This is an e-mail I just sent to Ed at SVS. Any of your opinions are apprecited.

Ed,

Really got around to setting up the two subs recently. Had a couple of unique issues
I would like your opinion on.

My room is 18x18 square. Carpet floor. Some glass, all doors can be shut.
Using GIK acoustic tri traps in the front two corners, some homade tube traps in
the back two corners. Gik panels at various points in the room. I am using an
SMS-1.

I have the two subs in the front two corners of the room. Plus/2 to the left,
Ultra/2 to the right. Ports are facing towards the front wall.

Run the first test tone sweep, actually get a pretty good (flat) response.

First issue: Trying to get the smoothest response up high 80hz range. Play with
the phase on both subs. End up with the Ultra at 0 and the plus at 180. This gives me
an almost ruler flat response from 200 down to about 50. Is it normal to have one sub
out of phase like that?

Second issue: Huge room hump at 40hz. Using the SMS as a guide I adjust the parametric
eq on each sub. Frequency is the same, q is at half (12 o'clock), but cut is at 100%. This takes
care of about 2/3rds of the gain. Then I adjust the SMS to a minus 9.5. Only at 40hz.

So here is the final set up: Ultra/2 phase 0, Plus/2 phase 180. Both subs q 50%, frequency 40hz,
cut 100%. SMS-1 9.5 cut at 40hz only (no other adjustments are needed on SMS-1)

This gives me an amazing graph onscreen. As flat as I have ever seen. The question is using
this much cut on one frequency. Is it normal or ok to use that much?

Any thoughts are appreciated,

What listening impressions have you noted with it like this?

Tim

That phase setting seems odd with a symmetrical placement, but maybe the square room somehow causes it to work.

I don't think you need to worry about the big frequency cut. It is large boosts that will get you into trouble.

Let's see that graph.

My initial listening is "where's the bass" Ive been listening to that hump for so long I miss it.

I did not have my reference "U-571" so I couldn't really tell. I orignaly had
the Plus 2 in a different location. Couldn't get it real flat and I felt like I was
getting cancelation. Bass would sound real strong at certain frequencies and
go away at others.

If your frequency response is now very flat, you will find that you can run the subs a little hotter without sounding boomy.

That phase setting seems odd with a symmetrical placement, but maybe the square room somehow causes it to work.

I don't think you need to worry about the big frequency cut. It is large boosts that will get you into trouble.

Let's see that graph.

I guess the question is is it better to adjust phase to get a flatter response in the
upper frequencies or is it better to use the sms-1 and boost those frequencies.

Question: Which sub is it that is working in-phase best with the mains, the one at 0 or the one at 180? I would concentrate on getting the sub on each side working best with the mains on the corresponding side.

I guess the question is is it better to adjust phase to get a flatter response in the
upper frequencies or is it better to use the sms-1 and boost those frequencies.
IMO it is still good practice to adjust sub phase for minimal cancellation with the mains at your x-o frequency -- e.g. play an 80 Hz tone (a sweep of frequncies around the x-o is even better) through just your left main, and adjust the left sub's phase control for maximum volume -- then repeat on the right side.

I'd try doing this same process with your receivers distance settings on the subs first, though -- if your receiver allows you to vary the distance setting while a tone is playing this is very quick. Each sub may require it's own 'custom' distance setting, often up to 15 feet farther than the actual distance to the sub. Leave both phase controls at 0 while you get the distance delays set.

Picture of SMS-1 screen

You can get it closer than that if you want to, Sam, although you may have to adjust the Q of the sliders to do it --- I've got mine within +/- 1 pixel on the display over quite a bit of the range . . .