Shure SH55 Series II Руководство по эксплуатации онлайн [17/48] 776214

IEEE MILESTONE AWARD

Three technologies came of age during the 1930s, and a nascent technology was being nurtured.

Radio broadcasting, public address systems, and two-way radio communication became

commonplace in the 1930s, and television broadcasting was in development. One common

factor required for all was the use of a microphone.

A microphone is a transducer. The function of a transducer is to change one type of energy into

another type. A microphone changes acoustical energy (sound waves) into analogous electrical

energy. After the sound waves become electrical waves, they can be amplied, broadcast,

stored on disc, wire, and magnetic tape, or manipulated in other ways. A microphone was

the primary audio signal source for radio, public address, and television. Since the 1930s, a

microphone has been present at nearly every major event that has shaped the world.

In the early 1930s, the carbon element microphone was in common use. Though not

expensive, its audio quality was poor; it required a DC power source to operate; it had no

ability to reject unwanted background noise. There were also condenser element microphones

– expensive and fragile, and crystal element microphones – adversely affected by heat and

humidity.

In 1939, Shure began to manufacture microphones with dynamic elements. This dynamic

element microphone was, in essence, a loudspeaker in reverse. Instead of a paper cone, there

was a circular, aluminum diaphragm. Glued to the diaphragm was a voice coil wound from

miniature wire. The voice coil was positioned in the middle of a miniature permanent magnet.

Sound waves from the talker moved the diaphragm (suspended like a trampoline), which,

in turn, moved the voice coil. A tiny voltage was induced in the voice coil because of the

magnetic eld. This voltage was the electrical equivalent of the sound wave.

Precision manufacturing techniques were necessary to create a dynamic microphone element,

but the underlying design was simple. The result was a reliable, rugged microphone that was

inexpensive, required no external power, and could be made by the thousands with repeatable

tolerances. Yet the dynamic element microphone did not solve the problem of unwanted

background noise.

Unwanted background noise (ambient noise) is often a problem wherever a microphone is

used. In a radio studio, the background noise might originate with the audience whispering

or turning program pages. These noises would be distracting to the radio listener at home.

In two-way radio communications (re, police, medical), unwanted background noise would

reduce the intelligibility of the messages being sent and could result in loss of life. In public

address systems, unwanted background noise can be the root cause of acoustic feedback -

that annoying squealing and howling that occurs when a public address system is turned up

too loud. The unwanted background noise is the amplied sound waves emanating from the

loudspeakers. When the loudspeaker sound waves are picked up by the microphone, the waves

are re-amplied again and again, and a “feedback” loop is created.

A directional microphone is a necessary tool to reduce the pickup of unwanted background