The RCA Type KU-2A
uni-directional microphone

MI-3043-B with Three Prong Plug
MI-3043-C with Six Prong Plug

Description
The MI-3043-B (and -C) Uni-Directional micro­phone consists of two ribbon type micro­phone units suspended in a common air gap. One of the units is open to sound waves both in front and back and operates on the pressure gradient principle. It is known as a velocity micro­phone. The other unit has a tube connecting with a damped acoustical labyrinth, sealed to the back side of the air gap, and responds to pressure variations in the sound wave. It is known as a pressure micro­phone. The outputs of the two micro­phones are connected in series and the vector addition of the voltages generated by the two micro­phones produces a directional characteristic as shown in Figure 3. The MI-3043-B and MI-3043-C are identical except for the difference in the connector plugs as stated in the title.

The ribbon and magnet assembly is enclosed in a perforated housing. The housing provides protection against dust and mechanical injury, and, to a certain extent, reduces wind noises. The acoustical labyrinth (or folded tube) associated with the pressure micro­phone section is contained in the cylindrical center part of the micro­phone. The impedance matching transformer and a compensating network is mounted in the hemispherical shell at the end of the micro­phone.

Sensitivity
The sensitivity of these micro­phones is of the same order as that of other quality micro­phones used in sound film recording. By connecting the micro­phone output for twice the impedance for which the amplifier input was designed, the micro­phone output level may be raised by 3 db.

Directional characteristics
These micro­phones have a very uniform response on the front side with the sensitivity de­creasing slowly as the angle of the sound source with the maximum response axis increases (See Figure 3). Minimum response is at the rear of the micro­phone where the attenuation relative to the sounds along the maximum response axis is 14-20 dB. The axis of maximum response is on a line passing through the center of the ribbon and perpendicular to the plane of the ribbon.

Response
The Uni-Directional micro­phone has practically uniform frequency response within its oper­ating range. (See Figure 4.) When the micro­phone is located less than two feet from the source of sound, the low frequency response is increased somewhat although not to the same extent as with a velocity micro­phone. For sound sources more than three feet from the micro­phone this effect is negligible. The frequency response is not appreciably affected by changes in the angle of incident sound over an angle of 75 degrees each side of the axis of maximum response on the front of the micro­phone. An increase in high frequency response may be obtained by disconnecting the high frequency equalizer (See Figure 4).

Connections
The MI-3043-C micro­phone is provided with a six contact connector plug using two contacts in multiple for each of three connections. (Refer to the schematic diagram, Figure 8.) The MI-3043-B is provided with a three-contact connector plug. Connections are shown in Fig. 8.

Portions copied from RCA Publication No. 1B-37007-2,
Uni-Directional Microphone, MI-3043-B, MI-3043-C

The mic seen in the top three photos, S/N 1062, went for $3,600 on eBay on August 5, 2004.

Download the Technical Data booklet for this mic.

This mic’s unofficial nickname is “the skunk.”