Folks,

In the other thread titled "Auto-EQ Question(s)" you can read about how it looked like my new SMS-1 was not working.

I spent the entire weekend agonizing over it. Reading the manual. Searching online forums. I exchanged email messages with Gonk (thanks again Gonk) and even Steve at Outlaw jumped in with a help message of his own (on a Sunday to boot!). But I just couldn't figure out how to get the most basic of SMS-1 operations to work: namely the auto-EQ.

Basically it was drawing a perfectly flat response curve fom 15-100 Hz from the get-go. No slider action. Nothing.

This morning I re-read all of my correspondence and the proverbial light bulb went off over my head. The "solution" was there all along. And you are not going to believe it!

My SMS-1 actually does work. It works exactly as described on page 8 of the owner's manual. It works with the way I set it up. The problem was....my three sub configuration works even better than it does!

This morning I remembered that when I took one sub offline I got a small change in the response from 20 Hz down. The engineer in me says that this is a good thing; it's an indication that something is happening. It got me thinking. What happens if I take two subs out of the equation and go with one?

Huge difference!

First, here's my sub location / configuration.

Back left corner: B&W ASW-1000. Call it sub 1.

Front wall: two Velodyne Servo 1200 subs - placed at "prime number" coordinates from each side wall (not in the corner). Call the one on the left sub 2 and the one on the right sub 3.

I've connected my subs direct to one of the SMS-1 LFE outputs. I've connected the mic to its input - and placed the mic at my seating position. I've connected my Model 950's LFE output to the SMS-1 LFE input - but for the purpose of the auto-EQ routine, that's not needed since the "loop" is formed only between the SMS-1, subs, and mic.

I pressed 8-9-0 on the SMS-1's remote to reset it to its default settings.

Then I ran the auto-EQ (3-2-1) with just sub 1 on. The response was pretty flat from 50-100 Hz so nothing happened with the sliders there. But it fell off (unevenly) below that. The SMS-1 applied (step by step, as each sweep happened) a max boost at 20 Hz. This left a pretty flat curve from 20 Hz down, and the remaining droop between 25-50Hz was within 2-3 dB. I guess I could have then used the SMS-1 manual mode to fix it.

Then I did 8-9-0 again (to reset the SMS-1 to default) and this time engaged only sub 3. Ugly curve this time to begin with and this time the SMS-1 used every slider available, (some max boost, some max cut - mostly a big cut with the lower sliders, big boost with the upper ones) to get a pretty flat response curve - that again was good enough for "auto" and which could have been touched up manually.

But it was back to 8-9-0 again with only sub 2 in the picture and...similar results to what happened with sub 3 (as you would expect for identical subs placed in mirror positions to one another). Lots of cut with the bottom three sliders. The mid stayed the same, and lots of boost on the upper sliders. Similar curve to sub 3's in the end. Some unevenness at all frequencies - but easily within 2-3 dB of flat.

So then I do 8-9-0 and turn all three subs on and...I get a perfectly flat line from 15Hz to 100Hz - right from the get go! Dang. The three sub configuration IS giving me perfectly flat response without the SMS-1's help! Actually there is a 1 dB dip, 2-3 Hz wide, centered at 42Hz, and the same thing at 100Hz. After that the response falls off above 100Hz - which is apparently the upper limit of the auto-EQ function.

So the SMS-1 was working as designed. It had to work very hard to equalize just one sub. And not at all to do all three.

I never ever would have thought this possible. I knew that I had worked hard to find ideal placements for the three subs and to level balance them perfectly with respect to each other. But perfectly flat response from 15-100 Hz? Never in a million.

So now I'm left with a real problem. Why keep the SMS-1 when it's working perfectly - but not doing anything? As I said, the trace is perfectly flat for all three subs. If I were just running one sub, it would be a great help. But I'm there already. I might try manual mode, with my mains and the 950 in the loop. My mains are themselves huge and flat down to 28 Hz and I've crossed them over at 40Hz. I know now that if I want to bump that up to 80 or even 100 Hz that the subs will give perfectly flat response below that.

I also have a much more modest home theatre in my family room that everyone else uses. It only has one sub. I might move the SMS-1 there to see what it can do.

Regardless, this has got to be one for the SMS-1 record books! A customer who thought his SMS-1 was not working - because it did not have to work!

Finally, I should add that I recently (ie. in the last two weeks) re-did my main HT. It's laid-out different. I've added acoustic treatments. I put a lot of thought into the sub placements. I guess it paid off.

This is also a testament to the benefit of using multiple subs to smooth out room response. So get out those chequebooks folks and start ordering that extra LFM-1 or two!

Jeff Mackwood

This really is a cool deal. You've got a way to document frequency response in the space, and the result is a discovery that all your work with sub placement and acoustical treatment (and your trio of subwoofers) has achieved an ideal condition: flat response across the subs' range. As much as I've enjoyed tinkering with my SMS-1 to address an array of mild but noticeable dips and peaks (noticeable once removed, at least), this seems like a case where the SMS-1's tricks aren't required. Definitely a strong case for room treatment, optimized sub placement, and the "smoothing-out" benefits of multiple subs.

Yep - the default slider positions are all below 100Hz, and the auto EQ processes don't adjust the sliders' frequency settings. Of course, you can manually move them up and down at your discretion. If I remember correctly, they can go up to 120Hz.

Jeff, et al,
What is the "prime number coordinates" process for finding the front wall spot?

Ted,

Nothing complex. Perhaps "prime number" is a bit of a misnomer, but not too much so.

I simply situate the subs in positions where they are not at exact multiples of some room dimension. So if I had a room that was 12 feet wide, I would not place two subs exactly 4 feet apart (and four feet from each side wall) if I were placing them along the front wall. I'd instead place them at 2 (a prime number) feet apart, 5 (another prime number) feet from each side wall (as an example). You're basically trying to break it up so that they are not going to easily set up a bunch of standing waves. I'm no physics expert, but this approach seems to have worked well for me.

Of course we can't all start with a fresh sheet when laying things out, so just do the best you can - and avoid some really obvious dimensional matches.

Hope this helps.

When you say "not 4 ft apart" you mean from center of driver (or center of box) to other center, I assume? I will first try the "sub in listening postion" and walk the room with the mike. It'll be interesting if the front wall measurements are like you say...likely so, as not to create many room modes. My coffered ceiling is a pain, as is the room in general. It's too stiff (double drywall and on cement slab).

Anyway, thx.

wow. That is an unbelievable tale.

Jeff, if you don't mind me asking, how big of a "sweet spot" do you get in your setup? Do your multiple subs set up peaks and nulls away from your listening location?

I'm going to guess that it actually isn't too bad, and that careful treatment and room placement helps throughout the entire room... reason I ask is I'm planning (someday) to run something vaguely similar, viz. two "full range" subs co-located with mains and a third "LFE only" in a mode-disrupting position, and wondering how painful the setup might be.

Your experience is encouraging, if amazing!

This is where the tale gets even better.

With the multiple subs etc, the bass response is incredibly smooth throughout the whole room. In effect everywhere except right at one of the subs. I can tell just by walking around and listening / feeling.

I did do my calibrations at the sweet spot BUT I actually placed the mic in several other positions around the room (on other chairs, on the floor in a couple of places, on a rack of DVDs, etc.) and the response in each case was incredibly flat. Most of the time there was just a change in the upper frequencies and a little bit elsewhere. So much so that a few times I had to "talk into the mic in a Lou Rawls sorta way" to see an honest-to-goodness bumpy trace. This was all with three subs running.

Given my experience with just one sub running, measured at the sweet spot, I would guess that the room response would be quite "lumpy" throughout with just the one sub running. When I run just one sub and walk around, I can really notice the peaks and dips.

I suspect that the greatest reason(s) for this extremely flat response are:

1. The use of three subs
2. The fact that they are not all identical types. In my case the Velos seem to provide the lowest end while the B&W handles the upper end - at least from what I saw when I did them one at a time
3. The placement of the subs.

As far as acoustic treatments go, I've actually not added anything specifically targetting the bass region - like bass traps. I have treated about 50% of the wall and ceiling surfaces with acoustic panels - but they really target the mids and highs. The bass taming is really done through layout and the fact that the entire rear "wall" is in fact my equipment rack / heavy curtain - which then opens up to the rest of the basement. The floor has a nice area rug - on concrete. The furniture consists of three minimal leather / wood chairs and ottomans (IKEA Poang) - so there's no huge bass absorbing sofa.

It's probably as much good luck as good planning - but without the planning it never would have been.

ps. I actually run four subs. The fourth being a homebuilt (using Polk drivers / passive radiator) with an external NAD power amp. It's fed the output from a dbx100 ("subharmonic synthesizer") which I use "to taste" (and in moderation) depending on the source material. It's basically reproducing artificial bass in the 27.5 - 55 Hz range. It's particularly usefull with recordings that are bass-shy to begin with. Since it is used in addition to the other three subs, the SMS-1 calibration was done with it turned off. Come to think of it, when it is off it might even act as a bit of a bass trap - with its 15 inches of driver surface area being vibrated by the surrounding air pressure. But that's just a guess on my part.

Jeff Mackwood

Thanks for that. I just looked at your HT pictures -- quite a rig you've got! The sub placement and the room treatment look quite well thought out to me.

P.S.: Nice whisky, too. If you're an Aberlour fan, you owe it to yourself to try their A'bunadh at least once.