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GFM 132
The Neumann solution
The GFM 132 boundary-layer microphone has
a unique, computer generated shape that to-
tally avoids these disadvantages. The path
lengths from each edge point to the center of
the transducer are distributed evenly for all
wavelengths within the fre-
quency range.
This design eliminates any pos-
sible linear distortion of fre-
quencies caused at the location
of the electro-acoustic trans-
ducer by the interaction of the
incoming primary sound field
with the secondary sound field
from diffraction at the edges of
the plate.
The operating range of the plate reaches from
the lowest frequency causing a pressure dou-
bling in front of the plate to the upper limit of
the audible range.
The microphone features a smooth frequency
response for all angles of incidence, with a slight
rise in amplitude in the upper frequency range.
This assures that all sound sources, even dis-
tant ones, will be recorded with clarity and pres-
ence.
Acoustic features
• The microphone provides high output vol-
tage through pressure doubling at the
boundary surface.
• Identical diffuse- and free-field frequency
response. Its advantage is that the apparent
tonal balance of a moving sound source is
independent of the distance and direction.
• The special geometric shape prevents ang-
le-dependent coloration in the vertical and
horizontal planes.
• There are no comb filter effects in typical
applications, for example on a speaker's
desk, as they would occur through reflec-
tions, using conventional microphones.
• The hemispherical polar pattern is inde-
pendent of the frequency, producing
a spatial sound with presence and ex-
cellent transparency.
• As is common for a pressure transducer,
the microphone is insensitive to structure
borne noise and air movements.
• The microphone reproduces with great ac-
curacy very low frequencies if the
boundarylayer is adequately large.
• In surroundings with good acoustics the
GFM132 creates incredibly realistic
AB-stereo recordings, taking advantage
of delay and intensity differences in the
audio signal.
Electrical features
The GFM132 uses transformerless circuitry
and operates on 48 V phantom power. The
usual output transformer is replaced by an elec-
tronic circuit.
As with traditional transformers, this design en-
sures good common mode rejection and pre-
vents RF interference that may influence the
balanced audio signal. The microphone features
high output capability and extremely low self
noise. It provides exceptionally clean sound re-
production free of coloration.
Attenuation
The microphone has a 10dB
attenuation switch to prevent
the input of the following unit
from being overloaded.
The switch is located next to
the cable connector at the side
of the GFM 132 boundary lay-
er microphone.
Application Hints
• An ideal stereo pair for AB technique
• For round table discussions
• Quick and easy installation for the “fast interview”
• Invisible spot mic for
- harp,
- cello,
- double bass,
- acoustic guitar
• Excellent bass response when used as main mic
for drums
These are just some of the most common
applications. We recommend additional experimen-
tation to gain maximum use from this microphone.