You can also place the center speaker below a TV or projection
screen, although on top is by far the more common position. Wherever
you place it, the speaker should be aimed toward the listening position
to produce the best frequency response there. Some models tilt up
or down or have a support you can adjust for the correct angle.
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 Dipole
surround speakers should be placed alongside the listening position
for best results and are usually mounted on the side walls, slightly
above the listener. Position the driver sides so they fire forward
and backward, with the "null" side of the enclosure facing the listener.
They should not be aimed directly at the listening position.
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Next come the left and right surround speakers. The rules here
are a little different than for the front speakers because the surrounds
are typically used to create diffuse, ambient sound in order to
heighten the illusion of an all-encompassing sonic environment —
especially with movie soundtracks. Many surround speakers are dipole
or bipole designs that radiate from both front and back to enhance
the sense of spaciousness.
But multichannel DVD-Audio or Super Audio CD music recordings tend
to sound best when you use direct-radiating, or "monopole," speakers,
since they often have smoother frequency response than dipoles and
a less diffuse sound quality.
What kind of surround speakers should you go with? If you plan on using
your system primarily for movies, I recommend a dipole or bipole
design. If for music, use monopoles. If you want the best of both
worlds, there are a few receivers that let you switch between two pairs
of surround speakers.
Surround speakers should be placed to either side of the listening position
and slightly to the rear — not in the back of the room
unless absolutely necessary. They are usually mounted on the side walls,
but placing them on stands works just as well. Avoid aiming dipole speakers
directly at the listening position, since this will weaken the sense of
a diffuse sound field. These speakers are best placed with their driver
sides facing forward and backward, with the null side of the enclosure
pointed toward the listener. Monopole speakers, on the other hand, are
best placed on the side walls facing toward the listener but above ear
level.
6.1-Channel Sound
A number of 6.1-channel formats have appeared recently: Dolby Digital
Surround EX and two flavors of DTS-ES (Extended Surround) —
Discrete and Matrix. Each of these formats adds a back surround
channel to the usual home theater configuration, using one or two
additional speakers (and amplifier channels) to create a more realistic,
quasi-360° sonic environment and smoother pans between the surround
speakers.
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 One
way to set up a subwoofer is to place it at the listening position,
at the same height as the listener's head. Then move along the boundary
of the room with your ear at the same height where the subwoofer
will be, listening until you find the place where the bass sounds
"tightest" (not boomy or mushy). Place the subwoofer there. (Don't
place it too far away from the main speakers, though, or the imaging
may be inconsistent.)
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If you're one of the lucky ones who own a 6.1-channel receiver,
you'll want to set up your additional speaker or speakers along
the rear wall, at the same height as the left and right surround
speakers. If you opt for dipoles, have them fire to the left and
right along the rear wall, with the null toward the listening position.
(If this isn't satisfying, you can even try rotating them so that
they fire toward the ceiling and floor.) Direct-radiating speakers
should be aimed forward.
I'm Gonna Add Some Bottom
No home theater system is complete without a subwoofer for the powerful
sonic impact and realism that only true low-frequency extension can provide.
It's sometimes said that you don't have to be as fastidious with setting
up a sub as with your main speakers because frequencies below around 100
Hz are nondirectional. This isn't entirely true (unless you're planning
on putting the subwoofer in the bathroom). Placing the sub in a room node
will eliminate much of the bass, while placing it in an area that selectively
reinforces bass might make it sound boomy. Experiment with placement for
best results, and use common sense — don't place a sub too far away
from the main front speakers or the imaging may be inconsistent.
I generally recommend starting with a corner placement and moving
away from that only if you can't get proper balance using all the
system's bass-management controls. Another approach is to set the
subwoofer on a table at the listening position, so that its driver
is at the same height as the listener's ears. Then go around the
room on your hands and knees, listening to the bass at the same
height that the subwoofer will be at once it's placed on the floor.
Once you've found the spot where the bass sounds "tightest" (not
boomy or mushy), place the sub there.
