The 411 on 7.1 Surround Page 2
The left and right surround speakers should be mounted slightly behind the listening position, facing the center of the room. But if you're using dipole speakers for surrounds (dipoles have drivers that fire off to each side of the speaker cabinet, instead of toward the listener), they should be mounted high on the wall directly to each side of the listening position. Mounting the surround speakers above ear level might seem to contradict the earlier advice about how to position the front speakers, but surrounds usually handle sound effects and other cues that are meant to create a sense of space, so you want the sound to be as diffuse as possible. This means you can place the speakers 2 to 3 feet above ear level, which allows the sound to reverberate in the back of the room, bouncing off the ceiling as well as the walls.
If the room's side walls are too far from the listening position, putting the speakers on stands is an easy if somewhat awkward solution. Ceiling speakers are another option. (But, as was mentioned earlier, you should think twice about using in-wall or ceiling speakers unless you have solid DIY skills or are willing to hire a professional installer.)
Bringing Up the Rear
For a 7.1 setup, you'll need to decide between the differing recommendations of Dolby and THX on where the two rear speakers should go. THX advises having the speakers no more than 3 feet apart when using its Ultra2 processing, while Dolby recommends spacing them the same distance apart as your front left and right speakers. The THX way makes sense if you're using the Surround EX format or "faux" 6.1- and 7.1-channel formats like Dolby Pro Logic IIx and DTS Neo:6, where the signals to the rear speakers are essentially identical. But since the Dolby TrueHD and DTS-HD Master Audio formats on Blu-ray Discs and HD DVDs can carry different signals to each of the speakers, the wider spacing Dolby recommends will probably produce better results with these formats.
If you have a 6.1 setup, you can simply place a single rear speaker in the middle of the room's back wall, in line with the center speaker. But it should be positioned at the same height as the left and right surrounds, to help keep the sound that's emanating from the back of the room consistent. (For more on speaker placement, see "Step by Step: How to Position Your Home Theater Speakers" on our Web site.)
Space for Bass
Unless you've got some especially beefy full-range speakers in your system, you'll need to add a subwoofer to deliver deep bass - the ".1" in 5.1, 6.1, and 7.1 setups. The best location for a sub is usually in a corner, since having the sound reflect off the converging walls can help reinforce bass output. But it's wise to keep the sub at least a foot out into the room. If placing the subwoofer in a corner makes the bass boom, feel free to try it in other locations. (Because subs are usually heavy, you might want to move it from place to place by putting it on a rug or a large towel and then pulling it into position.) Another idea is to put the sub in the listening position and then move around the room, listening for where the bass sounds strong but not boomy. This obviously beats lugging a subwoofer all over the place. (For more on finding the right location for your sub, see "Subwoofer Setup Secrets" on our Web site.)
If you properly position your speakers for surround, you'll be rewarded with sound that's as good as - or better than - what you can get at a movie theater. With enough time and patience, you'll have an experience that definitely beats having to get to the cineplex early just to sit in the sweet spot.