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Proximity Effect
Unidirectional microphones such as the BETA 87C progressive-
ly boost bass frequencies by 10 to 15 dB at 100 Hz when the mi-
crophone is at a distance of about 6 mm (1/4 in.) from the sound
source. This phenomenon, known as proximity effect, can be used
to create a warmer, more powerful sound. To prevent excessive or
“boomy” low frequency sound during close-up use, the BETA 87C
bass response gradually rolls off. This provides greater control and
helps the user take advantage of proximity effect.
Wind Noise
The BETA 87C has an integral wind and pop filter which pro-
vides excellent protection against most wind and breath noise. Un-
der adverse conditions, such as high winds or close proximity to a
“problem” vocalist, the optional foam windscreen can be used.
Impedance
A minimum load impedance of 800 ohms should be used for
maximum signal handling and minimum distortion. The load may
be as low as 150 ohms, but a reduction in output level and output
clipping level will result.
SPECIFICATIONS
Transducer Type
Condenser (electret bias)
Frequency Response
50 to 20,000 Hz (see Figure 2)
TYPICAL FREQUENCY RESPONSE
FIGURE 2
Polar Pattern
cardioid (see Figure 3)
TYPICAL POLAR PATTERN
FIGURE 3
Output Impedance
Rated at 150 ohms (100 Ohms actual ±20%)
Recommended minimum load impedance: 800 ohms
Sensitivity (at 1,000 Hz)
Open Circuit Voltage. . . . . . . . . . . . . –51 dBV/Pa (2 mV)
(1 Pa = 94 dB SPL)
Output Clipping Level
1000 Ohm Load at 1,000 Hz. . . . . . . –6 dBV (0.5 V)
Maximum SPL
139 dB at 1,000 Hz (0.25% THD, 1000 Ohm load)
Self-Noise
22 dB typical, A-weighted
24 dB typical, weighted per DIN 45 405
(equivalent sound pressure level; measured with true rms volt-
meter)
Dynamic Range
117 dB (maximum SPL to A-weighted noise level)
Hum Sensitivity
–5 dB equivalent SPL, maximum, in a 1 mOe field (60 Hz)
Signal-to-Noise Ratio
72 dB at 94 dB SPL (IEC 651)*
*S/N ratio is difference between 94 dB SPL and equivalent SPL of self-
noise A-weighted.
Polarity
Positive pressure on diaphragm produces positive voltage on
pin 2 relative to pin 3 of the output connector. See Figure 4.
BETA 87C BLOCK DIAGRAM
FIGURE 4
Power
Phantom Supply Requirement . . . . 11 to 52 Vdc, positive
at both pins 2 and 3
Current Drain. . . . . . . . . . . . . . . . . . . . . . . . .1.0 to 1.2 mA
Connector
Three-pin (XLR) professional audio
Case
Aluminum construction with painted blue metallic finish, and
hardened steel grille with nickel satin chrome plating
Dimensions
See Figure 5
OVERALL DIMENSIONS
FIGURE 5
Net Weight
Net: 207 grams (7.6 oz)
Packaged: 565 grams (1.24 lbs)
Environmental Conditions
Operating: –18
° to 60° C (0° to 135° F)(relative humidity <90%)
Storage: –29
° to 74° C (–20° to 165° F) (relative humidity <80%)
CAPACITOR
(ELECTRET)
CONDENSER)
CARTRIDGE
BLUE
GREEN
FET
IMPEDANCE
CONVERTER
LF
RESPONSE
FILTER
CLASS A
COMPOUND
AMPLIFIER
REGULATOR
REVERSE
VOLTAGE
PROTECTOR
BALANCED
TRANSFORMER
RFI
FILTER
21 mm
(
53
/
64
in.)
51 mm
(2 in.)
192 mm
(7–
9
/
16
in.)