Abacus C‑Box Series

Can these small two‑way monitors really deliver accurate sub‑bass information at the mix?

There’s a widespread belief among project‑studio owners that genuinely insightful sub‑50Hz monitoring is simply beyond the capabilities of any affordable two‑way nearfield design. Yet, in principle, even a small woofer can generate those kinds of sub‑bass frequencies — it’s just that you won’t get much listening level before the driver reaches its excursion limits and distortion creeps in. In response to this inherent volume cap, pretty much all manufacturers in this space now design their speaker cabinets to resonate at low frequencies, thereby significantly boosting the low‑frequency acoustic output before the woofer‑cone excursions start maxing out.

The resonance is usually created using a frequency‑tuned reflex port or passive radiator, both of which involve some unwelcome sonic trade‑offs. Typically the bass level of resonant two‑way nearfields falls off rapidly below 50Hz, such that the lowest octave all but disappears and you’ll struggle to judge the relative balance of low‑frequency components either side of the fall‑off point. Low‑frequency time‑smearing is another a common problem, making kick transients sluggish and generally smudging low‑frequency instrument layers together so that it’s tough to distinguish between them.

But what if a manufacturer decided not to accept these trade‑offs, and pursued superior low‑frequency accuracy instead, at the expense of sheer output welly? Well, that’s exactly what the German company Abacus Electronics have been doing for years, and it’s their current C‑Box active nearfield range that’s the subject of this review.

Home On The Range

The C‑Bass 10 is based around a 10‑inch woofer.There are three speakers in the range. The C‑Box 3 and C‑Box 4 are two‑way closed‑box designs, which have similar phase‑plug tweeters but woofers of different diameters (10cm and 14cm respectively). Despite their diminutive dimensions, the loudspeakers boast low‑frequency extension down to 35Hz and 32Hz respectively at the ‑6dB point, and useful audibility of energy well below that because of the comparatively gentle low‑end roll‑off characteristics of closed‑box cabinets. Where you need higher listening levels, these speakers can be joined by the C‑Bass 10, a closed‑box subwoofer based around a long‑throw 10‑inch driver. Simple 2.1 bass management is built into the sub’s cabinet, with controls for level and phase, for the crossover’s high‑pass and low‑pass filter frequencies, and for a sub‑bass cut EQ that helps compensate for low‑frequency ‘room gain’ in small studios.

There’s plenty more technical information on the Abacus website, so I won’t bother parroting that here, but there is one aspect of the hardware that studio users definitely need to be aware of: all the C‑Series audio connections are on unbalanced RCA phonos. I didn’t encounter any problems at all in my own studio tests (and the speakers have very low self‑noise too), but I do use a filtered mains supply and I kept all my cables as short as possible, so I can’t say how much unwanted electromagnetic interference these speakers might pick up under less favourable conditions.

Talking Loud

Let’s get one crucial question out of the way first: how loud are these speakers? Well, this depends on the bass content of the mix you’re listening to. The worst‑case scenario is anything with the kind of powerful sub‑50Hz kick/bass fundamentals that most quickly max out the woofer’s clean driver excursion — tracks like Arizona Zervas’s ‘Roxanne’, Justin Bieber’s ‘Boyfriend’, or Stormzy’s ‘Big For Your Boots’, say. For the C‑Box 4, in practical terms that means keeping the listening volume low enough that you can easily have a conversation over the top without raising your voice. While this feels loud enough for mixing purposes, it won’t give you much of a physical bass sensation, so you have to get used to judging low‑end balances by what you hear rather than what you feel. Nor will this kind of playback volume impress visiting clients, hype up a band fresh from their first live‑room take, or inspire a room full of musical collaborators — all scenarios where monitoring wallop usually pays dividends.

For the smaller C‑Box 3, mixing LF‑heavy productions is unquestionably a quiet listening experience. This is a speaker that should be within a metre of your head to maximise what you can hear, and you’ll want to minimise background noise in your workspace too. Under those conditions it’s still just loud enough for professional‑level work, in my opinion — but it’s right on the cusp!

The C‑Box monitors feature built‑in high‑pass filtering (which can come in handy when you need a little more level at the expense of bass extension), and are fed from unbalanced phono inputs.Whichever C‑Boxes you use, though, you need to take care with your monitoring volume to avoid unwanted distortion. Unfortunately, the speakers provide no visual overload indication to guide you in this respect, so there’s an element of trial and error involved here. I found that experimenting with sine‑wave tones helped me develop a sense of how much clean headroom was on offer at different frequencies, but despite this I regularly found myself pulling down my monitoring volume to check whether some bass harmonic I was hearing was in the mix itself or whether I was just driving the woofer too hard. One useful little dodge, though, is that if you’re willing to sacrifice some bass extension (perhaps while mixing your guitar and vocal parts), then you can use the C‑Box’s onboard high‑pass filter to cut away the most headroom‑hungry low frequencies, so you can listen to the rest of the spectrum louder.

Naturally, if you supplement either C‑Box with the C‑Bass 10, that reduces the strain on the C‑Box woofer, opening up much louder playback levels. With the C‑Box 3, I was still a bit reluctant to push things beyond a fairly moderate level (and with the crossover frequency set quite high, around 100Hz or so), but with the C‑Box 4 I felt comfortable turning things up as loud as with my own Blue Sky Pro Desk system — in other words, as loud as I’ve needed for any mix I’ve done in the past 20 years!

4 Reference

But what about the actual sound? Well, let’s start with the C‑Box 4s on their own, because it’s easier to discuss the rest of the range in relation to those. The headline here is that the low‑frequency extension is extraordinary for such a small speaker. Subby bass lines that simply drop off the bottom of typical resonant nearfields (things like Justin Bieber’s ‘Boyfriend’, Stormzy’s ‘Big For Your Boots’, and the Pussycat Dolls’ ‘Takin’ Over The World’) came through with commendable clarity, as did the challenging bottom‑octave kick layers in Michael Jackon’s ‘Invincible’ and the subterranean rumbling underneath tracks like Skunk Anansie’s ‘Infidelity (Only You)’ and Post Malone’s ‘Circles’.

The evenness of the low‑end balance is also a real highlight, with the inconsistent weight of the upright bass parts in Sarah Jarosz’s ‘Take Me Back’ and the Steeldrivers’ ‘Hanging Around’ both mercilessly exposed, for example. Sub‑30Hz frequencies are certainly quieter than they should be (so the power differential between the lower and higher fundamentals of that Stormzy track isn’t as lopsided as I’d expect, for instance), but they’re nonetheless still audible enough to provide a great deal of useful mixing information in terms of the timing, envelope parameters, and relative balance in that zone.

I’ve never heard such stunningly clear low end from a speaker at anything like this price!

The cleanliness of the bass transmission is another strong point — as long as you keep the monitoring volume within tolerance, of course! Sine‑wave synth basses remain as stark and featureless as they should be, and you’re informed straightaway about the kick‑drum LF distortion on One Direction’s ‘Drag Me Down’, Anderson Paak’s ‘Lockdown’, and even Coldplay’s otherwise incredible‑sounding ‘Magic’. As with many closed‑box speakers, the LF time‑domain response is very well‑controlled too, delivering not just the focused kick‑drum impact of David Guetta’s ‘Don’t Leave Me Alone’, Zedd & Alessia Cara’s ‘Stay’ or Dua Lipa’s ‘Don’t Start Now’ with ease, but also damping the ends of low‑frequency events assertively enough to beautifully diffentiate between the complex layered bass confections of Ariana Grande’s ‘Side To Side’ and Christine & the Queens’ ‘Christine’. That last track in particular was hard to stop listening to, in fact, as I’ve never heard such stunningly clear low end from a speaker at anything like this price!

Overall Sonics

Tearing myself away from the bass hyperbole for a moment, the rest of spectrum has much to recommend it as well. The tonal character feels slightly forward in the 3‑4 kHz zone, but once you’ve acclimatised to this there’s an unhyped naturalness and precision to the sound that I found eminently well suited to mixing work. With most small speakers, there’ll be a few of my reference tracks where I’ll find myself scratching my head and wondering why they’re suddenly sounding unfamiliar. Here, however, everything I threw at the C‑Box 4 felt natural and believable — not just (literally!) hundreds of reference tracks, but also a number of active mix projects. The high end manages to be both open and smooth, yet doesn’t underplay the excessive sibilance of Madonna’s ‘Sorry’ or the spiky vocal transients of Olivia Rodrigo’s ‘Vampire’ and Alison Krauss’s ‘Paper Airplane’.

The subwoofer provides independent control over the high‑ and low‑pass filters, as well as an additional sub‑bass filter, and fully variable phase control between 0 and 180 degrees at 80Hz.Time‑domain fidelity across the board feels no less forensic than it does at the low end, and the listening experience is full of detail. The loose clustering of the percussion in Michael Kiwanuka’s ‘Home’ was exquisitely rendered, for instance, as were the surreptitiously automated effects levels in Sierra Hull’s ‘25 Trips’. But I was especially struck by how well this speaker can resolve and interrogate complex distorted textures full of electric guitars and cymbals (such as the Darkness’ ‘Growing On Me’, say), how quickly it identifies unwanted distortion artefacts, and how brutally it communicates the audio consequences of heavily crushed productions such as Devlin’s ‘Watchtower’, Imagine Dragons’ ‘Radioactive’, or Panic At The Disco’s ‘High Hopes’. The stereo imaging felt very dependable, and there was decent front‑back depth too, although on both cases nothing beyond what I’d typically expect of this speaker’s market peers.

With such a potent combination of bandwidth, detail, speed and tonal discrimination, this speaker really shines when working with acoustic music styles or any kind of high‑stakes vocal production — both applications where I think the slight midrange forwardness plays into your hands as a mix engineer. The nuances of audiophile productions such as The Goat Rodeo Sessions or Sheffield Labs’ direct‑to‑stereo orchestral recordings came through wonderfully, for instance, as did the gorgeous vocal textures of Solomon Burke’s ‘Don’t Give Up On Me’, Crowded House’s ‘Four Seasons In One Day’, and Norah Jones’s ‘Sunrise’. It was easy to scrutinise the more intense processing of mainstream chart vocals too, with stand‑out vocal productions such as Hailee Steinfeld’s ‘Starving’, Little Big Town’s ‘Girl Crush’, and Alan Walker’s ‘Faded’ leaving me in no doubt about their superiority.

But there’s one more vital trump card the C‑Box 4 possesses: its enormous balancing power. The level of every instrument, voice and effect. The relative levels of consonants, transients and mechanical noises. The level balances between different frequency ranges. It’s this kind of balance discrimination that the C‑Box 4 provides in spades. Furthermore, the insightfulness of its tone and balance comparisons between different mixes is invaluable when referencing your own mix work against commercial productions.

Overall, then, the C‑Box is a mightily capable mixing tool and (deep breath) the best all‑round mixing speaker I’ve yet come across at this price. Now, I realise that’s quite a bold claim, but I think the low‑end capabilities on their own already leave the vast majority of the competition standing, and once you factor in the top‑notch balancing/referencing acuity and the tremendous presentation of vocals and acoustic sounds, I just don’t see any serious contenders from a mixing perspective. No product is perfect, of course, and there are certainly louder and more aesthetically ‘pleasant’ speakers available for similar outlay, but this is currently the most affordable speaker system I’d personally be happy using for my own professional mix work.

C‑Box 3 & C‑Bass 10

Much of what I’ve said about the C‑Box 4 also applies to its smaller sibling. Certainly the C‑Box 3’s core balancing capabilities and time‑domain definition lose very little ground by comparison. The low‑end reach of such a tiny woofer is, if anything, even more remarkable, but nevertheless can’t quite match up to the C‑Box 4 in this respect, and left me less confident in my mix decisions below 30Hz. Partly this was just the challenge of picking out such frequencies at the speaker’s necessarily very low monitoring level, where the equal loudness curves can’t work in your favour. In fact, in general the C‑Box 3’s low playback volume required me to give the mix a good deal more mental focus in order to winkle out details. To be fair, I think the degree of detail’s almost as good as with the C‑Box 4, but you definitely have to work harder to pick everything out!

In addition, the smaller model’s just a slightly less appealing listen: a touch harder‑sounding in the midrange, and a little light around 200Hz, giving the tone a hint of ‘shoutiness’ that takes some getting used to. Again, though, once you’ve acclimatised, tonal relationships between different instruments in the mix feel very natural, and it delivers similarly solid and dependable tonal comparisons for mix‑referencing purposes. So while it loses out somewhat to the C‑Box 4, the C‑Box 3 is still a phenomenal little mixing speaker on its own merits.

Adding in the C‑Bass 10 subwoofer was a treat, loosening the playback volume restrictions and extending the C‑Box’s clean, nimble low end pretty much straight to the centre of the earth! Any residual doubts I had about balances in the lowest octave when working without the subwoofer were swiftly banished and, with a pair of C‑Box 4s and the C‑Bass 10, I was soon mixing with the same speed and confidence as on my own Blue Sky system.

Lord Of The Lows

The C‑Box 3 and C‑Box 4 trailblaze an exciting alternative approach to small‑studio mix monitoring, and I think you’d be daft to overlook them if they’re within your budget. In combination with the C‑Bass 10, both C‑Boxes also create very cost‑effective 2.1 systems — although I’d definitely recommend saving the extra money for the C‑Box 4s if you can. And, just stepping back for a moment, I think it’s brilliant that a smaller speaker manufacturer like Abacus can still challenge the dominance of more established global brands, because it’s all of us customers who end up reaping the rewards of that kind of healthy competition.