Bookshelf Speakers — ATC SCM11

The SCM11 is a passive stand-mount model with two drivers from ATC whose name reflects its internal cabinet volume of eleven litres. This second-generation version became available in mid-September 2013, sharing its launch with the smaller SCM7, and the pair were the first ATC passive models fitted with the in-house SH25-76 tweeter. The warranty runs for 6 years. At launch the UK price was 1,200 GBP, against 810 GBP for the SCM7, and the US price was later quoted as 2,199 USD.

Key specs that matter

The drive units are a 25 mm neodymium soft dome tweeter and a 150 mm CLD mid-bass driver, divided at 2.2 kHz. ATC gives a response of 56 Hz to 22 kHz at the -6 dB points, and each pair is matched to within 0.5 dB. Sensitivity measures 85 dB at 1 W and 1 m, nominal impedance is 8 ohm and the maximum SPL is 108 dB. The coherent dispersion window spans plus or minus 80 degrees horizontally and plus or minus 10 degrees vertically. Cabinet dimensions are 381 x 232 x 236 mm (height, width, depth), with 28 mm more depth once the grille is on, and the weight is 10.9 kg per speaker.

Engineering and use context

CLD stands for Constrained Layer Damping, the technology applied to the mid-bass cone, which has a 45 mm soft dome built into its centre, a precision undercut pole piece and a hand-wound flat wire voice coil in a large motor assembly. The SH25-76 tweeter was developed to suppress rocking modes through a dual suspension, has a complex shaped soft-dome diaphragm that extends the treble range, uses a short edge-wound coil in a long, narrow gap with a 1.5 tesla neodymium magnet, and is loaded by a precision-machined 5.5 mm alloy waveguide. For the revised crossover ATC chose ceramic wire-wound resistors, big air-cored inductors and capacitors of metallised polypropylene. The curved enclosure is braced and laminated to raise its rigidity. Terminals are binding posts accepting 4 mm plugs, wired for bi-wire use. Veneers are Cherry and Black Ash, and the painted versions come in Satin Black and Satin White.

Pairing

ATC specifies a partner amplifier of 75 to 300 W. The flat impedance curve was a stated design aim so that the SCM11 presents an easy load, and the split terminal panel lets one stereo amplifier drive it over two cable pairs.

Alternatives

Below it sits the ATC SCM7 stand-mount, using a 125 mm mid-bass unit in a seven-litre cabinet that weighs 7.5 kg.