Shure SR108 User Guide
222 HARTREY AVE., EVANSTON. IL. 60204 U.S.A.
AREA CODE312/866-2200 CABLE: SHUREMICRO
@
TWX: 910-231-0048 TELEX: 72.4381
OPERATION AND SERVICE INSTRUCTIONS
FIGURE
SR108 SPEAKER SYSTEM
A.
DESCRIPTION
The Shure Model SR108 Extended Range Speaker
System is a rugged, heavy-duty, two-way speaker system designed primarily for high sound-pressure-level
reproduction of wide-frequency-range program material in sound reinforcement applications. The
can be used with Shure Model SR105 or similar high-
power amplifiers, in either a single-amplifier mode
(conventional full-range operation with passive crossover) or, with a Shure Model
over, in a biamplification mode of operation. The
is also ideal for monitoring applications requiring wide
frequency response and high signal level capabilities.
When properly installed and connected, the
provide outstanding performance in critical, high-level
applications due to its extremely wide frequency response, low distortion and smooth dispersion characteristics. The
ohms and is designed to operate with up to 57 volts
rms input (200 watts continuous program material). In
SR108 has a nominal impedance of 16
SR106 Electronic Cross-
SR108
SR108
SR108 will
DATA
SHEET
I
the biamplification mode, the low-frequency section
accepts up to 200 watts and the high-frequency section
up to 100 watts of continuous program material. The
SR108 can be used either direct-coupled or with a
constant-voltage 70-volt line using a Shure
Transformer.
The superior sound quality of the
through the use of six eight-inch low-frequency speakers, mounted in a linear array in a front-ported,
loaded, bass reflex enclosure (fourth-order Butterworth
response) plus four high-frequency drivers coupled
to a single radial horn. The front-porting bass reflex
design of the enclosure provides extreme
quency enhancement, and horn-loading optimizes the
lower mid-range frequencies. A built-in series-type
passive crossover network is used with single-amplifier
inputs, and includes a four-position high-frequency
attenuator switch (LOUDSPEAKER OPERATION).
The LOUDSPEAKER OPERATION Switch is also
used to select between the single-amplifier, passive
crossover input and separate high- and low-frequency
inputs for operation in the biamplification mode. The
Shure Model
the proper low-frequency and high-frequency signal
splitting ahead of the power amplifiers for biamplified
operation.
The high-frequency section of the
tains automatic protection circuitry to avoid driver
damage at extremely high input levels. Additional
high-frequency driver protection is included in the
amplification mode to protect against damage from
low-frequency signals.
The
SR108 is a portable unit, and is primarily designed for easy installation either indoors or in
a protected outdoor environment, such as under an
open pavilion. The system is supplied with a
(50-foot), 18-gauge, rubber-jacketed connecting cable
with phone plugs. (A second connecting cable-Shure
RKC4, not supplied-is required for operation in
No.
the biamplification mode.) The upper right rear section
of the
durable wood, coated with black, scuff-resistant, textured vinyl. All adhesives used in the
moisture-resistant, and internal bracing is provided to
minimize vibration and maximize structural integrity.
The metal grille assembly is finished in durable gold
enamel. The radial horn is ruggedly constructed of
high-density, structural urethane foam, with fastening
hardware selected to provide strength and minimize
corrosion and visible wear. The
with an integral rear-panel handle and two heavy-duty,
hard-rubber wheels for mobility.
SR108 contains a cable storage compartment.
The
SR108 is constructed of 15.9 mm
SR106 Electronic Crossover provides
MODEL SR108 EXTENDED
RANGE SPEAKER SYSTEM
1
A102A
SR108 is achieved
horn-
low-fre-
SR108 also con-
bi-
15.2111
(5/8
in.) heavy
SR108 are
SR108 is equipped
Copyright
27A1355
1977,
(QC)
Shure Brothers
Inc.
Printed
in
U.S.A.
SPECIFICATIONS
Power Rating
(Program Material)
Single Amplifier
Low-Frequency lnput
(Biamplification
High-Frequency lnput
(Biamplification
Power Load for
Constant-Voltage
Operation
Impedance
Frequency Response
Crossover Frequency
Sound Pressure
Level (SPL)
Total Harmonic
Distortion
Phasing (Polarity)
Single Amplifier
Biamplification
High-Frequency
Section
........................
Horizontal Distribution
Vertical Distribution
Operating Temperature..
Storage Temperature
Connectors
......................
Overall Dimensions
(see Figure E)
Weight
..........................
Construction
lnput..200 watts max.
Mode)..200 watts max.
Mode)..100 watts max.
....................
....................
....
....
..................
....................
Input-.Positive voltage applied to phone
Mode..Low Frequency: Positive voltage
......
....
..............
-64.5 kg (142 Ib) incl. cable
....................
39 watts
(25-volt input, 16 ohms)
50 watts
(70.7-volt input, through
optional
A102A Transformer)
36 ohms nominal for both con-
ventional full-range and biamplified operation (see Figure B)
40 Hz - 15 kHz
(see Figure C)
2600 Hz nominal
ElA rating: 54 dB at 9.2m (30
feet) from 1 milliwatt; equivalent to 102 dB at
1.2m (4 feet)
with I-watt input
Less than 2% at 1 kHz and 10
kHz; less than 3% at 100 Hz
1.8m
(6
[measured at
feet) and
106 dB SPL]
plug tip produces positive
sound pressure.
applied to phone plug tip produces positive sound pressure.
High Frequency: Positive voltage
applied to phone plug tip pro-
duces negative sound pressure.
120" radial horn
..140° (see Figure D)
90" (1 kHz -10 dB)
-
7" to 43°C (20" to 110°F)
-
29" to 71 "C
(-
20" to 160°F)
Two parallel-wired phone jacks
for each input: conventional
full-range, low frequency and
high frequency
1730 mm height x 495 mm width
x
517 mm depth (68% in.
X
19% in. x 20% in.)
15.9 mm
(%
in.) wood, black
vinyl finish, gold-painted metal
grille, anodized aluminum rear
panel rails, structural urethane
foam horn
Supplied Accessories
Optional Accessories
80
70
60
5
0
40
30
20
10
0
20 40
60
100
200 400 600 IK 2K 4K 6K IOK 2OK
IMPEDANCE CURVE
105
0
-
95
X
Y
u
5
1
75
20
/I I
40
LWDSPEAKER OPERATION
I
W
I00
TYPICAL FREQUENCY RESPONSE
I-
TYPICAL HORIZONTAL POLAR PATTERN
....
One 15.2m (50-foot) heavy-duty
cable with phone plugs
....
A102A 70-Volt Transformer
A50XC 15.2m (50-foot) Extension
Cable with male and female
phone plugs
RKC4
15.2m (50-foot) Heavy-Duty
Cable with male phone plugs
(for biamplified operation)
FREQUENCY
FIGURE
200
400
FREQUENCY
(HZ)
B.
TO Z"
STERAMAN
SWW
1111l1
WO IK 2K 4K
(HZ)
I
I lllllll I\U
BK
FIGURE C.
LEGEND
-----
...........
'?
8
I(::
KHz
1
FIGURE D.
(RKC4)
IOK
20K
r""::
CONENTICUM
r.~?
(4-
3/8
IN.)
FULL-RANGE
lpUr
n
PASSIVE
mgmER
I
FULL RANGE
HIGH-FI1EWENCY
O\
ATTENUATION
FIGURE
OVERALL DIMENSIONS
E.
CIRCUIT DESCRIPTION
In conventional, full-range, single-amplifier opera-
tion, input signals from the power amplifier are con-
nected to the
parallel-wired jacks to a series-type, passive LC
crossover network composed of two capacitors and
two inductors (see Figure F). The crossover provides
a 6
dB1octave rolloff for the low-frequency speakers
and an 18
drivers. The inductance of the low-frequency speaker
voice coils provides an additional 6
resulting in a total of 12 dB1octave low-frequency
rolloff.
Low-frequency signals are routed from the crossover directly to the six low-frequency speakers through
the rear-panel LOUDSPEAKER OPERATION Switch.
The low-frequency speakers are wired in two parallel
sets of three series-connected speakers, providing
a total nominal impedance of 16 ohms. High-frequency
signals are routed from the crossover through the
LOUDSPEAKER OPERATION Switch attenuator network which provides high-frequency level adjustments
of -4, -2, 0, and
of the switch. From the attenuator network, high-
frequency signals enter a protection circuit designed
to prevent damage to the high-frequency drivers by
extremely high signal levels. Signal levels greater than
28 volts rms (approximately 50 watts) for longer than
15 milliseconds are sensed through a diode bridge,
causing a relay to engage high-wattage resistors
which decrease the high-level signals to the highfrequency drivers by approximately
cuitry automatically resets itself when the
quency signals drops below a safe threshold level.
The output of the protection circuitry feeds the four
SR108 through the uppermost set of
dB/octave rolloff for the high-frequency
dB1octave rolloff,
+2 dB in the first four positions
7
dB. The cir-
high-fre-
1
BUW
LOI-FREOUENCI
WUT
0-
high-frequency drivers which are wired in seriesparallel and provide a total nominal impedance of
16
ohms.
Operation in the biamplification mode is accomplished by feeding separate high- and low-frequency
signals from an external 2600 Hz electronic crossover,
such as the Shure Model
through separate high- and low-frequency power amplifiers, such as the Shure Model
plifier, to the
of the
LOUDSPEAKER OPERATION Switch in the
position, the internal passive crossover of the SR108
is bypassed, and the low-frequency signals are routed
directly to the low-frequency speakers. High-frequency
signals also bypass the attenuator network, going di-
rectly from the LOUDSPEAKER OPERATION Switch
through the high-frequency protection circuit and a
12
filter serves to protect the drivers from low-frequency
transient signals produced by connecting input cables
to the power amplifier, turn-on thumps, or operating
errors.
SR108 (see Figure G). With the rear-panel
dB1octave filter to the high-frequency drivers. The
AUDIO CWSOLE ELECTRONIC
8mCn
SR108 BLOCK DIAGRAM
HlGH and LOW FREQUENCY input jacks
CROSSOVER
(2600HZ1
BIAMPLlFlED OPERATION
1
FULL-RANGE
SHOWN
FIGURE F.
FIGURE G.
1
w
N
FULL
RAW€
WKN
SR106 Electronic Crossover,
SR105 Power Am-
HIGH POWER HIGH-FREQUENCY
AMPLIFIER
r-------1
I
BlAMP
SRlOB
SPEAKER SYSTEM
DRIVERS
I
INSTALLATION
General
In planning a sound system using the SR108 Ex-
tended Range Speaker System, care must be taken
to observe the horizontal (140") and vertical (90")
sound distribution. Maximum coverage for sound reinforcement installations is generally obtained with
SR108's on each side of the sound source and as
far forward as possible. Assuming a single
to either side of the sound source, the SR108's should
be positioned so that an imaginary line from the
center of each
audience area. For "clustered"
SR108 runs to the back row of the
SR108 installations
SR108
'
!
3
covering a wide area, each SR108 should be positioned so that its angle of coverage slightly overlaps
that of the
SR108 next to it as their sound output
enters the audience area.
The problem of audience penetration may be likened
to illuminating a dark area with a floodlight: the object is to provide maximum area coverage (audience)
with the available floodlights
(SR108's). At the same
time, care must be taken to avoid illuminating reflective surfaces. A blinding reflection (echo or
"slap-
back") may be more of a problem than inadequate
coverage of the desired area.
Of the remaining common sound installation problems, acoustic feedback can usually be dealt with
by judicious placement of
SR108's and microphones,
and/or the use of feedback filters on the audio console. Extreme background noise or acoustic absorp-
tion generally requires a greater volume level to
maintain an acceptable sound level. However, it must
be remembered that excessive sound levels may be
intolerable to that part of the audience nearest the
SR108's. In this case, or in those cases where the
architectural design leaves audience areas that are
not reached by the
SR108's, the use of secondary or
auxiliary speaker systems should be considered.
Conventional
The
SR108 is designed to accept program material
Full-Range Direct-Coupled Operation
where the average power level reaches 200 watts on a
continuous basis. However, sine-wave or pink or white
noise signals of levels approaching 200 watts should
be avoided in that their duty cycle is much greater
than that of program material. Consequently, when
setting up or adjusting a sound system with
SR108's,
avoid the use of high-level, continuous-type test signals. It should be pointed out that the various speaker
input jack pairs are for paralleling additional speakers
not
and
amplifiers.
CAUTION
Amplifier damage may result if two amplifiers are plugged into parallel jacks.
To insure safe operation of
SR108's with program
material inputs, do not connect any input jack to
an amplifier or amplifiers with output capabilities
greater than shown in Figure
H.
70-Volt Operation
The
SR108 Speaker System may be used on a constant-voltage, 70.7-volt line by using a 70-volt transformer such as the Shure Model
A102A. This trans-
former provides power taps of 50, 25, 12, and 6
watts and speaker impedance taps of 8 or 16 ohms
(see Figure J).
In the
biamplification mode, connect A102A trans-
formers using one transformer for the high-frequency
input and one for the low-frequency input. Connect the
low-frequency amplifier 70-volt line to the power tap
of one
A102A transformer, choosing the tap that produces the desired power level. Connect the high-frequency amplifier 70-volt line to the power tap of the
other transfomer offering the most suitable balance
of high- to low-frequency sound. First try the
high-
frequency power tap that is one-half the power of
the low-frequency tap.
Listen to program material
--
-
f
0
DO
NOT
WITH
THAN
MANUAL
INPUT
HIGH FREO
El
AMP
FULL RANGE
'
'OW
BIAMP
I
I
I
LOW FREO SECTION BIAMP OPERATION
I
I
IXlERNAL LOW
0
CONNECT
AN
OUTPUT
THE
VALUES
FOR
ADDITIONAL
CONTINUOUS
POWER
TO 16 OHMS
100
WATTS
FREa
;,"As
LOUDSPEAKER
I
I
CONVENTIONAL FULL-RANGE OPERATION
16
OHMS
P1SS
REOUlRED (1600HZ bOB/OCTAVE) llOUlRlD i1600HZ I1OB/OCTAVBl
THIS SPEAKER CAN PRODUCE SOUND PRESSURE LEVELS WHICH MAY
CAUSE PERMANENT HEARING DAMAGE AFTER PROLONGED EXPOSURE.
CROSSOVER NETWORK
CAUTION
LOUDSPEAKER
POWER
INDICATED
AMPLIFIER OUTPUT SHOULD NOT EXCEED
CONTINUOUS
POWER
TO 8 OHMS
200
WATTS
400
WATTS
PARALLEL
I_I
-
16 OHMS
WARNING
FIGURE
.
TO
OR
VOLTAGE
BELOW.
INFORMATION.
CONTINUOUS
POWER
TO 4 OHMS
400
WATTS
800
WATTS
CONNECTION
(1
HIGH FREO SECTION
1)
EXTERNAL
H.
A
POWER AMPLIFIER
RATING
SEE
INSTRUCTION
CONTINUOUS
OUTPUT
VOLTAGE
40
VOLTS
RMS
57
VOLTS
RMS
1
PARALLEL
-
BIAMP OPERATION
16
OHMS
HIGH
PASS CROS1016. N11WORK
GREATER
PEAK
65
VOLTS
92
VOLTS
3
0
SPEAKER INPUTS
through the sound system and adjust the high-frequency power tap if a different
high-frequency/low-
frequency balance is desired.
Phasing (Polarity)
The
SR108 is phase-wired for conventional, fullrange operation as follows: A positive voltage applied
to the CONVENTIONAL FULL-RANGE OPERATION
lnput Jack tips will produce a positive sound pres-
sure below 2600 Hz and a negative sound pressure
above 2600 Hz. In biamplified operation, a positive
voltage applied to the LOW
FREQ/BIAMP OPERA-
TION lnput Jack tips produces a positive sound pres-
sure, and a positive voltage applied to the
FREQ/BIAMP
OPERATION lnput Jack tips produces
HlGH
a negative sound pressure. This conforms to the
requirements of the
SR108 internal passive crossover network, which provides the proper phase relationships at the crossover frequency.
When using the
SR108 in biarnplified operation
with an external active electronic crossover network
and separate power amplifiers, the following considerations should be given to phasing: When using a
Shure Model
cal power amplifiers (Shure
power an
SR106 Electronic Crossover and identi-
SR105 or equivalent) to
SR108, the phasing is correct. Dissimilar
high- and low-frequency power amplifiers may be
A102A
POWER
70.7
"HOT"
V
GROUND
LlHE
-I
02=w
0
12W
0
COM
50-6 WATTS
FIGURE
SYSTEM
J.
70-VOLT OPERATION
I
I
J
used as long as all low-frequency sections are in
phase with one another and all high-frequency sections
are in phase with one another. A potential problem
exists only when there is a phase reversal between
the high- or low-frequency sections of the speaker
systems in use. To check for a possible out-of-phase
condition, the following listening test should be per-
formed on both high- and low-frequency sections
of the
SR108's at a time (using one SR108 as a phase ref-
erence) with the same program material (vocal material, or pink noise). Connect the
plifiers,
Turn on the sound system and adjust for a moderate
level. Disconnect the high-frequency driver input ca-
bles. Stand approximately mid-way between the two
SR108's and listen to the program material while
reversing the "hot" and common leads to one of
the low-frequency speaker sections. (This may be
accomplished by wire-reversing or by a simple
wired, double-pole, double-throw switch.) Use the
connection that gives a localized sound, centered between the
tion.
phasing.
disconnect the low-frequency sections. Perform the
same test as above. Correct phasing will provide a
localized sound, centered between the
correct phasing is indicated by the sound appearing
to come predominantly from one
from one
around the audience area. NOTE: In a mixed system
(both conventional full range and biamplified) the
high-frequency driver sections are normally out of
high-frequency signals must be reversed to assure
that the high-frequency drivers of all speaker systems
are in phase. This may be accomplished with a Shure
A15PR Phase Reverser at the high-frequency amplifier
input or the
SR108's. The test should be made feeding two
SR106, power am-
SR108's, and program input equipment.
CAUTION
Do not interchange high- and low-frequency
speaker cables. Damage to high-frequency
drivers from high-level, low-frequency signals may result.
cross-
SR108's; this is the correct phase connec-
A
diffuse, directionless sound indicates improper
AWLlCEI-TO-SPEIKER DISTANCE VEETl
AMPLIFER-TO-SPEAKER DISTANCE IYLTLRSI
RECOMMENDED WIRE GAUGE:
FIGURE
DIRECT-COUPLED AMPLIFIER OUTPUT
Reconnect the high-frequency driver sections and
SR108 to another as the listener moves
phase with one another. Therefore, the biamplified
SR106 high-frequency output.
K.
SR108's; in-
SR108 and to shift
Wiring
The cables used to connect the SR108 should be at
least 18-gauge and rubber-jacketed. Determine the approximate distance from the amplifier to the
and refer to Figures K or L to find the proper wire
gauge for direct or 70-volt amplifier output (with
A102A transformer) operation. Recommended cables
for the sizes listed in Figure K and L are:
Gauge
AWG 18
AWG 16
AWG 14
AWG 12
AWG 10
*Cross-section of American Wire Gauge (AWG)
To avoid frequency cancellations, poor coverage,
dead zones, etc., resulting from improper speaker
phasing, the
The cables listed above are color-coded to ensure
that identical connections are used for each
SR108
cord ("zip cord") is phase-coded with a ribbed outer
jacket, color-coded threads, or tinned and untinned
conductors.
supplied with the
operation, connect the right-angle plug to a phone
jack marked CONVENTIONAL FULL-RANGE OPERA-
TION and twist the cable downward behind the locking
bar to prevent accidental disconnection. The other
phone jack may be used for additional, parallel-con-
nected SR108's. When not in use, the cable may be
stored in the compartment at the top right of the rear
a second cable (Shure
input phone jacks. The same wire gauge constraints
to operation in the biamplification mode. Two separate
cables (four wires) should be used for amplifier-to-
SR108 interconnection in biamplified operation. Note
that the
ever, the wire gauge of the common wire should be
one size larger than the gauge indicated in Figure
given to positioning of the cables. While most local
Placement
marily designed for free-standing operation. In posi-
tioning for optimum sound coverage, care must be
taken to locate the
away from areas where the movement of performers,
hookup. Note that even common 18-gauge lamp
When using the 15.2m (50-foot), heavy-duty cable
panel.
When wiring the SR108 for biamplification operation,
provide connections to both the
listed above for conventional full range operation apply
SR108 high- and low-frequency inputs are
isolated and a three-wire cable could be used; how-
When wiring the
electrical codes do not require locating speaker
cables in conduits or raceways, make sure that cable
placement minimizes traffic interference and physical
abuse to the cable or
The SR108 Extended Range Speaker System is pri-
Belden
8460, 8461,
9720, 8452
I
y28471,
1
1
1
I
1
SR108's must be wired in proper polarity.
#
8473
8477 3.3
-
SR108 in conventional full-range
RKC4) must be obtained to
SR108's consideration should
SR108.
SR108's on stable surfaces and
Area (mm2)*
0.8
1
1.3
1
2.1
1
I
5.3
HIGH and LOW FREQ
SR108
amplifier-
K.
be
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