Bookshelf Speakers — ATC SCM100ASL Pro

The SCM100ASL Pro is a three-way active studio monitor from ATC (Acoustic Transducer Company), founded in London in 1974 by the Australian engineer Billy Woodman whose factory today stands at Aston Down in Gloucestershire. It is aimed at larger control rooms, where it works as a main or midfield monitor, and it sits in the professional range between the SCM50ASL Pro, with a 9-inch woofer, and the SCM150ASL Pro, which moves to a 15-inch bass unit and a bigger box.

Key specs that matter

Three drivers made by ATC share the baffle - an S-Spec tweeter of 25 mm with dual suspension, the 75 mm Super Dome midrange and a 314 mm (12-inch) bass unit built to full SL specification. An onboard grounded source tri-amplifier delivers 350 W in total, divided as 200 W for bass, 100 W for the midrange and 50 W for the tweeter. Amplitude linearity stays within 2 dB from 65 Hz to 17 kHz, and the free-standing -6 dB points fall at 32 Hz and 25 kHz. Continuous output reaches 115 dB SPL at 1 metre. Coverage is coherent across plus or minus 80 degrees in the horizontal plane and 10 degrees in the vertical. The cabinet measures 832 x 398 x 581 mm (HxWxD), and each speaker weighs 55.2 kg.

Engineering and use context

Because every driver has its own power amplifier, the division at 380 Hz and 3.5 kHz happens at line level, before amplification, using fourth-order critically damped filters with phase compensation. Each amplifier pack is set up individually at the factory for frequency, gain and phase correction. The SL tag stands for Super Linear magnet technology, which ATC pairs with underhung voice coils to keep distortion low as level rises. Protection against overload comes from FET circuits that briefly pull back gain on every channel. Two screwdriver trims sit on the rear panel - one sets the input level needed for full output anywhere between 1 V and 2 V, the other adds up to 6 dB of low-frequency lift centred at 40 Hz. A clip indicator warns when the amplifiers reach their limit. The midrange dome defines the acoustic axis, so ATC advises placing it at or just below ear level, and asymmetric cabinets go with midrange and tweeter on the inner side. Units left and right are matched within 0.5 dB, and the warranty runs for 6 years.

Pairing

Signal enters through a single male XLR socket with an input impedance of 10 kohm per leg, so a mixing desk, monitor controller or line preamplifier with balanced outputs connects directly. Unbalanced RCA sources can be wired with an adapted cable, and no separate power amplifier is needed.

Alternatives

The ATC SCM150ASL Pro keeps the same tri-amplifier and crossover points but fits a 375 mm bass driver in a 150-litre enclosure, reaching down to 25 Hz.