look on the amp for a switch that says high pass/full/low pass. Set it to low pass.

What headunit is this going through?

If the amp has no built in filter, you need something that is wired up between the speaker and the amp. a large coil type device that cuts the high frequencies.

Is the amp stable at 1 ohm?

Is the woofer dual voice coil and what ohms are each voice coil?

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U