The third compact, sealed box two-way loudspeaker to come my way in a month is also the longest established and most affordable. The SCM7 is Gloucestershire based ATC’s smallest model at only 12 inches high, the 7 in the name referring the volume in litres. It is very much a proper ATC, however, with in-house drivers and an elegantly tapered, boat tail section cabinet.
The story behind this model goes back to ATC founder Billy Woodman’s days at Goodmans where he was a big fan of the Maxim, also a compact two-way. When Billy started making complete loudspeakers rather than just drivers he wanted to build something of a similar size that had wider bandwidth, lower distortion and greater dynamic range. The first speaker he built to meet those demanding goals was the SCM10 in 1992, that had an 5inch ATC mid/bass driver with a Vifa tweeter and went down very well in some markets but proved a little large for others. It evolved into the A7 with a revised mid/bass driver that was optimised for the smaller box paired with a neodymium powered tweeter from Vifa once more. In 2001 that in turn evolved into the first SCM7.
In 2013, ATC delivered the current, third generation SCM7 that you see before you, this was the first to feature the company’s own tweeter, developed in-house by Richard Newman, alongside a proprietary ATC mid/bass driver. It was also the first showing of the formed and laminated curved side cabinet that is now seen across the SCM range and developed to increase both stiffness and damping, not to mention reducing internal reflections.
Not many loudspeaker companies build their own tweeters, let alone smaller brands like ATC. It’s a particularly exacting and demanding job if you want to do it consistently, and if you want results that don’t vary from batch to batch consistency is important. The SH25-76 soft dome tweeter is derived from the 75mm midrange driver that the company makes for its three-ways. It has a dual suspension system that’s designed to suppress rocking modes at high output levels and combines a short, edge-wound voice coil in a long, narrow magnetic gap. This combination being used to ensure minimum distortion without the need for ferrofluids which can apparently dry out over time. It has a high powered neodymium magnet with a heat treated top plate in order to dissipate the heat that high power operation generates and thus minimises compression. The alloy waveguide that surrounds the dome on the outside is engineered for good dispersion and low resonance.
Both tweeter and main driver have so-called underhung voice coils, which doesn’t mean that they are lacking in the cohones department, quite the opposite, it means that the magnetic gap is longer than the voice coil that moves within it. The idea being that the magnet exerts greater control over the voice coil throughout each excursion resulting in better linearity and lower distortion. The crossover is a second order type with a 12dB/octave roll off that employs air-core inductors and large capacitors so that this element will not get in the way of long term, high level listening. ATC is heavily involved in pro audio so they are used to making loudspeakers that have to work long and hard, and while that isn’t necessarily what we in the musical appreciation fraternity need very often, it does confer a degree of reliability in the long term that inspires confidence.