BeoMic BM4 Microphone

BeoMic Microphone

Production: 1962 - unknown

Bang & Olufsen Beomic 3 (150 ohms) and Beomic 4 (multi- impedance) models were pressure-gradient full-bass microphones with a perfect figure-eight directional pattern.

Features: No resonance peaks. Extremely smooth response. Bi-Directional - no side pickup. No frequency discrimination, front to back. High efficiency Nu-Metal transformer placed in microphone housing. Switch for muting and voice/music conditions. The miniature non-corrosive duraluminium ribbon was only 0.0001" thick and its weight only 1.3 mg. This negligible mass prevented any resonance within the audio range. Shock and blast proof. Ball swivel for tilting to any position.

BeoMic BM4 Microphone technical specifications

Specifications: Dimensions 195mm high, 30mm diameter 
Impedance, switchable 50 ohms, 250 ohms and 40 Kohms balanced 
Response M position: 20-11000 c/s +/- 2,5 dB 
T position: 10 dB lower at 100 c/s 
Sensitivity M position, 50 ohms: 88 dB below 1V/µbar 
M position, 250 ohms: 81 dB below 1V/µbar 
M position, 40 Kohms: 60 dB below 1V/µbar 
T position, 4 dB lower 

Response Frequency Characteristic: 
M (Music) Position: From 20 till 11,000 c/s +/- 3 dB 
T (Close Talk) Position (8-16") Rolled off below 100 c/s: 12 dB 
RTMA Microphone Rating GM (sensitivity): -158dB; Hum Sensitivity (RTMA) GH: -145 dB. RTMA Standard SE - 105. BM 3. Open Circuit Voltage Level: -88 dB, OdB = 1 Volt per Microbar 
Output Impedance: Nominal 80 ohms 
Rating Impedance: 150 ohms 
BM 4. Open Circuit Voltage Level: 
"L"-Position: -88 dB 
"M—Position: -81dB 
"H"-Position: -60 dB 
OdB = 1 Volt per Microbar 
Output Impedance: 
Nominal at 1000 c/s; 100 ohms 
Rating Impedance: 150 ohms 
Nominal at 1000 c/s; 450 ohms 
"H" position:  
Nominal at 1000 c/s; 60 k ohms 
Rating impedance: 40 k ohms 
Size: 7,75" x 1 3/16" 
Weight: 15 ozs approx. 
Cable: supplied with 20 feet twin cond. shld. 
Transformer type: 8016-JS for matching BM3 to a high impedance amplifier input available on special order 
mounting: Bayonette detach to 5/8" x 27 thread

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