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KM 66 - The Figure-8 for an Even Sound Field
Occasionally, by combining elements of existing products,
previously unknown possibilities are discovered. One ex-
ample of this in Neumann’s product history is the KM 66,
a switchable-pattern miniature microphone first produced
in 1966.
In developing this micro-
phone, Neumann com-
bined two cardioid cap-
sules from the KM 64 in a
special way: the dia-
phragms face away from
each other with a spacing
of 10 mm; the backplates
are separated by an ellip-
tical divider. The result is
a capsule combination pro-
ducing excellent polar pat-
tern characteristics, even
in the extreme low-fre-
quency range. Even at
40 Hz, the rear-to-front
differential for each single capsule is 20 dB!
In an even (diffuse) sound field, no appreciable change in
on-axis (0 degrees) response occurs when switching from
omni to cardioid pattern. Also, when the backside capsule
is added (for omni), there is less than a 10% increase in
output voltage from the microphone.
In contrast, polar diagrams
of typical dual-diaphragm
microphones indicate that
the reverse attenuation of
the cardioid pickup pat-
tern decreases remarkably
towards the low frequen-
cies. When the two cap-
sule halves are activated at
the same time, the back-
side part adds a much
higher share of the whole
signal. This generates an
narrower figure-8 pattern
in the low frequencies and
an uneven response due to
changes in distance.
In the KM 66, the cardio-
id and figure-8 patterns
feature an accurate representation of low frequencies, even
in such a case where the microphone is used at a greater
distance from the sound source. This near-ideal carioid cap-
sule with its unique attributes is a great asset to other mi-
crophones utilizing it: the KM 64, U 64, KTM, KM 74 and
the legendary KM 84.