Home Review ATC C4 MK2 subwoofer – great!

Review ATC C4 MK2 subwoofer – great!



  • Sounds very good
  • Loop-through capability
  • Musical character


  • No DSP or measuring options
  • Large and heavy

Price: € 5260

Build quality


Living with a subwoofer can be somewhat addictive. This is evident when we combined the ATC C4 MK2 at home with the ATC SCM40A: a pair of active floorstanding speakers. Do these really need a subwoofer? No, of course not. But it is nice … and it does add some extra depth to the music (pun intended).

If you ask a random person on the street what a subwoofer is and what it does, you will not only get a strange look, but you will probably get the wrong answer. The vast majority of people will think that a subwoofer mainly gives more bass. That might be the case in a MediaMarkt surround system; in a hifi and high-end audio system, it is certainly not. At least: if it is properly tuned.


A good subwoofer that is properly tuned is inaudible. It mixes so well with the existing speakers that it disappears: the bass then blends seamlessly with the mids and treble of the main speakers. Not only in terms of loudness, but also in terms of phase (time) and timbre.

This seems easy, but it is absolutely not. Integrating a subwoofer properly is still a daunting task even for a seasoned enthusiast. Your author has long shunned subwoofers because they are a particularly tricky device to test. It takes a lot of time to get them right AND the effect varies enormously from speaker to speaker how to integrate them. In short: you really need to try them at home. Never buy a subwoofer without trying it at home.


Okay: a subwoofer should in fact be inaudible in a system. What it offers you is palpable bass. That is, if it is a powerful subwoofer.

This subwoofer also makes the midrange and high frequencies sound more open and that gives an extra illusion of space in the music. That effect – scale and tangible bass – is almost impossible to achieve without a subwoofer. At least: not with “normal” speakers. Bookshelf or floorstanding. They have to get really big and powerful to achieve this without a subwoofer. At least: that has been our experience.

The ATC C4 MK2

To get right to the point: the ATC C4 (MK2) is a big and heavy subwoofer. You can see it on the right (with a gimbal on it; apologies Helios!). It doesn’t look that big in the picture, but I can guarantee you that it really is a big subwoofer.

Now we can complain about that, but the fact is: to produce deep, tight and powerful bass you simply need volume. 70 liters in this case. And added to that is the need for a big driver (woofer) with a big magnet…. simple as that.

ATC has developed a new driver for the MK2: the SS75-314SC. That, of course, says nothing. The unit has a diameter of 314mm and has a large neodymium magnet with a diameter of 15cm mounted to it. A brand new 300-watt Class AB amplifier drives the woofer.

Tame it!


Now we previously tried the C1 MK2 in the living room. That was not a success for several reasons. The C4 MK2 solves most of the problems. There is a possibility at the back to loop things through via XLR. So the line out of the preamplifier goes to the ATC C4 MK2 and from the C4 it goes to – in our case – the active SCM40’s. Great!

What is also very nice is the higher gain of the ATC C4 MK2. The C1 (MK2) had too little gain for our room. This is pretty weird, because on paper the differences are not that big. Indeed, the driver is the same: also a 314mm (12-inch) woofer and an amplifier of 200 watts drives it. That should be enough. But it wasn’t.

However, we almost have to tame the C4; this is truly a beast! When we put on the movie TRON, the wooden floor board vibrate and the books almost fall from the shelves. So beware of this brute. We measured the Sub carefully to make sure everything is balanced. REW is great software for that.

Another thing that works better acoustically for us is that the C4 is front firing. The C1 was down firing. That just doesn’t work as well with the wood floor at your author’s home. Down firing may look tighter; it’s not always a good solution.

Type test
Single Test
Speaker class
Speaker type
Speaker system
Signal control
Frequency range
22 Hz
1-way (broadband)
Amplifier power (total)
300 Watt
  • Width: 46 cm
  • Depth: 50 cm
  • Height: 57 cm
Weight speaker
42 Kg
Production country

Winkels met ATC

Emrikweg 25
2031 BT Haarlem, NL
Korevaarstraat 2 e-f
2311 JS Leiden, NL
Hennesweg 20
6035 AD Ospel, NL


  1. I admit I have very little knowledge as to use of subwoofer. In your test set up pic of system I note the subwoofer is positioned away from the system at right angles, I don’t understand how the sound from the subwoofer can integrate with the ATC 40A speakers….? Would not the sound come away from one direction, or do subwoofers haves some magical way of integrating into the sound with out having to face the listener?

    • Low frequencies have no direction. Not like midrange or treble that can even form some sort of beam. Every room has an optimal position in terms of a subwoofer. This was a good spot in my room. In line with the speakers is – most of the time – optimal. But that was not possible in this case.

  2. I have a couple of JL Audio e-110 subs that I used with the SCM40A and now the SCM50 ASLT’s. Because of my living room’s layout (and following one reviewer in TAS), I’ve stationed the subs alongside the mains. On the advice of ATC, I set the subs’ crossovers at ~48Hz and 40Hz, respectively and, like yours, Phase=0. I’ve also let the ATC’s run full range. One thing I found important for sound quality, at least with a wood foundation, was to get the subs off the floor, initially with short phenolic board platforms using AV Room Service EVP’s and now with custom 15″ cubic stands on Isoacoustic Gaia II’s. I found that sacrifices a bit of deep bass for greater overall clarity. The other (ironic) thing is that in the process of setting up the subs, I asked the advice of an ATC honcho, who while making the xover suggestions mentioned, was at the same time adamantly opposed to using subs with either model. He wrote that not only were subs unnecessary with these speakers, but also that he’d not heard a sub, including ATC’s own(!), which melded well with their speakers.