Shure 1947 catalogue microphones

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AfifllJSTIC DEVICES

CATALOG No. 157

FOR INFORMATION ON SHURE PICK-UPS
AND CARTRIDGES SEI CATALOG No. 158

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BASIC CONSIDERATIONS

MICROPHONE APPLICATIONS

Three Basic Types: A microphone is an
instrument for converting sound energy into electrical
energy. This is accomplished by Shure Brothers through
three fundamental types of microphones: carbon,
crystal, and dynamic. Each employs a specific funda-
mental principle of operation. Obviously the application
determines the type of microphone to be used.

Carbon: In the carbon type, direct current flows
through the microphone. As the pressures and
rarefactions of the sound wave occur at the dia-
phragm, they cause the movement of the diaphragm
of the micrOphone to press and release the carbon
granules, decreasing and increasing the resistance
of the microphone. Pulsating direct current results, the
pulsating or alternating part having the same wave
form as the original sound wave. High output level
and ruggedness are characteristic of a carbon micro-
phone. It is also practically unaffected by heat and
humidity. Its high output is advantageous wherever
space and weight are a factor, due to the fact that
one or two preamplifier stages may be eliminated.
The carbon microphone is widely used by military
services, police, amateurs, airline and railroad com-
panies for mobile communications.

Crystal: Crystal microphones employ Bimorph
Rochelle salt crystals. The crystal element consists of
two Rochelle salt slabs which are assembled in
such a way that they respond to bending stresses.
The two slabs are provided with three foil electrodes
so that the assembly is capable of generating a po-
tential between the inner and outer foils when sub-
iected to a strain or bend.

In actual construction, a drive pin is connected to
one or two corners of the crystal and the other end
of the drive pin is attached to a diaphragm. The
movement of the diaphragm and drive pin bends the
crystal in accordance with the pressure of the sound
wave. This creates an alternating potential of sub-
stantially the same wave pattern as the sound wave.
A crystal microphone does not require a separate

voltage or current source. The output of the micro-
phone can be connected directly to the grid of an
amplifier tube.

Crystal microphones are excellent general purpose
microphones. They are available in specially designed
models for communications use as well as standard
models for public address and recording. Crystal
microphones are also built by Shure Brothers for
special applications, such as measuring of sound level,
etc.

DYI'ICIMIc: The moving-coil dynamic micrOphone
consists of a coil element attached to a diaphragm.
The coil element is suspended in a magnetic field. The
sound wave, acting upon the diaphragm, causes the
coil of wire to cut lines of flux in the magnetic field,
with the result that a voltage is generated by the coil.
This voltage is alternating in nature and corresponds
to the original form of the sound wave on the dia-
phragm. ,

Shure Dynamic Microphones are available in a
variety of models. Some are ideal for low cost com-
munications work; others are perfect for high quality
public address; and some models have been eSpecially
designed for high quality broadcasting.

The advantages of a dynamic microphone are
many. It is available in low or high impedance, thus
permitting the use of long cable lengths. Shure
Dynamic Microphones are very rugged and are not
affected appreciably by severe conditions of weather,
humidity, and handling.

Polar Response Characteristic: The
microphone is the heart of the sound system. The
difference between having a good or bad installa-
tion begins with the proper choice of the micrOphone.
When you select a microphone, the greatest considera-
tion should be giwn to the polar response of the unit,
more commonly known as the pickup pattern."
Polar response characteristic describes the variation