subwoofer setup problem

I am trying to mate an ACI Titan II with my Thiel 22. The Thiels go down to 30 hz but the lowest crossover on the Titan is 35hz. Thus, there is an annoying overlap in frequency. I am considering several possible options and would appreciate some input. They are (1) get a REL sub whose lowest crossover point is 28 hz. (2) get an active crossover and cross my mains at a higher point. (3) use a passive 65hz filter between my preamp and amp that ACI has.
The passive filter is the cheapest route but will it do more harm (to the sound of my thiels) than good?

Greg,You would do better to try setting it higher than 35Hz before you change subs or cross overs. Try moving things around a bit as well. Sounds to me like you would have a huge hole or suckout instead of an overlap the way you have it set up. My sub is set up differently than the ACI or REL so maybe I am way off on this one?
The general rule-of-thumb for integrating subs and main speakers is to allow a one-octave overlap. Hence, if your main speakers were flat to 40 Hz, you'd want the subwoofer's crossover point to be about 80 Hz.
Scott, is that the case when the main speakers are not rolled off?
That was my idea as well but I have no experience with subs that are not really bi-amped with some sort of slope on the main speakers.
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 (, 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.

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.
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.
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.
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.
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
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
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.
Sean: TL's unfortunately haven't been mathematically modeled the same way closed and vented boxes have, so their rolloff is somewhat open to debate. I haven't seen a source I trust enough to say for sure. One author stated 18 dB/octave but I believe this was based on empirical data, not theory. In my mind, I would think that based on how TL's work, they will be lot closer to a vented rolloff than a closed box. The difference, of course, is that they are VASTLY better damped when done properly. TL's are still an untapped gold mine, IMO. They have so much potential and so little interest. And not even the so-called experts seem to be able to give good answers to even the most basic questions about them; there is an astonishing amount of disagreement and error in the literature about the most basic of concepts and equations. Someday....
I talked to my brother about TL's and his thoughts were that test data suggests an appr 6 dB per octave roll off. Obviously, this will vary with the specifics of each design. He commented that overall output levels are lower in efficiency than if the driver was used in a sealed design. He also stated that the woofer / mid-woofer increases in linear output as frequency rises i.e. the output on a graph looks more like a very linear but gradual decline as frequency decreases. There aren't any major "hills & valleys" ( impedance peaks ) like those found on most other vented designs.

While all of those comments tend to coincide with the measurements that i've seen and read about, the only one that i would question would be the one about roll-off. I did some digging and came across the following. This was taken directly from Vance Dickason's Loudspeaker Design Cookbook ( 5th edition ) page 73 / 74: "Looking at the response graph in fig 4.1, it is obvious that a TL's frequency response is similar to a sealed enclosure, but with an even more shallow rolloff, probably accounting for the opinion among TL aficionados that TL's are capable of producing very deep bass."

This does somewhat support my brothers' comments although it does not give a specific figure in terms of dB's per octave. He probably arrived at the 6 dB figure after studying various graphs & data.

Vance goes on to say that many proponents of TL's claim superior transient response to vented ( not hard to believe ) and even sealed designs. According to various testing, his conclusion is that they are extremely similar to a sealed box design with a Q of .7 or so. As you and others may be aware, most "fast & tight fanatics" will tell you that the "fastest & cleanest" bass occurs at a sealed Q of .5 or so ( ala Dunlavy and a select few others ). Obviously, TL's are still not quite as fast or clean as fully optimized sealed boxes but are still miles ahead of typical bass reflex designs.

This coincides with my experience in that i do like TL's, but still prefer a sealed design. If i absolutely HAD to choose some type of vented design though, it would be a TL. Sean

Sean, I agree, a sealed box of Q 0.5 is very hard to beat, but it's also extremely large if it's going to have good extension. It also has to be shaped and stuffed properly to absorb all the midbass and midrange output off the back of the cone, something that you get "for free" with a TL. Vented enclosures are just plain bad: poor damping and low output in the deep bass, and almost no absorptive material inside, which means the sound bounces around and comes back out through the cone and the port. All for a little extra efficiency? Yuck. I'm with you, for main speakers, give me a sealed box or a TL anyday. For subs, I'll make one exception: RELs with ARM loading, a "damped" form of reflex loading, where the frequency range is so low that it avoids these problems.
Karls, i think that most people don't realize that a vent is only "tuned" or "effective" at the one specific frequency that it is resonated at. As such, they are an absolute "mess" anywhere outside of that range and typically do WAY more harm than good.

Of course, i'm strictly talking about sound quality here as one can show tons of impressive arguments on paper. That is, if all you want is an increase in efficiency and bass extension. Yes, the vent does give you a greater quantity of bass, but it is done at the expense of quality. This can be seen with all of the ringing / poor transient response that takes place with a vented design Then again, i'm sure that i'm preaching to the choir on this one.

Hopefully, this will stir up a few others to check into what we are talking about and bring in some new converts to what is considered "old" technology. What is hard to believe though is that vented designs actually pre-date sealed designs. I guess that after listening to all of those early bass reflex models, they had to do SOMETHING to make it listenable. Hence the "breakthrough" technology of a sealed box.

Thank God for Edgar Vilchur and Henry Kloss !!! Sean
Try the passive filters. I use them and find them very transparent. Not only that, they have improved the sound of every main speaker I've tried them with. Because they roll off at a gradual 6db octave rate, they make the transition smoother AND improve the dynamics of the mains. I'll be real surprised if you aren't able to get seamless with the Titan II, my Jaguars are strong to low 30s but with the 85Hz filters and my Titan IIs set around 50Hz it is superb. I was actually able to greatly reduce a major room peak for smoother, more extended bass than with the Jags alone.