Active Crossover Recommendations

Peter, I didn't go quite far enough in my comments. I believe that in a subwoofered system, one needs to run the main system as full-range as it and you can stand. With your 988s, I believe you'd increase their power-handling capacity substantially merely by removing most of the low bass from their signal. That can be done with a 40- or 50Hz hi-pass filter point; I'd start with a 50. Then set the woofers' crossover points and levels wherever you want that SOUNDS good. The point is to keep your fine-sounding main system doing about 90% of the work, and sounding GREAT at it, of course, while increasing power-handling a bit AND adding lo-bass capability. The trick will be to find PLACES for the woofers to blend well with the main system.

I've done something similar in biamping my Eminent Technology 8s. Initially I duplicated ET's c. 40Hz MR hi-pass filter point with an active filter in the amps. I then eliminated the hi-pass filter and have been running the MR panels wide open. I THINK it sounds better. At least I've eliminated the sound of one cap and its inherent phase errors.

If those 'Cary EL34 triode amps' are Rocket 88s, their 150K-Ohm input impedance would create a 48Hz filter with a 0.022µF cap.

Good luck. Pls let us know what you do.
.

Peter,

Try Bryston 10B sub ccrossover with following settings..
High Pass 100 - 110Hz 18 DB slope
Low Pass 50Hz 18DB slope
+3 DB sub volume

or

just run quads full range and use crossover to roll off sub only around 40hz....volume maybe down 1-2db
Dan

Go to the ACI website they have some passive filters in 2 flavors ($30-40) that I am going to try 1st. before I start on the electronic path. I am trying to bi-amp w/ ML-9s.
MMM

Whoops - I guess I've been offline for a couple of days. Jeffreybehr - thanks for your suggestions. In about a month I'll have a preamp that has 2 sets of RCA outputs: 1 with caps that are selected to roll off at 80hz into my 100kohm Cary SLM70 monoblocks, and one without any filters. I will try it both ways: 1) passive filter on the high frequencies and active filter built into the subs, and 2) active filter (Bryston) on both. For now, I can only work with the Bryston, until I get my other preamp.

The sub options include: 1) a pair of TBI Magellan VII's, and 2) a single ACI Titan. The TBI's only have phase reverse whereas the Titan has fully adjustable phase. I'm not looking forward to moving the subs around, but it has to happen! The TBI is very fast, which is why I bought them (to keep up with the Quads). I needed 2 because they aren't that powerful, plus I believe in stereo subs. If the single ACI works, I would likely buy a second.

Thanks all for your comments. Check back on this thread in about a month for a summary of my results (I hope).

By the way Jeff, what is the equation for calculating the capacitance for a passive crossover frequency based on the input impedence of the amp?

Thanks, Peter