Holy Crap What have I done?

I want to clarify what was covered by Swampwalker: If you put a capacitor on the input of the amp to give it a first-order high-pass at 65 hz or so, you can NOT run the sub's crossover from the main amp's speaker terminals. This is because this amp no longer accurately covers the range below the crossover point. So you MUST either use a second pair of outputs off the preamp or use a Y adaptor off the preamp output to drive the amp and the crossover ICs.

And yes, this is just a line level passive crossover as Eldartford states. And "just" is the keyword.....nothing less, nothing more.

John

Have any of you played with the inexpensive outboadr crossover fron Velodyne? It looks to be quite powerful for figuring out what frequency and crossover slope works best with a given system. After figuring this out you could get the tweaky audiophile hardware to do the same job. Might be worth picking up a used one if it pops up.

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

Howard - anything new to mention?

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