Primer
Crestron
Surround Sound
What We Hear in a Room
The first sound to arrive from an audio system is direct sound. This is
also considered the on-axis sound. Direct sound occurs when the
speaker is angled toward the listener, and this is the best possible sound
the speaker produces.
Early reflections are heard next, which follow the direct sound by a few
milliseconds and are not as loud as the direct sound.
After the reflections we hear the reverberation of the rest of the room.
These reverberations can come from multiple directions at a lower
sound level. Together, they cause a confusing soundscape if not dealt
with properly.
Rooms also contain resonance that can emphasize and attenuate certain
frequencies. The resonance depends on the location of the listener and
the placement of the speakers. The effects of resonances are often
experienced at the lower range of frequencies.
Very often we cannot overcome all of these deficits, however we can
work with them and turn them in our favor.
We begin by selecting good quality speakers that provide a smooth
(flat) frequency response over the given drivers operational
frequencies.
Placing a speaker too close to a reflective surface, such as a wall,
adversely affects the audio by presenting an inaccurate, heavy sound.
The sound-reflecting wall acts like second speaker, increasing the
sound level but decreasing clarity. This situation can be resolved by
adding some absorption material.
You can use a variety of materials, such as acoustical foam and
acoustic fiberglass. Even a drapery can help absorb the reflection. A
room that is too acoustically “live” or “dead” does not sound good. A
mixture of the two creates the most realistic home theater environment.
If you have a room that is relatively “live” sounding, use a speaker
equipped with a horn tweeter for good directionality. It can be aimed
towards the listener and away from reflective surfaces.
Speakers Placed in Cabinets
Although best placement for a speaker is about one to three feet from
the nearest wall, we do not always have that option. Many home
theaters incorporate cabinets to add a warm feel to the room and hide
the electronic equipment. Placing a speaker in a cabinet can hinder
speaker function, especially if the speaker is improperly positioned and
mounted in the cabinet.
The speaker should be as close to the front of the cabinet as possible.
As a speaker is placed deeper in the cabinet, more boundaries interfere
with the sound.
How the speaker is mounted in the cabinet is important. If the cabinet
vibrates, you should acoustically uncouple the speaker from the
cabinet. This vibration can transfer from the speaker to the cabinet,
reducing the full sound capability of the speaker. Placing the speaker
on mounting posts (that may be provided) or on a platform designed to
reduce vibration transmission can help.
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Surround Sound
Primer – DOC. 6122
