subwoofer setup problem

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.

Full agreement with Sugarbrie - you want a fair amount of "underlap". You might want to start with the crossover point close to half an octave below (or perhaps even a bit lower) where the mains start to rolloff. Trying the REL Strata with my Dunlavy SM-1s (-3dB somewhere in the mid-40s), the best crossover point seemed around 32Hz. In your system, you would need to be even lower, so it seems unlikely that the ACI would integrate as well as the REL, even though the ACI rolls off faster. You might have a slight suckout from setting the crossover in the mid-20s, but it won't degrade the sound of your Thiels.

Kadlec, does your preamp have a subwoofer output? Then you wouldn't need to spend any money on crossovers. You couldn't run the Thiels in full range of course. I would go this route before I chose (2) or (3).

Karls, I though Thiels were rolled at 6db? I don't actually know what the difference is (in technical terms) but it's the assumption I've been going under when reading other threads about roll off. I have Thiel 1.5s but I'm pretty sure Jim Thiel designs all his speakers very similarly.

I would try 3) first since it is relatively inexpensive, and ACI has a good return policy. I have also read ACI owners who have commented very favorably. Plus a simple capacitor (which is really all the filter is) is not going to cause much sonic degradation in frequencies above 65Hz.

If that doesn't work I'd bite the bullet and get a REL. I have a strata3 with the rolloff frequency set to 28Hz to complement Spica Angelus. If I set the frequency much above 30Hz it sounds awfully muddy ... could be just like you're describing.