Oh my. How horn speakers polarize opinion within the audiophile community.
They are rather like Marmite, the iconic British savoury spread consumed by devotees on toast or buttered bread. For equally as many though, Marmite is almost literally the spawn of the devil.
English speaker designer and maker Simon Mears – and it’s my bad that I failed to ask him where he stands on the subject of Marmite – is most definitely a horn-ophile, so much so that he’s spent the last decade or so in a quiet and dogged quest to understand the theory and practise of horns and turn it into musical reality for living-room consumption.
I use the term living room quite deliberately. Mears designs and makes horn speakers under the Simon Mears Audio brand that are intended to be not listening room- but living room-friendly, with all that this implies for their size, and the need to win the aesthetic approval of all the people who inhabit the homes where they are installed.
From a technical standpoint this is not just a tall order, but one bound by the immutable laws of physics. A speaker using only horn-loaded drivers has to be big if it is to convincingly transduce the human voice and acoustic instruments across the broadly 60Hz to 1000 Hz range that most occupy. But to reach down to cover the left-hand, the sub-30Hz extreme of the concert piano or organ, a horn speaker has to be positively enormous.
Mears’ first commercial speaker is the Ucello, named after the Italian mathematician and painter Paulo Ucello (1397-1475) who was said to have obsessed about how the use of perspective could create a sense of visual depth in his art. The Ucello is a three-way horn speaker that does not plumb the frequency depths, in fact it reaches down only as far 56Hz, trading full-range performance for relatively living-room friendly size.
So, by the standard of many horns, Ucellos are not huge. Even so, they stand 78cm (w) X 96cm (h) X 50cm (d) (31” X 38” X 20” for those on the other side of the pond. -Ed.). But, by virtue of some rather distracting sexy curves that result from Mears’ use of tractrix horn profiles executed in multiple layers of ply, and by cabinet making of an extraordinarily high standard – we’re talking antique restoration grade here or top-notch bespoke furniture making – they don’t appear quite as bulky as might be expected. What undoubtedly helps this sleight of hand greatly too is that unlike other contemporary horn speakers such as, for example, Avantgarde Trios, the Ucellos have an all-in-one approach, rather than treating the individual horns as separate but interconnected elements.
The look of the Ucellos is inspired by the Belle, a domestic speaker designed by Paul Kilpsch and manufactured from 1971 to 2005. However, unlike the Belle whose tweeter was placed above the mid horn, Mears has placed the mid and tweeter horns in his Ucellos on the horizontal axis, adjacent to each other and 80cm from the floor, the tweeter to the outside or wall side of each speaker, with the bass cabinet underneath.
The Ucello carcass is made from high grade 18mm and 24mm Baltic birch ply veneered in a choice of finishes. The review speakers, a pre-production and demo pair, were clothed externally in pale figured maple, with darker figured pear wood veneer contrasting nicely on the mouth of the bass cabinet, and all finished in satin hard wax oil. Despite being development hacks they were nonetheless way better finished than some production speakers I could, but won’t name.
The tractrix loading horns of the Ucello mid and tweeter drivers are formed from built-up plywood stacks, machined to the appropriate profiles, then finished by hand. While the tweeter horns are circular when viewed front-on, those of the midrange drivers are horizontal ellipses. Circular horns offering the same sonic performance would have been simply too large, so they have effectively been squashed top to bottom with no discernible degradation in sound quality, says Mears.
Inside the speakers things get even more intriguing. After listening to and working with compression drivers and horn types from pretty much every manufacturer in the world over the last decade or so – some of them such as Western Electrics and Lowther-Voigt that are no longer manufactured – Mears has used drivers from the Italian vendor B&C because, he says, they offer the softer, smoother, more organic sound that he prefers, rather than the drivers and horns of yore, some of which are responsible for horns having the poor reputation they do in some circles.
The Ucellos’ midrange drivers are 2” throated affairs with a composite diaphragm while the tweeters are 1” throated with Mylar diaphragms and able in free space to extend to 18kHz. The woofers are 15” cone drivers by Eminence, backwards firing and loaded by a folded horn.
To design and supply the crossover networks required to persuade this trio of drivers to work in tandem, Mears enlisted US-based Albert Klappenberger whose own company ALK Engineering is well known for restoring and hot-rodding Klipsch originals. In the review pair of Ucellos the crossovers were in plain sight since the pre-production cabinets lacked back panels. Production Ucellos will have sealed backs, broken only by speaker cable binding posts, and a pair of solid brass rotary attenuation controls.
Klappenberger calls the crossovers Extreme Slope, but those who know what they are looking at will recognise a 4th order design, neatly executed and with some nice components. The curious will note Clarity Caps, and hand-wound inductors – solid core for the woofer and litz for the mid and tweeter –all mounted firmly and neatly on a dense board. Each Ucello has two crossover boards. Horizontally mounted, the mid section crossover features a transformer with multiple taps so that attenuation can be adjusted in one dB steps over an 18 dB range, while the tweeter crossover, mounted vertically and to the side, provides for attenuation of up to 12dB in one dB steps. As previously noted, this range of adjustment will, on production Ucellos, be made available to the user via knobs on the rear panel of the speakers.
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