THX Ltd. was founded by legendary filmmaker George Lucas to improve the entertainment experience at commercial theaters and at home.
In addition to typically being reserved for the most full featured receivers THX certification guarantees the same high-volume sound you would experience at a commercial theater in your home. To gain certification, the receiver must pass severe bench-tests covering every aspect of audio performance.
To gain THX Certified Select certification (previously known as Select2), home theater receivers must pass 2,000 severe THX laboratory bench-tests in 75 categories covering 14,000 data points to assure reference performance in every respect. With uncompromising sound-quality exceeding world-class standards, you can feel theater sound as the filmmaker intended. THX Certified Select products are for medium sized rooms, up to 2,000 cubic feet in size, with a 10-12 foot viewing distance from the screen.
THX Certified Ultra (previously known as Ultra2) products bring the cinematic experience to larger home theaters, 3,000 cubic feet in size, with a viewing distance of 12 feet or greater from the screen.
More information on THX website: