Shure 488A, 488B User Guide
222 HARTREY AVE.. EVANSTON.
AREA
CODE
@
31z/3~~-9000 . CABLE:
I
L.
60204
SHUREMICRO
Noise Cancelling Controlled Reluctance Microphones
GENERAL
The Model 488 Series microphones are designed for
voice reproduction in those applications requiring rejection 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 dependable performance in all types of outdoor and
indoor activities.
Model 488 series "Noise Cancelling" microphones
are the result of extensive research, and represent a
significant improvement over conventional communications 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, operating 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 communication activity in mobile and fixed station use, as
in Police, Fire, Utility, Forestry and Transportation
Services; Commercial; Industrial-including radio telephone, 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; transportation terminals). Because of its high impedance
and high output, the Model 488A may be used in installations where only a moderate length [up to 15
1
meters (50 ft.)
ance Model
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 clearance 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 control an external relay or switching circuit. Model 488A
may be used with any amplifier with an input impedance of 100,000 ohms or more.
of cable is required. The low imped-
4888 is designed for use in installations
U.S
A.
DATA
SHEET
If additional cable length is required for the
MODELS
"SONOBAR"
488~
AND
488A, a
three-conductor (one conductor 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 single conductor shielded cable may be used to extend 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 microphone circuit and to control an external relay or switching circuit. Model
4888 is wired for balanced-line
operation, and is recommended for use where long
cable lengths are required or under conditions of severe 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 applications where a normally open switch is required.
488~
Copyright,
27A200
(ND)
1962,
Shure
Brothers
Inc.
Printed
in
U.S.A.
A. To modify the 488A for a normally open microphone
switch, proceed as follows:
1. Remove the three #5-40 round head screws
from the back of the microphone case. (Caution:
the microphone cartridge is spring loaded,
and care must be taken to hold the two halves
of the microphone case firmly together).
2. Separate the case front and back and remove
switch button. See Figure C.
3.
Remove the #5-40 round head switch mounting
screw and lock washer, holding the switch
assembly in the case back.
4. Disconnect or clip the white cable lead from the
switch solder lug.
5. Strip the insulation from the white lead approximately
lug at the bottom end of the switch.
NOTE: In certain instances, if switch sequence is
critical, it may be necessary to remove the effect
of the shorted switch on the cartridge. This can be
done by insulating the shorting contacts with a
piece of "spaghetti" tubing or a piece of insulating
tape.
6.
Re-assemble the switch in the case back, using
screw and lock washer removed previously.
7.
Replace switch button in case back. Also be certain that the cartridge-shield retaining springs
are in the proper position.
8. Place case back on case front and firmly press
cases together. Fasten with the three #5-40
screws and washers previously removed.
6
mm
(VI
in.) and solder to unused
ACOUSTIC CONSIDERATIONS
The important characteristics contributing to the
total noise reduction of the 488 Series Microphones
are shaped frequency response, directionality and
distance and direction discrimination.
The acoustical elements are arranged to optimize
performance in the frequency range of 200 to 4000 Hz.
The results achieved are the elimination of all sounds
outside of the desired frequency range and proper con-
trol of those sounds within the desired range.
The 488 microphones reject noise through their in-
herent directional properties and discriminate against
unwanted sounds arriving from a distance in favor of
sounds arriving from a near source.
The microphones operate on the pressure-gradient
principle and have two sound entry ports, spaced a
small distance apart.
In order to obtain the best noise cancelling perform-
ance with the Model 488 Series, the microphone must
be used as "close talking." The lips should be as close
to the microphone grille as comfort will permit, with a
distance of approximately
1 in.) providing the greatest discrimination between
the voice sounds and background noise.
No special precautions beyond ordinary care are
necessary in operation of the 488 Series microphones.
They will operate very satisfactorily under all ordinary
conditions of humidity, heat, and cold. Dropping the
microphones or other severe mechanical shocks
should be avoided.
6
mm to 25 mm
('/4
in. to
The Model 4888 is supplied with the microphone
circuit opened by the switch in the normal position of
the switch. The microphone may be modified for use
in applications requiring the microphone circuit to be
shorted in the normal position of the switch.
B.
To modify the 4888 for normally closed microphone
switch, proceed as follows:
1. Remove the three #5-40 round head screws
from the back of the microphone case. (Caution:
the microphone cartridge is spring loaded and
care must be taken to hold the two halves of the
microphone case firmly together).
2. Separate the case front and back and remove
switch button. See Figure C.
3.
Remove the #5-40 round head switch mounting
screw and lock washer, holding the switch as-
sembly in the case back.
4. Disconnect or clip the white cable lead from the
switch solder lug.
5. Strip the insulation from the white lead approx-
imately
to the switch blade next to the blade with the
green lead connections. This is the blade that
the switch button pushes against. The outside
solder lug may be bent out of the way to aid
soldering.
6.
Re-assemble the switch in the case back using
screw and lock washer removed previously.
7. Replace switch button in case back. Also be
certain that the cartridge shield retaining springs
are in the proper position.
8.
Place case back on case frogt and firmly press
cases together; fasten with the three #5-40
screws and washers previously removed.
6
mm
(1/4
in.) and solder this white lead
SPECIFICATIONS
Frequency Response:
200
-
4000 HZ
Output Level (at
Model 488A
Open Circuit Voltage
EIA Microphone Rating
Gm (Sensitivity)
Model 4888
Open Circuit Voltage
Power Level (into 200 ohms) - 56.0 dB*
EIA Microphone Rating
Gm (Sensitivity)
*O dB = 1 volt per 100 microbars
"'0 dB = 1 milliwatt with 10 microbars
***Reference, EIA Standard SE-105, August, 1949.
Microbar = one dyne per square centimeter.
Measurements at 9.5 mm
Recommended Load Impedance:
Model 488A
Model
Cables:
Attached, recoils to
Case:
High impact gray "Armo-Dur"
Dimensions:
See Figure D
Net Weight:
340 grams
Shipping Weight:
510 grams
4888
1000
. . . . . . . .
. . .
. .
. . . . . . . . . . . .
.
.
. . . .
. .
(3/4
Ib)
(1
'YE
Ib)
Hz):
. . . . .
.
-
17.0 dB* (.141V)
-
147.0 dB***
. .
. . .
.
-
37.0 dB* (.014V)
*
.
. .
.
.
-
148.5 dB*
(%
in.) from sound source.
.100,000 ohms or more
. . . . . .
0.3m (1 ft) extends to 1.5m
. .
. .
.
*
.I50 to 250 ohms
(5
ft)
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