Floor Loudspeaker Reviews

The story's been often told: 30 years ago, British speaker manufacturer KEF was asked to design a small, spherical loudspeaker that could be used in a European project to research room acoustics. The speaker had to have wide, even dispersion, so KEF's solution was to mount the tweeter coaxially, on what would have been the woofer's dustcap. That "point source" drive-unit, called the Uni-Q, began appearing in KEF's commercial speaker models in 1989, starting with the Reference 105/3—but it wasn't until the appearance of KEF's 50th-anniversary loudspeaker, the LS50, which I reviewed in December 2012, that I felt that the Uni-Q drive-unit had fully fulfilled its promise, at least in a speaker I had auditioned in my own room.

The penultimate stop on Bob Reina's British Invasion Tour of Affordable Loudspeakers (footnote 1) brings us to the doors of KEF. Although KEF is a large and well-established British firm, I've noticed that their product lines have not been as visible in the US as those of, say, B&W, Wharfedale, or Mission. In fact, the last time I heard a KEF speaker, it was the company's then-flagship design, at a Consumer Electronics Show nearly 20 years ago! Before that, when I lived in London, KEFs were ubiquitous, down to the older, entry-level designs tacked to the walls of the ethnic restaurants I frequented. My strongest KEF memory is a cumulative one: Every KEF speaker I've ever heard, regardless of price, venue, or setup, has always produced good, convincing sound.

KEF and I go way back. As a very young man in the 1960s, I was obsessed with building speakers, and that was just about the time that KEF founder Raymond Cooke was revolutionizing driver design by using new synthetic materials for cones and surrounds, and experimenting with such innovations as transmission-line–loaded midrange drivers. I found it all very heady and, by direct import from the UK, obtained versions of the oval, flat-diaphragm B139 woofer, the Bextrene-coned B110 and B200 woofers, and the T-15 and T-22 dome tweeters. Fifty years ago, this was all cutting-edge speaker technology.

In the late 1980s, KEF, then as now a leader in bringing new technology to loudspeaker design, developed a unique coincident driver that positioned the tweeter in the throat of the midrange/woofer cone. In a flash of inspiration, they dubbed it the Uni-Q, and the driver immediately not only found its way into the company's more upscale speaker designs, but also became a key element in a major European research project on room acoustics. That study's results appear to have been inconclusive, but the Uni-Q lives on as the defining element of KEF loudspeakers.

After reviewing a long series of minimonitors, I am now working on what may well be an equally varied selection of large floorstanding loudspeakers. This trend began with my review of the Sonus Faber Cremona Elipsa in the December 2007 issue, and continues this month with the Series 2 version of the KEF Reference 207, until recently the flagship model from this English manufacturer (footnote 1). I reviewed the original Reference 207 in February 2003, and was very impressed by what I heard.

By now most readers will be familiar with the relatively new tuned-cavity method of low-frequency loading. Such designs have popped up all over the place of late, especially in those little satellite/woofer systems, but KEF can rightly lay claim to generating the design's theoretical basis, as JA described in his review of the KEF R107/2 loudspeaker in Vol.14 No.5 (May 1991). Essentially, the technique consists of loading the rear of a woofer in a conventional fashion—usually a sealed box—but also loading the front of the driver into another enclosure, ducted to the outside. Basically, the design acts as a bandpass filter with its response centered on the port-tuning frequency. The rolloff is smooth and rapid on either side of this frequency, providing a natural low-pass characteristic but thereby virtually mandating a three-way system. If properly designed, this configuration offers a number of theoretical advantages. The radiating element is actually the air in the port, which is low in mass. Low distortion is possible, as is relatively high sensitivity.