Floorstanding loudspeakers — ATC SCM20SLT

The SCM20SLT is the floor-standing form of the SCM20, the two-way design from ATC of Aston Down, Gloucestershire. ATC describes this tower as its top two-way floor-standing model and has kept it in continuous production since 1996. The passive version, sold as the SCM20PSLT, has evolved through three driver and crossover revisions, and an active SCM20ASLT with an on-board amplifier pack is offered as well. Performance matches the stand-mounted SCM20SL Classic, so the choice between them comes down to looks.

Key specs that matter

Two ATC drive units are used - a 150 mm SB75-150SL Super Linear mid/bass driver rated at 8 ohm and a 25 mm SH25-76S S-Spec soft dome tweeter with dual suspension rated at 6 ohm. They cross over at 2.2 kHz. Anechoic cut-off at the low end is 55 Hz (minus 6 dB) and the upper limit is 25 kHz, with pairs matched to within 0.5 dB. System sensitivity is 85 dB for 1 W at 1 m, and the load is 8 ohm nominal with a 5.5 ohm minimum. ATC recommends amplifiers of 75 to 300 W. Maximum output per pair is 108 dB continuous and 114 dB peak, measured with IEC weighted pink noise at 1 m. The passive tower is 990 mm high, 239 mm wide and 344 mm deep and weighs 24.7 kg.

Engineering and use context

The mid/bass unit works in a compact sealed cabinet, which ATC chose for precise timing and useful output below the cut-off. Internally the enclosure is built heavy and inert, with bracing for stiffness and bitumastic damping panels placed at critical points to suppress resonance. The second-order crossover is hand-made by ATC with high-grade film capacitors and the company's own air-cored inductors, which it uses for their lack of hysteresis and lower distortion. Heavy-duty bi-wire terminals take the amplifier connection. The active SCM20ASLT swaps the passive network for a 250 W amplifier pack with 200 W for the mid/bass and 50 W for the tweeter, and it weighs 30.2 kg. Finishes include several real wood veneers, satin black and white paint and piano gloss options.

Pairing

The low sensitivity and the recommended power window point to a solid-state amplifier of moderate to high output. ATC suggests its own P1 and P2 power amplifiers, SIA2 integrated amplifier and CA2 or SCA2 preamplifiers, and notes that the modest load suits most other electronics.

Alternatives

The passive SCM50PSLT is ATC's three-way tower above this model, with a 234 mm bass driver and a 1003 mm cabinet.