subwoofer setup problem

Really depends you how the sub and crossover workds. REL subs work best with no overlap. For a speaker that goes to 40Hz, most REL users would set the sub at 34Hz to 38Hz depending on placement. The REL owners guide acutally sais most user make the mistake of setting the sub too high. They recommend a low setting and turning up the volume until it integrates.

Sugarbrie, should I assume from what you are saying that the REL uses a steep slope so that there is not much output above the x point? Hum?

I really don't know about the technical details. The Stratus and Storm has settings down to 22Hz (not 28). The Stratus has room response down to 18Hz, the Storm 16Hz. They were built to compliment the main speakers, not replace them. Call and talk to the folks at Ambrosia Audio in LA (www.ambrosia.com), or the distributor Sumiko.

My Aerial Acoustic 10T's reproduce down to a stated 26Hz and probably lower. My Triad Platinum 18 inch sub's lowest cutoff is 50Hz which is the setting I use. The volume is quite low on the sub and perhaps due to it's placement in the room I do not notice any hump and is stable to 18Hz. The integration has worked quite well.

Before giving up or buying aftermarket tweaks, I would look first at lowering sub volume and then sub placement within the room. In my 13 x 18 room, the sub is about 1/3rd distance away from the nearest corner along the long wall.

-IMO

The REL rolloff is at 12 dB/ octave. This matches best with sealed speakers which also roll off at 12 dB/oct. Vented speakers such as the Thiel 2 2 roll off at 24 dB/oct. But I seriously doubt that they are flat to 30 Hz, most likely they start falling at around 40 Hz, in which case the ACI will blend ok. Perhaps they are set up in your room to have a peak at 30 Hz, which is good when they are running alone but a disadvantage when trying to integrate with a sub. Having experience with various subs, I would strongly disagree with the above statement that there should be an octave of overlap-- this will give an absolutely horrible 60Hz hump that might be good for rap, but not much else. If anything, the REL should have an "underlap", that is, the rolloff point on the REL should be set well below the -3dB point of the mains. In my experience, that is how they work the best. So in answer to your questions, yes, a REL will integrate much better than the ACI. A separate active xover is probably not the best answer; the good ones are expensive and if you're going to spend that kind of money, far better just to buy a bigger REL. The passive crossovers will perform better than you expect, but make sure you understand the math behind them so you can choose the proper values for your particular amp.