Understanding surround sound is very important. Room size, room shape, sound proofing, selection of
sound equipment, etc. They are all important.
The following section contains excerpts from "How Surround Sound Works" by Tom Harris
Full article is available at http://www.entertainment.howstuffworks.com/surround-sound.htm
Going to the movies today is a very different experience from going to the movies 70 years ago -- the picture is
clearer, most of the movies are in color, and the admission price is a lot higher. But the biggest change is
probably the sound experience. In movie theaters of the 1930s, the entire soundtrack was played on a single
speaker or collection of speakers positioned behind the movie screen. Today, theater audiences expect to
hear sound coming from every direction; and the technology that once characterized only movie theaters is
now fairly standard in home entertainment centers.
Two-channel recordings, in which sound is played on speakers on either side of the listener, are often
referred to as stereo. This isn't entirely accurate, as stereo (or stereophonic) actual refers to a wider range of
multi-channel recordings. Two-channel sound is the standard format for home stereo receivers, television
and FM radio broadcasts. The simplest two-channel recordings, known as binaural recordings, are produced
with two microphones set up at a live event (a concert for example) to take the place of a human's two ears.
When you listen to these two channels on separate speakers, it recreates the experience of being present at
Surround recordings take this idea a step further, adding more audio channels so sound comes from three or
more directions. While the term "surround sound" technically refers to specific multi-channel systems
designed by Dolby Laboratories, it is more commonly used as a generic term for theater and home theater
multi-channel sound systems. In this article, we'll use it in this generic sense.
There are special microphones that will record surround sound (by picking up sound in three or more
directions), but this is not the standard way to produce a surround soundtrack. Almost all movie surround
soundtracks are created in a mixing studio. Sound editors and mixers take a number of different audio
recordings -- dialogue recorded on the movie set, sound effects recorded in a dubbing studio or created on a
computer, a musical score -- and decide which audio channel or channels to put them on.
Over the years, there have been many different approaches to surround sound. Walt Disney's "Fantasia"
(1941), one of the earliest surround-sound movies, immersed the audiences in classical music. Disney
sound engineer William Garity took separate recordings of each orchestra section and mixed them to
produce four distinct audio tracks, which were recorded as optical tracks on a separate reel of film.
The four tracks drove different speakers positioned around the theater. In an equipped theater, the music
seemed to move around the auditorium, an effect achieved by sound panning. Panning involves fading a
sound (a violin melody, for example) from one audio channel while building it on another.
To show "Fantasia" in surround sound, a theater needed an additional projector to play just the soundtrack,
as well as an expensive receiver and speaker assembly.
This surround-sound system didn't catch on (the necessary equipment was prohibitively expensive), but by
the late 1950s, many Hollywood movies were encoded with simpler multi-channel formats. Several different
theater setups emerged in this era, including the famous Cinerama and Cinemascope, but most of them
used the same basic sound technology. As a whole, these systems were referred to as stereophonic sound,
or simply theater stereo.
Stereophonic sound used four or more analog magnetic audio tracks around the edges of the film. Magnetic
tracks could not produce as clear a sound as the conventional optical audio tracks, and they tended to fade
over time, but they took up a lot less space on the film. The standard film format did not have enough room for
more than two optical tracks, but it was possible to squeeze as many as six magnetic tracks around the film
In the stereophonic system, three to five channels drove speakers behind the movie screen. The popular four-channel system
included one channel driving a speaker on the left, one channel driving a speaker on the right, one channel driving a center
speaker and one channel driving surround speakers along the sides and back of the theater. Some systems boasted five
separate channels behind the screen and one surround channel.
In these movies, most of the sound is recorded on the front channels so that the words seem to come from the screen. When
an actor speaks on the left side of the screen, the dialogue sound comes from the left speakers. When an actor speaks on the
right side, the sound comes from the right speakers. Most dialogue is also channeled to the center speakers, which serves to
anchor, or focus, the sound on the screen. The rear track (or tracks) are typically reserved for "effect sounds," such as ambient
background noise or a voice coming from off-screen.
In the 1970s, Dolby Laboratories introduced a new sound format based on this same configuration.
Like stereophonic sound, the original Dolby Stereo® had three front channels and a surround-sound channel. But instead of
using magnetic tracks, it reverted back to the superior optical track technology to allow for clearer sound playback. Dolby
stereo also used an advanced noise-reduction process, which improved sound quality further. Today, Dolby Stereo is the
analog sound standard, thanks to its superior sound quality and relatively simple installation.
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Later movies followed the "Star Wars" model, using the surround track to create fantastic effects, as well as fill in background
noise to establish a scene's setting. In later versions of the surround-sound system, theater owners could hook up a
subwoofer to handle extremely low-frequency sounds (a crossover unit can separate out these sounds from both audio
tracks). Many moviemakers use the subwoofer to create a powerful rumbling in the theater, shaking the audience when there
is an explosion or earthquake on-screen. The subwoofer channel in both analog and digital surround-sound systems is
sometimes called the low frequency effects (LFE) channel.
In 1982, Dolby launched Dolby Surround®, a version of Dolby Stereo for home entertainment systems. Dolby Surround
reproduces the effect of Dolby Stereo in the theater, but it works a little bit differently. The audio channels are encoded as
magnetic tracks on video tape or broadcast as a television signal, rather than put down as optical tracks. The speakers are set
up in the same basic way as in a theater, except the original home Dolby system only had three channels --- left speaker, right
speaker and rear speaker. In 1987, Dolby introduced Dolby Pro Logic®, which had an additional channel for a front central
Imagine the look on your guests'
faces as the drapes close and lights
dim automatically, a screen drops
from your ceiling and the rich,
thundering tones of true digital
surround sound embrace them from
speakers hidden in the walls.
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