Here is a vintage 1950s RCA Type 77-DX velocity ribbon poly-directional microphone. This microphone was thoroughly serviced by Wes Dooley of AEA, and is currently studio ready. This example is in very excellent cosmetic condition and works perfectly.
The RCA Type 77-DX Poly-directional Microphones MI-4045-F and MI-11006-C are high-fidelity micro phones of the ribbon type which may easily be adjusted to obtain a variety of directional patterns. Since the MI-4045-F micro phone is primarily intended for broadcast use, it is finished in satin chrome and a low-gloss umber-gray enamel. The frequency response of a velocity micro phone is essentially uniform when the sound source is at least three feet from the micro phone, but the low frequencies are accentu ated when the sound source is closer to the micro phone. Speakers and singers are often required to stand close to the micro phone, and the low-frequency accentua tion which occurs is undesirable except when special effects are wanted. To solve this problem, a jumper connection is provided on the micro phone terminal board that provides either of two degrees of compensation for close talking. When the jumper is in the M (music) position no compensation is provided, and the response is essentially uniform from 50 to 15,000 cycles per second, provided that the announcer or musical instrument is at least three feet from the micro phone. However, the announcer may move as close to the micro phone as 12 inches when the jumper is in the V1 position, or seven inches when it is in the V2 position, without causing objectionable low-frequency boost. (V1 -10dB shelf at 100hz, V2 -15dB shelf at 100hz) This particular example has been modified with a switch for easy switching between M and V. The plate is marked U, N and B, as symbols for the uni-directional, non-directional and bi-directional pat terns. Three additional markings L-1, L-2 and L-3 are used as reference points for other directional patterns which may be obtained.