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Sunound
Sound
tn developing the Ml Actives for use as left, center and right front channel sources,
we wanted them to be useable in both audio/video and audio-only ,,matrix,, type
applications. We discovered twq already available solutions to the large ,,wall-of-
mono" effect produced by Dolby Pro Logic when playing audio,only material. The
first is easy. Most home audio Dolby Pro Logic receivers will let you take the center
channel out completely by putting the receiver in the "phantom,, (no center drannel)
mode. It preserves the classic stereo effect of the front channels while adding rear
surrotmd. This method works well with most stereo-only recordings which have no
surround encoding. But it's mudr better if the rear channels have true makix (mono)
surround (like applause) encoded in the mix.
The second method of using Do\
Pro Logic gets the center drannel back into the
mix. Most of these same home audio receivers have an audio-only surround mode
which sigfficantly attenuates the output of the cerrter drannel in relation to the left
and right. The audible benefit here is that the mix sounds like a stereo only
recording but the center image (like a vocalist) becomes a haril centet. There is no
image wander, as the frequencies drangg for instance. And the classic list€ning
"sweet spot'' expands dramatically, allowing for accurate soundstage and instrument
placement when listening far off-axis. (This attenuating of the center channel for
audio only is also employed by advanced professional matrixed decoders such as the
Circle Surround Mles Tedmology and Lexicon units.)
Placement of the center lUll Actine speaker
in the studio
The left, center and right speakers should allbe placed in an arc so that the distance
of all drivers to the listener is identical (see page 29). The equilateral listening
triangle as described earlier for stereo (two-cnannel) playback should be retained,
with the center speaker placed oertically in the center, exactly between the left and
right (vertical) Mt Actives
It iloes not tutter what type of M1 Actioe is used for the center spalcer (hoeeter in or hreeter
out), Since MI Actioes are solil as pairs, a Fchannel system requies thc purcluse of a single
speakcr, bteaking up a pir. Sone ilealns nq rquest that you pwchase in pirs only; others
tnay be ablc to anange purdtax of a single unit. For tlu rear clunnels, we recommend a
minor-inuge pair, although this is less citiul than in the front.
As discussed above, for music-only recording the sigrr.al level to the cmter channel
will be attenuated over the levels of the left and right speakers. As a starting point we
would recommend that you setthe c€nter dramel level -6dBbelow the left and right
channels. To get these levels faidy accurate a white or pink noise source (sudr as
from a test CD) is very helpful along with an inexpensive sound level rneter (such as
the Radio Shack cal no. 392050).
If you are recording audio'for-video, the center drannel signal level should be lfte
wne aslelt and right channels. The left, center, right speaker layout configuration
can remain the same as for an audio-only mix. With all front speakers operating at
equal levels, the "sweet spot" listming area will become very large but the "wall-of-
mono" effect mentioned above (in regards to music) will be of little cons€quence
since most of the dialogue will be mixed specifically into the center charmel.
MIAC'TUE
RH4CI
TAil'AL
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