Handbook for Sound Engineers

530 Chapter 16

16.6.4 Base Station Microphones

Base station power microphones are designed specifi-
cally for citizens band transceivers, amateur radio, and
two-way radio applications. For clearer transmission and
improved reliability, transistorized microphones can be
used to replace ceramic or dynamic, high- or low-imped-
ance microphones supplied as original equipment.

The Shure Model 450 Series II, Fig. 16-82, is a high
output dynamic microphone designed for paging and
dispatching applications. The microphone has an omni-
directional pickup pattern and a frequency response
tailored for optimum speech intelligibility, Fig. 16-83. It
includes an output impedance selection switch for high,
30,000: , and low, 225: , and a locking press-to-talk
switch.

The press-to-talk switch can be converted to a
monitor/transmit switch with the Shure RK199S
Split-Bar Conversion Kit. When the optional split-bar
Transmit/Monitor Switch Conversion Kit is installed,
the monitor bar must be depressed before the transmit
switch can be depressed, requiring the operator to verify
that the channel is open before transmitting. The
monitor bar can be locked in the on position. The
transmit bar is momentary and cannot be locked.

16.6.5 Differential Noise-Canceling Microphones

Differential noise-canceling microphones, Fig. 16-84,

are essentially designed for use in automobiles, aircraft,

boats, tanks, public-address systems, industrial plants,

or any service where the ambient noise level is 80 dB or

greater and the microphone is handheld. Discrimination

is afforded against all sounds originating more than ¼ in

(6.4 mm) from the front of the microphone. The

noise-canceling characteristic is achieved through the

use of a balanced port opening, which directs the

unwanted sound to the rear of the dynamic unit

diaphragm out of phase with the sound arriving at the

front of the microphone. The noise canceling is most

effective for frequencies above 2000 Hz. Only speech

originating within ¼ in (6.4 mm) of the aperture is fully

reproduced. The average discrimination between speech

and noise is 20 dB with a frequency response of

200–5000 Hz.

16.6.6 Controlled-Reluctance Microphones

The controlled-reluctance microphone operates on the

principle that an electrical current is induced in a coil,

located in a changing magnetic field. A magnetic arma-

ture is attached to a diaphragm suspended inside a coil.

The diaphragm, when disturbed by a sound wave, moves

the armature and induces a corresponding varying

voltage in the coil. High output with fairly good

frequency response is typical of this type of microphone.

16.6.7 Handheld Entertainer Microphones

The handheld entertainer microphone is most often

used by a performer on stage and, therefore, requires a

special frequency response that will increase articula-

tion and presence. The microphones are often subjected

to rough handling, extreme shock, and vibration. For

live performances, the proximity effect can be useful to

produce a low bass sound.

Figure 16-82. Shure 450 Series II base station microphone.
Courtesy Shure Incorporated.

Figure 16-83. Frequency response of the Shure 450

Series II microphone shown in Fig. 16-82. Courtesy Shure

Incorporated

20 50 100 200 500 1000 5000 10,000

+10

0



10

Relative response—dB

Frequency—Hz