Pros: Efficient vented design, relatively easily to balance with rest of system
Cons: Not quite as accurate as the very, very best (and much more expensive) subwoofers
...way back in 1982 (when subwoofers were an esoteric, tweaky audiophile item; the term was unknown in the mass market) I was first introduced to Velodyne. A grad school classmate had a ULD-12 (a classic, early Velodyne) in his system, and feeling the warmth (and power) that item added to the low end was truly thrilling. I'd love to have added a similar sub to my stereo at the time, but I didn't happen have $800 of spare change handy.
Fast forward to 18 years later, and I'm finally settled and "wealthy" enough to pursue adding some serious low end to my home system. To my surprise, as the home theater market has expanded (introducing the term "subwoofer" to laypeople) Velodyne has followed, now offering less expensive versions of their infamous black boxes through Circuit City. But are these class items like the Velodyne I remember from years earlier? Or are they like the cheapo Mercedes, highly diluted versions of the flagship models?
Well, before I answer that question, some context: the CT-120 -- which employs a 12 inch driver -- was the second tier in a four model line (the other members being the CT-150 with a 15 inch driver, the CT-100 with 10" and the CT-80 with an 8"). The three smaller models all employed the same basic design, with CT-150 adding not just the biggest speaker but also a more sophisticated level of circuitry -- similar to that employed in the top of the line Velodynes -- to monitor and adjust the driver velocity and phasing.
So, what you in essence get with the CT-120 is the largest and most powerful version...of Velodyne's most stripped-down design. However, the good news is that does not result in "stripped down" sound: to the contrary, the output of the CT-120 is powerful, warm and solid, not stressed, cold and boomy like that of many other "mass market priced' powered subs.
In practice, like most better audio components, I have found the CT-120 to be highly sensitive to the material being run through it. Good recordings with accurate, low bass (anything from Telarc as example) sound almost -- not quite as -- but almost as good as what I remember the ULD-12 sounding like. No, the CT-120 isn't quite as warm and solid as the ULD-12 at the very bottom, but definite shades of what the latter sounds -- and feels like -- are definitely present in the CT-120.
The CT-120 is also a truly "dual use" (music and video) sub. If you're looking to for the wow element of feeling all the proverbial low end thuds and bangs on action movie soundtracks, this sub will deliver, with plenty of couch-shaking punch. But nicely it can also do justice to low end orchestral passages or pipe organs on good audio recordings (they have presence and are firm, not muddy).
By the way, one important lesson that stems from that performance is that weight is often a very good starting barometer of subwoofer quality. Shopping for a 12 inch powered sub? One that weighs 60 lbs. -- which is what the CT-120 tips the scales at -- likely has a beefier speaker magnet (in this case, an almost three and a half pound slug of iron) , heavier internal bracing and thicker MDF walls than one that weighs 38 lbs. And trust me, the solidifying benefit of that additional 22 pounds can be heard.
In my moderate sized listening room, the 120 watts of internal amplification driving the CT-120 is almost overkill at times, so I find myself trotting over to it from time to to time to adjust the output level (yes, a remote would have been a nice addition here). I also find that tweaking the crossover point has a large impact on sound. Or to summarize, for the truly finiky, this (or for that matter any good powered sub) really isn't a "set it and forget it" proposition - you have to constantly manage a sub to really get the most out of it.
In closing, a technical note: for what it's worth, I employ my CT-120 as a solo element in the speaker chain; i.e., I don't pass the output to the main speakers through it. Page five of the owners manual shows how one can do the latter, in essence using the CT-120 as a filtering crossover unit (employing either line level or speaker levels inputs/outputs). Velodyne states that letting the CT-120 remove the lower frequencies going to your main speakers both helps balance the system and increases power handling ability of your main receiver or amplifier.
That process does do both these things, but one can readily argue they are unnecessary and even counterproductive. First, you are using a good powered sub like this to primarily support frequencies below 40Hz, a region where most main speakers (outside very expensive, large audiophile tower types) produce little or no meaningful output. Secondly, by running your main speaker signal through the sub you are potentially adding signal degradation, by forcing the output going to the main speakers to pass through multiple crosovers (audio gospel 101: the less processing in a signal chain, the better).
To work around this, I run a line output from my tube premap directly to the CT-120, letting the internal electronic crossover in the Velodyne remove the higher frequencies it doesn't need. Simultaneously, my main speakers -- an original set of the first generation Cambridge Soundworks Ensemble system -- are driven directly by a tube power amp which is being fed a full range signal from the other line output on my preamp. That main power amp -- a refurbished and upgraded fifty year old Dynaco ST-70 -- already has more than enough headroom to properly drive the Ensemble and the volume control on the CT-120 easily lets me balance it with them.