In-line xover question

Kal- I was trying to decribe something that resembles a Rothwell attenuator (whereby it connects to the amplier input and accepts the IC from the source or preamp), but acts as xover serving to limit the low frequencies to the amplifier.

Thank you.

I guess what I am referring to is a "passive high-pass RCA type plug-in filter".

Kr4-Looks like Parts Express handles Harriosn Labs. Do you have experience you can share? Thanks for the help.

Audiokinesis-
Thanks for taking the time to respond to my post. Guess I opened a can of worms. I'll try to answer your questions best I can. This experiment came about when I installed a pair of in-line filters I had on hand which xover at 65hz. After a few minutes ajdusting the low pass on my subs (which only go down to 40hz), I was relatively pleased by the results (which cleaned up the bass quite a bit) and now assume I can do even better. My main speakers are front vented (VSA 4JR) and I run a pair of old Velodyne HGS-10 subs crossed over at 40hz (I do not know how steep the low pass filter is on the subs-are you referring to slope?). The NHT X2 filter Bob-reynolds (thank you) suggested is intriquing as well.

Audiokinesis-

Thanks again for the time you devoted to my question. I'll try your suggestions and report back. Certainly the possibilities of what could be (thank you bob_reynolds) have me thinking about getting serious about implementing a more sophisticated ("purpose-designed" per Kr4) crossover like the NHT X2. Any suggestions?

Many thanks.