Table Of Wire Losses; Wiring Considerations - JBL 4671 Instruction Manual

FIGURE 4C. CADP DISPLAY; HF HORN AIMED 10° DOWN
Screen]
HF Horn
1 0 ' h i g h
Further evidence of this benefit is shown in the
CADP (see reference) coverage plot shown at B. Here,
the front-to-back variation in coverage is only 5 dB, and
this means that the majority of patrons will receive excel-
lent coverage. Compare this with the coverage shown at
C. Here, we have tilted the high-frequency horn down by
only 10 degrees! The resulting coverage variation has
increased to 8 dB.
Only where there is a pronounced rake (8 degrees
or more) to the floor should the system be angled slightly
upward toward the back wall. This can be accomplished
by placing a strip of wood beneath the front edge of the
loudspeaker.
C. Wiring Considerations:
All JBL network and transducer terminals are color
coded so that consistent polarity (phase) of all systems
is assured.
In the following systems, all connections between
transducers and networks should be between like coded
terminals. In other words, red to red, and black to black:
4671
4672A
4674A
In the following systems, the low-frequency section
should be wired red to red and black to black, but the
Nornalized direct
12'
field.
high-frequency section should be wired in reverse
polarity:
4670B
4673
The reason for this has to do with the precise posi-
tioning of the high-frequency driver with respect to the
low-frequency acoustic center. There is one-half wave-
length shift at the crossover frequency in these systems
which requires the polarity change to maintain proper
summation with the low-frequency section.
Wiring from the projection booth to the screen loud-
speakers should conform to local codes. The wire gauge
selected should be such that electrical loss at the loud-
speaker does not exceed 0.5 dB. For most applications
in smaller houses, AWG # 1 2 (2.053 mm) copper wire
will be sufficient. The table shown in Figure 5 shows the
wire resistance for various double runs of copper at var-
ious gauges. For 8-ohm loudspeakers, the total wire
resistance should not exceed 0.552 ohms.
FIGURE 5. TABLE OF WIRE LOSSES
W I R E R U N ( D O U B L E ; C O P P E R ) N O . 1 0
1 0 M ( 3 3 ' )
2 0 M ( 6 6 ' )
3 0 M ( 1 0 0 ' )
4 0 M ( 1 3 2 ' )
5 0 M ( 1 6 5 ' )
6 0 M ( 2 0 0 ' )
F O R 8 H L O A D , L I N E R E S I S T A N C E S H O U L D B E 0 . 5 5 2 O R L E S S .
2kHz
N O . 1 2 N O . 1 4 N O . 1 6 N O . 1 8
. 0 2 . 0 3 2 . 0 5 . 0 8
. 1 2 5
. 0 4 . 0 6 4 . 1 0
. 1 6 . 2 5 0
. 0 6 . 0 9 6 . 1 5 . 2 4 . 3 7 5
. 0 8 . 1 2 8 . 2 0 . 3 2 . 5 0 0
.1
. 1 6 0 . 2 5 . 4 0 . 6 2 5
. 1 2 . 1 9 2 . 3 0 . 4 8 . 7 5 0
9