THX Ultra: Denotes an original, very strict, certification from Lucasfilm. The Ultra suffix was introduced with the introduction of THX Select (see THX Select) to differentiate the two certifications. The main difference is that THX Ultra is designed for very large rooms based on American dimensions, while THX Select is intended for rooms with a floor area of up to 30 square meters (with a room height of 2,50 m).
