Review: QSC KS212 active cardioid subwoofer

Having recently experienced the latest K.2 series of point source PA speakers from QSC, I was very keen to hear their latest subwoofer. The K series from QSC has achieved much success in the active PA market, with the latest ‘dot-two’ versions raising the game further. Notably, their newly improved built-in Class D amplifiers, ought to prove potent in this new subwoofer too.

The main cause for intrigue however, has to be the fact the KS212C is a cardioid subwoofer. While cardioid subwoofers aren’t exactly a new idea, I’m unaware of another active cardioid subwoofer in a single enclosure, especially at this price point. Even QSC are claiming this is a “world’s first-in-class” solution.

I’ve been fortunate to use many cardioid arrangements of subwoofers on several large concert and festival stages, and it’s fair to say there are many considerations to be aware of. If however, QSC have successfully produced a unit that delivers all the benefits of cardioid subwoofers to the smaller stage, the benefits will speak for themselves.

Designed for the Road

Before I run away with what my ears thought about this new design, I must mention the practical aspects. Firstly, there’s the simple fact if you’re using these with a standard stereo pair of satellite speakers, such as the K.2’s, then you only need one KS212C. Sure enough certain scenarios don’t always permit this style of configuration, or two could extend the low-end, but just one sub will compliment a pair of K.2’s competently.

Besides only needing a single unit in a standard application, I believe they’re reasonably compact too. Subwoofers capable of matching the KS212C’s performance will generally be larger. This subwoofer sports two long excursion 12” drivers, each in their own 6th order bandpass chamber, behind a 3.6kW Class D power amp. Weighing in at 40kg, moving them around is made easy by heavy-duty casters, but I was able to lift them in and out of the van and down a few steps by myself.

The rest of the build quality is equally heavy duty. These are solid units, just as you would expect from QSC. The rear panel is well designed with everything you would expect, including a clear LCD display with an easy to operate menu. There are two inputs, each with “thru” outputs, so you can use a single subwoofer with two satellites setup in stereo.

One point to note for some users is that the “thru” outputs are exactly that. i.e. they’re not post a high-pass filter. Unlike other products, the main speakers are intended to apply a high-pass filter themselves, just as the QSC K series do. The filter on the KS212C is for its own low-pass setting, which can be set to either 80 or 100Hz.

Packing a Punch

Thanks to the inherent physics at play in a cardioid subwoofer design, there can be cause for concern over its response, especially at different distances and positions. My take on the KS212C, is that QSC seem to have played well to it’s natural performance ability.

What do I mean by this? Well, if you compared this subwoofer to a one with a 15”, 18” or 21” driver, then you would probably feel the extreme lows (<45Hz) more prominently. In turn, some of these subs with larger drivers can feel “loose” or “soft”. Whilst the KS212C does drop surprisingly low, that’s not what this sub delivers best. Here, I believe QSC has gone for what many of us would consider as the punchy region; 45Hz-80Hz. Unsurprisingly, what you might expect from dual 12” drivers, but with very capable transducers that really can move the distance.

For example, I found I could achieve a really punchy kick drum sound very quickly. What’s more, this “tight” low-end aspect to the mix transmitted well through the venues I tested the system in. I was really impressed and personally much prefer a more exciting and dynamic response, than one that can sound “flappy”. Within the region that I found these subs to deliver their best, I also didn’t experience anything untoward.

The KS212C produces it’s cardioid effect through complex processing, so that the mirrored arrangement of the drivers in their independent chambers, interact through two ports on the front and two on the rear. The interaction at the rear produces a cancellation, whilst the interaction at the front produces summation. QSC claim the result is 15dB’s higher at the front compared to the rear. I actually believe this is a very fair measurement as the drop at the rear is considerable.

While we could discuss pros and cons of cardioid subwoofers for various applications until Christmas, I will just add that the KS212C presents a surprisingly versatile solution. Without adjusting anything (what could typically be complicated system processing settings), you can use these subs in a matter of ways. I did try two KS212C’s in a stereo arrangement, which provided a surprisingly even coverage, despite the usual concentration in the centre. There weren’t any worrying holes in the coverage however, and even the sides of the room had plenty of energy. Two units on top of each other, lying on their side in the centre of the stage was hugely powerful as you would expect. However, this does compromise the rear rejection slightly and I believe typically impractical for most stages that the K series is intended.


I was really impressed with the performance of the cardioid effect from the KS212C, which leads on to all the usual benefits of cardioid subs. To compliment this, QSC seem to have achieved this without impacting all the other usual areas of concern, such as general output power and dispersion of frequencies generated. I believe this is partly because of the concentrated bandwidth that these subs are effective in. However, I applaud this as the result is a tight and punchy response, which sounds exciting.

This new box from QSC brings a new and exciting approach to PA design for small to medium sized venues. It offers a solution that was previously complicated to achieve, delivering a professional result. Complete with casters, aluminium handles and solid construction, QSC have somehow managed to top their well-known build quality too.

Key Features:

3600 Watt Class D power module

Dual 12-inch long excursion drivers; Dual 6th order
band-pass design

15 dB SPL attenuation front-to-rear

Two M20 threaded sockets (one on top, one on side) accept
35 mm speaker pole

RRP: £1,408 ($1,822)