14
The 5000 Series three-way loudspeakers were developed over an intensive two year period, with much of
the later work done at the Academy of Motion Picture Arts and Sciences, in Beverly Hills, California, with technical
input from the Academy Theater Standards Committee, which includes many of Hollywood’s leading studio
sound personnel. The aim was to produce a new state of the art design that could truly do justice to digital sound
tracks, with their demanding effects and virtually flat power bandwidth. The advantage of the three-way systems
is the reduction in distortion which the three-way concept affords through splitting the overall acoustical load over
multiple elements, use of multi-amplification and digital control, and the use of rapid-flare drivers and horns for
significant improvements in high frequency distortion.
B. Cinema Playback Level Calibration:
The actual level requirements on the filmmaker’s dubbing stage are established by relating them directly
with modulation level on the recorded medium. For magnetic media, this is established as 85 dB-SPL in the house
when the modulation on the track is so-called zero level, or 185 nanowebers/meter. This last quantity has to do
with recording technology, and we need not concern ourselves with it further, except to note that modulation
peaks often exceed zero level by 8 to 10 dB. Thus, the peak output per loudspeaker may be only 95 dB. Good
engineering practice allows additional headroom of 6 to 8 dB above this, so it is clear that the values we have
listed in Tables 1A through 1D are not excessive in the cases of the larger houses. In the smaller houses, we can
certainly use smaller amplifiers than indicated in the table; but even then, the cost of the added power is very
slight, while the benefit is substantial. The amplifier output powers recommended in Tables 1A through 1D are in
accordance with the suggestions made by Lucasfilm Ltd. (5) in the specification of THX
®
systems.
C. JBL Driver Developments:
Our studies have indicated that, in passive systems, maximum power input to the screen loudspeakers is
essentially network limited. As a result of this, many cinema applications ordinarily will not require the high power
Vented Gap Cooling (VGC
™
) performance designed into the 2226 driver. A more recent model, the 2035, was
subsequently designed with a 76 mm voice coil, retaining the same sensitivity of the 2226. Resulting economies
can thus be passed on to the user.
In biamplified systems for larger houses we strongly recommend that the 2226 LF transducers be used,
because of their higher peak power and transient capabilities.
Figure 12 shows the horizontal off-axis response of the dual low frequency 4638 system, which
incorporates two of the 2035 transducers.
Table 1D. Output capability of the 5000 Series Loudspeakers:
Model:
Sensitivity:
Rated Power:
Maximum level )dB) at: (1W @ 1m)
1 m:
12 m:
14.2 m:
16.4 m:
18 m:
5671
97
600 W
124.8
103
101.7
100.5
99.7
5672
100
1200 W
130.8
109
107.7
106.5
105.7
5674
103
2400 W
136.6
115
113.7
112.5
111.7
Figure 12: Horizontal-axis response of JBL 4638 LF system
