Specifications

Stereo Sphere Microphone KFM 6
smaller version: KFM 360
– head-related stereo microphone for loudspeaker
reproduction
– very good imaging and sense of depth; good localiz -
ation, very natural sound
– with qualities of a dummy head when headphones
are used for listening
– natural sound with superior low-frequency performance
– for phantom powering (12 V or 48 V)
Stereo microphones such as the KFM 6 are distinguished
by the sim plicity of the recording technique and of the
setup. Only two microphones and recording tracks are
required, and with the KFM 6 only one microphone
cable is needed.
The KFM 6 sphere microphone is the embodiment
of a stereo microphone design using an acoustic baffle.
It bears some resemblance to a “dummy head“ and
follows some of the same principles – but while dummy
head recordings can provide excellent results, they are
suitable only for headphone listening. The “Sphere“
microphone was developed so that similarly convincing
results could be achieved for loudspeaker playback. To
fulfill this objective the microphone must provide not
only interaural arrival-time cues, but also spectral-vs-
angular incidence information. A further requirement
was that the frequency response on the main axis of
the microphone in the free sound field and also the
frequency response in the diffuse sound field remain
flat. (See G. Theile: “On the naturalness of two-channel
stereo sound,” AES/SMPTE Joint Television Con ference,
Jan. 1991, Detroit)
In constructing the KFM 6, two special pressure trans-
duc ers are mounted flush on the surface of a sphere
20 cm in dia meter, an acoustic baffle having especially
favorable properties.
Normally two pressure transducers placed so close
to each other would not provide a convincing stereo
image. How ever, the sphere between the capsules
creates a frequency-dependent emphasis of level differ-
ences comparable to that which occurs naturally
between the human ears.
The frequency response on the stereo main axis of
the KFM 6 is flat when measured at the output of either
channel. If a sound source moves around the sphere,
the level in the one channel will increase by the same
amount as it decreases in the other. This is brought
about by the unique construction of the microphone
capsules, the effect of the sphere as an acoustic baffle,
and some special electronic circuitry built into the
amplifier. As a result, the energy sum of the two chan-
nels is largely independent of the angle of sound inci-
dence and shows essentially flat frequency response in
both the direct and the diffuse sound field. Further more,
the directionality of the microphone is essentially con-
stant throughout the audio frequency range.
These features, combined with an exceptionally flat
response that extends down to the very lowest fre-
85
Sphere Stereo
WKFM
windscreen
KG
ball-and-socket joint