Specifications
Whereas THX/THX Ultra was specified and designed for rooms "up to" 3000 ft3, THX Select took that
requirement down to 2000 ft3. Both the requirements of the amplification and the output of the
speakers were scaled back appropriately, placing THX in the hands of a whole new audience who could
not have otherwise afforded it.
When it comes to amplification, continuous output tests are run on up to one, four, and five channels
(simultaneously) of an Ultra product, but only one at a time on Select. With all products, the dynamic
amplifier tests are done on up to all available channels. Ultra amplifiers must be stable on all channels
to 3.2 ohms and swing an 18A peak, while Select products must be stable into 4 ohms (front channel) and
8 ohms (surrounds), and swing peaks of 12.5A and 6.2A respectively.
So, right off the bat, Select amplifiers have a lower bar to reach, but ultimately in meeting it, they will
still cleanly drive any reasonably designed speaker to reference level in a Select-size room. What we are
talking about here is the idea that the lower powered equipment can get a THX certification that will
assure consumers that the really affordable stuff has met certain standards like the high-end equipment.
The THX Controller section features are no different between Select and Ultra, which is why you'll never
see a Select preamp/processor (SSP), only Select Receivers.
THX Select speakers, other than having reduced output requirements as compared to Ultra, do not have
the same requirement for a narrow vertical listening window, because in a Select-size room you are apt
to be close to the speakers and floor/ceiling reflections are that much less of an issue. While THX Select
surround speakers are still recommended to be dipole in design, conventional monopole designs are
permitted for a few reasons, the main being that dipoles are, by their nature, expensive (having twice as
many drivers as a conventional monopole), which goes against Select's mandate for a more affordable
system.
Select subwoofers of course have reduced output requirements as compared to Ultra.
Ultra 2: The Second Age
In 2001 THX revamped their Ultra program into Ultra2.
Ultra 2 Processing
One of the catalysts of the revamp was the enthusiastic consumer embrace of THX Surround EX and the
7.1 speaker layout that it implies, but Surround EX decoding only "works" well if the sound track was
implicitly encoded for it, otherwise the surround sound filed tends to collapse to the center surrounds.
At the same time, multi-channel music was becoming more of a presence in the market, and speaker
arrangements for music vs. movies were at odds with each other, with movies favoring a very diffuse
sound field produced from the sides, and music favoring more in-your-face surround, with the source
being more "behind" you.
With Ultra2, THX came up with a single system and speaker configuration which would work for
everything.
Whereas THX Surround EX simply called for two more surround speakers at the back of the room for the
then new sixth channel, Ultra2 replaced them with a pair of monopole speakers specifically placed right
next to each other. Somewhat like the way two-channel stereo can "position" sounds between two
speakers, THX with their new process they call ASA, or Advanced Speaker Array, is able to "position"
virtual surround speakers between the side surround speaker and the corresponding rear speaker (it's not
really that simple, but it is the best way to visualize it). So while Ultra2 controllers still offer THX
Cinema and THX Surround EX modes, THX introduced three new THX modes with Ultra2 which use ASA:
THX Ultra2 Cinema. This mode is identical to THX Cinema, except it does a "soft EX decoding", giving us
some output from the rear, but does not allow the sound to collapse there. Surround sound
predominantly comes from the side dipole speakers.
THX Music. This mode differs from the above in two ways. First, using ASA, the surrounds are virtually
positioned between the side and corresponding rear speaker, a position usually favored by multi-channel