(4) The Unidirectional Pickup Pattern. The pickup pattern for this microphone looks like a
candle. It accepts sound only from the 0, point with the better microphones. Poor quality microphones
may pick up slightly from the 90 and 180 points, but this sound quality will have a loss of frequency
on the lower end of the scale.
Figure 2-24. Unidirectional pickup pattern
(5) In both the bidirectional and unidirectional type microphones, the lobe shapes result from
the design characteristics developed by certain manufacturers.
(6) Impedance Values. Impedance values are as follows:
(a) 600 ohms or less - Low impedance.
(b) 1000 ohms or higher - High impedance.
Impedance values of microphones determine microphone cable length. High impedance microphones
generally develop poor signal-to-noise ratios, low or insufficient input signals, or loose frequency
response, if the cable is longer than 25 feet (7.62m). Low impedance microphones may use cables of
unlimited length.
(7) Noise. Noise is inherent in some types of microphones, particularly in carbon
microphones. Most manufacturers list noise in their specifications rated in dbms.
(8) Distortion. Distortion equals the amount of wave form change present in a signal for a
specific microphone.
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