ATC C4 Sub Mk2

The ATC C4 Sub Mk2 is a high-performance active subwoofer designed to bring true studio-grade low-frequency performance into home audio and cinema systems. In addition, it is engineered to integrate seamlessly with a wide range of ATC loudspeakers for both stereo and multi-channel setups.

The C4 Sub Mk2 delivers deep, controlled bass with high precision. As a result, it reproduces the lowest octaves of the audio spectrum without losing clarity, even at high listening levels or during demanding film soundtracks.

Proprietary 12-inch sub bass driver

ATC uses its in-house SS75-314SC 12-inch (314 mm) driver in the C4 Sub Mk2. Therefore, it accurately reproduces frequencies below 160 Hz with excellent control. In addition, the short-coil design operating in a long magnetic gap reduces distortion across the full dynamic range.

High-power Class A/B MOSFET amplification

The subwoofer integrates a 300 W Class A/B MOSFET amplifier. As a result, it delivers stable and clean power with low distortion. At the same time, it ensures consistent performance during both music playback and cinematic use.

Precision low-frequency reproduction

The driver and amplifier are designed as a matched system. Therefore, the C4 Sub Mk2 achieves tight control and accurate bass response. In addition, this integration helps maintain detail and timing in the lowest frequencies.

Flexible system integration

The C4 Sub Mk2 includes variable low-pass filtering along with adjustable gain, polarity, and phase controls. As a result, it can be precisely tuned to match different loudspeakers and room acoustics. Furthermore, it integrates easily into stereo, home cinema, and AV systems.

Ideal partner for ATC loudspeakers

The C4 Sub Mk2 is designed to complement ATC models such as the SCM19, SCM20, SCM40, SCM50, and SCM100. Therefore, it extends system bandwidth and improves low-frequency performance. In addition, it enhances overall system scale and impact without compromising tonal balance.

Main Features

High-performance active subwoofer
Designed for studio-grade low-frequency reproduction
12-inch (314 mm) proprietary ATC sub bass driver (SS75-314SC)
300 W Class A/B MOSFET amplifier
Short-coil / long-gap motor design for low distortion
Variable low-pass filter
Adjustable gain, polarity, and phase
Optimised for stereo, home cinema, and AV systems
Designed for seamless integration with ATC loudspeakers
Hand-built in England
6-year warranty

Specifications

Acoustic Specifications

Bass Driver	1 × SS75-314SC, 8 Ω
Low Frequency Cut-off	22 Hz (−6 dB, half space, low-pass filter @ 80 Hz)
Low-Pass Filter Settings	50 Hz / 65 Hz / 80 Hz / 320 Hz (−6 dB, 4th order Linkwitz-Riley)
Maximum SPL	110 dB continuous / 116 dB peak (IEC weighted pink noise @ 1 m, half space, LPF @ 80 Hz)
Sensitivity	+4 dBu ref. 88 dBC (single channel, gain +6 dB, level 0 dB, LPF @ 80 Hz)

Electronic Specifications

Amplifier Type	Grounded Source MOSFET Class A–B, convection cooled
Output Power	300 W into 8 Ω
THD+N	< 0.003% / −90 dB (100 Hz, 300 W into 8 Ω, over 90 kHz bandwidth)
Balanced Inputs	2 × XLR female (pin 2 hot)
Input CMRR	90 dB @ 200 Hz
Input Impedance	20 kΩ (differential)
Balanced Outputs	2 × XLR male (pin 2 hot)
Output Impedance	100 Ω (differential)
Frequency Response	< 2 Hz (−3 dB) – 320 Hz (−6 dB, LP filter controlled)
Gain Control	0 / +6 / +10 dB
Level Control	0 to −11 dB (1 dB steps, 21 dB total range)
Phase Control	0° – 180°
Polarity Control	In-phase / Out-of-phase
Limiter	ATC Active FET momentary gain reduction
Sensitivity	1.55 Vrms for full power (gain 0 dB, level 0 dB)
Mains Input	115 V / 220–230 V (factory set)
Power Consumption	Idle: 8 W / 14 VA 1/8 power: 170 W / 230 VA Full power: 500 W / 600 VA
Additional Control	Mute via 6.35 mm (¼”) jack, latching footswitch (not supplied)

Physical Specifications

Dimensions (H × W × D)	568 × 464 × 500 mm (22 15/16” × 18 1/4” × 19 11/16”)
Net Weight	42 kg / 92.6 lbs