RCA 44-BX

From the 1939 RCA catalogue:

Type 44-BX ... The Standard Microphone of Broadcasting

TНЕ ТУРЕ 44-BX Velocity Microphone was developed by RCA engineers to meet a long standing need for a microphone capable of reproduction fidelity equal to that of the other equipment of a modern broadcast station. It is not to be compared with other types of microphones for it is totally different, both in construction and in operation; and, because of its unique features, so far excels in reproduction quality as to be properly placed in a class by itself.

The Type 44-BX Velocity Microphone, unlike other types of microphones, has no diaphragm-the moving element being, instead, a thin metallic ribbon so suspended as to be able to vibrate freely between the poles of a permanent magnet. Because of its lightness, the motion of this ribbon corresponds exactly to the velocity of the air particles and the voltage generated in it is, therefore, an exact reproduction of the sound waves which traverse it. More-over, since it has no diaphragm and is open in construction so that air flows freely through it, the Type 44-BX Velocity Microphone is free from the effects of cavity resonance, diaphragm resonance and pressure doubling, which cause undesirable peaks in the response of all pressure type microphones. As a result it provides reproduction of unequalled uniformity and smoothness over the whole audio range.

Advantages of the Type 44-BX Velocity Microphone are not limited to superb reproduction fidelity for the special characteristics represent an almost equally attractive feature. The directional pattern is of the "figure eight" type, giving the microphone a bi-directional characteristic. This is a feature of considerable convenience as it provides a pickup configuration corresponding closely to average studio dimensions. Not only does it allow placing of artists on both sides of the microphone but it also, because of the dead sides, greatly reduces reflection from side walls.

While the Type 44-BX Velocity Microphone is very sensitive, it is extremely rugged and, in general, better suited to stand hard usage than are most other microphones. Moreover, because it is constructed almost entirely of metal and because of the low impedance of the ribbon, it is unaffected by temperature, humidity or changes in air pressure. Used either in the studio or in the field, this unit makes an extremely good appearance. The shape is attractive and the new finish-chrome and black- is modern.

Matching mountings are available. A shock-proof mounting is furnished.

Above is our own frequency response measurement for a pair of RCA 44BX ribbon microphones.

Output Impedances: 50/250 ohms

Output Level: -49 VU

Frequency Response.... 30-15,000 Hz

Finish: ... polished black and chromium

Mounting Dimensions: ½" pipe thread

Wikipedia Entry for RCA 44 Ribbon Microphones

Scan of the RCA 44BX 1956 specification available at World Radio History 

About the 44B at the Coutant website

The RCA 44BX appears in the RCA broadcast equipment catalogue of 1939, Page 8.

The photograph of Slim Gaillard is from the Los Angeles Daily News Photographic Collection at the UCLA Library.