speakers off sub crossover

[jucas]

So I'm looking for an opinion, and a bit of technical advice.

As there's no speaker outs on my sub, and the amp I'm getting doesn't have a speaker size setting or a crossover setting, is it possible to get something to remove some of the lows that are going to my bookshelves so that my "sub" can do that work? I'd assume that it'd have to just be a high pass filter between my speakers and the outs on the amp, but doe's this even exist short of me building one? Also, will this probably color the sound somewhat or are crossover's passive enough that they should theoretically not alter the signal much (other than removing the lows)?

Also, my speaker's -3dB frequency is 70 Hz so is this even worth while. My sub's crossover goes up to about 120Hz, but at this point it's probly getting fairly directional and I have limited options for placement so I guess that's probably a factor. And finally, even if I cut like 30 Hz from the low end, is it really enough to make a difference to my bookshelve's performance? Being as small as they are, they aren't exactly designed to be getting a lot of low end so will this even make a difference?

Thanks for all the help, and sorry about the long post.

-Chris

[markw]

...or a HT unit with a LFE out?

[jucas]

Sorry, that slipped my mind,

It's off a rotel RA-02 two channel integrated that I don't believe has an LFE out, but rather a pre amp out. I was just interested if this was possible as it seems silly to have my speakers covering range that my sub could easily be handling. Reduce their load a little maybe.

Thanks

[sam9]

Before you go and add gear and make mods consider the possability that the main speakers' natural roll off may be sufficient to allow you to integrate the sub sucessfully. It is nearly impossible (or at least really, really difficult) to do this entirely by ear. Also don't forget the room interaction plays a roll, too.

I think what you need first is more information. The least cost way to get it is a test disc, plus a Radio Shack SPL meter. With this and some graph paper you can graph out a room response curve. Using this you can see how well the sub integrates and try some adjustments including position\, phase (if it doesn't have a control, you an just swap wires), ans XO level. I suggest you try this before investing in more gear. Even if you end up going for more gear, you will have a lot more knowlege to help you make a good selection