Re: Question about JL 300/4?
The "Slash" series JL amps put out the same power at any load from 1.5-4 ohms. If you parallel two speakers on one channel of the amp, the power produced by the amp does not increase and the two speakers must share the available power. In the system diagram you linked to, the resistor acts as an attenuator on the rear fill speakers and serves to redistribute the power between the front and rear. Without the resistor, the front and rear speakers would each get 37.5 watts. With the resistor, the front speakers are getting 56.25 watts and the rear are getting 6.25 watts and the resistor is turning 12.5 watts into heat. Not the most efficient use of power but it does properly (somewhat anyway) distribute the sound front to rear.
If you are curious I can walk you through the math to derive all this.
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