Bookshelf Speakers — ATC SCM20ASL Pro

The SCM20ASL Pro is a compact two-way active studio monitor from ATC, the British loudspeaker maker known for its professional monitors and in-house drivers. ATC positions it for near-field listening, for left, centre and right channels in small to medium control rooms, and for surround channels in larger rooms. The version covered here is the Mk2, which combines the company's own drivers with a built-in bi-amplifier pack.

Key specs that matter

The bass and midrange driver is a 150 mm Super Linear unit with a 75 mm voice coil, type SB75-150SL, and the tweeter is a 25 mm dual-suspension soft dome, type SH25-76S. The discrete MOSFET Class A/B amplifier pack delivers 200 W to the woofer and 50 W to the tweeter continuously at 1% THD. The crossover is set at 2.1 kHz with a second-order slope of 12 dB per octave. Amplitude linearity is ±2 dB from 80 Hz to 20 kHz, and the -6 dB limits are 55 Hz and 25 kHz when the speaker stands free of walls. Dispersion is ±80 degrees horizontally and ±10 degrees vertically. Maximum continuous output is 108 dB per pair at 1 m. The input is a female XLR, with a 1 V or 2 V sensitivity switch and a trim of 0 to -6 dB, covering 1 to 4 V overall, and an input impedance of 10 kOhm per leg. The cabinet is 450 mm high, 250 mm wide and 343 mm deep, with 48.7 mm more at the rear for the amplifier pack.

Engineering and use context

Relative to the cone, the voice coil is large, which spreads heat over a greater area and keeps the driver's behaviour stable at high levels. The dual-suspension tweeter holds its dome at two points to control unwanted movement. The amplifier sections have very low measured distortion, 0.0006% at 100 Hz for the woofer amplifier and 0.0022% at 10 kHz for the tweeter amplifier, and the tweeter amplifier's upper -3 dB point is 230 kHz. Signal to noise ratios are 112 dBA for the woofer channel and 109 dBA for the tweeter channel. The crossover is critically damped and phase-compensated. A rear shelf control at 80 Hz adjusts bass from -2 to +3 dB in 1 dB steps. Protection includes FET gain reduction with a front limit LED, a thermal trip and DC offset protection. Maximum power draw is 381 W or 483 VA. The monitor is designed for vertical orientation, and it can be wall-mounted on a K&M 24120 bracket after modification of the cabinet.

Pairing

The balanced XLR input takes a signal directly from a preamplifier, audio interface, mixing console or DAC with volume control. The switchable sensitivity matches both consumer and professional output levels.

Alternatives

The ATC SCM25A Pro is the three-way active near-field monitor from the same professional range.