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Noise Cancelling Controlled Reluctance Microphones
GENERAL
The Model 488 Series microphones are designed for
2 2 2 HARTREY AVE.. EVANSTON. I L. 6 0 2 0 4 U.S A.
@
AREA CODE 3 1 z / 3 ~ ~ - 9 0 0 0
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CABLE: SHUREMICRO
voice reproduction in those applications requiring re-
jection of unwanted noises. These "Noise Cancelling"
Communication Type microphones are essentially
"pressure-gradient" units using the balanced armature
controlled reluctance principle and are designed for
clear voice response of high intelligibility. The units
are not affected by heat or humidity and provide de-
pendable performance in all types of outdoor and
indoor activities.
DATA
MODELS 4 8 8 ~ AND 4 8 8 ~
SHEET
"SONOBAR"
Model 488 series "Noise Cancelling" microphones
are the result of extensive research, and represent a
significant improvement over conventional communica-
tions microphones (including carbon) having anti-noise
features. This achievement in better noise reduction is
reflected in its performance since it exhibits directional
properties and superior discrimination against noise or
unwanted sounds coming from a relatively distant
source, over an unusually wide frequency range.
The 488 series microphones are equipped with heavy
duty push-to-talk switches. They are designed to stand
up under severe operating conditions and constant
usage. The switches are field tested for long life, op-
erating in excess of one million cycles.
APPLICATION
Model 488 Series microphones are designed for
noise cancelling voice reproduction, and are especially
recommended for all types of outdoor-indoor com-
munication activity in mobile and fixed station use, as
in Police, Fire, Utility, Forestry and Transportation
Services; Commercial; Industrial-including
radio tele-
phone, amateur radio, and similar applications. The
microphones are exceptionally suitable for outdoor and
indoor public address and call systems in noisy areas
(factories; forges; airplanes; lobbies; restaurants; trans-
portation terminals). Because of its high impedance
and high output, the Model 488A may be used in in-
stallations where only a moderate length [up to 15
meters (50 ft.)
1
of cable is required. The low imped-
ance Model 4888 is designed for use in installations
where long cable lengths are required.
INSTALLATION
The microphones are provided with a mounting
bracket for permanent placement with the associated
equipment. The bracket has mounting holes with clear-
ance for No. 8 screws (See Figure A).
CONNECTIONS
Internal switch connections of Models 488A and 488B
(as supplied) are shown in Figure B.
Model 488A is a high-impedance unit and uses a
three-conductor
retractable cable (one conductor
shielded), and a double-pole, single-throw, leaf-type
switch to control the microphone circuit and to con-
trol an external relay or switching circuit. Model 488A
may be used with any amplifier with an input imped-
ance of 100,000 ohms or more.
If additional cable length is required for the 488A, a
three-conductor (one conductor shielded) cable should
be used to provide for the extension of both the micro-
phone and relay circuits. If the relay circuit is not used,
a single conductor shielded cable may be used to ex-
tend only the microphone circuit.
Model 488B is a medium-impedance unit (150-250
ohms) and uses a four-conductor retractable cable
(two conductors are shielded), and a double-pole,
single-throw, leaf-type switch to control the micro-
phone circuit and to control an external relay or switch-
ing circuit. Model 4888 is wired for balanced-line
operation, and is recommended for use where long
cable lengths are required or under conditions of sev-
ere hum disturbance. Model 488B may be connected
to a medium-impedance amplifier or an amplifier with
a high-impedance input. In the latter case one of the
Shure Model A95 Series Line Matching Transformers
should be used to couple the medium-impedance line
to the input of high-impedance amplifiers.
If additional cable length is required for the Model
488B, a four-conductor (two conductors shielded) cable
should be used to provide for the extension of both
the microphone and relay circuits. If the relay circuit
is not used, a two-conductor shielded cable may be
used to extend only the microphone circuit.
When used near a radio transmitter, use the mini-
mum length of cable consistent with
placement
requirements.
The microphone cable shield and associated equip-
ment should be securely connected to an effective
earth grounded water pipe (fixed station use), or to an
effective mobile chassis ground to eliminate shock
hazard to the user.
The Model 488A is supplied with the microphone
circuit shorted by the switch in the normal position.
The switch has been constructed with an extra blade
and the microphone may be modified for use in ap-
plications where a normally open switch is required.
Copyright, 1962, Shure Brothers Inc.
27A200 (ND)
Printed in
U.S.A.
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