Set of specifications and certifications designed by Lucasfilm to ensure optimum reproduction of movie sound and video in movie theaters and home theaters (Home THX program). HX was originally started to ensure high quality sound in movie theaters. For that purpose, it included specifications for ambient noise (noise from air conditioners, other theaters, etc.), projection screen brightness, sound pressure level (volume), quality of speakers and amplification, etc. THX was meant to bring the quality of the mixing studio where movie soundtracks are produced to the theater going audience. THX strove to recreate the experience the director had and intended as he and his staff created and edited the movie. To this end, THX became very successful and is known as a symbol of quality in movie theaters around the world. he Home THX program began to bring the director’s vision into the home much as it had been done for the movie theater world. Home THX certifies products that meet certain minimum specifications, requires certain functional components in the electronics and particularly in the preamplifier/surround sound processor, sets specifications for speakers used, and certifies installers to create and install Home THX home theater systems among other things. The various minimum aspects of a full THX certified home theater system include a THX certified preamplifier/surround sound processor, certified amplifiers, certified interconnect cables and speaker wire, certified subwoofer, certified surround channel speakers, certified center channel speaker, and certified front left and right speakers. THX also certifies laserdisc and DVD players, equalizers, receivers, and acoustically transparent projection screens (screens with microscopic holes allowing speakers to be placed behind them with little or no sound quality degradation). HX components are typically all of high quality since they must meet fairly stringent guidelines. However, not all THX equipment is excellent and certainly equipment that does not feature THX certification may be of THX quality or better. THX sets minimum requirements, but products may certainly exceed those requirements. HX certified speakers must exhibit certain characteristics. The subwoofer must play from 80 Hz down to or below 20 Hz. The surround channel’s speakers must be of a dipole design (two sets of drivers on either side of a cabinet wired out of phase), and they must be placed on the side walls directly out from the listening position and up about six feet. The three front speakers (left, center, right) have to reproduce sound in a broad horizontal plane but be fairly directive in the vertical plane (this is to reduce floor and ceiling reflections while allowing the greatest number of people to hear the sound in an acceptable way). The speakers must be able to achieve high sound pressure levels for extended amounts of time without distortion. HX certified preamp/processors must have Dolby Pro-Logic surround sound capability at a minimum (many now have Dolby Digital and/or DTS as well). The basic surround sound function is then modified with THX designed and licensed technology (Re-Equalization, Timbre Matching, and Decorrelation). e-Equalization generates a slight roll-off of the high-frequencies in movie audio to compensate for an artificially boosted high frequency used due to movie theater acoustics. Movie theaters roll-off the highs slightly due their design so a little high frequency signal boost is applied to compensate, however, that boost is not need in a home theater resulting in an overly bright sound. imbre Matching alters the timbre of the surround channels to more closely align with that of the front channels. Due to the surround channel speakers’ position on the wall above the seated position their timbre or specific sound quality aspects are changed versus the main speakers requiring adjustment to more closely match all the speakers in the system. ecorrelation splits up the mono surround sound channel in an analog, matrix surround program into two channels and slightly differs the information sent to each channel so that the sound field is more diffuse and encompassing. This technique is not used with 5.1 discrete digital surround sound systems since they possess stereo surround sound channels. HX certified amplifiers must meet certain qualifications such as the ability to generate sustained output into 4-ohm loads with low distortion. xcellent surround systems can be developed and installed with no THX certified components at all, or systems can be designed melding THX certified components and non-THX certified components with excellent results. In order to achieve the greatest benefits of THX using a minimum number of THX components, one needs a good quality subwoofer, a THX certified preamp/processor, and some dipole or bipole surround speakers (they do not necessarily have to be THX certified). In order to create a true THX system, however, all THX components should be used throughout the sound chain. HX has served to enhance and advance the state of the art in home theater systems, and a THX system using good quality components is a sure-fire way to get a top-notch movie theater experience at home (when the system is properly installed and designed to meet the needs of a particular space).