Holy Crap What have I done?

Thanks, guys. This unit has the standard 100Hz crossover frequency. Originally I thought this was the best place for it, given the slope diagrams on Marchand's website. It occurs to me, though, that asking my down-firing sub to reproduce frequenies over 100Hz - against the maker (ACI) recommendations - is foolish. I plan to order an 85Hz module today and see how that goes.

Right now I have the sub's crossover set 10Hz higher than the crossover, but I'm not sure that's where it should be. Is there a standard relationship I should be looking for between the electronic crossover frequency and the sub's crossover frequency? Big, I don't think my ACI Titan will allow me to truly bypass its LP filter altogether, but I'll check. That would certainly be best.

Stephenson, I'm delaying room treatments because I'm moving in 3-4 months. I'll certainly look at treatments in the new place, though.

Eldartford, I always enjoy your posts. Thanks for helping me out. I look forward to whatever other thoughts you guys have on this!!

Howard

Whew! This is getting complicated, but I appreciate the input. Let me give you guys more history, an update, and then we'll see what your thoughts are.

About 6 months ago I realized my system (http://forum.audiogon.com/cgi-bin/fr.pl?vdone&1107477492) badly outclassed my Velodyne CT-120 sub, so I started looking at alternates. I read about the REL approach to setup, and ran cables from my amp to the high-level imputs on the sub, then cable from the sub's high-level outputs to the monitors. The bass slam and overall bottom end was a HUGE improvement! The problem here, of course, is that the sub in my room sits 4' behind the speakers and a couple feet outside the right speaker, so I'd have to run long (read: expensive) runs of cable from the sub outs to the speakers. Next, I tried the ACI filters, which are 6db/octave slopes, but they didn't produce nearly the effect the high-level connections did. Mike at ACI told me two intersting things: the high-level filters on their subs aren't nearly the quality required for a high-end system (and I think this is true of almost all subs); and that if I wanted a good, steep slope I'd need an active crossover. Hence the XM9 purchase.

I did try bypassing the crossover for my mains and only routed the sub through crossover, and the "magic" returned to my system. It was even slightly superior to what it was without the crossover in line. I did try turning the sub's crossover all the way up to 250Hz, but it produced huge, boomy bass, which surprised me. The crossover should have prevented that. The crossover was a kit, assembled by an authorized dealer, so I suppose it could be improperly, but I'd like to save that as a last resort.

I ordered 2 sets of crossovers today; 65 and 85Hz. We'll see what happens.

As for my setup: one amp powering both monitors and the sub is internally powered. The speakers do have magnificent passive XO's, rebuilt by Jim Salk with the finest parts available in the Murphy-designed crossover.

Thanks for your continued ideas. I'll keep trying your ideas and reporting back on how well they work in my system.

Thanks again!
howard

Dbld,

I liked the system well enough as it was in my last post to leave it alone. Unfortunately, my new house in Kansas has all-shhetrock walls, which are presenting some acoustic issues that I need to figure out how to address. I've read enough negative things about both the REL and Velodyne DD series subs to prevent me from puchasing a new sub for awhile - which is good because it forces me to focus on the room acoustic issue. :)

In the new room I did have a "first-time" experience: I head sounds on a stereo recording behind me and to my right. It was so bizarre I had to replay the song to be sure I didn't imagine it! Very cool.

I'm going to try running the crossover in the path of the main speakers again and tweaking controls in the next week or two as unpacking will allow, and post a note about how the system settles in without room treatments.

Thanks for asking for the update.

Howard

Dbld,

I will have to look and see which XO module I installed. I'm pretty sure it was the 85Hz. I never went back to running my mains through the high pass. I'm fairly convinced I could tweak the controls all day long and it just wouldn't be the same. I'll try again running high-pass through the XO Sunday when I get to Kansas and report.

Howard

Dbld,
The XM44 is certainly a higher-quality unit. I'm not dissing the XM9, because it's great for what it does, but after more listening in my new hom I'm convinced I just can't get my speakers to sound as open and airy with it in their line.