LIST PRICE: $1,899
The QSC KS212C is a dual 12-inch cardioid subwoofer that can be paired with several different QSC cabinets (including the K8.2, K10.2, and K12.2 point source boxes, among others). The term “cardioid” refers to the fact that, unlike traditional subwoofers, this product is intentionally not omnidirectional (see figure 1). It provides about 15 dB less SPL in the rear, which is particularly useful to control low end in two major ways: 1) it reduces low end on the stage, and 2) it helps prevent some low end from bouncing off the wall behind the subwoofer. This has the result of cleaner, tighter bass in the room and may also help clear up low-end feedback problems.
It also may create a more pleasant environment for those on stage.The concept of a cardioid subwoofer is not new, but historically it has required the use of two or more subwoofer boxes and additional processing to create the effect. This can be a pain for many users, especially since it requires additional technical knowledge and set up time, and it requires you to own more boxes. Thankfully, several manufacturers offer subwoofer enclosures that create this cardioid effect internally, thus making it simple and cost-effective for a lot of people.
Design notes
Before we get into how it sounds, I want to address several of its design elements. One of my favorite features on this subwoofer has nothing to do with its sound quality. QSC thoughtfully included casters on the rear of the box, making load-in and load-out a breeze. Simply tilt the box onto its back and roll into position, then tilt back again (off of the casters) for stability. It also includes standard M20 speaker pole sockets on both the top and side. Ordinarily, you’d keep the subwoofer upright and use the mounting socket on top to support a suitable QSC loudspeaker. However, you can lay this sub on its side and stack another on top for extra low end. In that case, you would simply use the other pole socket to support your primary loudspeaker.
For smaller environments where you want punchy, controlled low end, combined with the benefits of a cardioid pattern, this box performs very well.
The rear panel is well designed and includes a number of things you’d expect. There are a pair of inputs, each with a “thru” port to pass the signal on to your primary loudspeakers. The reason there are two inputs is so one subwoofer may be used as part of a stereo PA system. Inside the subwoofer, these two inputs are summed together, but they are kept discrete at the “thru” outputs. This allows you pass your stereo mix to the subwoofers first and then, via the “thru” connections, to the main loudspeakers.It’s worth noting that the “thru” ports carry an exact copy of the input signal. That makes sense, of course, given the term “thru.” However, some readers may be familiar with subwoofers that provide an internal crossover function and only send the high-passed content (meaning bass has been removed) to the main loudspeakers. In the case of this product, the main loudspeakers are expected to handle the high-pass filtering themselves (which all of the QSC K-series products do).The rear panel also provides a simple menu system to choose between a low-pass filter frequency of either 80 Hz or 100 Hz (depending on what main loudspeakers you’re pairing it with); delay adjustment; a scene system to store custom presets; and even the ability to disable the front and/or rear LED’s. There is also an analog gain control. Everything on the rear panel is intuitive to navigate and didn’t require consulting the manual.
And now for the fun part I used several test signals to assess the sound quality and behavior of this sub. First, I used pink noise to get a sense of its overall sound quality. I have tuned enough sound systems that I can tell a lot about a product’s quality simply from that. I also played a number of musical selections through it, and finally I used a swept sine wave to get a good sense of its frequency response and SPL capability. With each of the three above tests, I was pleasantly surprised with the KS212C’s performance. You might ordinarily expect to need larger (15- , 18-, and even 21-inch) subwoofers to get significant amounts of punchy low end. However, this box gets very loud and sounds clean and “tight.” The swept sine wave tests, in particular, proved that this box quite easily meets its stated frequency response (44 Hz-104 Hz), and still has a reasonable amount of energy below that. The response was not completely flat through that range, but that’s fairly common and acceptable in my opinion. There is still an important place in the market for larger subwoofers, of course. This is not a product for large spaces or for particularly low frequencies. However, for smaller environments where you want punchy, controlled low end, combined with the benefits of a cardioid pattern, this box performs very well. It gets fairly loud and sounds very good.
I also gave this sub a thorough stress test. My expectation is that a well-designed, modern, powered PA product should be sufficiently protected from abuse by good limiter implementation. At first, I simply pushed up program content until I saw the limiter light (on the rear panel) blinking. The subwoofer continues to sound good even while in limiting. I then increased the signal level by more than 20 dB, such that the limiter light stayed on continuously. I left this running for quite some time.
The subwoofer never fumbled, never over-heated, and, once I reduced the levels back to normal, sounded just as good as my initial tests. In other words, this sub is rugged. Admittedly, this was hardly a scientific test, and I didn’t do it for several hours, but I am reasonably convinced that it is designed to handle serious abuse gracefully.Throughout all of my testing, I would frequently walk behind the subwoofer to get a sense of how well the cardioid behavior held up, especially at different frequencies. In all cases, it performed exactly as expected. The level out front can be almost uncomfortably loud, and the level in the rear is significantly (and therefore pleasantly) lower.If you choose to use more than one sub, and they are stacked or placed directly side by side, the manufacturer states that the rear rejection will not be as strong. For example, with two stacked subwoofers, the rear rejection drops to 12.5 dB. With three subwoofers, it drops a bit more to 10 dB of rejection. However, this can still be a helpful amount of rejection, and may be a reasonable tradeoff in the pursuit of more low end in the room. If you need to maintain the 15 dB of rejection, just space the subs a box-width apart.
I noticed that the casters rattle slightly during heavy operation, but it’s not too troublesome. If it becomes a problem, the noise can be avoided by inserting the cardboard pieces that are wedged into the casters during shipping. Overall, this is fairly powerful, good-sounding subwoofer that performs as advertised. It seems to be rugged, it is conveniently designed, and the directivity provided by its cardioid pattern provides nicely controlled low end. And, while it is designed for use with other QSC loudspeakers, I can imagine it would work very well in many different situations.
