At around a healthy 90dB efficiency and with a benign 8ohm nominal impedance, I doubt you’ll have much trouble in finding an amplifier that will drive the K1. My advice would be to push the boat out in this department because the speaker will reward quality. The recently reviewed and very cost-effective Moonriver integrated amplifier springs to mind as a vice-free, well-priced option, but I spent most of my time listening to it with my trusty Vitus SIA-025. With this in place and operating in pure Class A, it took about a week of constant use from new before I thought the speaker came together musically. For this reason, I would always prefer to review a well run-in pair of speakers every time. When I first installed the K1, they were tonally cool, detailed, sharp and overly tight, but the ribbon and the bass/mid drivers were on no more than informal nodding terms. As the days passed, that 165mm unit loosened up, and they advanced toward a full handshake. It’s always fascinating to hear the noticeable ways that speakers develop with use, as with a week to ten days of intense exercise. The K1 became more musically whole and tonally expansive. The drivers, crossover and cabinet had formed a musical partnership, and I began to experiment with positioning.
They are actually quite forgiving in this respect and I had decent results near a rear wall but better with them standing in more free air which I certainly preferred. As ever, toe-in needs a bit of experimentation, never easy with a heavy stand-mount. Perhaps the reputation that ribbon drivers have with regard to high-frequency vertical beaming needs factoring in but these ribbons don’t strike me as being particularly guilty in this respect. If you want a clean-cut and fully detailed musical picture, you’ll likely end up with them directly facing the hot spot, but I eased that a little with a small toe-in angle without any significant drop off at high frequencies but I liked the driver integration and slightly relaxed presentation more.
It’s a fairly straightforward design, classic even, but there’s something so musically focussed about a properly designed two-way stand-mount with high quality drivers and a great crossover. It’s the sense of uncomplicated articulation coupled with a very focussed, free and dynamic bass that sits at the heart of great two-way designs, and the K1 is a superb example of that philosophy, with such a taut and stiff cone material as Kevlar, a synthetic Aramid fibre, the K1 drives with a real sense of purpose and most importantly, control. It is very fast with considerable transient power and the ability to translate what is happening in the bottom end with rhythmic flow and movement that grew more and more impressive as the hours and days passed. If you want to delve into what a bass player is doing, then the K1 will tell you in detail. Fast or slow, attack or decay, start or stop, it’s right there, on the button every time. But don’t ignore the influence of the ribbon in translating the music down here, either. That crossover is immaculately matched to the control of the drivers and the cabinet, and the speaker never wanders into vague territory. Dreaming Spirits from Mark Egan and Arjun Bruggman [Wavetone] features that singing fretless bass carries distant memories of the great Jaco and certainly has the whiff of Weather Report within its harmonic progressions cascading rhythmic signatures. This is a spacey, moody album full of soundscapes that speed and dart around the room, invoking a sense of floating mystery. The K1 was extra special here. That tweeter and its subtleties of tonal shading, control and texture really bring the music into the room. It is never wispy or remotely brittle, and I mean never. The bass/mid unit just sings, and the integration with the ribbon projects the music outside the speaker boundaries. In a word, it is seamless, and I used this album as a gauge for the K1’s run-in status over several weeks and as things improved tonally, so did the balance between technical precision of the speaker and the humanity of the musicians. It is easy to listen to the melody and the unique character of that fretless bass at any level. It’s picture painting in sound, and the K1 just glides through it with ease and great delicacy.
Every time I sat for a listening session with this ProAc, I was struck by its clean-edged directness and the neat, compact shape of the music. Suppose you like low-frequency bandwidth and love to feel that initial and compressive impact of a bass drum, then you won’t be disappointed. The sheer weight and punch is dramatic and, most importantly, clean. I ran through a few Billy Cobham albums, and it was good to hear his agility at the bottom of the kit potently expressed. Zero cabinet effects are dragging the tempo down. The interplay between Billy and his numerous bass players over the years was great because that strict sense of taut, bang, bang, bang pistonic drive that comparatively few speakers manage is easy work for the K1.