What is the simplest and cheapest way to add an adjustable frequency subsonic filter to an amp that doesn't have one?

I want to filter out all frequencies below the tuning frequency of my ported sub box.

I keep seeing these digital bass processors but have no idea what they are or what they do, or if they'll even do what I'm looking for.

 

Buy an external active crossover, or use a HU that has a built-in crossover.

You can find basic crossovers such as the AudioControl 2XS or Coustic XM-series for relatively cheap if you look around.

 

you can buy my Alpine amp that has selectable 15Hz and 30Hz Subsonic filter

 

Well the head unit I just bought doesn't have it built in, so I need an add-on.

I guess I'm supposed to be looking for an external crossover, even though I only have a amp for my sub, not my highs and mids?

 

http://www.hlabs.com/products/crossover/

 

Phoenix Gold Bass Cube. You get a 1band EQ for the bass and an adjustable infrasonic filter.

 

www.audiocontrol.com, have a look through their website as there is huge number of devices that will work for you. Couple up a line driver, crossover and subsonic filter for example.

 

That Phoenix Gold Bass Cube seems to be the best solution to my problem so far.

Very simple and in a single device like I want, but I don't know if it's cheap or not.

All I really need is a subsonic filter here... The EQ is a bonus that would help with the lack of bass from my factory speakers in the frequency range of 80Hz or so where the amp crossover kicks in.

I need to know where I can buy these things though as well. For a REASONABLE price... On the cosumer end that is, not the seller.
$35 is a good starting point.

 

Check ebay for cheap prices.

Newbie time!!! -> Why do we run a subsonic filter and what should we set it at?

 

I'm not finding any cheap prices on that Bass Cube anywhere. Kind of frustrating.

I did find this though...

eBay.ca: SOUNDSTREAM PQ-7 BAND PARAMETRIC EQUALIZER CROSSOVER EQ (item 120115043391 end time 07-May-07 19:31:16 EDT)

Probably wouldn't fit my definition of simple, but it seems to be cheaper than the bass cube.