Specifications

Metrics Tested on THX DVD Players:
Video Level
Sync Level
Bar Tilt
2T K Factor
Pulse/Bar Ratio
Sin x/x Response
Sin x/x Group Delay
Chroma Level
Its important to note that the Ultra2 controller has a setting for the distance between the two rear
speakers, the default being <1ft as depicted above, yielding the most spacious sound field. The
alternate setting of 1-4 ft can be used to "favor" the music playback mode. By moving the physical rear
speakers apart, there is less of a "virtual speaker", with more of the surround sound in Music mode
coming from the monopole rear speakers.
Ultra2 Hardware
THX Ultra2 also raised the bar for speaker performance. While output, sensitivity, and distortion
requirements stayed the same, off-axis performance requirements changed dramatically. THX also
changed how they measure the performance.
Smoothness of off-axis performance is now emphasized rather than attenuation as called for in Ultra.
Recent research makes it clear that speakers with off-axis performance which is completely free of peaks
and dips in amplitude response sound better that those with peaks and dips (even if attenuated). If a
room has unacceptably strong ceiling and floor reflections, it is possible to correct that with acoustical
treatments (something more and more consumers are willing to do), but poor off-axis linearity is
something you can't fix after the fact.
They've also broken up the linearity requirement with Ultra2 into three bands of the audible frequency
spectrum: Low, mid, and high. The ± dB window is quite tight in the mid-band, with greater variation
allowed for the low and high. This requires that a speaker be quite accurate in the critical mid-band
while still giving the designer enough latitude to keep their company’s signature "voicing". Frankly, we
find this last item a little disappointing, since we are somewhat opposed to the notion that a speaker
should ever have any sort of unique "character". THX's answer is that they realize no speaker is absolutely
100% perfect in this respect, and their banding of the spectrum simply forces a manufacturer to
concentrate the greatest effort on the band that matters most.
In addition, subwoofers now need to be anechoically flat to 20 Hz. THX did this because their research
shows it give them a better match with the rolled-off energy from the satellite speaker. Because these
new subs may get shoved into a corner and end up with TOO MUCH at the bottom end, THX Ultra2
controllers include a Boundary Gain Compensation which, when selected during set-up, rolls-off the
bottom end of the subwoofer signal to compensate if an Ultra2 sub is getting too much help from the
room itself.
Select2
In 2005, THX Select was revamped to Select2. Intuitively, Select2 inherits from Ultra2 the ASA
(Advanced Speaker Array) along with the modes that use it: THX Select2 Cinema, THX Music, and THX
Game. As such, support for 7.1 speaker configuration is no longer optional as it was with Select
(products can include only five channels of amplification, but they must provide the full 7.1 line-level
output).
The S/N (signal to noise) requirement was increased 9 dB with Select2. THX tells us that while, at first,
some manufacturers grumbled at the extra design work that would take, all certified products have
managed to meet the new requirement.
Some Things We're Not Crazy About
In 1998, THX launched certification for DVD Players,
and we were a little disappointed to say the least.
While on paper their goals for DVD Player design are
first rate (see metrics list at right), they quickly
brought their testing and certification integrity to
question with the very first Certified DVD Players such
as the Pionner DV-09. More recent offerings from the
likes of Denon fair much better, but we would be
remiss if we were to not mention this "sour" launch and
there are still models which fall well short of our own