Question regarding subwoofers

2) Did a pair of subs affect imaging much? IOW, could you discern enough left/right to make it worthwhile?

I’ll just answer this one from personal experience and give a resounding “yes!” I’ve heard several $$$ systems that employed dual powered subs, and when the subs were turned off the whole soundstage and sense of space literally collapsed. I’d call that more than worthwhile. Just do it!

The one thing that really matters is the one thing you don't mention: crossover frequency. It should be below 100Hz, and 80Hz is even better. 

This is because bass this low in frequency, you cannot localize it. If a sub is putting out any energy above about 100Hz you will localize it and that is why your bass seems to be coming from one spot. 

Below 80 you can't tell where the sub is, you can only tell there's more bass. Where the bass is coming from, your main speakers provide those location cues. Also since you can't localize there is no L and no R.

Look at my system. https://systems.audiogon.com/systems/8367 There's five subs. They're spaced asymmetrically around the room. There's one up front that's left of center, and I never have any idea its putting out any bass at all. Never can tell any of them is putting out anything. At all. Only hear plenty of good clean clear articulate dynamic and extremely deep bass. In spite of all the different drivers and cabinets and locations the bass is beautifully integrated seamlessly into one enveloping sound stage.  

So your solution is: 
Move the center sub to near one corner. Set it to 80. Adjust the level. Buy as many more subs as you can, put them near to - but not all the same distance from - the other corners. Adjust them all. Enjoy better bass than you ever heard before. 

Its kind of a new thing. Been around 20 years but news travels slow. Do a search- Swarm subwoofer system, Distributed Bass Array. You will see.

To get a reference point, listen to jazz with the subwoofer turned OFF. Is the bass still centered? If so, the sub may NOT be to blame. Regardless, the sub crossover frequency should be set no higher than 80Hz or bass localization, as mentioned by MC, will result. If you know the LF -3dB of the Acoustats is, that's where I would set the sub crossover frequency. Then, it's simply a matter of adjusting the sub gain to suit your listening tastes.

As for new subs, the number and size would depend primarily on room size and listening preferences. I would work with what I had before going that route.

If you can tell where the woofer is, its crossed over too high as @millercarbon points out. If it does not make any output above 80Hz it won't attract attention to itself. Your Acoustats go lower than that with ease, so this should be a simple matter of resetting the crossover point.

The distributed bass array is a good tip.

+ 1 @turnbow, adding; a sub enclosure with two drivers ( 8" for example )
will displace as much air as a single 16 " driver.
Larger Drivers are heavier and benefit more robust motors as would any driver.
Servo feedback subs tend to be accurate IMO.

rego199 posts10-28-2020 3:00pm
"....a sub enclosure with two drivers ( 8" for example )
will displace as much air as a single 16 " driver...."

That’s not quite correct. An 8" driver has a cone area of 50 sq.in so two 8" drivers would equal 100 sq.in. A 16" driver has a cone area of 201 sq.in. Cone area varies to the square of the radius.

Ah, for those not familiar with the SB-1 subwoofer, it is passive: The power amp's speaker output goes into the Sub where it passes through the sub's crossover. The upper and mid signals then comes out of there to the full range panels. Inside the sub there's a crossover but it has no adjustment, no internal amp. On the back of the sub, there's a volume control. Unfortunately I never had the proper manual, only the manual for the SB-2 which says it was selectable between 60 and 80Hertz so I'm guessing the SB-1 was at one of those two points. BTW the Acoustats by themselves are pretty gutless down low. 

@millercarbon: 5 subs? LOL I've visited your virtual system. Perhaps in our next home I'll have a single-purpose music room but for now, a 'swarm' of subs is out of the question. (Besides, I rather enjoy my current wife.) However I must disagree with your implication that bass is non-directional. I have moved the subwoofer in the past to different locations and please believe me when I say that I could tell you where it was (and wasn't) in the soundstage. 

@rego: I'm encourage by your statement that two 8" drivers move as much air as a single 16" driver. I will research that a bit further.

I only have room for one Sub and can only be position to the left of my Maggie's My Sub is the SVS Ultra 13 and is crossed over at 70 Hz
through my Oppo BD 105  blu-ray player
When l listen to music with extensive bass l can't tell its coming from my sub but rather within the sound stage of the music 

I have a single 8” dual vc Velodyne DLS (Servo) powered sub. DSP crossover. Remote control. -3 dB at 32 Hz. I have it crossed over at 100 Hz. Bass always sounds like it’s coming from wherever the imaging says it should be, whether center, back, left or right.  Plenty of clean and articulate bass for me. My main source is vinyl; very few LPs go below 30 Hz, so it’s perfect for my setup and my tastes. I listen to all kinds of music, mostly. I just can’t justify these other bass everywhere setups.  

Some subwoofers offer a great deal more in the way of calibrated filtering and  adjustability without digitizing the rest of the system and may satisfy your needs in your room.  

I believe jrwaudio's SVS Ultra has an easy to use auto setup process that also allows the user to manually tweak things to taste as well as some adjustable presets. Check out the Ultra User Manual on line. You'll get a better idea of useable modern processing and connectivity. Have fun with it.

@musicfan2349 if you can easily locate your sub in your room then it is not integrated well, one way or another. Either crossed over too high, gain too high, or some combination of placement and the others. Some rooms are very tough to nail, and that is where the multiple sub concept works. It is possible to integrate a single sub and make it “disappear”, but that requires speakers that dig down pretty low and a cooperative room/setup. Overall, it is much easier to get 2+ subs to integrate as a whole. But one can be done...

Using 80Hz as the x/o frequency is not the whole story: what’s the order of the filter? A 1st-order filter is only 6dB/octave. A sub so used is still putting out a lot of sound at 160Hz (an octave above 80Hz). If using 80Hz, the filter must be very steep, like 4th-order (24dB/octave).

“However I must disagree with your implication that bass is non-directional. I have moved the subwoofer in the past to different locations and please believe me when I say that I could tell you where it was (and wasn’t) in the soundstage.”

OP, It appears you missed the whole point. If your system is properly calibrated, you won’t be able to localize main speakers or subs in the room from your listen chair (sweet spot). Please read it again what @millercarbon and others are saying. And yes, two subs are always better than one (small or large) if you can’t accommodate 4 (DBA or Swarm setup).

“The one thing that really matters is the one thing you don’t mention: crossover frequency. It should be below 100Hz, and 80Hz is even better.

This is because bass this low in frequency, you cannot localize it. If a sub is putting out any energy above about 100Hz you will localize it and that is why your bass seems to be coming from one spot.

Below 80 you can’t tell where the sub is, you can only tell there’s more bass. Where the bass is coming from, your main speakers provide those location cues. Also since you can’t localize there is no L and no R.”

I used to use a pair of Dynaudio BX30 subs time aligned and crossed over with my Dynaudio BM15as at around 80 hz as essentially a three way system.  If I sent full range to the BM15as and all the low end info to just one of the two subs I could absolutely tell where it was coming from.

Then I got a trio of JBL M2s (LCR) and a single JBL SUB18 located between the center and right M2 along the front wall.  The crossover is at 55Hz and there is no sense of directionality from the sub whatsoever.  If your mains are suitably full range to cross over that low you can't hear where the sub is located.

Hi Musicfan, I used Acoustats with 2 SB-1's for years. The SB-1 has a downward firing 12 " woofer in what has been described as a Helmholtz resonating enclosure. It is a great subwoofer. It is bigger than most subwoofers now and it is passive. Your biggest problem is that you need at least two of them and finding a second one in good condition is going to be hard. 
Right now I use 2+2's with my own subwoofer system. Please visit my system page and have a look to get an idea. You have very much the same situation with your 1+1's. They are full range Line sources and require line source subwoofers to match them correctly. We can discuss this on the side if you like. 

Mike 

Below 80 you can’t tell where the sub is, you can only tell there’s more bass. Where the bass is coming from, your main speakers provide those location cues. Also since you can’t localize there is no L and no R.”

Totally agree, but one thing I’ve noticed — and I have no data or other knowledge to back this up — is that with one sub as compared to multiple I do notice what I’ll call a “pressure” difference coming from the direction of the single sub that doesn’t exist with two or more subs.  Everything “sounds” even, it just doesn’t “feel” as even, if that makes any sense.  Not sure if this was addressed at all above, but just a personal observation.