subwoofer setup problem

I agree with Karls. Depending on the mains and their roll-off slope, it is typically best to "underlap" than to overlap. This is due to the fact that the mains and sub(s) will sum their total output by the time the sound gets to your listening position.

Even though the sub is not running at full steam ABOVE the cut-off frequency and the mains are not running at full steam BELOW the cut-off frequency, each would be contributing appr half of the total output. Kind of like how they take nearfield measurements from a woofer and then from the port / passive radiator and splice them together. Both are resonant within their own ranges but sum together to produce one final curve or output level.

I would also suggest keeping subs away from the corners of a room. All you'll get there is a boomy thud, massive room nodes and a complete lack of "quality" making it hard to blend to the mains. The only time that a sub should be corner mounted is if it has pathetically low output to begin with and you're trying to do "earthquake effects" for HT. Otherwise, forget about that type of installation for music reproduction.

Besides the "thuddiness", the low frequency sound waves now have a longer distance to travel coming all the way from the corner as compared to the mains that are probably situated closer to you. Due to the time delays involved, the bass would always seem to "lag behind" ( because it IS "lagging BEHIND" ) the rest of the music.

Try to situate the sub close to the mains and directly between them if at all possible. Not only does this minimize the reinforcement that occurs due to room gain in the corners, it tends to stabilize and focus the bass imagery. The amount of time delay between the various drivers is minimized, producing a more coherent sound wave that arrives at your ears within a few milliseconds of each other. Bass is far more natural due to relying on the drivers output rather than room reinforcement and blending to the mains is far simpler.

Once you get the basic package somewhat dialed in, you can experiment with moving the sub forward or back ( this affects the apparent bass "attack" and time of delivery ), fine tuning the crossover point, adjusting the output level, etc... Keep in mind that one adjustment will affect the other, so you'll have to decide how "picky" you want to get. Hope this helps... Sean
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My transmission-line ported Vandersteen 1Cs are rated to be 3dB down at 38 Hz. I got excellent integration of my Titan II LE (located slightly forward and to the right of the Vandys) with the sub's crossover set 24db down at about 40 Hz.

Mostly because of power handling concerns about the Vandersteens (when I wasn't around), I got ACI's 65 Hz passive filters for between my preamp and amp. I turned up one of the Titan II LE's crossovers to somewhere between 55 and 60 Hz and left the other crossover at around 40 Hz to achieve integration that's at least as good as it was before. It also resulted in a slightly improvement of the upper bass and midrange from my 2-way Vandersteens. There is increased open-ness and "air" in the music.

For Leoturetsky: low-freq rolloff is a function of the physics of sealed vs. vented boxes, and it cannot be adjusted by the designer, it just is. Sealed boxes roll off at 12 dB/oct and vented boxes at 24 dB/oct. There are minor variations in the response right around the "knee" of the curve, depending on the "Q" of sealed boxes and the particular alignment of a vented box, but they all go to the same slope below that. Listening rooms add a boost of 6 dB/oct beginning when the wavelength equals the largest room dimension, and often this coincides approximately with the rolloff of the speakers. This will modify the actual in-room rolloff of a sealed box to 6 dB/oct and of a vented box to 18 dB/oct. This is why sealed boxes have a noticeably slower rolloff in the deep bass than vented ones.

Karls, please correct me if i'm wrong, but don't TL's ( transmission lines ) roll off at a different ( slower ) rate than a typical vented speaker ? I know that their characteristic resonance peaks respond VERY differently than a ported or passive radiator design. Then again, there are more than a few variations amongst TL designs too... Sean
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As a REL owner I should tell you to dump the ACI and buy REL, but I won't because I think that the ACI might work just as well.

The above threads are interesting physics descriptions ported vs vented etc etc but I think your best advice (from Sean I think, no not the same Sean) was to make sure the sub is well away from the corners ... I agree that subs in corners sound awful boom, boom boom).

I think you are correct to state that the overlap is the problem and I agree with all other posters that subs should underlap rather than overlap the mains in order to avoid muddy bass.

So I still think that 3) should be your first step for the following reasons :

1) ACI wouldn't sell the filters if they didn't think they work.
2) it's cheap and they are returnable if you don't like them.
3) It will stop any overlap, and might even improve the clarity of the main speakers since the drivers are not trying to reproduce low bass (leave it to the sub).
3) buying a different subwoofer is much more expensive, and may not be necessary after adding the filters.

I would try to resolve the issue with ACI before anything else. My REL sub is great but I'm sure your ACI is just as good if correctly set up.

Good luck, and please post back to let us know if you solve the problem.