Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer

Introduction to the Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer

Crystal Acoustics is an Internet-direct manufacturer that specializes in THX certified 5.1 and 7.1 systems. I’ve reviewed two sets of Crystal Acoustics 5.1 systems, both of which earned high marks for their high value at low cost. Those systems incorporated a THX Select certified subwoofer. Crystal has now come out with its first THX Ultra2 certified subwoofer, the TX-12SUB. As SECRETS’ resident sub geek, I just had to try it out.


  • Design: Powered Subwoofer, Ported Enclosure
  • Driver: One 12″
  • Amplifier: 200 Watts RMS, 400 Watts Peak
  • THX Ultra2 Certified
  • MFR: 15 Hz – 350 Hz
  • Dimensions: 18.5″ H x 13.8″ W x 18.5″ D
  • Weight: 63.8 Pounds
  • MSRP: $749 USD
  • Crystal Acoustics
  • SECRETS Tags: Subwoofers, THX, Ultra2

Design of the Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer

The TX-12SUB uses a single 12″ driver, powered by a 200 watt rms (400 watt peak) amplifier. The naming convention is a little confusing, in that the “TX” is the higher-end Ultra2 certified sub, while the “THX” is the Select certified model. The TX-12SUB has the same dimensions and weight as the THX-12SUB. In fact, the only difference in the published specifications between the two subs is that the Ultra2 certified TX-12SUB is rated with flat anechoic response to 20 Hz, and in-room response down to 15Hz; while the Select certified sub is rated to 35Hz anechoic and 19Hz in-room response.

So where does the increased low frequency response come from? The TX-12SUB, from all external appearances, is identical to its Select-certified cousin, the THX-12SUB. Both subs use a ported design, with two large flared and dimpled ports on the rear of the unit. If you read a lot of subwoofer reviews (and why wouldn’t you?), you know that ports are perhaps the most cost-effective way to increase the low frequency output of a sub. Everything from a wine glass to the space shuttle has a natural resonant frequency, and subwoofers are no different. The resonant frequency of a sub depends on several factors, including the size of the enclosure and the ports. If you really want to dig into the technical details, check out our article here. The oversimplified version is that subwoofer designers use ports to increase the low frequency output by allowing the enclosure to resonate at a lower frequency than the natural resonance frequency of the driver.

Of course, there’s no such thing as a free lunch, and with ported designs the downside is usually a phenomenon known as group delay. Because the port resonance starts (and ends) later than the original sound from the driver, it can result in muddy, boomy bass (think about the sound emanating from that low-rider truck stopped next to you at the traffic signal and you get the idea). Ported designs are also subject to “chuffing” from air moving through the port. The flared dimples are intended to reduce chuffing, along with placing the ports on the rear of the enclosure.

Since the published specs for the two subs appear identical, my suspicion was that the increased low frequency response of the TX-12SUB might have come from some creative port tuning. So I posed the question to Crystal’s CEO/Head of R & D Vassilis Tsakiris. Here’s his response: “Actually the two subwoofers are substantially different even though they use the same heavy duty woofer (with double large magnets and total weight of 9.5kgs!) and the same size cabinet. The difference is due to the new electronics design of the amplifier that directs more power below 35Hz down to 20Hz.  So there is more power in the lower octave with clear advantages not only in the measurement but also in the listening experience.”

The THX Ultra2 specification calls for four TX-12SUB’s. The use of multiple subs is a subject of debate, but a substantial body of research (including seminal work by Harman International) suggests that the use of four subs, one along each wall, offers smooth frequency response across the room and reduces the impact of standing waves. However, for this review, I would have to settle for just one TX-12SUB.

Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer In Use

The Eagles Hotel California DVD-Audio is one of my favorite demo discs for many reasons, including contrasting low frequency mixes from song to song. The title track opens with loud, sustained whole notes on the bass, EQ’ed for a fat sound (the working title of the song was “Mexican Reggae”). The following song, New Kid in Town, features a crisp, snappy rhythm with Randy Meisner’s bass and Don Henley’s kick drum playing in tight formation. On both tunes, the Crystal produced surprisingly clean bass, without any bloat or boominess that one would expect from a dual-ported sub with a 12″ driver.

I have a theory that the idea for Inception originated from a group of very stoned people sitting on a couch. One of them says, “Can you imagine a movie about people in a dream, but they know that they’re dreaming?” Another says, “And then it turns out to be a dream inside a dream!” Followed by a third couch potato saying, “Wait! And then there’s another dream inside that dream–Whoa!” OK, maybe it didn’t really happen that way. In any event, Inception is a real audio-visual treat, with the usual explosions, gunfire and car crashes augmented by entire city blocks tilting on their sides and various other hallucinatory images, all accompanied by rumbling and shaking. The TX-12SUB excelled with the prominent (dare I say overly prominent?) mid-bass of the soundtrack, causing strong vibrations under my feet.

Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer On the Bench

Following my normal protocol, all bench tests were performed with the Crystal sub in the middle of the room, to avoid interaction with corners and walls. Except as noted below, all measurements were taken from one foot at a height equal to the center of the speaker.

Some comparisons to the THX-12SUB Select sub are worth noting. Distortion vs. output at 100 decibels and 31.5 Hz is essentially identical for both subs. I measured the Select sub at 108 db with only 3.9 THD+N, but didn’t push it farther. I was not as timid with the Ultra2 sub, and at 31.5 Hz reached 110.7 decibels before bumping up against 10% THD+N. Keep in mind that 3 decibel increase required a doubling of power.

The difference in low-end extension between the TX-12SUB and the Select2 certified version was more pronounced. The THX Select sub was rated by Crystal to 35 Hz, a somewhat conservative figure as I measured 10% THD+N at 27 Hz.

However, the Ultra2 certified TX-12SUB is a completely different animal. It measured below 10% THD+N all the way down to 12 Hz.

Crystal Acoustics lists 15 Hz as the bottom of its useable output, and I wondered just how much oomph it could deliver at that subsonic level. Would you believe 98 decibels of 15 Hz output under 10% THD+N! Plus, the first odd-order harmonic (at 30 Hz) barely registered 50 decibels, while the second-order harmonic (at 45 Hz) was at 78 decibels. Since our ears tend to interpret odd-order harmonics as harsh unpleasant sounds, the predominance of even-order harmonics is yet another positive test result for the TX-12SUB.

Here are the in-room response graphs, the frequency dip corresponding with room-based nulls as the microphone (simulating the listening position) moves farther out into the room.

Conclusions About the Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer

What can I say about a sub that is THX Ultra2 certified, capable of substantial power all the way down to 15 Hz, and sells for $749? Crystal Acoustics has yet again showed its talent for making high value, low cost home theater equipment. Definitely recommended.