2. Frequency response variation due to treble losses as a result
of absorption and “narrowing” of the pattern at high frequen-
cies, causing weakening of highs as the microphone is moved
away from the sound source.
3. Variation in ratio of direct to reverberant sound.
4. Tendency of a microphone to favor the nearest sound source
due to a combination of these items, plus the influence of
inverse square law. Inverse square law states that for each half-
ing of source-to-microphone distance, the sound pressure level
quadruples
.
Other Types of Microphones
For the same ratio of direct to reverberant sound, omni-direc-
tional microphones must be closer to the sound source than car-
dioid or bi-directional microphones. Microphones should gen-
erally face the sound source head-on; if not, treble losses due to
phase cancellation can result. The exception here is for large
condenser microphones, which often give the flattest response
at an angle of about 10-20 degrees (off axis), where phase loss
and diffraction effect offset each other somewhat.
Proximity Effect and Working Distance
The Sound That Is “More Real than Real”
Ribbon microphones have long been renowned for “rich bass.”
This effect is largely due to the fact that ribbon microphones
generally have excellent bass response to begin with, and at the
same time exhibit an effect known as “proximity effect” or
“bass tip-up.”
As illustrated in the following graph, a typical bi-directional
ribbon microphone will have a flat frequency response at a dis-
tance of about six feet from the microphone, but at shorter dis-
tances the bass response becomes boosted; the effect becomes
13
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