Subwoofers

Crystal Acoustics TX-12SUB THX Ultra2 Certified Subwoofer

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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.