We’re thrilled to share another shining review of the K300 Mk.3, this time from Paris Kotsis of Sound Plus magazine in Greece. Full translation below!
THE BRITISH SCENE IS INEXHAUSTIBLE AND OFTEN "BIRTHS" CREATORS WHO CHANGE THE FLOW OF THINGS. ONE SUCH CASE IS KERR ACOUSTIC, WHICH PRODUCES THE MOST BALANCED TRANSMISSION LINE SPEAKERS ON THE MARKET.
Transmission lines have the unique advantage of being free from the “box”, as the rear wave of the loudspeakers exits after a long journey inside the cabinet, reinforcing the low frequencies. This means speed, immediacy and control as the rear wave does not produce resonances inside the cabinet and therefore does not disturb the movement of the cone, as in a conventional reflex or closed cabinet loudspeaker. Transmission lines excel in the deep low range, having the softest roll-off of all designs and, due to the internal path, their cabinets are more inert. As you can see, transmission lines, a special case of which are back loaded cones, excel in dynamics and low distortion and seem to be the optimal loading option, before moving on to open baffles which are even freer but have issues with size and cancellations.
Why then do we not see more examples of transmission line speakers on the market, which is dominated by 99% bass reflection? Firstly, because due to the internal structure the construction is more complex and the size of the cabinet larger. Secondly, because effectively damping the mid and upper low frequencies of the back wave within the path, so that only frequencies below 80Hz exit the “mouth” of the transmission line, is not an easy task. And thirdly, because at the final opening of the line, some of the low frequencies are reflected back, creating cancellations. Somehow, manufacturers choose not to mess with the genre and “get away with” a reflection tube tuned to a specific frequency, instead of aiming for the broader spectrum that the transmission line amplifies. Typically, a non-optimized transmission line design will have midrange leaking out of the opening, some emphasis on the deep lows, and some cancellation in the upper lows, usually in the 150–200Hz range, resulting in a sound like a satellite with a poorly tuned subwoofer.
It is with this gifted but feared type of loading that British designer Jes Kerr decided to “fight,” who started Kerr Acoustics in 2017, seeing a gap in the high-end market, as there was no other transmission line loudspeaker with a ribbon tweeter and a marine plywood cabinet. Yes, you read that right, Jes Kerr’s design effort started from two assumptions. First, that MDF degrades the performance of the transmission line and, second, that given a perfected TL loading, a tweeter with very low moving mass is needed to match the lightning-fast low-end speeds that the loading produces. Simple things, in other words, with a heavy dose of common sense. The designer is a music producer, lives in the live scene and plays himself, so he has a solid criterion for real sound, he has been building speakers since he was eight years old and has a large collection of speakers that he has restored and "tweaked", having had the help of his father since childhood, who is actively involved in the company.
TRANSMISSION LINES AND RIBBONS
The K300 is Kerr's smallest model, in a range of just four models, which is divided into two levels. Low are the two-way K300 and K320 (the floor-standing version of the former) in the Mk3 versions with Scanspeak woofers and high are the three-way K200 (base, 3-inch mid-dome, 10-inch radial woofer) and K100 Mk2 (floor-standing, 3-inch mid-dome, 12-inch radial woofer) with Volt cones and domes. In the first two models, the tweeter is the Fountek Neo X2.0 with a ribbon length of 60 mm. In the two larger models the Neo X3.0 with a ribbon length of 80 mm, both equipped with a matching m/s that raise their very low resistance (0.02Ω) to 8Ω and slightly “tweaked” by Kerr. In the test speaker, the moving mass of the tweeter ribbon is just 0.027 g, six times less than that of an AMT folding ribbon tweeter. The cabinet material in all Kerr is Baltic birch plywood in two thicknesses (18 and 24 mm) and the cabinets are made by hand. In the K300 of the test, the woofer is the Revelator 18W/4531 of 165 mm with a “slotted” wood fiber cone and is connected in phase with the ribbon tweeter.
The most difficult part of the design according to Jes Kerr is the filter and it is what was improved in the 3rd generation of the speaker. For the two-way models, the company uses a 2nd order filter with a cross point at 1.95KHz and six materials, two carbon film resistors, two polypropylene film capacitors and two air coils. The K300 has a minimum impedance of close to 5Ω and very good sensitivity, so 50W is enough to drive it properly. It provides a pair of terminals and the low extension is very good, close to 35Hz. Of course, the cabinet is bulky as it extends strongly in the depth (almost as deep as it is tall) but this is not visible in the space, so the K300 will not occupy our living room. They are produced with various veneers but we can also order them in the color of our choice and they are accompanied by magnetic covers.
The K300 is a speaker that has solved most of the problems we encounter in the high-end, as it has extremely low distortions in a very wide range, top speed of transitions, explosive dynamic contrasts, continuity from another planet and disappeared colorations and resonances. It essentially has no cabin sound, that is, its box is more invisible than the B&W 805D4 and it practically plays with the freedom and openness of an open baffle or a membrane speaker. In relation to these, it is more specific and more disappeared in space, because it is smaller and brings fewer obstacles to the sound stage it sets up. In comparison, electrostatics lag behind in dispersion next to it and their stage is limited by the dimensions of the membrane and the open baffles do not provide such tangible focus and clarity, especially at the periphery of the stage.
Of course, the small Kerr cabinet leaves some euphonic traces of wood in the upper lows if the speaker is not set up correctly, which is the key point to reproduce its sound. The overall balance of the low is less "canned" in relation to the reflex speakers and is "tuned" in the space with more effort and better precision, almost like in a dipole. In our room, the K300 smoothed out its low-end curve at a distance of 80 cm from the rear wall (measured from the inner corner of its back), it probably can handle it closer, but further out there were small discontinuities in the curve that “warmed up”, as mentioned above, the timbre in the upper lows. At 80 cm, the low-end response is ideally balanced, becomes full and velvety, dense and crystal clear, with a transparency that simply does not exist in conventional tube speakers that cannot avoid the weight, thickness and slowness produced by the internal wave in the cabinets.
Therefore, when we talk about transparency in conventional speakers, we almost always mean the frequencies after 200–250Hz, while further down the spectrum we talk about volume, warmth, etc. This does not mean that the K300 is thin at low frequencies, but it does not have the easy, permanent volume that conventional loads give at some frequencies. It has the superior loudness that one would expect from a 6.5-inch woofer without box accents and it gives it in a way that is crystal clear, detailed, coherent and, above all, with exemplary focus, where the images on the stage are large and uncompressed, almost like a rear funnel. In other words, the K300's bass is like an open window, free and bright, not like a basement, dark and closed.
And when it "thunders" in the big dynamic bursts, then you understand that the contrast is superior to any conventional "box" because nothing hinders the movement of the woofer. So, some percussion may sound a little smaller than a reflex speaker, but when we put in a church organ the volume becomes enormous! It offers superior variety, depending on the recording. This is maintained throughout the low range, from deep bass to the upper lows where the transmission lines often empty, thus providing an amazing combination of extension, resolution and dynamic range. The treble is obviously charismatic, with absolutely top-notch resolution, speed and transparency and one really does not notice when the tweeter takes over, as there is no discontinuity with the woofer.
It is enough to set them with a little toe in, because on the axis a small emphasis is perceived in the last octave 10–20K. We did this with the 805D4, so the spectrum was balanced, but the K300 is inherently more balanced, with less of a dip in response between the two speakers (2–5KHz) caused by the in-phase operation. The in-phase element, however, is what gives life to the timing and causes shivers with the immediacy it gives. From this point of view, the K300 is perhaps the best I have heard, as the speaker synchronization, the British are always first in this, they balance the speeds of the transitions famously, but very rarely do they do it with such outrageous speeds of converters and cabinets, where the slightest detail is magnified.
In other words, putting a ribbon on a transmission line takes guts and it is no coincidence that we have never seen it on the market before. Needless to say, all the speaker's feats in bass, treble, stage, dynamics and timing simply serve the most expressive, free and brilliant midrange that the high end category has to offer in two-way base speakers. Embossed, lightning-fast, dense and fleeting where necessary, the little Kerr's midrange has a huge variety of timbres and saturation, recreating the timbre of each instrument with naturalness.
Ultimately, even a week after the start of the test, I am unable to give any sonic character to the K300, every morning I press play and simply listen to the recording, not the speaker. It is no coincidence that these days I played most of the SACDs on our universal and the Clearaudio turntable caught fire, as I could not get enough of these more organic formats. It is a STAR !!!!
RATED: ***** // 4.9
PROS: FOCUS • COLOUR • OPENNESS • ANALYSIS • VARIETY OF VOLUME • DYNAMICS AND COLOR
CONS: NEEDS CAREFUL SETUP • ONLY ONE SET OF TERMINALS • NEEDS STANDS
SOUND PLUS MAGAZINE ISSUE 48 // APRIL 2025
AUTHOR: Mr. PARIS KOTSIS