I am trying to help a member here on SSA with his home theater sub project.

He is currently using a Fi 12" SSD in 1 cube sealed with polyfill running off of a 1400w Behringer amp.

He is changing his setup to a Mach5 18" running off the same amp but ported tuned to around 18hz.

His amp only has a 30hz or 50hz roll off choice.

I have searched and searched for crossovers that have a subsonic filter on them that can be tuned to roll off around 15-20hz. I'm trying to find one for under $150, $80-$120 is more ideal.

I have came across Harrison Labs 20hz FMOD adapters.

This is currently the only thing i have found. Is it ok or worth using?

IT's just for movies and the occasional song from what i understand.

The F-MODS are based on a specific input impedance of the amp. If his amp has a different input impedance, then the cut-off frequency can be off by as much as 50%.

Look at the Reckhorn EQ's from Creative Sound Solutions (Canada) or the Elemental Designs EQ.2.

-Robert

I wouldn't even bother with a subsonic. If the box is tuned to 18 Hz, excursion probably isn't a problem until you're below 15 Hz and there's hardly anything down there. If the sub can't hard bottom I would just let the suspension do the work those few times that you might have a peak at 10 Hz... hell, the amp itself my roll off down there and do the job for you.

Secondly, I wouldn't use the Behringer "low-cut" filter under any circumstances. In the 2 amps that I tested, turning the low cut filter on not only cut out the very lows, but it put a 12 dB peak in around the cutoff!

FMODS suck

i went with the eQ.2. I am very happy with it besides the auto turn-on feature. This should have been taken out of the whole unit.

There is no reason whatsover to put a high pass filter on anything tuned below 20Hz. It will be fine. I have been building H/T subwoofers for 15 years and have never, ever needed a high pass filter on something tuned that low...

I agree with Rybaudio and 95honda. There really isn't a reason to need one. When you tune that low it's almost a mix between ported and sealed, and the sub probably won't begin to unload until 10-12 hz. Which I'm not sure if I've ever heard anything that low in a movie or music.

there are a lot of movies now that have things that will go down to 5hz. i just want to be on the safe side. an example would be the parts where the alien pods come out of the ground in war of the worlds.

you could build a passive subsonic by wiring a few big inductors together. I have never thought about doing that so I'm not sure what it would take.

the thing is that i already have the eQ.2 processor. it does the job.

well I really was also addressing that to Shizzzon, who made the thread.

he made the thread for me. sorry, i didn't say anything.

oooohhhhhhh.

well, I guess discussion is over then.