No Highpass/Subsonic for Subwoofer?

[travicles 10+ year member]

Alright this may be a simple fix but I don't know it. I have a MB Quart ONX4125 amplifier with two channels bridged to a Sundown SA-8 tuned to 35 hz. The problem is that my amp's highpass filter only goes down to 60 hz and my headunit has no highpass. What should I do for highpass?

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[justafifteen 10+ year member]

You don't use highpass for a subwoofer, you use lowpass

 

[travicles 10+ year member]

I thought that was only for sealed boxes.. but for ported, one must use a filter?

 

[travicles 10+ year member]

I think I may have found the answer... how does this look?

1 Mono F-Mod FMOD Subsonic filter 30hz HP Sub Crossover - eBay (item 300526946314 end time Mar-17-11 21:30:50 PDT)