Secrets Q & A
- Written by Brian Florian
- Published on 30 November 2007
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.
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
2T K Factor
Sin x/x Response
Sin x/x Group Delay
Composite and Y/C Chroma Delay
Chroma Differential Gain
Chroma Differential Phase
Burst Amplitude Differential
Flesh Tone Phase Error
AM Chroma Noise
PM Chroma Noise
Chroma Correlated Noise (IM)
Chroma Burst Frequency Leakage in Y
Chroma Burst Frequency
H Sync Timing
Another THX product which leaves us scratching our heads is cables, and that's NOT a reflection on THX. It's no secret cables are a high margin item, but the THX cables we've seen take it to a whole new level. It's important to remember that THX doesn't tell people how to price or market their products. If a cable or wire passes the signal for which it is intended with acceptable integrity, THX will give it a license to use their name. They can't help it if the licensee goes on to position and price the product as something it is not. In fact, some of the THX interconnects we've played with employ ridiculously tight RCAs which only give a false impression of superior connection while introducing the risk of breaking your equipment from the force required to plug or unplug them.
One nice thing about THX and cables, however, and indeed the I/O jacks on THX equipment, is that they have a comprehensive color coding scheme. Unfortunately, THX has not pushed it as hard as they should have, and most products either fail to use the color coding scheme, or don't use it comprehensively. Another nice THX cable thing that THX let go of was their standard for a single DB-25 multi-channel connection. My 10 year old Rotel five-channel THX amplifier has this input. If I had a THX controller with the corresponding output, I would have only one cable between them, not five. THX tells us it fell by the wayside because no one was willing to put it on their product for fear of it being seen (incorrectly) as a "degraded signal path".
As far as THX DVD titles, every one we've come across has exquisite sound, but on occasion perfection in the video quality is debatable. It might be excellent, but not exquisite. Some titles exhibit the all too common halo/ringing artifact, but further investigation is warranted before we pass final judgment (it has been suggested that, at least in the case of Lucasfilm's own Star Wars Episode I, it was an artifact of the green screen process which "crept through" to the hi-def master).
You can get some of the THX benefits without actually having THX-certified equipment.
Many non-THX receivers are using the same combination of bass management crossover slopes as THX, and simply using a THX speaker set, or a non-THX set with the same FR alignment, will net you the same perfect crossover. Although difficult to find and identify, there are properly designed dipole speakers which are not THX-Certified (Paradigm models come to mind).
There are many examples of excellent, non-THX high power amplifiers which will fit right in with the rest of the THX pieces, though if you are picky, you'll want to do your homework to make sure it mates perfectly with the rest of your stuff.
We've already mentioned not worrying about THX-Certified cables. And, you can look at our own DVD Player Benchmark to find out what you need to know when picking a player.
You could (and should!) acoustically treat your room, and as a result be able to accommodate a wider variety of speakers, maybe even negate the benefits of Re-Eq, but even in that situation, THX equipment can't hurt, so you might as well put some on your shopping list.