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AMPLIFIER-TO-SPEAKER DISTANCE (FEET1
200 400 600 800 1000 1200
36
-
32
0)
i
28
Y
2
24
Y
0
1
20
P
3
16
L
J
I2
0
8
4
0
50 100
1% 200 250 300
AMPLIFIER-TO-SPEAKER DISTANCE
(METERS1
FIGURE
8.
RECOMMENDED WIRE GAUGE VS.
AMPLIFIER-TO-SPEAKER DISTANCE:
DIRECT OUTPUT
gauge. This procedure should be followed for each speak-
er cable connected to the DIRECT OUTPUT Connectors
(8,9) of the Amplifier. If a point plotted on the graph falls
between two of the wire gauge lines, the larger of the two
should be the wire gauge used. This will limit the power
loss in the cable to less than 10%.
The graph of Figure 9, Page 8, provides wire gauge
recommendations for use with the 70-volt output of the
SR105A Amplifier. A 70-volt line is usually used for dis-
tributed speaker systems where many speakers and long
cable runs are involved. The wire gauge value determined
from the graph would be satisfactory for the entire cable
run in a distributed speaker system. However, it is possible
to reduce the wire size in increments as the speaker load
becomes less toward the end of the cable run or as
branches are split off the main line. The economy of such
an arrangement will vary depending upon the details of
each installation and should be evaluated accordingly.
AMPLIFIER-TO-SPEAKER IMPEDANCE MATCHING
DIRECT SPEAKER OUTPUT
In order to obtain maximum transfer of Amplifier power
to the speaker load at the direct speaker output and reduce
distortion, the total impedance of the speaker load should
be as near to four ohms as practical under the existing
circumstances (see Figure 6, Page 7). If the speakers
being used have a rated impedance of 16 ohms (such as
the Shure
SR102 and SR103), then four such speakers
connected in parallel present a total load impedance of
four ohms to the direct speaker output of the Amplifier.
This is
an,ideal match to the Amplifier. If, as often happens,
an exact match is not possible, it is desirable to have a
speaker load higher than the Amplifier minimum load im-
pedance.
In general, if more than one speaker is to be connected
to the DIRECT OUTPUT Connectors
(8,9) of the Amplifier,
a determination should be made as to which method
-
series, parallel or series-parallel interconnection of speak-
ers
-
will provide the best match to the Amplifier. To cal-
culate the total impedance of a number of speakers con-
nected in series, merely add the individual speaker im-
pedance values together. To calculate the total impedance
of a number of speakers of identical impedance connected
in parallel, divide the impedance of one speaker by the
number of speakers in the group. For example, the total
impedance of three 16-ohm speakers connected in parallel
is 16 divided by
3,
or 5.3 ohms.
In the event that a group of speakers of different individ-
ual impedances are connected in parallel, the total
impe-
AMPLIFIER-TO-SPEAKER
DISTANCE
(FEET
I
a
W
0 100 200 300 400 500 600 700 800 900 1000 1100 1200
AMPLIFIER-TO-SPEAKER
DISTANCE
(METERS)
FIGURE
9.
RECOMMENDED WIRE GAUGE VS.
AMPLIFIER-TO-SPEAKER DISTANCE:
TO-VOLT OUTPUT
(SRlOSA ONLY)