The RCA Type BK-1A
semi-directional pressure microphone (1952)

RCA Type BK-1A, MI-11007, on Desk Stand KS-11, MI-11008

Description
The Type BK-1A pressure Microphone is a high-fidelity instrument of the pressure-actuated type, especially de­signed for announcing and remote pickup. Its smooth response and frequency range (60 to 10,000 cycles) make it suitable for reproducing both music and speech. It is effectively non-directional when mounted vertically and is semi-directional when mounted horizontally.

The moving element consists of a lightweight molded dia­phragm attached to an annular coil assembly which is placed within a magnetic field. Coupled to the dia­phragm is an acoustic circuit so proportioned that the diaphragm velocity remains essentially constant for a constant sound pressure from 60 to 10,000 cycles. The coil is connected to a transformer which provides output impedances of 30, 150, and 250 ohms.

When mounted vertically the BK-1A Microphone is non-directional with the higher frequencies uniformly atten­uated. When mounted horizontally, the microphone is essentially non-directional for frequencies below 2,000 cycles, and the higher frequencies are attenuated more as the angle with the perpendicular line to the dia­phragm increases. Figure 3 shows the relative direc­tional output or pickup with the microphone hori­zontally positioned.

The BK-1A Microphone is particularly recommended for broadcast announcing and remote pickup. It is a small, lightweight microphone which may be carried in the hand for interview and mobile use or used with a stand. The relatively high output level, which provides a good signal-to-noise ratio, is advantageous for remote work. When it is used in the open air, its construction makes the effect of air currents practically negligible. The micro­phone is also excellent for many studio applica­tions which require a non-directional or semi-direc­tional microphone.

Caution: Airtight joints above the foot of the BK-1A Microphone are essential to its proper operation. Use a good grade petroleum jelly to seal the joints when re-assembling after servicing.

Figure 2 — Frequency Response

Figure 3 — Directional Patterns.

Three photos above courtesy of Darrin Warner, Big D Broadcast Exchange

Photo courtesy of Ron Harter

President Lyndon Baines Johnson

David Brinkley and Chet Huntley

President John Fitzgerald Kennedy

Download the instructions for this mic.

This mic’s unofficial nickname is “the ice cream cone.”
For historical reference only, original price was $79.50.
Microphones on this site are not for sale.