. When placed in a plain wave sound field, this equal sensitive line with
variable delay produces wave interference in the common cavity at the front of the
transducer unit.
e. The magnitude of the interference will depend on the angle between the
plain wave and the axis of the tube. The directivity of a line microphone is a
function of frequency; the lower the frequency, the broader the polar pattern (fig
311).
33
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