JBL Cinema 300 - Specifying and Installing Surround Channels

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B. Specifying and Installing Surround Channels:
1. Surround channel assumptions:
• Moderate power surrounds (cone/dome): Sensitivity: 91 dB SPL, 1 W at 1 m, typical; power
rating: 100 watts continuous.
• High power surround (HF horn): Sensitivity 96 dB SPL, 1 W at 1 m, typical; power
rating: 250 watts continuous. Note: Maximum output difference about 9 dB.
2. When to use which surround model?
• For houses with seating no greater than 200 patrons, use either moderate or high power
surrounds.
• For houses with seating greater than 200 patrons, always use high power surrounds.
3. How many surrounds?
• In most houses the ideal number will be 12 to 16.
• Normally, specify at least four surrounds on the back wall.
• An exception here is in very small houses, where there may be two on the back wall. In
this case a total of eight surrounds (three on each side; two on the back wall) will be
sufcient.
4. Surround wiring:
• Always use a “home run” from the booth to each surround loudspeaker.
• Do all of the loudspeaker paralleling in the booth.
• Select wire gauges that will ensure insertion loss no greater than 0.5 dB.
5. How to position the surrounds:
• The front-most surrounds are normally 2/3 the distance from the back wall to the screen.
• The back-most sidewall surrounds should be about nine to 12 feet from the back wall.
• Surround density should be about one unit for each nine to 12 feet along the walls. (See
Figure 42)
6. Surround height and wiring:
• Height should normally be 12 to 15 feet above the oor.
• The high frequency axis should be aimed at the seats along the opposite wall.
• When possible, the surround positions should follow the rake of the oor. (See Figure 43)
7. Be prepared for Surround EX:
• Ideally, the three surround channels should have the same output capability.
This calls for an equal number of loudspeakers per channel.
• When possible, specify surrounds in a quantity divisible by 6 (12, 18 or 24) in order
to ensure optimum load paralleling. (See Figure 44)
Figure 42: Surround channels, perspective view.