Bookshelf Speakers — ATC SCM7

The SCM7 is the smallest two-way passive stand-mount in the ATC hi-fi range, and its model number gives its internal cabinet volume of seven litres. The current third version went on sale in mid-September 2013, launched together with the SCM11 as the first ATC passive models to use the company's own SH25-76 tweeter. ATC covers it with a 6-year warranty.

Key specs that matter

A 25 mm neodymium soft dome tweeter works above the 2.5 kHz crossover point, and a 125 mm SC mid-bass unit covers the range below it. ATC rates the response at 60 Hz to 22 kHz at the -6 dB points, with left and right speakers matched to within 0.5 dB. Sensitivity is 84 dB at 1 W and 1 m into a nominal 8 ohm load, and the maximum SPL is 103 dB. Coherent dispersion is quoted as 80 degrees either side horizontally and 10 degrees either side vertically. The cabinet measures 300 x 174 x 215 mm (height, width, depth), the grille adds 28 mm of depth, and each speaker weighs 7.5 kg.

Engineering and use context

The SH25-76 tweeter has a dual suspension that suppresses rocking modes, a short edge-wound voice coil running in a long, narrow magnetic gap, a shaped soft-dome diaphragm and a 1.5 tesla neodymium magnet, with a precision-machined 5.5 mm alloy waveguide ahead of the dome. The mid-bass driver carries a 45 mm soft dome at its centre and is powered by a 3.5 kg magnet system, with a ribbon wire voice coil hand-wound in-house. For this generation ATC fitted metallised polypropylene capacitors, large air-cored inductors and ceramic wire-wound resistors in the crossover. The old stepped baffle was dropped in favour of a curved cabinet that is braced and laminated for rigidity. Binding posts accept 4 mm plugs and are set up for bi-wiring. Owners can order the cabinet in real Cherry or Black Ash wood veneer, or with a Satin White or Satin Black paint finish.

Pairing

ATC recommends an amplifier rated between 75 and 300 W for this model, the same bracket it gives for the SCM11 and the floorstanding SCM40, even though the SCM7 is the least sensitive of the three. A flat impedance curve is part of the design brief, so the amplifier is not faced with deep dips in the load. With the bi-wire terminals, two cable pairs can run from one stereo amplifier.

Alternatives

The ATC SCM11 is the next stand-mount up, with an eleven-litre cabinet, a 150 mm CLD mid-bass driver, 85 dB sensitivity and a weight of 10.9 kg.