ATC Launches C4 Sub Mk 2 Active Subwoofer System

The Acoustic Transducer Company (ATC) has announced the production of the C4 Sub Mk 2 active subwoofer system. Designed to unite the highest standards of driver and electronics engineering in a single system, the C4 Sub Mk 2 deploys the all-new proprietary 12-inch SS75-314SC sub-bass driver, powered by a newly developed 300-watt class AB amplifier design, both elements hand-built and installed within a substantial cabinet at the company’s Stroud-based production HQ

The C4 Sub Mk 2 features the new SS75-314SC sub-bass driver, the first to be purpose-built for an ATC sub-bass system and developed by the R&D team to reproduce the lowest four octaves of the audio band. In order to achieve this, the design exploits ATC’s signature long-gap/short-coil configuration to its natural limits with a long 30mm magnetic gap, surrounded by a 6-inch/150mm N48M Neodymium magnet — the most powerful ever assembled by ATC and a first for the company. In support, the wholly redesigned motor system features a new rubber roll-surround for high excursion capability, a new spider for optimized compliance geometry, and high flow motor venting for low noise and compression.

As well as minimizing distortion, this short-coil long-gap configuration ensures the voice coil remains within the motor structure — even at high drive levels — maximizing cooling, reducing power compression, and improving reliability. Turbulent air noise within the driver is minimized by a large, flared vent running through the center of the motor structure, which has the added benefit of increasing voice coil and motor cooling.

Consequently, the C4 Sub Mk2 delivers an extended low-frequency response while avoiding electronic equalization. Instead, the more elegant combination of exceptional transducer engineering and a marginally larger cabinet volume is used. The simplicity of this approach reduces phase shift and group delay, aiding the integration of the sub with the partnering loudspeakers.

New 300W ATC Amplifier

The all-new 300-watt Class AB design is precisely optimized to the requirements of the new driver, resulting in fast, dynamic bass with minimal coloration. Two balanced line inputs provide connectivity for stereo or AV/home cinema systems while two balanced outputs are available to feed partnering “main” stereo loudspeakers or to daisy-chain multiple subs. Low-pass filters are analog, 4th order Linkwitz-Riley, with filter frequency options ensuring optimal integration with partnering speakers. In addition, an industry-standard 80 Hz low-pass filter and an ‘off’ option (for use with external processing) is joined by a polarity switch, variable 180-degree phase adjustment and a stepped attenuator over a 21 dB range for precise level matching.

The C4 Sub Mk 2 Cabinet

Hand-built and finished at ATC’s cabinet factory and sharing styling with the brand’s Classic and Tower series loudspeakers, the C4 Sub Mk 2’s 70-liter cabinet employs 25mm/1-inch-thick panels and heavy bracing. It’s available in standard Cherry, Black Ash, Walnut, and Oak real-wood veneers, as well as Satin Black and Satin White finishes, or in premium Rosewood, European Crown Cut Walnut, Burr Magnolia, and Pippy Oak real-wood veneers, with the option of high gloss over veneers and black/white piano lacquers also available.

In-Use

The size and performance of the C4 Sub Mk 2 make it a natural complement for ATC SCM19, SCM20, SCM40, SCM50, and SCM100 active/passive systems and high-performance loudspeakers of a similar size. Multiple subs can be employed to further elevate performance in larger rooms or when partnering larger loudspeakers. Buffered linkable inputs and outputs make connection of multiple subs easy.

Designed and engineered with a focus on resolution and integration, the C4 Sub Mk2 delivers a more balanced and coherent experience for the listener, extending the low-frequency response without masking details or changing the tonal character in the upper bass/lower mid-range. It provides an upgrade path to customers owning smaller loudspeakers and lacking space for larger stereo loudspeakers whilst also strengthening ATC’s options in AV applications.