Neumann.Berlin GFM 132 User Manual

Product Information

GFM 132

Boundary Layer
Microphone

www.neumann.com

Georg Neumann GmbH, Berlin • Ollenhauerstr. 98 • 13403 Berlin • Germany • Tel.: [phone] • Fax: [phone]
E-Mail: [e-mail], [e-mail], [e-mail] • Web: www.neumann.com

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

• Boundary layer microphone

• 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.