ATC C4 Sub Mk2

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C4 Sub Mk2 Active Subwoofer - Proprietary 12-inch driver, optimised motor mechanics and a 300W Class AB amplifier combine to deliver exceptional levels of performance for audiophile music and film devotees.

World renowned for its signature high output, low-distortion audio engineering and trusted by musicians, studios, live sound engineers and audiophiles over five decades, The Acoustic Transducer Company (ATC) is proud to announce the production of the C4 Sub Mk2 active subwoofer system. Designed to unite the highest standards of driver and electronics engineering in a single system, the C4 Sub Mk2 deploys the all-new proprietary 12-inch SS75-314SC sub-bass driver, powered by a newly developed 300W class AB amplifier design, both elements hand-built and installed within a substantial cabinet at the company’s Stroud-based production HQ.


ATC sub-bass driver

The C4 Sub Mk2 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 an exceptionally 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 optimised compliance geometry, and high flow motor venting for low noise and compression.

ATC C4 Sub Mk2 12-inch sub-bass driver details
  1. High-excursion rubber roll-surround.
  2. Spider with optimised compliance geometry.
  3. 30mm/1.2" magnetic gap energised by high energy neodymium ring magnet.
  4. High flow, low noise motor vent.

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.  Turbulent air noise within the driver is minimised by a large, flared vent running through the centre 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 equalisation, unlike many subwoofers available today. 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. 

ATC C4 Sub Mk2 back view connections

300W ATC amplifier

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 while two balanced outputs are available to feed partnering ‘main’ stereo loudspeakers or to 'daisy-chain' multiple subs. 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.

The C4 Sub Mk2 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 litre cabinet employs 25mm/1" thick panels plus 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 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.


ATC C4 Sub Mk2 Features:

  • High performance sealed box design using 12” / 314mm ATC proprietary sub-bass driver
  • Ideal partner to SCM19, SCM20, SCM40, SCM50, SCM100
  • Suitable for use in stereo, AV and home cinema applications
  • On-board 300W convention cooled discrete MOSFET class A/B amp
  • 2 x balanced XLR inputs
  • 2 x balanced XLR outputs (un-filtered/processed)
  • User adjustable gain, low pass frequency, polarity and phase settings
  • 6 Year warranty
ATC 12” SS75-314SC subwoofer driver

ATC 12-inch SS75-314SC sub-bass driver


Acoustic Specifications
Drive Unit – Bass: 1 x SS75-314SC
Low Frequency Cut-off: 22Hz (-6dB, half space, low pass filter set at 80Hz).
Low Pass Filters: 50Hz, 65Hz, 80Hz, 320Hz. (-6dB, 4th order Linkwitz Riley).
MaxSPL: 110dB continuous, 116dB peak (IEC Weighted Pink Noise, 1m, half space, low pass filter @ 80Hz).
Sensitivity: +4dBu ref. 88dBC (single channel driven, Gain +6dB, Level 0dB, pink noise, low pass filter @ 80Hz).

Electronic Specifications
Amplifier type: Grounded Source MOSFET based Class A-B, convection cooled
Output Power: 300W into 8Ω
THD+N: <0.003%/-90dB, at 100Hz, 300W into 8Ω over 90kHz bandwidth
Balanced Inputs: 2 x Rear Panel Mounted Female XLR, pin 2 hot
Input CMRR: 90dB at 200Hz
Input Impedance: 20kΩ (differential)
Balanced Outputs: 2 x Rear Panel Mounted Male XLR, pin 2 hot
Output Impedance: 100Ω (differential)
Frequency Response: <2Hz (-3dB) – 320Hz (-6dB, set by panel-controlled LP filter)
Low Pass Filters: 4th Order Linkwitz Riley
Gain Control: 0, +6dB, +10dB
Level Control: 0dB -11dB in 1dB steps. Total range 21dB with use of Gain switch
Phase Control: 0-180° ref. Input
Polarity Control: In-phase/Out-of-phase ref. Input
Limiter: ATC Active FET Momentary Gain Reduction.
Sensitivity: 1.55Vrms for full power (single channel driven, Gain 0dB, Level 0dB)
Mains Input: 220-230V or 115V – Factory set. Please observe panel markings and labels!
Power Consumption: Idle 8W/14VA. 1/8th Power 170W/230VA. Full Power 500W/600VA.
Additional: Mute via ¼”/ 6.35mm Jack socket, controlled via latching footswitch*.
*Footswitch supplied separately, latching type, ¼”/6.35mm jack connection.

Physical Specifications
Dimensions: (H x W x D): 568 x 465 x 519mm / 22 3/8 x 18 5/16 x 20 7/16 inches
Heatsink protrudes a further 40mm / 1 9/16 inches from rear and optional spikes add an additional 22mm/ 7/8 inches to height.
See data sheet (to follow) for a detailed drawing.
Net Weight: 42kg

Finish Options
Standard veneers - Cherry, walnut, oak, black ash.
Standard finishes – Satin black, satin white.
Premium veneers* – European crown cut walnut, pippy oak, rosewood, burr magnolia, burr poplar.

ATC Entry full range user manual ATC Entry full range user manual
Manual Packaging Info
ATC Subwoofers:
ATC C6 Sub ATC C4 Sub mk2 ATC C1 Sub mk2
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