Bookshelf Speakers — ATC SCM20

The SCM20 in the ATC hi-fi catalogue is the passive SCM20PSL, a two-way stand-mount hand-built in England and in continuous production since 1990. ATC describes it as its highest-performing passive two-way stand-mount, and it is part of the Classic series, where the same cabinet is also offered as the powered SCM20ASL. A 6-year warranty applies. A professional sibling, the SCM20PSL Pro, is housed in a 450 x 250 x 294 mm cabinet weighing 18 kg and is aimed at near-field work in control rooms and LCR surround monitoring in smaller rooms.

Key specs that matter

ATC fits the 150 mm SB75-150SL mid/bass driver, an 8 ohm unit, while treble is handled by the 25 mm SH25-76S, rated at 6 ohm, with the handover at 2.2 kHz. The low-frequency cut-off sits at 55 Hz and the high-frequency cut-off at 25 kHz, both measured at -6 dB in anechoic conditions, while amplitude linearity is held to plus or minus 2 dB from 80 Hz to 20 kHz, and speakers are matched to within 0.5 dB. System sensitivity is 85 dB at 1 W and 1 m. Maximum SPL is 108 dB continuous and 114 dB peak per pair at 1 m, measured anechoically with IEC-weighted pink noise. Nominal impedance is 8 ohm, with a minimum of 5.5 ohm. Each cabinet measures 440 x 239 x 325.5 mm (height, width, depth) and weighs 16.9 kg net. The coherent dispersion angles are plus or minus 80 degrees horizontally and plus or minus 10 degrees vertically.

Engineering and use context

The SL in the bass driver's name stands for Super Linear, an ATC magnet technology aimed at lowering third harmonic distortion, and the driver uses a 75 mm voice coil. The S-Spec tweeter has a dual suspension and works without ferrofluid for cooling. A second-order crossover network is assembled from film capacitors and air-cored inductors, and the rear panel carries bi-wire inputs. ATC lists a wide choice of cabinet finishes - Black Ash, Burr Magnolia, Cherry, European Walnut, Rosewood, Oak, Pippy Oak, Walnut, Piano Black, Piano White, Satin Black and Satin White - with custom colours also available.

Pairing

The recommended amplifier range is 75 to 300 W. Within that span ATC advises an amplifier delivering at least 200 W per channel, and the bi-wire inputs allow separate cable pairs for the bass and treble halves of the crossover.

Alternatives

The ATC SCM11 is a smaller passive stand-mount with a CLD mid-bass driver.