SCHOEPS BLCg - Handbuch (Seite 3)

hemi-supercardioid
+6 dB
9 dB
in a free sound field
on a boundary layer,
e.g. floor or wall
supercardioid
sensitivity: 0 dB
random energy effi-
ciency: 6 dB
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BLCg
3
English
-1 dB -2 dB -4 dB -10 dB
2h h h/2 0 distance
h
sensitivity
Boundary-Layer Adapter
BLCg
– turns any directional (e.g. cardioid or super-
cardioid) CCM Compact Microphone or MK
capsule with Active Cable into a boundary-
layer (PZM) microphone.
Advantages of the boundar-layer technique:
– unobtrusive microphone placement possibili-
ties (no stands or hanging fixtures required)
– directional microphones can be used to
compensate for the distance-dependent
drop in sound level (see Fig. 2)
– no comb-filter effect (comb-like frequency
response due to selective deletion resulting
from interference between direct and dif-
fuse sound).
If a transducer is placed upon (or within) a
large, sound-reflecting surface, its output volt-
age will be twice that of an equivalent trans-
ducer in a free sound field:
In practice, however, it is perfectly sufficient
to fasten the microphone against the boundary
surface you have available, e.g. on the floor,
on the wall, or on as large a sound-reflecting
surface as possible.
A carpeted floor is not sonically “hard”, it
absorbs too much high-frequency sound. You
can compensate against this by laying a large
wooden board under the BLCg, for example.
When recording voices, a tabletop is per-
fectly adequate. In the interest of obtaining a
balanced frequency response, however, the
microphone should not be placed at the cen-
ter of the table plate.
Boundary-layer microphones convey “less space”
– the recording turns out “dryer” than with the
same microphone in a free sound field. That
gives it considerable “reach”, but without the
high-frequency roll-off for off-axis sound which
is typical for shotgun microphones.
In theory an ideal transducer of this type
would have a membrane of infinitesimally small
size, and would be mounted flush with an infi-
nitely large, perfectly sound-reflecting surface.
A rubber ring built into the bottom of the
plate prevents inadvertent rotation of the plate
or marring of the surface on which it is placed.
Given the solid-borne noise sensitivity of di-
rectional microphones (cardioids, supercar-
dioids), it may be necessary to use insulation
in the form of a thin felt or foam mat or a
low-cut filter.
Diameter: 61 mm
Surface finish: matte gray (g)
micro-
phone
Fig. 2 As an actor moves away from a micro-
phone lying on the ground, he moves further
into the central axis of the microphone, and
the sound level drops surprisingly little.
Recommendation:
supercardioid CMC 641 (= CMC 6 microphone
amplifier and MK 41 microphone capsule) or
CCM 41 compact microphone
.
Fig. 1