Prior to obtaining the 990, I was running a B&K Ref 30 prepro with an ICBM (Magnepan version) between the prepro and power amps. Front left and right speakers are Magnepan 1.5s (pretty close to full range) and the center channel is the Magnepan MGCC-1. Never mind the other speakers - this question is complicated enough!

Use of the ICBM was necessary due to the Ref 30's very limited bass management and the limits of the Magnepan MGCC-1 center channel speaker. The MGCC1 speaker only goes down to about 160 Hz and most subs aren't designed to go that high. The Magnepan version of the ICBM was designed to allow the bass below 160 Hz to be routed to large front speakers. This is done by switching on the ICBM L/R Recombine switch.

I'm trying to figure out if this setup can be accomodated with the 990 without the ICBM. I'd like to have as few components (and cables!) as possible in the signal path. I can set the 990's center channel crossover frequency to 160Hz, but I think this just sends the bass below 160Hz to the subwoofer.

Has anyone on this forum encountered this issue in their system? Any ideas if and/or how it can be setup without the ICBM?

Thanks,
-Brent

I use the ICBM maggie ed. with 20r mains and cc2 for center. So far it looks like you still need the ICBM for spliting the center signal, though there is now a sub setting: LR+LFE that I will try. What I did to minimize the impact to the main's midrange was to activly bi-amp, and use the ICBM after the low side of the main x-over, this gives great results, with minimal consequences. Also, this works correctly with SACD/DVDA as well.

Thanks for the reply, blaineh. Seems like a good approach. It can be easily adapted to my (passive biamp) configuration.

From what I understand, the L/R + LFE setting only controls what goes to the sub, not what goes to the L/R.

May I ask what xover are you using for the active biamping? I'm hoping to borrow an active xover to experiment with active biamping of the 1.5s.

-Brent

The ICBM is quite a bit more of a sophisticated crossover device, than the crossovers in both the 950 and 990, plus it is a analog device, so you are able to crossover analog and digital signals, where as the 950 and 990 bass mgmt, only pertains to the digital realm. I kept my ICBM, i don't think i could live without it now !!

I use a deqx; about 3k$, however, I have tried with good success the Behringer dcx 24/96. However, I have heard great things about marchand xovers if you like analog. I really need the steep (up to 300db octave) slopes a digital gives me, as the 20s suffer from standing waves/cancelation. I am sitting at 96db now for low to mid/high, 24db to sub.
Tell me though: I have read the manual on recombine, It seems that if I set the CC2 freq to 200 (2x 100) then what is below 200 does go to the mains, and currently I have the mains set to bypass, so output is full range. (actually in my situation, it is only 40hz to 325hz as xover by the DEQX, and the below 40 of the mains goes to the sub.) What I want is the 40hz cutoff be handled by the ICBM, but the manual makes it sound like if recombine is on, and mains set to 40, then the sub output will be 40 and below, but the mains will still be full range (at least as much of the range as I feed it) Is this true? Or does it apply the 40hz high pass to the mains output too?

blaineh,

Yes, I read the ICBM manual the same way you do. When using recombine, it looks like we have two main / subwoofer options:

(1) Main set to bypass - no sub output from mains goes to the sub.

(2) Main set to X Hz - bass below X Hz from mains is also sent to sub.

In both cases, a full range signal is sent to the mains.

I'm thinking the following configuration might cover all the bases (heh heh, pun intended)...

In the 990 speaker setup, indicate there is NO subwoofer.

On the ICBM, set the main xover to bypass.

Place a second active xover - xover freq set to 40Hz and a summing block for the bass output -
between the ICBM main outs and the main (bass) power amp.

The bass out from the second active xover goes to your sub.

Of course, depending on the xover order(s), this may shoot your bass phase information all to hell, but it should give you the freq response you are looking for from each speaker: All bass below the ICBM xover frequencies go to main ICMB outs. The second xover then routes all bass below 40 Hz to the sub.

Since you are biamping the mains, you won't be sending the high freq signal through the double xover maze.

-Brent

Thanks
I thought that might be the case.
The mains, the primary xover (The DEQX, or Behr for that matter) correct for pase of the units downstream. I do have a 2nd standard ICBM, that I use for rears/side that go to a 2nd sub in the rear. I was thinking of using that for the fianl xover, with sides (mmgs) going into the 1st maggie ICBM, and rears into the 2nd standard, with output of mains from 1st going into the mains into 2nd, main out to bass panel and sub out in stereo to stereo subs...