User's Manual

square law. The inverse square law states that for each halving of source-to-microphone
distance, the sound pressure level quadruples.
Other Types of Microphones
For the same ratio of direct to reverberant sound, omni-directional microphones must be closer to
the sound source than cardioid or bi-directional microphones. Microphones should generally face
the sound source head-on; if not, treble losses due to phase cancellation can result. The exception
here is for large diaphragm 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.
As illustrated in the following graph, a typical bi-
directional ribbon microphone will have a flat
frequency response at a distance of about six feet
from the microphone, but at shorter distances the
bass response becomes boosted; the effect becomes
increasingly pronounced as the distance between the
microphone and the sound source is reduced.
This bass-boosting characteristic can become quite
intense and, if desired, can be corrected by
equalization. However, for a multiple microphone
setup, the pronounced bass boosting (due to
proximity effect) can be turned to an advantage. If
an instrument, such as a trumpet, is extremely close-
miked and the bass is cut to restore flat response,
unwanted low-frequency sounds are cut back by
upwards of 20dB compared to an unequalized
microphone with a flat response. This discrimination
is independent of the microphone’s polar response.
Another area where proximity effect can be turned to an advantage is to make things sound more
“real than real.” For example, many voices and certain musical instruments produce fundamental
frequencies within the bass range (below 150Hz or so) but the fundamentals are weak. If a
microphone that has no proximity effect and a rising high frequency response is used on an
upright piano, or on a person with a thin, weak voice, the recorded sound is likely to sound even
thinner than it was in real life. In contrast, using a microphone with strong proximity effect on
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Typical relationship of microphone distance
to frequency response for ribbon-velocity
bidirectional microphone.