Dolby sound systems.
The Dolby Sound Laboratories is an 'old' firm and have improved the quality of sound since the late 60s. At this time they improved the sound quality on tapes. They made the Dolby A-type system for professional applications and Dolby B-type systems for consumer applications. Have a look at your cassette player back home (if you still got one) and you will most likely see the name Dolby systems or their double D-logo.

In the 70's Dolby revolutionized home entertainment with the Dolby Stereo and the Dolby Surround sound systems. The Dolby Stereo is a four-speaker sound system. If you have a centered speaker for dialog, left and right for music and the surround speaker for atmosphere. Click here to see a drawing of the Dolby Surround system.

In the 90's the Dolby Surround developed into Dolby Digital. This is a six-speaker sound system. This sound system got the same four speakers as the Dolby Surround plus one extra surround speaker and a sub for low-frequent sound. Click here to see a drawing of the Dolby Digital sound system. The Dolby Laboratories have developed a third generation sound system. This sound system is also a six-channel system and is named AC-3.

The phantom menace is the first film using a new Dolby sound system. This is named Dolby SEX, Dolby Surround EXperience. In addition to the six channels in Dolby Digital (Center, left front, right front, sub, left surround and right surround speaker) Dolby SEX is using a 7^th speaker. This is located above the rear surround speakers. Click here to see a drawing of the Dolby SEX system. The Dolby sound systems are copyrighted by Dolby studios.

SDDS
The Sony Dynamic Digital Sound sound-system is the only eight-channel sound-system available at the moment. In addition to the 7 speakers in the Dolby SEX system there is a additional speaker placed above the front speakers. This sound system is also the only one exclusively used by movie teathers.

THX
I believe that the THX sound system is the best sound system available today. It is not just a digital sound system - it is an experience. In a typical THX-theater there is a silent air condition-system, a non-echo environment, the sound is supposedly to be the same wherever you are seated. The entire room is sound-isolated so the wievers will hear nothing but the sound from the movie. There are even special chairs in these theatres - they are suppose to reflect as much noise as if they where seated by a person.

According to George Lucas sound is fifty percent of the movie experience. When he saw "The empire strikes back" in 1982 at a movie theatre he where disappointed. Not because of the quality of his film, but because of the sound experience. Therefore he asked Tomlinson Holman to do something about this and find a way to improve the sound quality. Tomlinson Holman was at the time chief of the sound-department of Lucas film Ltd. He documented everything that had influence on the sound experience, such as echo, size of the room, isolation of the air-condition system and noise from movie theaters next door and so on. Based on this he made certain specifications and named it THX Sound System Program. The début of THX was in 1983 at the premiere of "Return of the Jedi". It was soon to become a standard sound system of movie theaters.

No one can really tell what the acronym THX means. Some believe the name is taken from George Lucas' first movie: THX 1138. Others believe the acronym means Tomlinson Holman eXperience. George Lucas will not tell which of these is the right definition. If you would like to read more about the THX system see thx.com. T

Please note this is a short description of the mentioned sound systems. If more info is required please visit their homepages.