Yamaha DSP-A3090 Operation Manual page 16

Speakers and Speaker Placement
Your full seven-speaker system will require three speaker pairs:
the MAIN SPEAKERS (your normal stereo speakers), the FRONT
EFFECT SPEAKERS and the REAR EFFECT SPEAKERS, plus the
CENTER SPEAKER. You may also be using a subwoofer.
The MAIN SPEAKERS should be high performance models and
have enough power handling capacity to accept the maximum
output of your audio system.
Other speakers do not have to be equal to the MAIN
SPEAKERS. For precise sound localization, however, it is ideal to
use high performance models that can reproduce sounds in full
range for the CENTER SPEAKER and the FRONT and REAR
EFFECT SPEAKERS.
Place the MAIN SPEAKERS in the normal position.
Place the FRONT EFFECT SPEAKERS further apart than the
MAIN SPEAKERS, on either side of and a few feet behind and above
the MAIN SPEAKER pair.
Place the REAR EFFECT SPEAKERS behind your listening
position. They should be nearly six feet up from the floor.
Place the CENTER SPEAKER precisely between the two MAIN
SPEAKERS. (To avoid interference, keep the speaker above or
below the television monitor, or use a magnetically shielded speaker.)
If using a SUBWOOFER, such as a Yamaha Active Servo
Subwoofer System, the position of the speaker is not so critical
because low bass tones are not highly directional.
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Main speaker Effect speaker
Subwoofer
Center speaker