Shure 508B, 508C User Guide
DATA SHEET
No.
18612442C
DATE:
SUBJECT:
"Stratoliner" Dynamic Microphones
508 Series "Stratoliner" Dynamic Microphones
GENERAL :
directional pickup characteristics. The three
models differ only in output impedance as described
under "Connections" below.
The microphones operate on the principle of a
moving-conductor in a magnetic field. A high flux
magnet is used in the magnetic circuit, which together with a specially designed moving system and
associated acoustic network, provides high efficiency and smooth peak free response.
The case is attractively streamlined for improved acoustical performance and for modern appear-
ante. Each microphone is provided with a built-in
receptacle and shielded rubber jacketed cable with
microphone plug attached.
APPLICATIONS:
equipment, and similar applications. Extreme ruggedness and immunity to severe temperature and
humidity conditions are inherent in the design. The
frequency response characteristic is wide range (see
Fig. B) providing high quality reproduction of sound
from 70 to 7,000 cycles. The pickup characteristic
is of the conventional semi-directional type. (See
“Acoustic Considerations”). A swivel is provided
which permits pointing the microphone toward the
source of sound. When turned to the vertical position the microphone becomes non-directional in the
horizontal plane and artists may be placed all
around it without frequency discrimination.
INSTALLATION :
stand. Shure floor stands are especially recommended because of the effective isolation against floor
vibration which they provide. For overhead suspension, an A35B Suspension Adapter may be used.
CONNECTIONS :
pregnated transformer with high permeability, core.
The output impedances and cables furnished with the
three models are listed below:
Model
508A
508B
508C
Low impedance models 508A and 508B are recom-
mended where long cable lengths are required.
permissible line length is practically unlimited
since neither the level nor the frequency response
is appreciably affected by reasonable lengths of
line. As shown in the table below the cable loss is
very small. When long lines are used care should
be taken that the cable does not parallel A.C. power
lines for long distances to avoid A.C. hum induction.
Cable Length
25 ft.
250 ft.
500 ft. 0.8 db 0.2 db
1000 ft.
2000 ft.
(* Based on 2-conductor #20 equivalent, twisted and
shielded)
Copyright, Shure Brothers, 1941.
Models 508A, B, C are pressure
dynamic microphones with wide-range
frequency response and typical semi-
Models 508A, B, C are suitable for
public address, recording, call sys-
tems, communications radio telephone
All microphones have the standard
5/8"-27 thread and may be mounted on
any Shure desk, banquet, or floor
Due to the very low impedance of the
moving conductor,
an internal high-quality vacuum-im-
Impedance
35-50 ohms
200-250 ohms
high impedance
Loss in Level*
Model 508A
25 ft. two-conductor
25 ft. two-conductor
25 ft. single-conductor
db
0
0.4 db
1.6 db
2.9 db
all models include
Cable
Loss In Level*
508BModel
db
0
0
db
0.4 db
0.7 db
The
(over)
Low impedance models 508A and 508B may be fed
into a standard low impedance input amplifier (as
shown in Fig. A-3) or into an amplifier with high
impedance input (Fig. A-2). In the latter case
Shure Model A86A Cable-Type Transformer is available
for coupling the low impedance line to amplifier.
The double-winding primary permits coupling a 35-50
ohm line or 200-250 ohm line to the high impedance
input of the amplifier.
High impedance model 508C may be used with any
crystal microphone amplifier or other amplifier with
an input impedance of 100,000 ohms or more (see Fig.
A-l). For best high frequency response the total
cable length should not exceed 25 feet; longer cable
lengths may be used with some loss of high frequency
response. The additional loss at 5,000 cycles is of
the-order of 2.5 db for an additional 25 ft. length
of cable (50 ft. total) and 6 db for an additional
50 foot length (75 ft. total).
OPERATION:
phones. They will operate efficiently and dependably under all ordinary conditions in hot and cold
climates. To retain the full strength of the highly
efficient permanent magnet and to maintain alignment
of structure, dropping or other severe mechanical
shocks should be avoided.
ACOUSTIC
CONSIDERATION:
excellent for high-quality reproduction of music and
speech. 508 Series microphones may be termed semidirectional with polar characteristic as shown in
Fig. C. Note the smooth contours at all frequencies,
due to acoustic streamlining. The pickup angle is
unusually wide; it is permissible to include the
sources of sound within an angle of approximately
140° at the front of the microphone without introducing appreciable frequency discrimination.
When turned to the vertical position, the
microphone is substantially non-directional in the
horizontal plane.
November 1944
Models 508A, B, C
No special precautions beyond ordinary care are necessary in the operation of 508 Series Dynamic micro-
A frequency response curve typical of
all models is shown in Fig. B. The
smooth wide-range characteristic is
Printed in U.S.A.
SPECIFICATIONS
Voltage Sensitivity:
Model 508A
Model 508B
Model 508C
Recommended Load Impedance:
Model 508A
Model 508B
Model 508C
Height Overall
Height, Case
Width
Thickness
Finish . . . . . . . . . . . .
Net Weight (with Cable). . . .
Shipping Weight. . . . . . . .
Code Word. Model 508A. . . . .
Code Word, Model 508B. . . . .
Code Word, Model 508C. . . . .
List Price . . . . . . . . . .
* See Fig. D.
71.8 db below 6 milliwatts for 10 bar
signal when loaded with 35 to 50 ohms.
71.8 db below 6 milliwatts for 10 bar
signal when loaded with 200 to 250
ohms.
63 db below 1 volt per bar when loaded with 100,000 ohms or more. This
iS equivalent to 0.7 millivolts per
bar across 100,000 ohms or more.
35 to 50 ohms.
200 to 250 ohms.
100,000 ohms or more.
(a)* . . . . .
(h)* . . . . . 2-1/2"
(b)* . . . . .
(c)* . . . . .
Irridesc. Gray Chrome
508A, B, C
4"
2-1/2"
4-7/8"
2-l/4 Lb.
2-3/4 Lb.
RUDOC
RUDOD
RUDOB
$27.50
GUARANTEE:
date of shipment from the factory provided all instructions are complied with fully. In case of
damage, return the microphone to the factory for repairs. Our guarantee is voided if the microphone
case is opened.
Each microphone iS guaranteed to be
free from electrical and mechanical
defects for a period of one year from
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