Neumann.Berlin GFM 132 User Manual

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Product Information
GFM 132
Boundary Layer Microphone
www.neumann.com
Georg Neumann GmbH, Berlin • Ollenhauerstr. 98 • 13403 Berlin • Germany • Tel.: +49 (30) 417724-0 • Fax: +49 (30) 417724-50 E-Mail: headoffice@neumann.com, engineering@neumann.com, catalog-info@neumann.com • Web: www.neumann.com
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he GFM 132 is a boundary layer micro­phone. Through computer simulation Neu­mann optimized the design to be free of any comb filter effects due to reflec­tions, typical of other such mi­crophones.
The smooth frequency respon­se for all angles of incidence ex­hibits a rise in the upper fre­quency range. This assures that all sound sources, even distant ones, will be recorded with cla­rity and presence.
Therefore, typical applications are for live recordings, such as in the orchestra pit of opera houses, theaters, and on stage.
The back of the microphone has non-slip pads for its use in a horizontal or inclined positi­on, and holes for wall suspension. It is supp­lied with a wooden case and a wind screen.
Features
• Pressure transducer
• Frequency independent hemispherical directional characteristic
• Identical diffuse- and free-field response
• No angle dependent coloration through patented triangular form
• No comb filter effects
• Insensitive to structure-borne noise
Background
Boundary-layer microphones are generally char­acterized by the following features:
They have an identical flat frequency response in the diffuse-field and free-field;
They have a hemispherical polar pattern, in­dependent of the frequency;
They have a 6 dB higher output level through pressure doubling at the boundary surface.
Until recently, neither the potential of identi­cal diffuse- and free-field response, nor the ideal hemispherical polar patterns throughout the entire frequency range have been achieved by any known boundary-layer microphone. Cir­cular, square, or rectangular plates were used to mount the acoustic transducer and to pro­vide the “live” sound reflecting surface for pressure doubling at high frequencies.
However, such shapes have disadvantages: The sound pressure level at the position of the transducer depends on the frequency and the incidence angle. The incoming primary sound field is superimposed upon the second­ary sound field resulting from diffraction at the edges of the plate. As a result, boundary-layer microphones using circular, square or rectan­gular shaped plates generate linear distortion, such as comb filter effects, of frequency and polar response.
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GFM 132
The Neumann solution
The GFM 132 boundary-layer microphone has a unique, computer generated shape that to­tally avoids these disadvantages. The path lengths from each edge point to the center of the transducer are distributed evenly for all wavelengths within the fre­quency range.
This design eliminates any pos­sible linear distortion of fre­quencies caused at the location of the electro-acoustic trans­ducer 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 dou­bling 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 dis­tant ones, will be recorded with clarity and pres­ence.
Acoustic features
• The microphone provides high output vol­tage through pressure doubling at the boundary surface.
• The microphone reproduces with great ac­curacy very low frequencies if the boundary layer is adequately large.
• In surroundings with good acoustics the GFM 132 creates incredibly realistic AB-stereo recordings, taking advantage of delay and intensity differences in the audio signal.
Electrical features
The GFM 132 uses transformerless circuitry and operates on 48 V phantom power. The usual output transformer is replaced by an elec­tronic circuit.
As with traditional transformers, this design en­sures good common mode rejection and pre­vents 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 re­production free of coloration.
Attenuation
The microphone has a 10 dB 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 lay­er microphone.
• 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 ang­le-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 reflec­tions, using conventional microphones.
• The hemispherical polar pattern is inde­pendent of the frequency, producing a spatial sound with presence and ex­cellent transparency.
• As is common for a pressure transducer, the microphone is insensitive to structure borne noise and air movements.
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 experimen­tation to gain maximum use from this microphone.
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Delivery Range
Microphone GFM 132 Plug-on Windscreen Microphone cable Wooden box
Catalog No.
GF M 13 2 ......................................................blk ....... 007100
Selection of Accessories
Battery supply, BS 48 i ........................ blk ....... 006494
Power supply, N 248 EU .................. blk ....... 008537
Power supply, N 248 US ................... blk ....... 008538
Power supply, N 248 UK .................. blk ....... 008539
Microphone cable, IC 3 mt ................ blk ....... 006543
A complete survey and detailed descriptions of all accessories are contained in the accessories catalog.
Meaning of color codes: blk = black, ni = nickel
measured in free-field conditions (IEC 60268-4), tolerance ±2 dB
Technical Data
Acoustical operating principle ................................................ Pressure transducer
Directional pattern .................................................................................... Hemispherical
Frequency range ..................................................................................... 2 0 Hz...20 kHz
Sensitivity at 1 kHz into 1 kohm .............................................................. 18 mV/Pa
Rated impedance .................................................................................................... 50 ohms
Rated load impedance ................................................................................. 1000 ohms
Signal-to-noise ratio, CCIR1) (rel. 94 dB SPL) ............................................. 70 dB
Signal-to-noise ratio, A-weighted1) (rel. 94 dB SPL) .............................. 80 dB
Equivalent noise level, CCIR1)................................................................................ 24 dB
Equivalent noise level, A-weighted1)............................................................ 14 dB-A
1)
according to IEC 60268-1; CCIR-weighting acccording to CCIR 468-3, quasi peak; A-weighting according to IEC 61672-1, RMS 2) measured as equivalent el. input signal
Errors excepted, subject to changes • Printed in Germany • Publ. 01/08 058156/A03
Neumann is a registered trademark of the Georg Neumann GmbH in certain countries.
®
Maximum SPL for THD 0.5%2)........................................................................ 137 dB
Maximum SPL for THD 0.5% with preattanuation2)......................... 147 dB
Maximum output voltage ...................................................................................... 10 dBu
Dynamic range of the microphone amplifier (A-weighted) ............ 123 dB
Supply voltage (P48, IEC 61938) ......................................................... 48 V ± 4 V
Current consumption (P48, IEC 61938) ......................................................... 2 mA
Matching connector ..................................................................................................... XLR3F
Weight .................................................................................................................................. 46 0 g
Width ................................................................................................................................ 213 mm
Depth ...............................................................................................................................168 mm
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