Kerr Acoustic

K320 mk3 Loudspeaker

£7,495

Almost all loudspeakers on sale today are box designs, with wood or fibreboard cabinets. Most of these are bass reflex-loaded, which is to say they have a port in the cabinet that allows air to move freely in and out as the drive units move back and forth. This lets designers get plenty of bass out of reasonably compact cabinets and confers efficiency and/or ease of drive. Reflex ported speakers go loud with relatively low-powered amplifiers and don't normally present a punishingly low impedance to the power amplifier. In other words, you get a decent bang for your buck – so what's not to like?

Well, as a boy back in the late nineteen seventies, I became fascinated with speaker design and started building my own rudimentary creations. My bible was the classic hobbyist tome that is Gilbert Briggs, Loudspeakers: The Why & How of Good Reproduction (1948), which I read avidly from cover to cover. It explained the pros and cons of different types of cabinet loading and explained why reflex ports aren't beyond reproach. Unless done carefully, they can produce lumpy 'one note' bass, and also deliver poor transient speed. From that moment on, I became intrigued by cabinet loading in loudspeakers.

Since then, experience has taught me that some bass-reflex designs can work very well – yet there are more ways than one to kill a cat, so to speak. Many serious speaker geeks go for either infinite baffle designs or transmission lines. The former is a personal favourite, where the speaker cabinet is sealed off from the outside atmosphere. IBs tend to sound tighter and tauter than reflex ported designs in the bass, less lumpy low down, and often cleaner in the midband too. The downside is that they can be buggers to drive, and always ask more of an amplifier – lots of watts are required, as well as strong current driving ability.

L-R: Jes Kerr and Cameron Jenkins (Stranger High Fidelity) with a pair of Kerr Acoustic K100s

Transmission line designs like the Kerr Acoustic K320 mk3 floorstander you see here take another and quite different route to musical nirvana. You could call them "the thinking man's reflex port" because they do vent the cabinet to the outside air but do so in a far more sophisticated and controlled way. Unwanted rearward energy from the woofer cone is more effectively managed than with a bass-reflex design and extracted from the rear of the driver and the rear baffle, where it would otherwise cause trouble. TLs are hard to do well, but when working as intended, offer a tauter and deeper bass than bass reflex designs and a more neutral midband too.

"In a 2-way design like the K320", says designer Jes Kerr, "driver loading is also responsible for the majority of the midrange content… The cone can typically move more freely than in many bass reflex or infinite baffle enclosures over a wider bandwidth, due to a more even 'acoustic impedance' of the air mass behind the driver. This makes for better transient speed and keeps the electrical impedance of the driver smoother, as it's not fighting against a narrow-q port tuning frequency in the case of a BR, or the 'acoustic spring' effect of an IB."

TLs are easy to get wrong, which is why I think many speaker manufacturers shy away from them. Another issue is cost, as you're effectively building a long, folded baffle – think of it as a tunnel – inside a speaker cabinet, which is more time-consuming both to design and to manufacture. Then you've got the headache of properly damping it to manage airflow whilst minimising resonances. And typically, to get the best from the breed, you need a largish cabinet too, which isn't cheap either.

CONSTRUCTION TIME

Former professional drummer and music producer Jes Kerr has packed a lot into his relatively short time on the planet, including getting a BSc in Audio Engineering, specialising in loudspeaker design. "I was fuelled by a love of music from the age of eight, but it wasn't until my degree dissertation that I attempted a transmission line", he tells me. "This was a large three-way featuring a 12-inch woofer. I studied Martin J. King and John Risch in great depth, which gave me a solid grounding in understanding TL technology and its implementation." He launched Kerr Acoustic in June 2017, after eighteen months of research and development. His first product was the K100, a high-end transmission line speaker featuring premium materials and components and incorporating a ribbon tweeter.

Today's Kerr Acoustic range comprises the aforementioned monster K100, now in mk2 guise, the more compact K320 floorstander you see here, now in mk3 guise, and the K300 standmounter, also now a mk3. "The K320 mk3 coincided with the outsourcing of our cabinetry to the experts at Timberworx in Sheffield in August 2020," Jes tells me. "All cabinet walls are now bonded together with 45-degree mitre joints, something that would have been virtually impossible for us to achieve in-house with our limited facilities. This allows for greater physical contact area between the cabinet walls, which in turn helps with cutting down on unwanted panel resonance, resulting in a more acoustically inert cabinet."

The 1,020x195x395mm (HxWxD) box, weighing a chunky 25kg, is made from 18mm Baltic Birch plywood with a 24mm front baffle. This is an expensive and difficult way of making a speaker cabinet, but very effective – hit the speaker with your knuckles, and you get a dead, fast-decaying 'thunk'. A range of wood veneer finishes is now offered, in addition to the original satin and high gloss lacquer finishes. Magnetically affixed speaker grilles are standard. The result is an extremely well-built product – as good as you'll get at this price – that's attractive to look at, reasonably compact, and room-friendly. It's a good size for average listening rooms.

The driver complement is almost as interesting as the cabinet design. A true ribbon tweeter is fitted, a modified 50mm Fountek Neo X 2.0 unit. I'm a big fan of these, as they're super fast and detailed with far less mass to move than any dome-type high-frequency unit. The K320's ribbon weighs 0.027g compared to ~0.5g for a good dome and ~0.2g for an AMT tweeter – giving a total moving mass eighteen times lower than an average dome. A 165mm Scanspeak 18W/4531G01 mid/bass driver marries up to this. This uses a light wood-fibre cone, which at 165mm is the largest driver that can be fitted to the relatively narrow baffle of this compact floorstander.

The 2-way K320 mk3 crosses over at 1.95kHz, using a six-element, second-order (12dB/octave) crossover. In my view, 3-way loudspeakers are inherently better, but again everything is a trade-off in speaker design, as it is in life; the Kerr Acoustic uses an expensive cabinet and two premium-priced drive units, which is arguably better than a cheaper cabinet with three less expensive drivers. Jes says he's fitted specially selected components to the crossover, hand-soldered using point-to-point wiring. Unique air-core inductors, hand-wound in-house, are used, along with polypropylene film capacitors and carbon film resistors. The speaker turns in a decent quoted 90dB (2.83V/1m) efficiency figure and is said to drop to an impedance of 5.2 ohms at its lowest point, which shouldn't upset most modern amplifiers. Claimed frequency response is an impressive 24Hz to 45kHz.

THE LISTENING

I was struck by how clean, straightforward, and open sounding the K320 mk3 is in my listening room. Indeed, you're not really aware that it is a transmission line design at all – such is its even yet wonderfully extended bass, relative lack of cabinet colouration, driver integration, and overall transparency. Its other stand-out characteristic is its transient speed, which I'd guess is a function both of its super-light ribbon tweeter and the cabinet loading system.

The funny thing is that upon first hearing it, the K320's sound was almost an anti-climax. The speaker is packed with trick technology, and yet nothing about it struck me as particularly special – there was no big, domineering aspect of its character that imprinted itself on every track I played. Yet, in my book, that's actually an early sign of a really good speaker because it shouldn't draw attention to itself or indeed how it was designed. When you've got over the idea of it not having a big ego of its own, you can sit back and enjoy the music – and truly appreciate its many strengths.

Having spoken at great length about this speaker's transmission line loading, you may find it odd when I say that although excellent, its bass is not the K320 mk3's defining characteristic. The speaker sounds so well integrated that there's no 'wow' factor for one particular facet of its performance. Indeed, cue up Tom Sawyer by Rush, and it's the lightning-fast transients that hit you foursquare between the eyes. Pump some serious power into this speaker, and it rewards you with a startlingly vivid sound, yet it's not in the least bit tonally forward and 'in your face'. Instead, this speaker can step out of the fray and let the music shine through. The track proved riveting to listen to, really capturing the power and pomp of this great rock band – at a time that was arguably its best period.

Such transient speed was a joy to behold with the leading edges of heavily struck snares or strummed electric guitars and worked hand-in-glove with the speaker's excellent dynamics. The thwack of percussion was a wonderfully physical sensation, especially hard hit rim shots, for example. For most sane people, this speaker goes plenty loud enough, but as you nudge up the volume control, it begins to ask questions of the amplifier driving it. As I basked in the electrifying sound of Rush, the K320 mk3 told me in no uncertain terms that it could do with some more power to play with…

I had been using my Sony TA-N86B power amp in full Class A mode, where it is rated at 30W RMS per channel, but it wasn't quite sounding right. Switching to Class AB mode, taking the amp up to a claimed 110W RMS per side, and my review pair of Kerrs really started having fun, delivering a grippier and more dynamic sound. Yet still, the sound was more polite than perhaps I would have liked, so I hooked it up to my current high-end integrated fave rave, Copland's CSA-150 integrated. This was even better still, with its 150W RMS of modern MOSFET firepower brought to bare. So the moral of the story is that if this speaker sounds a bit flat, then bring in the heavy artillery!

Only when driven by this Neanderthal of an amplifier, did the K320 mk3 really do its thing. Speed, dynamic articulation, and power all proved top-notch for a floorstander of this size, and then there's its other pièce de résistance – the bass. Let's be clear here, never does it deliver a massive nineteen seventies disco speaker booming noise – so even at high listening levels, your internal organs will remain in place. Instead, Kerr's magic is its ability to go down exceptionally low for a speaker of its size in a linear, controlled, and even way. This is quite a thing to hear because there's no obvious bump in the response. Rather, the Kerr just emits powerful low frequencies in a committed but judicious and measured way.

This is really impressive with electronic music – specifically early nineties techno – designed to be played through massive sound systems at open-air raves. Nookie's Give A Little Love, for example, is like two songs in one; it has an infectious lead piano riff, sampled vocal line, and crashing, high tempo percussion. That's all people with average floorstanders or standmounters of any description will ever hear. Listen on the K320 mk3, however, and you'll experience a bouncy sub-bass line modulating up and down, grumbling under the piano riff. At times it goes really low; I've heard some really high-end floorstanders that haven't matched its clarity and extension. Yet this speaker tracked the bassline in an attentive yet totally relaxed way.

The result was a soaring rendition of this old rave floor filler. Even at highish volumes via the Copland integrated, there was no complaining, and the physical exertions going on down below never impinged on what was happening further up. The dizzying speed of that tweeter married up with the bass line in a hugely satisfying way. I got similar thrills from Kraftwerk's Tour de France Soundtracks, another piece of music written with little regard for the sound systems it would later find itself being played on. The bassline bubbled along with oodles of thump yet fine control too, whilst further up the frequency range, the track came over with precision, detail, and poise.

Moving up to the midband, and there's an awful lot to like here, especially when the speaker has warmed up after fifteen minutes or so. You get a very balanced, smooth, and matter-of-fact sound that's laced with low-level detail. It's also exceptionally transparent, even for a speaker of this price. You can flick from say, Carole King's It's Too Late (1971) to Suede's Animal Nitrate (1993) and be transported in time and space. Listen to the former, and you'd accuse the K320 mk3 of being warm, soft, sweet, and spacious – maybe even coloured. Then move to the latter, and it's a hard, in-your-face and nasal speaker, with brittle upper mids and clangy treble. In other words, this speaker digs deep into whatever recording it is given and conveys it without prejudice. It's not about sugaring the musical pill, so to speak.

The ribbon tweeter fitted to the K320 mk3 is top-notch, at least for a speaker anywhere near this price. I've heard better, but you're into the realm of true esoterica – comparisons with which aren't really fair. When listening to it, I was constantly reminded of how crude almost all dome tweeters are, by comparison. The latter as a breed has more weight to move to emit sound, and the result is a slight suckout of air and space in any given recording and general coarsening of the signal. The Kerr's high-frequency unit, by contrast, proved deliciously delicate, a delight to hear reproducing hi-hat and ride cymbals. But there was more, as it's also great with lacerative harmonics from instruments such as electric guitars. Rat Race by The Specials was a treat, the lead guitar having a speed and scratchy incision that made the song all the more rhythmic. At the same time, this speaker handled the sparkling overtones of the piano and Hammond organ brilliantly. Everything sounded fast, vibrant, tactile, and alive.

Given that this loudspeaker is so good at everything else, you'd be surprised if it was sub-par in the soundstaging stakes. Not to worry, as bolstered by that excellent tweeter, it projected instruments into space with pinpoint precision. Kate Bush's Snowflake was quite a thing to hear; the producer positions the listener practically inside her piano and then hangs the main vocal line back a bit. The result was suitably ethereal, my review pair of K320 mk3s working wonders with immersive sound all around. Spatially, it's not the widest soundstaging speaker that I've ever come across, simply by virtue of its compact size. Yet, in terms of image precision and depth perspective, it is exceptional.

No loudspeaker is perfect, of course, despite what the manufacturers might claim. In the case of the K320 mk3, it puts on a great all-round performance with no obvious weakness to any aspect of its sound, bar one. That is purely down to its size. In medium-sized rooms, it comes across as plenty big and punchy enough, but put it in a larger space and/or really turn up the volume, and you're aware this is more of a welterweight than a heavyweight design.

This speaker does begin to compress slightly when really extended, and how can it not? This is your daily reminder that narrow footprint floorstanders with small diameter mid/bass drivers cannot reinvent the laws of physics, not even this one. So you do get some flattening of transients and a slight colouration in the midband when really going for it, and the general sense that its natural ease and poise are disappearing. Still, this won't be an issue for most people unless they have seriously big rooms and/or neighbours they hate.

THE VERDICT

I reviewed the first Kerr Acoustic K320 a couple of years ago and found it an excellent mid-price floorstander – and nothing really has changed. Indeed the latest mk3 version sounds even more neutral across the midband now and maybe even slightly more finessed up top. Bass remains excellent, as does its overall integration. Most important, however, is the fact that this is great fun to listen to. It steps aside to leave the music to its own devices, letting it bounce along with heady abandon. It's interesting that such a sophisticated speaker delivers such an accessible and enjoyable performance. Nothing is too much trouble; it just gets into the groove and parties. And so should you, I would humbly suggest, by hearing a pair if you possibly can.

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