This is REL's guide to setting up an ST.
You're all going to find this crazy, but this is the way I found the best position.
I moved the sofa out of the way, and placed the sub at the listening position, fired everything up to normal levels, with the sub to average everything. I then crawled along on my hands and knees to locate where the bass was 'collecting' There was one corner of the room where it sounded really good. I changed the orientation to face the sub width ways rather than length ways across the room (it's quite a rectangle at 10.5'X16'). Checked to see if conditions had changed, and they had but I still found that was the best place.
So, sub in the spot I found, room back to normal. I then adjusted the phase to counter boom (limit the frequencies so it's not adding to what the front speakers are already doing, but providing additional content underneath those frequencies. And then roughly adjust the level to around about where it needs to be so it's comfortable, but noticeably disappears when you switch it off.
Adjusting to 180 deg phase just completely cancelled some bottom frequencies out, even those the sub wasn't producing (I'll go into that later). Starting from the corner, I started to move the sub out diagonally, about 1cm at a time. There's an optimum 'sweet' spot when you try these positions out; mine was about 12/14cm from the corner.
I then tried rotating 90 deg to fire across the room again, and that really tightened it up. I checked by turning it back to notice differences, and it sounded woolly. I then fine tuned phase and gain again because repositioning and rotation will make a difference.
This all took about 1 1/2 hours, but it was sure worth it! So in answer to your question, spend some time testing different positions and firing straight along the room, or across it, or at an angle. I didn't try different angles as you can get yourself into a whole plethora of monotonous testing.
Regarding the frequency thing, it might help to read about frequency nodes and how pressure in your listening room works. There's a lot of physics involved so it can melt your mind if you're not careful, but for those of you in the pursuit of perfection, it's a must read.
Check out Walter Fendt's Java applets site, in particular the
Standing Longitudinal Waves page.
I'm afraid to say that my lounge was a very disappointing discovery after the Mrs and I moved in last year. I used this site to help me try and figure out what was going wrong. That's when I discovered the treaded bass node. I already knew that they existed, but I just didn't realise why and how. Now I wish I played drums and not bass guitar!
Anyway, do experiment with your set-up, it is worth it. Digging out tape measures and pen 'n' paper can help you plan your positioning better. Room designers use it for decorative planning, we can use it for HiFi and A/V.