[Alwayswantmore]

Have you had a chance to compare a single vs stereo subs in a small listening room? If so, how much improvement did the 2nd sub make?

I have one Force XL driven by Red Wine Audio Signature 30.2 in a 12 x 13 x 9' (ceiling) room. The room has been treated with GIK treatments, and I listen in nearfield position to single-driver 8" Hemp monitors.

It sounds very good, but wondering how much better the sound might be with second sub.

Hearing about your experiences is much appreciated. Kent

[timind]

Where is the sub placed in the room?

[Alwayswantmore]

Where is the sub placed in the room?

Speakers located near top wall in diagram below, facing toward wall with the closet and hallway. This is a 13’ wall.

ROOM



NEARFIELD POSITION



DETAILS

Sub Woofer
- 13.5 inches from front wall
- 4 feet 8” from left wall (on 13' wall)

Hemps
- Driver center is 34.5" from floor
- Driver centers are 6' apart
- Driver centers are 3' 9" from front wall
- Left speaker driver center is 3'  7" from left wall
- Right speaker driver center is 3' 5" from right wall
[Bryan from GIK suggests that I try moving the Hemps 6-9" closer together and 4-6" closer to the front wall, which I have not yet tried.]

Listening position
- Approximately 7' from front wall (on 12' wall)
- Ears are approximately lined up with driver centers (when reclined)

I’ve been working with  Bryan from GIK on placement. Here is a link to a blog on the small listening room, that is a work in progress: http://www.audiocircle.com/index.php?topic=57818.0

BTW: I had been thinking about moving to a sub made by the same company that makes my main speakers. But now I'm thinking I might be better off with 2 ACI Force XLs rather than a single sub from the other company.

[satfrat]

I love your cherry based Ekornes.

[Duke]

Always,

You can definitely expect smoother bass as long as the two subs are some distance from one another, like on opposite sides of the room, and preferably not in exactly mirror-imaged locations (although with the asymmetry at the other end of the room they can't really be in mirror-imaged locations anyway).

Think of it this way:  A single sub will inevitably produce a peak-and-dip pattern at the listening position due to how it interacts with the room.  If you move the sub somewhere else, the peak-and-dip pattern will change, and often substantially so.  And because these patterns will not (and cannot) perfectly overlap, the average of the two differing peak-and-dip patterns will almost always be smoother than either one alone - and usually quite a bit smoother.   

In my counter-intuitive opinion, a small room stands to benefit from having multiple bass sources more than a big room does, at least as far as bass smoothness goes.  Just don't put both subs in the corners.

Duke

[Alwayswantmore]

Always,

You can definitely expect smoother bass as long as the two subs are some distance from one another, like on opposite sides of the room, and preferably not in exactly mirror-imaged locations (although with the asymmetry at the other end of the room they can't really be in mirror-imaged locations anyway).

Think of it this way:  A single sub will inevitably produce a peak-and-dip pattern at the listening position due to how it interacts with the room.  If you move the sub somewhere else, the peak-and-dip pattern will change, and often substantially so.  And because these patterns will not (and cannot) perfectly overlap, the average of the two differing peak-and-dip patterns will almost always be smoother than either one alone - and usually quite a bit smoother.   

In my counter-intuitive opinion, a small room stands to benefit from having multiple bass sources more than a big room does, at least as far as bass smoothness goes.  Just don't put both subs in the corners.

Duke

Thanks. I take this to mean a smoother response curve. Will it likely translate into better definition / resolution too?

Bryan suggested I consider putting one center-front of the room and the other center-rear of the room. The rear sub would be behind my listening chair. This again I believe is for the same reasons you mention above (peaks and dips).

[bpape]

Centered front and rear is meant to help cancel some specific room issues.  The random approach can also work - it's just more trial and error.  In either case, dual subs definitely have some advantages if you're willing to spend the time to get them setup and positioned correctly, phase set correctly, etc.

Bryan

[Duke]

Always,

If the subs have a fairly steep-slope crossover and/or are crossed over low enough, then you won't be able to detect their location from lower midrange coming through.  In this case, you can place them wherever you want - including the way Bryan suggested.  You might try it Bryan's way, and then move one of the subs off to one side a bit to introduce some more asymmetry.  If I'm not mistaken, researcher Todd Welti found the format Bryan suggests to offer the smoothest in-room bass with two subs of the many different (but symmetrical) configurations he tried. 

Smoother-measuring bass will be smoother-sounding bass.  And often, more powerful bass!  Let me explain:  Typically, one or two bass frequencies are over-emphasized by the room's acoustics, causing notes at or near those frequencies to "bloom" or "boom".  So when we set the level of the subwoofer for best overall sound, we set it such that these frequency regions aren't loud enough to be really distracting.  As a result, the rest of the bass region may well be several dB lower than it really ought to be.  On the other hand, if you can bring those peaks down by a few dB, you can then bring the rest of the bass up by a few dB and get a more natural overall balance.

Now it might seem like equalization is the more cost-effective solution, but not necessarily so.  You see, the room-induced peak-and-dip patterns vary so much from one location to another than when you equalize out a peak for one listening position, you are probably deepening a valley for another listening positions  If you always listen from the sweet spot that's not a problem, but if you want good sound throughout the room then an equalizer's real-world usefulness is not as great as you would expect unless there is a frequency region that's a problem pretty much throughout the room.  On the other hand, with two spread-out subs not only will the frequency response  be smoother in the listening position, but it will be smoother throughout the room.

There is some argument for placing two subs to the extreme left and right of the listening position, assuming they meet the lower-midrange inaudibility requirements mentioned above.  This configuration is intended to give a greater sense of envelopment, or being in a large acoustic space.  The researcher who proposes this arrangement, David Griesinger, suggests configuring one of the subs to be 90 degrees out-of-phase with the other.   If your subs don't have a phase control that can be set at degrees, try it with one of them 180 degrees out of phase with the other, and introduce a few feet of asymmetry so they aren't both exactly the same distance from your ears.  Contrary to what your intuition tells you, the bass will not cancel out at the listening position.  You might lose a couple of dB of bass energy, but if so you'll actually be gaining in-room bass smoothness, and enhancing the illusiong of being surrounded by a large acoustic space.

I haven't actually tried the above with dual subs, but I have with a greater number and it seems to be beneficial.

Earl Geddes recommends a different set up procedure.  He likes at least three subs, preferably asymmetrical in all three planes (so, one of them will be closer to the ceiling than to the floor, if you can get away with it).  First set the level and crossover frequency of one sub for best possible sound.  Then introduce the second sub, and adjust its level and crossover frequency to provide the most improvement possible to the first sub.  If you have two different subs, start out with the one that goes the deepest.  If not, start out with the one closest to a corner.  If you use three subs, Geddes would probably suggest putting one of them in a corner, but keep the other two away from the corners.

For the record, the first person I can remember advocating dual subs was none other than Mike Dzurko, back in the 80's.  Seems to me that he had a nearly-fullrange three-way speaker kit, and recommended two subs with it as the optimum setup even though one sub would play plenty loud enough.  I think this was long before anyone had published any papers that would suggest two subs are better than one.  The nearly-fullrange main speakers might have been called Sapphires.  Does that ring any bells, Mike? 

Duke

[Alwayswantmore]

Wow! Thanks for the detailed background info.

The subs in question are ACI Force XLs, which have variable 0 - 180 degree adjustable phase controls. There are TWO crossover controls that can be set at the same -- or if desired -- different frequencies.

Recalling from memory, I believe each control is 6db / octive. Again while I'm not 100% positive, I believe this translates into 12 db / octive if set at the same frequency. Kent

Correction on slope -- Crossover: Dual adjustable Low-Pass: 35-250 12db/octave filters for 24db/octave total

[opnly bafld]

http://www.audioc.com/speakers1/forcexl/forcexldetail.htm

24 dB/oct increasing to 36

[Duke]

opnly bafld, that looks like a very high quality, very well thought-out plate amp Mike is using in the Force XL subwoofer. 

Duke

[Alwayswantmore]

http://www.audioc.com/speakers1/forcexl/forcexldetail.htm

24 dB/oct increasing to 36

Thanks -- directly from the PDF manual = "Crossover: Dual adjustable Low-Pass: 35-250 12db/octave filters for 24db/octave total"

[DR]

In my experience, one force should rock your world. By the photo, I think you might be sitting to close. Move back and let everything breath!

Also, cross that Force as low as your system can tolerate. The thing is amazing when you get it right.

[keenween]

I love the look of your setup. A bit off-topic...but how do you like the soundstage and imaging of your set-up? Also...do you sit nearfield because the room is small or that is your preference?

[Mike Dzurko]

Nice looking setup! First, I want to thank everyone for their input, I agree with pretty much all that has been said. Duke and Bryan have given some very good info about placement options for the subs. They are both very experienced in this.

The Force XL and Titan XL both have dual 2nd order filters. Used in tandem they are 4th order. With the acoustical rolloff of the sub itself, that becomes 6th order. The rapid roll-off is one of the reasons these subs sound so good and are impossible to localize once properly adjusted.

Generally speaking, it is easier to tweek a single sub setup to sound the best.  However, with the investment of a bit more time and effort, dual subs or even three or four, will yield even better results. A lot of our customers begin with a single sub, get comfortable with setup and adjustment, and then progress to adding subs. This approach works very well. I’d also suggest investing at least a Radio Shack SPL meter, or even better, some of the fine, inexpensive and sometimes free measurement software available for PC install. It is such a literal eye opener to be able to view response curves while experimenting with placements and adjustments. 

Budget is usually a consideration and I’d always recommend a single, high quality sub over a pair of lesser subs. It’s the weakest link in the chain thing.  If you start with a less than musical sub(s) that will always determine your system’s potential. If budget is a factor, start with a single high quality sub and you can always upgrade to additional subs. We offer a pair discount, however we can usually be talked into applying that discount when adding subs in the future. Just tell them Mike said it was okay 

Duke, thanks, you’re right, it is a pretty special amp that we use. Put a pair of them in a nice chassis, remove the custom subwoofer filtering components and the bandwidth limiting and you have a fine $1500-$2000 stereo amp.

[Alwayswantmore]

I love the look of your setup.

Thanks. It's a work in progress. Soon I hope to get around to painting the room, moving the plasma higher on the wall , putting a bronze metallic finish on the orange stand holding the GIK 242 between the monitors, adding wooden blinds on the windows, along with some music-oriented art, and finishing the GIK Tricorners to fill the 9' vertical space.

...but how do you like the soundstage and imaging of your set-up?

Even with minimal tweaking the systems sounds pretty d*mn good. But, honestly, without GIK treatments, I would not be a happy camper in such a small room. Follow the link above to my blog and you'll get an idea of how the systems sounds.

To be fair to Mike, I had not heard of ACI when I bought the monitors (but I do love the way they sound  ). On top of that, I have not heard any of ACI's monitor speakers that clearly have a strong following in this Circle. Note: Previously I did own a Vandersteen 2W with their expensive balanced crossover. From my experience, the Force XL holds its own when compared to the 2W for approximately 66% of the investment (not even counting $800 for Vandersteen's balanced crossover  ).

Also...do you sit nearfield because the room is small or that is your preference?

Yes. And yes, because it's a small room. I've had two brands of monitor speakers in a total of three rooms. In all cases I found near-field best. If you have a small room you owe it to yourself to give nearfield a shot.

[satfrat]

Do you push the chair back when watching the LCD or are you sitting on top of that too?

[Alwayswantmore]

Do you push the chair back when watching the LCD or are you sitting on top of that too?

We have his and hers Stessless Chairs (I'm tall, so mine is the BIG one!). Normally they are close to the back wall for watching movies, reading and such. The nearfield position is something I use for critical listening.

[satfrat]

I own a gloss black Force XL just like yours and I love mine. I have mine sitting next to the inside of my right loudspeaker on a 26" substand that I put together. For me & in my room, getting it off the floor and next to my mains made a huge improvement in it's integation with my room.  I hope in the near future to try a second sub in the rear or maybe to 1 side of the room. A rear location would be a whole lot easier tho.

Cheers,
Robin