How does a movie theater hookup its surround sound?

25th Sep 2003 23:50 #1

Member

I was curious as to how a movie theater hooks up its surround sound equipment? I mean, even though its professional grade equipment it still uses either 5.1, 6.1, or 7.1 decoding and most new theaters have about 20 or so speakers in each room. Do they hook it up so every 3 or so speakers is used for one channel or what? If anyone could shed some light on this topic that would be great!

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26th Sep 2003 00:21 #2

Solarjetman

Member

I am not 100% certain of this so take it with a grain of salt. I believe how it works is there are two channels which are converted to four sectors (front-right, front-left, back-right, back-left) Then a processor determines how out of phase the audio tracks are from each other. From this information it determines the volume level of the sound for each speaker placement. Thus, the same sound track can be used for a 10 speaker setup, or a 20 speaker setup. For example, if you have four speakers along the right wall labeled 1 through 4 with 1 in the front, and the sound is supposed to be slightly forward and to the right, then speaker 2 will play the sound louder than any other, speakers 1 and 3 will play it softly, and speaker 4 may not play it at all. But these amounts have to be determined on the fly, its not given by the sound track.

If you actually look at a piece of film, you may see several sound tracks. They are printed (or partially in the case of DTS) on a non-visible portion of the film. DTS sound for instance is a single line of dots which is used to sync with a CD-ROM on the audio rack, while Dolby digital can be found in-between the socket holes. There has to be some extrapolation involved because of the different tracks, and different theater layouts.

And from experience I can tell you, the audio equipment is quite large. The racks where I used to work were just slightly smaller than refrigerators. Much more processing power than home systems.