The ATC C4 Sub Mk2 is a high-performance 12"/300mm active subwoofer designed to complement ATC's active and passive loudspeaker range, suitable for stereo, multi-channel surround, and immersive audio systems. Its design prioritizes exceptional audio performance, delivering high sound pressure levels with very low distortion.
Function Description:
The C4 Sub Mk2 is a sealed-box (infinite baffle) subwoofer, chosen for its balance of sub-bass extension and driver control. The heavy and inert cabinet minimizes colouration. It features the SS75-314SC driver, meticulously optimized to reproduce the lowest three octaves of the audio band. This driver employs a short-coil operating in an exceptionally long magnetic gap, contributing to its high sound pressure levels and low distortion.
The subwoofer's convection-cooled amplifier is integrated into the rear of the cabinet. It offers two balanced inputs for mono or stereo sources. A pair of buffered, un-filtered balanced outputs allows connection to partnering active monitor loudspeakers, amplifiers, or for daisy-chaining multiple subwoofers.
Important Technical Specifications:
- 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).
- Max SPL: 110dB continuous, 116dB peak (IEC Weighted Pink Noise, measured at 1m, half space, low pass filter set at 80Hz).
- Sensitivity: +4dBu ref. 88dBC (single channel driven, measured at 1m, Gain +6dB, Level 0dB, pink noise, low pass filter set at 80Hz).
- 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.
- Input CMRR: 90dB at 200Hz.
- Input Impedance: Approx. 20kΩ (differential).
- Line Output Impedance: Approx. 100Ω (differential).
- Frequency Response: <2Hz (-3dB) – 320Hz (-6dB, set by panel-controlled LP filter).
- Gain Control: 0, +6dB, +10dB.
- Level Control: 0dB to -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 (full power): 1.55Vrms (single channel driven, Gain 0dB, Level 0dB).
- Power Consumption: Idle 8W/14VA, 1/8th Power 170W/230VA, Full Power 500W/600VA.
- Mains Input: 220-230V, 115V (factory set, observe panel markings and labels).
- Weight: 42kg.
- Dimensions: 568mm (H) x 465mm (W) x 519mm (D).
Usage Features:
- Gain Control: A 21dB range of gain control (0, +6dB, +10dB) allows for precise matching with various source levels. The +10dB setting is for low output level equipment.
- Low Pass Frequency Settings: Three low pass frequency settings (50Hz, 65Hz, 80Hz) and an 'Off' setting (320Hz) are available. The 'Off' setting is for use with external processing. All filters are 4th order Linkwitz Riley.
- Polarity Switch: Allows selection between in-phase (+) and out-of-phase (-) operation relative to the input signal.
- Continuously Variable Phase Setting: A 180-degree phase control enables fine adjustment of the phase relationship between the subwoofer and satellite speakers, aiding in time alignment.
- Outputs: Buffered, unfiltered, and fully balanced outputs provide a signal identical to the corresponding input terminals. This allows driving stereo amplifiers, active loudspeakers, or daisy-chaining additional C4 Sub Mk2 units.
- Footswitch Control: A single latching footswitch (not supplied) connected via a 1/4"/6.35mm jack can mute the subwoofer output. The mute function does not affect the outputs to primary loudspeakers. Multiple subs can be muted simultaneously via the 'Thru' jack.
- Room Interaction and Placement: The manual provides guidance on optimizing subwoofer placement to minimize room mode issues, recommending placement away from corners and mid-way between parallel walls. For multi-sub setups, placing one by each stereo monitor is suggested.
- Spikes/Feet: Supplied with 4 steel spikes for firm seating on soft carpeted floors, or fixed rubber feet for hardwood/concrete.
- System Integration: Detailed diagrams illustrate typical system configurations for stereo bass reinforcement/extension (mono or stereo subs) and multichannel surround/immersive audio. Recommended initial settings for various ATC loudspeaker models are provided.
- Listening Advice: Users are advised to start listening at low levels and gradually increase volume, as ATC subwoofers produce very low distortion, which can lead to underestimation of actual sound levels. The goal is for the subwoofer to be indiscernible as a separate element.
Maintenance Features:
- Fault Monitoring: The amplifier features fault monitoring for panel temperature and power amplifier DC offset. A single red LED illuminates to indicate a fault condition. In case of a fault, the subwoofer should be switched off, ventilation checked, and after 45 minutes, switched back on. Persistent faults require professional service.
- Cleaning: Surfaces can be cleaned with a dry duster. Heavy soiling on the cabinet or baffle can be cleaned with a cloth slightly moistened with a non-abrasive household cleaner. Drive units can be cleaned with a dry, lint-free cloth.
- No User Serviceable Parts: The product contains no user-replaceable parts and does not require routine service or preventative maintenance. Any malfunction should be referred to a qualified service personnel, dealer, or distributor.
- Warranty: All ATC products are guaranteed against defects in materials or workmanship for two years from the date of purchase. This period can be extended to six years by registering the product at www.atc.audio.
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