Learning Event 3:
DESCRIBE USES AND OPERATION OF THE CARDIOID MICROPHONE
1. Cardioid Microphone. Both television and motion picture productions have
suffered greatly from the fact that in order to pick up good sound, the microphone
must be reasonably close to the talent. On a television set this causes
difficulties for both the camera person and the sound person. These problems have
been overcome by the development and introduction of the cardioid inline
a. Two of the most important characteristics of any microphone are its
sensitivity and directional qualities.
b. Assuming a constant sound pressure source, increasing the distance of the
microphone from the source requires an increase in the gain of the amplifying
system after the microphone. This is accompanied by a decrease in signal to noise
ratio and an increase in environmental noises, such as reverberation and background
noise, to where the indirect sound may equal the direct sound. In other words, the
pickup deteriorates to where it is unusable.
c. Distance limitations can be overcome by increasing the sensitivity of the
microphone, and the effect of reverberation can be lessened by increasing the
directivity of the pattern. The inline microphone has these two desirable
2. Over the years the most commonly used microphone for boom operation and the
recording dialogue has been a gradient microphone with a cardioid directional polar
pattern, (fig 31).
a. In addition to the polar plot, the directional characteristics of a
microphone may be described as a ratio termed directive index. Directivity index
is a ratio of output voltage from a microphone in a sound field that arrives at the
microphone from all directions, to the output voltage of an omnidirectional
microphone, with equal sensitivity, in the same sound field.
b. The directivity index is a measure of nonaxial response; the lower the
directivity index the sharper the polar response.
3. For microphones of the bidirectional and cardioid type, the index is 3 to 1;
because of baffle effects, the polar response becomes narrower at higher
a. Figure 39 shows a graphical plot of the directivity index versus
dynamic gradient microphone with a cardioid polar pattern curves A and B.