A-17
Nº502 Media Console Appendix
Surround Sound Issues
Surround sound is a key component of modern multimedia
presentations. An action movie DVD may have great video, but the
moving image of an explosion offers little thrill to the viewer without an
accompanying BOOM! A tire-screeching vehicle entering the field of view
from the left is more effective if the accompanying audio also comes from
the left. The surround sound system is what makes it all work; hence,
properly setting up the surround sound system is essential. In most
installations, the seating positions pose a bigger problem than the system
setup.
The two key adjustments for each speaker are timing and level. The subtle
differences in timing of the sound coming out of each of several speakers
is what gives you, the listener, a sense of direction. These subtle timing
differences can be as short as a few milliseconds. If you are too close to
one speaker in the system, many of the audio effects will seem to come
from only that direction because the sound from the speaker arrives at
your ears too early. Since sound travels a bit faster than 1,100 feet per
second, each foot of travel takes just under a millisecond. So if one
speaker is 5 feet too close to you, its sound will arrive at your ears
approximately 5 milliseconds too early.
The surround processor distance settings allow the surround sound
system to delay the sound from each speaker just enough to realign them
all to each other. Levels must also be balanced because a speaker
positioned too close to you will be too loud compared to the other
speakers.
Perfect settings for level and distance apply to only one position in the
room. For example, if one set is 8 feet from every speaker in the room, no
other location in the room will also be exactly 8 feet from them all. A seat
to the left of that first one might be 3 feet closer to the left side speaker,
and the same amount further away from the right side speaker. No single
set of distances will fit both seat positions. Fortunately, our perception
will tolerate some deviation from “perfect” level and distance settings.
In the figure on the following page, the distance value for the side
speakers is set to a location about midway between the two seats, giving
an error of only 1.5 feet for both side speakers for both seats.
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