JBL Cinema 300 - Specifying and Installing Subwoofers

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8. Selecting surround ampliers:
• Choose stereo ampliers with a generous 4-ohm power rating equal to twice the
individual surround loudspeaker power rating.
• For example, using high power surrounds, select a stereo amplier that can deliver 500 watts
into four ohms.
9. If you have followed all of these rules:
• Surround coverage in the back 2/3 of the house will be uniform within ±2 dB.
• Fine-tuning of drive levels may further improve uniformity
• In deep houses, be prepared to zone surrounds with delay to maintain proper front/back
perspectives.
C. Specifying and Installing Subwoofers:
1. Subwoofer assumptions:
• Use 18” diameter drivers.
• Sensitivity: no less than about 97 dB, 1 W at 1 m.
• Power rating per-driver should be no less than about 400 watts continuous.
2. How many subwoofer drivers are necessary?
• A safe rule is to specify one sub driver for each 25,000 cubic feet of house volume.
• Always round upward; if your calculations indicate 5 1/2 subs, use 6.
• You can always specify more subs for greater impact.
3. Subwoofer powering:
• We recommend powering each subwoofer driver with its own amplier section.
• Choose ampliers with an output rating that matches each driver at its rated impedance.
Figure 43: Surround channels, stereo wiring. Figure 44: Surround channels, Surround EX wiring.