The C4 Sub Mk 2 active subwoofer system unites the highest driver and electronics engineering standards in a single system, so says the British-based Acoustic Transducer Company, better known in both pro audio and domestic hi-fi markets as ATC.

 ATC's C4 Sub Mk 2 features the all-new proprietary 12-inch SS75-314SC sub-bass driver powered by a newly developed 300W class AB amplifier design. Furthermore, both elements are hand-built and installed within a substantial cabinet at the company's Stroud-based production HQ.

The SS75-314SC sub-bass driver is the first to be purpose-built for an ATC sub-bass system and reproduces the lowest four octaves of the audio band, exploiting ATC's signature short-coil/long-gap configuration to its natural limits with an exceptionally long 30mm magnetic gap, surrounded by a 6-inch/150mm N48M Neodymium magnet.

In addition, the wholly redesigned motor system features a new rubber roll surround for high excursion capability, a new spider for optimised compliance geometry, and high-flow motor venting for low noise and compression.

We are told that as well as minimising distortion, this unprecedented short-coil/long-gap configuration ensures the voice coil remains within the motor structure - even at high drive levels - maximising cooling, reducing power compression, and improving reliability. Additionally, turbulent air noise within the driver is minimised by a large, flared vent running through the motor structure's centre while also increasing voice coil and motor cooling.

The C4 Sub Mk2 eschews electronic equalisation and instead relies upon “exceptional transducer engineering and a marginally larger cabinet volume”. ATC states that the simplicity of this approach reduces phase shift and group delay, aiding the integration of the sub with the partnering loudspeakers.

The all-new 300W class AB design is precisely optimised to the requirements of the new driver, resulting in fast, dynamic bass with minimal colouration. Two balanced line inputs provide connectivity for stereo or AV/home cinema systems. Meanwhile, two balanced outputs are available to feed partnering 'main' stereo loudspeakers or 'daisy-chain' multiple subs.

The low-pass filters are analogue, 4th order Linkwitz-Riley, with filter frequency options ensuring optimal integration with partnering speakers. In addition, an industry-standard 80Hz low-pass filter and an 'off' option (for use with external processing) are joined by a polarity switch, variable 180° phase adjustment and a stepped attenuator over a 21 dB range for precise level matching.

Hand-built and finished at ATC's cabinet factory, the C4 Sub Mk 2's 70-litre 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.

The ATC C4 Sub Mk 2 costs starts from US$5,999 (Standard finish).

Visit ATC for more information