A trademark for a special motion picture surround soundsurround-sound system specification developed by Lucasfilm in collaboration with audio engineer Tomlinson Holman. The acronym comes from both the name of George Lucas’ first feature film, THX-1138 and also from the initials of Tomlinson Holman eXperiment. Only the loudspeaker crossover network is manufactured by Lucasfilm; other components of the B-chain, including their placement and installation must be approved before the theater can be designated as “THX approved.” THX is a theater sound system specification, and as such does not involve any type of film audio format, as does Dolby Digital™, nor does it indicate that any of the film sound was produced by Lucasfilm Ltd.