FIGURE 13. WIRING THE SURROUND LOUDSPEAKERS
Figure 13 shows details of electrical hook-up.
Series-parallel wiring will be necessary to ensure that
each amplifier sees a proper load. Most amplifiers today
have a 4-ohm rating, and load impedances anywhere in
the 4 to 8-ohm range are acceptable.
JBL recommends that surround loudspeakers be
individually wired back to the projection booth for ease in
isolating problems and reconfiguring the loudspeakers
for split surround channels. AWG # 1 2 (2.053 mm) cop-
per wire will generally be sufficient for wiring the
surrounds.
E
Subwoofer Systems:
1. Background:
Special low-frequency effects in the motion picture
theater date back to the thirties, but the present interest
dates from Universal's "Sensurround" in the seventies.
Since that time, special low-frequency channels for cov-
ering the range from 20 to 40 Hz have become common
in large theaters, and the Dolby CP200 processing unit
has a summed output below 100 Hz that can be used di-
rectly for driving subwoofer amplifiers.
2. Implementation:
JBL manufactures the 4645 subwoofer system for
motion picture applications. This system, shown in Fig-
ure 14A, uses the 2245H 460 mm (18 in) transducer,
which is noted for its low distortion and for its total excur-
sion capability of 19 mm (0.75 in).
FIGURE 14A
4645 SUBWOOFER
PMAX =
300W
SENSITIVITY:
95 dB,
1 W, 1 M
18
8 UNITS =
12 UNITS =
Ail
LEFT
SIDE
RIGHT
SIDE
LEFT
SIDE
RIGHT
SIDE
5.3ft
