Best Surround Setup for 7.1?

What is the best location for the surround speakers in a 7.1 home-theater setup? Should both sets of surround speakers be on the back wall? Or should there be two speakers on the sides of the room and two speakers in the rear?
– Jeff Olejnik

You should definitely not put all four surround speakers on the back wall. As you can see in the diagram above, the front left and right speakers should be 60 degrees apart (±30 degrees from the center line), and the side-surround speakers are typically ±100 to 120 degrees from the center line—in other words, slightly behind the listening position, but still on the sides.

Notice that there are no angles specified for the back-surround speakers. That’s because the location of these speakers has not been well-defined, other than on the back wall.

THX specifies that, in many cases, the back-surround speakers should be right next to each other in the center of the back wall (shown on the left in the illustration above) so that a feature of THX-certified A/V receivers called Advanced Speaker Array (ASA) can be most effective. If you’re listening to Dolby TrueHD or DTS-HD 7.1 soundtracks, THX recommends that the back-surround speakers should be ±30 degrees from the center line behind you, as shown on the right. I separate the back surround speakers because not all systems have THX ASA, and more movies are being released with Dolby True-HD or DTS-HD 7.1 soundtracks.

Then there’s the issue of height. If your surround speakers are bipolar or dipolar—that is, they have two sets of drivers facing in more-or-less opposite directions—they should be at least two feet above the ear height of the listening position and aimed straight into the room, not angled downward toward the listening position. This helps enhance the diffuse soundfield these speakers are designed to produce.

With dipolar speakers, the two sets of drivers operate out of phase with one another, creating a null region directly between the sets of drivers. In this case, the null area should be aligned with the listening position, which means that dipolar side-surround speakers should be placed directly to the sides of the listening position, or ±90 degrees from the center line. With bipolar speakers, the two sets of drivers are in phase with each other, so there is no null region, and the placement is more flexible.

If the surround speakers are monopoles (one set of drivers facing in one direction), I would mount them just high enough to avoid one listener blocking their sound for another listener. They can be aimed directly into the room or at the “money seat,” depending on your personal preference.

Kevin Voecks, product development manager for Harman’s Luxury Audio Group (which includes the Revel, Mark Levinson, and Lexicon brands) strongly prefers monopoles to bipole or dipole surrounds because, he says, “Monopoles, as a class, are sonically superior to the best dipoles, and to a lesser extent bipoles. The need for such speakers, if it ever really existed, is long gone with the advent of discrete surround channels. They were once used mainly for special effects, but they are now typically ‘on’ most of the time, especially to pull music out into the room. This means that matching their timbre with the front speakers is more important than ever, and that it’s not appropriate for them to be very high in the room.”