Getting the Most Out of the Bidirectional Pattern
As described earlier, pressure-gradient microphones are inherently bidirectional, with equal sensitivity
to the front and back of the diaphragm. In a well designed mic, the only difference is the absolute po-
larity of the signal. (ref. Figure-1A)
1
Several paragraphs and diagrams in this manual have been adapted from: The Bidirectional Microphone: A Forgotten
Patriarch – by Ron Streicher and Wes Dooley; Journal of the Audio Engineering Society, Vol. 51, No. 4, pp. 211-225, 2003
April. A complete copy can be downloaded from the AEA website: www.ribbonmics.com.
Because the polar response of a pressure-gradient microphone obeys a cosine-law, the sensitivity
decreases evenly as the soundsource moves away from the primary 0° (or 180°) axis, until it reaches
90° (or 270°) where the microphone has a very steep null. (ref. Figure-1B) This is the deepest null of
all polar patterns — nearly -90dB in the plane of the diaphragm — with a well designed model. It is
important to realize that this null plane extends both laterally and vertically with respect to the princi-
pal axis of pickup.
Most people, when using a directional microphone, just aim it at the subject, giving little thought to the
overall polar response pattern. While this “point and shoot” approach might work in a simple recording
or PA situation, there is much more to consider when “the going gets rough.”
Careful aiming of the “nulls” of a microphone’s pattern often can be more critical to the quality of the
sound pickup than where the principal axis is pointing. Intrusive sounds, such as PA, monitor, rein-
forcement speakers, other nearby instruments, noisy air conditioning equipment, or other environmen-
tal noises, can be reduced significantly by proper aiming of the nulls of the microphone. By reducing
these unwanted sounds, the clarity of the pickup will increase dramatically. Your new AEA ribbon
microphone has a very deep null plane. Use it wisely and to your advantage.
