Crestron
Surround Sound
Primer
series have the same resolution. In playback, PCM ignores the
frequency dependent sensitivity of human hearing, and gives far too
much weight to high frequencies (above 12 kHz) in comparison to low
frequencies (below 4 kHz).
Various algorithms have been developed to compensate for the human
listener. These algorithms modify the digital signal to more closely
approximate natural sound. "Lossy" audio coders save storage space by
eliminating data that is redundant or unnecessary to reproduce good
sound quality, which is why they are also known as "perceptual"
coders. Dolby Digital, for example, can reduce the audio data up to a
factor of 15:1 compared to the source PCM audio data.
Speakers
Surround Speakers
Direct radiating speakers in a surround sound system provide very
precise sound imaging.
Dipolar and bipolar speakers provide a diffuse sound without creating a
specific point source. Dipolar speakers have two identical drivers
mounted on opposite sides of the cabinet operating 180 degrees out of
phase. Bipolar speakers have two sets of identical drivers mounted on
opposite sides of the cabinet operating in phase.
Surround channel speakers are similar to bookshelf speakers. Surround
speakers should have similar response characteristics to the other
speakers in a surround sound system to present a uniform sound
environment. This is also referred to as “timbre matching”.
NOTE:
When referring to loudspeakers, the term "Q" is a measure of
directionality. At low frequencies, the Q will always be low. At higher
frequencies, it gets larger, depending on the size of the drivers
involved. Thus, Q is a measurement of frequency-dependent radiation
pattern and polar characteristics. Q is also a measurement of the slope
of any peaks in loudspeaker, equalizer, or microphone frequency-
response curves.
SubWoofers
A subwoofer is a special type of speaker that reproduces only the lower
portion of the audible frequency spectrum (usually from 120 Hz down
to the lower limit of hearing, 20 Hz).
There are two types of subwoofers. Powered subwoofers have a built-in
amplifier. Non-powered subwoofers require an external amplifier and
may be connected to a separate amplifier or to the main sound system.
Subwoofers may be contained in a variety of different enclosures.
A subwoofer operates in an omnidirectional manner, meaning it can be
placed almost anywhere in the room. The human ear cannot locate the
origin of sound waves below 80 Hz, so low frequency sound waves
have no apparent direction in a closed room. The Dolby 5.1 digital
surround sound systems allocate a specific low frequency effects (LFE)
channel for subwoofers.
Primer – DOC. 6122
Surround Sound
•
15
