Holy Crap What have I done?

Man is this confusing! How can you put a crossover between the amp and preamp? Is this only in the subwoofer circuit? Seems to me that the inline filter would affect both the sub and the monitors, which would be the effect of more bass slam at the expense of mids and highs. This is what I think, and you guys tell me if I'm wrong. What Aggielaw originally had was a pair of speakers with a two-way internal passive crossover inside the box, and an ACI sub with a low-pass passive filter inside the box. If he adds a crossover in front of those crossovers, especially if it is a two way, he will really mess up the passive crossovers in the speakers. Unless I'm just not getting it, I would believe this setup is not good. And again, just my opinion, but I see no problem with the monitors rolling off naturally at 65Hz. I guess I don't agree with that article you read, Aggielaw.

"How can you put a crossover between the amp and preamp?"

It's called an active crossover. Read this for further details.

Besides the Marchand products, Bryston makes the very nice 10B that comes in a version optimal for subwoofers. If you really want to go high-end, the Pass XVR1 is quite a statement product.

The last thing I would ever want to do is have a subwoofer (that is optimal in the 85hz and below range) handle the very critical upper bass/lower midrange of the 3rd and 4th octaves. You clearly do NOT want the sub AND the mains both running in the 65-250 hz region! That will be a disaster to the instruments in this range. Keep the lowpass as low as you can go, just a tad above the natural roll-off of the mains and let the mains run full signal. You will certainly get the bass extension you want. The only issues will be coherency between the sub and the mains and finding an optimal location for the sub.

Please let us know how things progress.

John

Jafox...I beg to differ with you about running main speakers full range and letting their natural bass rolloff occur.
Of course the obvious reason not to do this is to keep the LF signal out of the main power amp. But it's good to keep the LF out of the speaker as well. Although the acoustic output may roll off, the woofer will still be trying, ineffectually, to reproduce those subwoofer frequencies. It doesn't help the upper bass and midrange to have the cone floping around unnecessarily.

Oh, I see now. Aggielaw must have multiple amps, and no passive crossovers in the speakers. I definately agree that you do not want to overlap the frequency range of the two woofers.

If you have not already ordered the 85Hz modules, it might be beneficial to order a pair of 65Hz modules also. Why? Two reasons:

1) With the 65Hz modules in place, run your speakers first straight from your pre. Then run the signal through the Marchand. There should be little to no difference between the sound you hear (excluding bass, remember the Marchand has a 24db/octive slope vs. your nOrh's natural rolloff). This will tell you if the Marchand is altering your signal in any way. (BTW, do you know if this unit was preassembled and tested vs. a kit?)

2) 65Hz is just under 2 octives below middle C (65.41Hz). Using the Marchand at this crossover point will allow your nOrhs to work their magic to this frequency. Since they normally start their rolloff at this point you can use the Marchand to "bump" the frequency response (+ or-) to smooth out the transition.

Try it with both speakers through the Marchand and see if you can get the sound you want. (be sure to set the crossover on your sub to the highest setting as suggested above (250Hz?). Then try it with just the sub signal going through the Marchand as others have suggested. Be sure to watch your cables as John suggested!

I understand the reasoning behind wanting to eliminate the bottom octive of the main speakers but in your case, the crossover would need to be at 130Hz!

At least you will be able to experiment more if you have at least two crossover points.

Keep us informed of your progress.