In constructing the KFM 6, two special pressure trans­duc­ers are mounted flush on the surface of a sphere 20 cm in dia­meter, an acoustic baffle having especially favorable properties.

Normally two pressure transducers placed so close to each other would not provide a convincing stereo image. How­ever, the sphere between the capsules creates a frequency-dependent emphasis of level differences 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 channels is largely independent of the angle of sound incidence and shows essentially flat frequency response in both the direct and the diffuse sound field. Further­more, the directionality of the microphone is essentially constant throughout the audio frequency range.

These features, combined with an exceptionally flat response that extends down to the very lowest frequencies, are responsible for the remarkably natural impression of space, depth and image typical of the KFM 6.

Some practical information about the KFM 6:

• The recording room should have a good sound.
• In practice, the recording angle+ of the KFM 6 has a fixed value of 90°.
• A LED pinpoints the stereo main axis. This is especially useful when the KFM 6 is positioned at some distance.
• The sensitivity of the KFM 6 is about 15 – 20 dB higher than that of a standard Colette series microphone.
• The KFM 6 can operate into unbalanced inputs with­­out any loss of level and without transformers. This requires a powering device with DC decoupling.
• Any standardized 12 V or 48 V phantom powering is suitable.
• When a 12 V phantom power­ing is used, the maximum SPL is reduced by 7 dB.
• In order to assure proper operation, make sure that both channels are powered simultaneously at all times.