KM 131 Miniature Microphone
condenser miniature microphone system consists of several active microphone
capsules with different directional characteristics, an output stage, and
Currently there are seven active capsules available: omni diffuse-field
equalized, omni free-field equalized, cardioid, wide-angle cardioid, cardioid
with bass roll-off, hypercardioid, and figure-8.
Through the modular construction of mic capsules and the output stage it is very
easy to adapt the system to a wide range of applications. The mic becomes nearly
invisible during work with cameras (film, video), on stage, or suspended from
the ceiling in a concert hall.
An active capsule can also be screwed directly onto the output stage. The result
is a compact miniature microphone.
The microphones are only 92 or 110 mm resp. long and 22 mm in diameter. They
consist of the condenser capsule and the output stage. Both parts can be
unscrewed from each other. The system offers several condenser capsules with
different directional characteristics.
Numerous accessories can be mounted between the capsules and the output stage.
The capsules attach to cables, capsule extensions, swivel mounts, table stands,
goose-necks, stereo mounts, and hangers. Therefore, it is very easy to adapt the
system to a wide range of applications.
The active capsule itself is only 35 or 47 mm resp. long. The KM 100 output
stage and the active microphone capsule may be separated by up to 50 m of
interconnecting cable. These cables are 3 mm in diameter, and therefore very
AK 20 is a pressure gradient transducer with the figure-8 characteristic,
realized with a single diaphragm. The diaphragm diameter is just 16 mm. All
sound field components reach the diaphragm directly. This results in identical
frequency response curves and output levels at 0° and 180° sound incidence.
Corresponding accessories allow combining the AK 20 with other active capsules
or microphones to obtain an MS-Stereo setup.
AK 30 is a diffuse-field equalized pressure transducer with a flat frequency
response up to 10 kHz (in the diffuse field). In the free sound field this
microphone has a boost of approximately 7 dB at 10 kHz.
AK 31 is a free-field equalized pressure transducer with a flat frequency
response up to 20 kHz (in the free field). In the diffuse sound field this
microphone has a high frequency roll-off above 5 kHz.
AK 40 is a pressure gradient transducer with cardioid characteristic. The
frequency curves are very smooth and match 0° sound incidence. Sound from
sources within a pickup angle of ± 135° is reproduced without any coloration.
AK 43 is a pressure gradient transducer with wide-angle cardioid characteristic.
Attenu- ation at 90° is 4 dB, at 135° it is 8 dB and at 180° it is 11 dB. The
frequency response curves for sound sources within an angle of ± 90° are
parallel up to 12 kHz.
AK 45 is a pressure gradient transducer with cardioid characteristic, similar to
the AK 40. However, it has an acoustic bass roll-off that is useful during
applications when subsonic and low frequencies may cause difficulties. The AK 45
is optimized for a flat low frequency response at a recording distance of 15 cm
AK 50 is a pressure gradient transducer with hypercardioid characteristic.
Attenuation of sound incidence from the side or rear is about 10 dB, with
minimum sensitivity at an angle of 120°.
The KM 100 is phantom powered (48 V) and uses transformerless output circuitry.
This has several advantages. It features high output capability and extremely
low self noise. It provides exceptionally clean sound, free of any coloration.
As with traditional transformers, this circuit approach ensures good common mode
rejection. The balanced output signal is protected against interference.
The construction is extremely compact. The entire microphone circuitry is on a
single hybrid module measuring only 2 cm² in area. It is built into the
microphone capsule, therefore the term “active capsules”.
All sensitive components are protected within the capsule. As a result, the
quality of the audio signal is never compromised through the use of accessories,
for example, when the capsule is detached from the output stage and mounted on a
cable or a gooseneck.
Even with a long cable between active capsule and output stage, the signal is
immune to external interference.
The output stage has a 10 dB switch. Attenuation is achieved by reducing the
capsule voltage to one third.
When the switch is on, the microphone is capable of accepting sound pressure
levels up to 150 dB without being overloaded.
To diminish the number of connectors within the KM 100 System some accessories
were modified. They can now be screwed directly onto the KM 100 output stage
without using the KA 100 cable adapter. The new accessories which include the
cable adapter, were renamed adding the suffix KA. For example: LC 3 is now LC 3
The separate KA 100 cable, needed for older accessories, will be available also
The KM 100 output stage has a 3-pin XLR connector.
Sound diffraction sphere
The SBK 130 A sound diffraction sphere slips onto the front of the KM 130/KM 131
pressure microphones. The diaphragm becomes an integral part of the surface of
the sphere. This affects the frequency response of the microphones.
While sounds coming from the front-half space are emphasized by up to 2.5 dB
between 2 kHz and 10 kHz, sounds arriving from the rear-half space are
attenuated by a maximum of 2.5 dB in the range above 5 kHz.
Since the sound diffraction sphere causes the pressure buildup of the KM 130/KM
131 pressure microphones to begin earlier, the frequency response rises smoothly
in the middle and upper range. This is similar to a typical pressure gradient
microphone, where the directivity increases with rising frequencies. However,
since the KM 130/KM 131 are pressure microphones, they maintain a linear
sensitivity down to the lowest frequencies.
This changing directivity allows to record at a greater distance from the sound
source, and makes the KM 130/KM 131 microphones especially suited as stereo main
microphones in A-B configurations.
By means of the AC 30 adapter cable two active capsules, AK 20 and e.g. AK 40
can be connected as MS stereo pair directly with the MTX 191 (A) matrix
amplifier. The XY or MS signal is then available at the 5-pin XLR output
connector of the MTX 191 (A), and the recording angle can be electrically remote
controlled. The output stages KM 100 are then not required.
The cardioid and hypercardioid microphones are also available as complete stereo
sets, SKM 140 and SKM 150, including all accessories in a single jeweler's box.
A further SKM 100-MS Stereo Set containing the microphones KM 120 und KM 140 is
microphones with 7 exchangeable capsules
• Active capsules, detachable up to 50 m from the output stage
• Great variability through capsule extensions and goosenecks
• Switchable 10 dB preattenuation
• Set includes windshield and microphone clamp
• Transformerless circuitry
• Extensive accessories
Omni diff. field eq
20 Hz ... 20 kHz
|Sensitivity at 1 kHz into 1
|Rated load impedance
|Equivalent noise level,
|Equivalent noise level,
|Signal-to-noise ratio, CCIR) (rel.
94 dB SPL)
|Signal-to-noise ratio, A-weighted) (rel. 94
|Maximum SPL for THD 0.5%2)
Maximum SPL for THD 0.5% with
|Maximum output voltage
|Dynamic range of the microphone amplifier
|Supply voltage (P48, IEC
48 V ± 4 V
|Current consumption (P48, IEC