Shure 1942 catalogue microphones

Page 2

Requirements: Before you select a micro-
phone, ask yourself the following questions:

1. For what application will the microphone be
used?

2. What-are the acoustic conditions of the instal-
lafion?

3. What range of frequencies must the micrOphone
reproduce?

4. How large a pickup area must the microphone
cover?

5. How long a cable must be run from the micro-
phone to the amplifier?

6. What are the gain and input impedance of the
amplifier?
7. Where will the micrOphone be used?

Your answers determine the type micrOphone you
should use.

Three BOSiC 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.

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. lt is also practically unafiected 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 fails 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.

Dynamic: 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. 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.

What Is Polar Response Charac-

teristic? The microphone is the heart of the sound
system. The difference between having a good or
bad installation begins with the proper choice of the
microphone. When-you select a microphone, the
greatest consideration should be given to the polar
response of the unit, more commonly known as the
pickup pattern. Polar response characteristic de-