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224 IX. SOUND-KECORDING EQUIPMENT AND ARRANGEMENT
to one inch has shifted the pressure-doubling peak of the microphone beyond 5000 cps from its former 3000 cps value ; the performance is now so smooth and consistent that the microphone is very well suited to sound pressure measurement — for which it was originally designed. This microphone is customarily used with a Western Electric RA-1095 amplifier, a single-stage amplifier using a "door-knob" 382A Western Electric tube. The output transformer in the amplifier may be connected for 30-50 ohms
JmtWr Fig. 46. RCA 44BX velocity microphone
^r (ribbon microphone).
Specifications — Type KB-5A (for Sound Films)
Output level (at 1000 cycles when terminated into matched load)*: -55 db (0 db = 1 mw) ; -63 db (0 db = 6 mw). Directional characteristic: Bi-directional — figure 8 pattern (see Fig. 46A). Frequency response: 30-10,000 cycles (see Fig. 46B). Output impedances : 250 ohms and 50 ohms (connected for 250 ohms when shipped). Dimensions: Length, including hanger: 10^"; Width: 4f"; Depth: 3|" ; Weight, including hanger (unpacked): 8^ lb. Stock identification: MI-3027-E.
Accessories
Suspension hanger: MI-4076-A. Program stand: MI-4090-A. Boom stand: MI4094-B . Announce stand: MI-4058-C. Cushion adaptor for stand mounting: MI3033-A. Suspension mounting: MI-3065.
impedance or for 200-250 ohms impedance; the output is some 25 db higher than unaided moving conductor microphones. When sound originates "head on," the response-frequency characteristic which shows a maximum output at 8000 cps has approximately the same response at 20,000 cps as at 1000 cps. The microphone and its associated amplifier weighs 1 3/4 pounds and is 7 3/4 inches long and 2 1/2 inches in maximum diameter; it requires 0.150 amperes at 6.3 volts for the heater of the electron tube and 180 volts at 3 milliamperes for plate supply for the * Input sound pressure of 10 dynes per square centimeter.