ATK2 3X Active Crossover Processor (Silver) – 8.5 Volts, 2-Way and 3-Way, Remote

Every audio system can benefit from a signal processor. Fine tune your subwoofer amplifier system by adjusting to the levels and frequencies your sound requires. Phase Shifts - Positioning switch 180 degrees shifts subwoofer output signals 180 degrees out-of-phase relative to front and rear output signals.

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