I have 2 left over speakers and i just had a crazy ideam 9.1 surrond sound! since i already have a 7.1 setup lke i said im just trying out the idea, so if i wear to do this would it be better to have the extra 2 as rears or fronts?

well i went ahead with 2 extra rears, and god it just sounds awesome now it really does sound like a theater in here!

Usually there are multiple surrounds in a movie theater.

The L/C/R are all behind the screen. Then there are side L/R, and rear L/R; either one of these can be doubled up, but I think doubling the rears will be better because there is more content available to them (4, 4.1, 5.1).

Doubling what !? Speakers... there wont any additional effect, because source sound has only max 7.1.. there no need in more channels, because 7.1 do the best job - 2 Rear, 2 Front, 2 Side, 1 center

It's true, there won't be any more detail from adding 2 extra speakers. The purpose being that the sound seems to come more from all directions. It's mostly preference. I would double speakers if you had a long room, and the extras were the same kind of speaker (or sound the same). Otherwise the difference between the speakers might be distracting.

Yeah i wasent doing it for anything like that, like he said ^ its just for More sound around the room

and how did you wire them? what receiver are you using? what source are you using that has '9.1' capabilities? you do know that when you hook up 2 8 ohm speakers in paralell(which is likely what you did) you get a 4 ohm load which unless you have an un godly deal with the devil kind of surround sound receiver it will likely die over time, it may be louder but it is also at a much higher distortion rate likely higher tehn .1% thd in this case as the unit is likely being ran way way way out of spec, and it will get worse as the unit heats up, i would strongly urge you to only run 5.1 or 7.1 if your receiver always for it, just hooking up speakers does not add depth or realism... it just makes noise

About sound systems you can read here...
http://en.wikipedia.org/wiki/Surround_sound

There is no 9.1 system (dubling speakers does not mean you can +2 `Number` for your current 7.1)

Modern theaters have >7.1 systems ... In big rooms you can double speakers (cinema if have 7.1 does it already), but it is still the same 7.1

Also you need movies with 7.1 sound tracks

thank you

You are right about the effects part, but there will still be a BIG difference in sound. I used to have a 5.1 set-up, then I added an extra sub, 4 extra surrounds, 2 more centers, and two more front left and rights. The difference it makes is that there are less "holes" in your surround system - it sounds much more powerful and engaging. So it certainly makes a huge difference.

I've had mine hooked up for a while like that with no problem. However, I do double up the speakers from the back of the actual speaker, instead of the receiver.