I would start out at around 6 feet spacing of your speakers and keep the tweeters at around ear height.  Probably could go 8 feet but general rule of thumb is half the distance from listening area which in your case is 12'.  You could go 8' and that would give you 2' from the walls.  If done corectly your ears will say it is coming from the center of the wall not from your 2 speakers.....Thats' what my 2 channel sounds like.  I will ask people where they believe the sound is coming from and they always say the center, nope the LF and LR.  As far as the sub some people prefer corner placement.  I have mine setup toward the LF in between center and LF.  Experiment with the sub placement.  Whatever sounds best in your room.  Some people go to a crawl method for sub placemet-I never have done that.  If you want to go that route do a search with crawl method for sub placement.  Hope this helps.  Also forgot to mention you said a bracket for mounting...you can do this but sometimes it is better to stay a 11/2'-2' from the wall, but experiment see what is best in your room.

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24 hours in a day ... 24 beers in a case ... coincidence?

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