THX (Tomlinson Holman Experiment) is a registered trademark named after its inventor, Tomlinson Holman of Lucasfilm. THX is the definition of audio reproduction quality for cinema sound. There are several THX variants, including one for home theater, THX-Home. When audio systems or components that meet the playback quality defined by THX, they can be certified and receive the THX logo.
THX-Home: This THX standard is modified to meet the requirements of home theater. This includes the optimization of audio channels, which means fewer speaker boxes are needed in the home. A THX processor in the AV receiver takes care of adapting and optimizing the sound quality to the home environment.
THX-Ultra: THX-Ultra corresponds to the original THX standard and is suitable for playback in larger rooms. THX-Ultra focuses on good sound quality and the localizability of sounds. The dispersion characteristics of the loudspeakers and dipole speakers are precisely defined, and the arrangement of the individual midrange and tweeter drivers is also of particular importance. To increase the sound content, reflections are reduced as far as possible. The peak volume value is 105 dB.
The THX Ultra format is available in two variants as THX Ultra and THX Ultra II. While THX Ultra is suitable for sound reinforcement of larger home theaters, version II supports surround sound according to 5.1 and 7.1, i.e. with five or seven speakers and a subwoofer, and also exact reproduction of 5.1 material on 7.1 systems.
THX-Select: THX-Select is suitable for smaller rooms and does not have such stringent requirements for the speakers and their arrangement as THX-Ultra. It can therefore also be used in the home. Inaccuracies in the room sound can be compensated for by tuning the sound. The peak volume level is 105 dB.
THX-Surround EX: This process was developed jointly by Lucasfilm and Dolby and offers 7.1 sound. It has two surround channels in addition to the front speakers and subwoofer. Both surround speakers emit the same signal, but it can be adjusted in terms of level and runtime for optimal sound sensation.