KFM 360



  • Compact
  • Extensive capability for post-processing, in either analog or digital domain
  • Digital and analog inputs and outputs
  • Analog-style controls
  • User-preferred settings can be stored and recalled
KFM 360 Sphere
KFM 360 Sphere Microphone
DSP-4 KFM 360
DSP-4 KFM 360 Processor

The complete Surround Microphone System consists of:

- the KFM 360 Sphere Microphone
- two Figure-8 microphones (CCM 8 Lg) with SGC-KFM clamps, and
- the DSP-4 KFM 360 Processor

These components are also available separately.

The central unit in this system is the Sphere Microphone KFM 360. It uses two pressure transducers, which can also be used for stereophonic recording even without the other elements of the system. Its recording angle is ca. 120°, thus permitting closer miking than with the larger stereo microphone KFM 6 (90°). The necessary high-frequency boost is built into the processor unit; when using the KFM 360 by itself, this boost needs to be provided externally.

Surround capability is achieved through the use of two figure-8 microphones, which are held beneath the pressure transducers by an adjustable, detachable clamp system with bayonet-style connectors (SGC-KFM). These two microphones should be aimed precisely forward.

With just this arrangement, four surround channels can be obtained through the use of two M-S matrices. The front and rear channels result from the sum (front) and difference (rear) of the omnidirectional and figure-8 microphones on each side respectively (see Diagram 1 below). The four resulting "virtual microphones" which this process creates will seem to be aimed forward and backward, as the figure-8s are. At higher frequencies they will seem to be angled more toward the sides. Their directional pattern can be varied, anywhere from omnidirectional to cardioid to figure-8; the pattern of the two rear-facing virtual microphones can be different from that of the two forward-facing ones. Altering the directional patterns alters the sound as well, in ways that are not possible with ordinary equalizers. This permits a flexible means of adapting to a recording situation -- to the acoustical conditions in the recording space -- and this can even be done during post-production, if the unprocessed microphone signals are recorded.

This four-channel approach yields a form of surround reproduction without a center channel-- something which we realize is not what everyone requests.

The greatest convenience and variety of settings will be obtained if the DSP-4 KFM 360 processor is used. A center-channel signal can then be derived from the two front signals, using the type of matrix described by Michael Gerzon. The front stereo image width is adjustable. An additional channel carries only the low frequencies (up to 70 Hz). To avoid perceiving the presence of the rear loudspeakers it is possible to lower the level of their channels, to delay them and/or to set an upper limit on their frequency response.

The directional patterns of the front-facing and rear-facing pairs of "virtual microphones" can be chosen independently of one another. The processor unit offers both analog and digital inputs for the microphone signals. In addition to providing gain, it offers a high-frequency emphasis for the built-in pressure transducers as well as a low-frequency boost for the figure-8s. As with M-S recording, matrixing can be performed during post-production, either by analog or digital means.


KFM diagram
Diagram 1: Derivation of right front / right rear signals

KFM 360 "Sphere Microphone"

- for 12V -- 48V phantom powering
- 2 pressure transducers, built into the sphere
- diameter: 18 cm
- recording angle: ca. 120°

Additional microphones for surround: Two figure-8s (CCM 8), each mounted above/below the pressure transducer

Analog inputs/outputs:  
   Microphone preamp with 48V
   phantom-powering; Impedance:
20 kOhms
   Output impedance: 100 Ohms
Digital inputs/outputs: AES/EBU 110 Ohms
Subwoofer channel: 70 Hz upper limit, 24 dB/oct. (critical IIR filter)
Dynamic range:
   A/D converter: 97 dB (peak)/CCIR, 108 dB A-weighted
   D/A converter: 87 dB (peak)/CCIR, 100 dB A-weighted
Coarse gain (microphone input):  +10 dB, +20 dB
Maximum input level (analog):  -14 dBU (+6 dBU)
Maximum output level: +6 dBU
Maximum sound pressure level:     130 dB SPL

Complete KFM 360 5.1 Surround Sound System: $17,845.00
KFM 360 Sphere Microphone with SGC-KFM mounting hardware
2x CCM 8 Lg compact bidirectional microphones
DSP-4 KFM 360 Surround Processor


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Most recent revision January 5, 2012