Audio T Verdict
The ATC C1 Sub Mk2 is designed to add genuine low-frequency extension without overwhelming the speed, clarity and tonal balance of a carefully chosen Hi-Fi or home cinema system.
Its hand-built 12-inch driver and 200W Class A/B amplifier provide the control needed for detailed music playback while retaining the scale and impact expected from film soundtracks.
Stereo RCA and high-level speaker inputs allow it to work with a wide range of amplifiers and AV receivers. Adjustable gain, low-pass frequency, polarity and phase provide the tools needed to blend the subwoofer with both ATC and suitable third-party loudspeakers.
Proper setup is essential. A subwoofer should extend the main speakers rather than draw attention to itself, so placement, crossover frequency, phase and level should all be adjusted carefully within the listening room.
ATC C1 Sub Mk2 Active Subwoofer
The ATC C1 Sub Mk2 is a compact active subwoofer developed for both two-channel music and multichannel home cinema systems.
It combines a hand-built 314mm bass driver with ATC's own 200W Class A/B MOSFET amplifier and comprehensive adjustment controls.
The C1 Sub Mk2 is an ideal partner for ATC's Entry Series and HTS loudspeakers, but its flexible inputs and controls also allow it to be integrated with suitable speakers from other manufacturers.
Designed for Music and Home Cinema
A well-integrated subwoofer can benefit much more than explosions and film effects. It can reproduce the lowest notes from bass guitar, piano, synthesiser, organ and orchestral percussion that smaller loudspeakers cannot deliver at full scale.
Relieving the main speakers of the deepest bass may also help the complete system sound more composed during demanding passages.
In a home cinema system, the C1 Sub Mk2 can reproduce the dedicated low-frequency effects channel while adding depth and authority to the bass redirected from the main and surround speakers.
Read our
guide to adding a subwoofer to a stereo system
for more information about the benefits and common setup mistakes.
Hand-Built 12-Inch ATC Bass Driver
The C1 Sub Mk2 uses a 12-inch or 314mm bass driver designed and hand built by ATC.
Its substantial motor assembly and ribbon voice coil are engineered to provide high excursion, low distortion and reliable control during demanding low-frequency passages.
ATC's experience in professional monitoring places particular emphasis on accuracy and dynamic range, helping the subwoofer reproduce bass information rather than simply adding indiscriminate weight.
200W Class A/B MOSFET Amplifier
The driver is powered by a fully discrete ATC 200W Class A/B MOSFET amplifier.
The Mk2 amplifier uses ATC's grounded-source circuit design, larger power supplies and improved protection circuitry to maintain control as output demands increase.
A front-panel indicator shows normal operation and warns when the protection system is being activated repeatedly.
Repeated Limiter Activity Means the Level Is Too High
If the overload or limiter indicator operates regularly, reduce the subwoofer level or the signal being sent from the source.
The protection system is intended to prevent harsh clipping, but it should not be treated as a normal part of continuous operation.
Low-Frequency Extension to 25Hz
ATC specifies a low-frequency cut-off of 25Hz at the stated minus 6dB point.
This allows the C1 Sub Mk2 to reproduce frequencies below the useful range of many standmount and compact floorstanding loudspeakers.
The bass heard in the room will also depend on placement, room dimensions, listening position and the crossover settings used throughout the system.
Maximum Output of 103dB
The C1 Sub Mk2 is rated for a maximum sound pressure level of 103dB under ATC's stated conditions.
This makes it suitable for music and cinema applications with ATC's Entry Series, centre-channel and HTS on-wall loudspeakers, as well as other appropriately matched compact speaker systems.
Larger rooms, very high playback levels or systems using substantially larger main speakers may require a more powerful subwoofer or a multiple-subwoofer arrangement.
Stereo RCA Line-Level Inputs
Two RCA line-level inputs allow the subwoofer to connect to a stereo pre-amplifier output, integrated amplifier pre-out or suitable AV receiver.
In a conventional stereo system, both left and right inputs should normally be connected so that bass information from both channels reaches the subwoofer.
When using a mono subwoofer or LFE output from an AV receiver, one RCA input can be used.
High-Level Speaker Inputs
Stereo high-level binding posts allow the C1 Sub Mk2 to receive a signal from the amplifier's loudspeaker outputs or from the input terminals of the main speakers.
This is particularly useful when the stereo amplifier does not provide a dedicated pre-amplifier or subwoofer output.
Correct positive and negative polarity must be maintained throughout the connection.
Use One Input Type at a Time
Connect the subwoofer using either its RCA line-level inputs or its high-level speaker inputs.
Do not connect both input types simultaneously unless ATC has specifically confirmed the proposed arrangement.
Summed Mono Line Output
A summed RCA line-level output combines the incoming left and right signals into a mono feed.
This output can be used to connect another compatible C1 subwoofer, making a dual-subwoofer installation possible without requiring a second set of outputs from the amplifier.
Each subwoofer in the chain requires its own gain, crossover and phase adjustment.
Why Use Two Subwoofers?
Two carefully positioned subwoofers can provide more even bass across a wider listening area than one subwoofer operating from a single room position.
The aim is not simply to make the system louder. Multiple subwoofers can help reduce the influence of individual room peaks and dips when they are positioned and adjusted correctly.
Results remain room dependent, and more equipment requires more detailed setup.
Adjustable Gain
The gain control determines the relative level of the subwoofer compared with the main loudspeakers.
Begin around the middle of the adjustment range and set the crossover frequency before completing the final level adjustment.
A correctly adjusted subwoofer should normally appear to extend the loudspeakers rather than behave like an obvious additional sound source.
Adjustable Low-Pass Frequency
The low-pass control determines the highest frequencies reproduced by the subwoofer.
A sensible starting point is close to, or slightly above, the main loudspeaker's published low-frequency cut-off.
Setting the crossover too high can make the subwoofer easy to locate and create excessive upper bass. Setting it too low can leave a gap between the main speakers and subwoofer.
Polarity and Continuous Phase Adjustment
The polarity switch and continuously variable phase control help align the subwoofer with the main speakers at the listening position.
Phase relationships are affected by the different distances between the listener, subwoofer and main speakers.
Adjust the controls while listening around the crossover region. The best setting normally provides the strongest, most even transition without making the bass sound detached or overblown.
A Practical Setup Sequence
- Connect either the line-level or high-level inputs.
- Begin with the gain around the middle of its range.
- Set the low-pass frequency close to the main speaker's bass cut-off.
- Play familiar music with clear, well-recorded bass.
- Adjust polarity and phase for the smoothest transition.
- Reduce the gain until the subwoofer stops drawing attention to itself.
- Check several recordings and more than one listening position.
- Make small final changes rather than altering several controls at once.
Room Placement
Low frequencies interact strongly with the dimensions and boundaries of the listening room.
Placing the subwoofer close to a wall can increase perceived bass output, while placing it in a corner usually produces a still greater increase.
Boundary reinforcement can be useful, but it may also exaggerate particular frequencies and make the bass sound uneven or slow.
Begin near the front loudspeakers where practical, then experiment with distance from nearby walls while checking performance from the main listening position.
One Position Will Not Work in Every Room
Room dimensions and listening position can create strong peaks and cancellations at low frequencies.
Moving the subwoofer or listening seat by a relatively small distance can sometimes make a greater improvement than changing the controls.
Allow Space for the Amplifier Heatsink
The published depth includes the rear amplifier and heatsink assembly.
Leave sufficient clearance around the rear panel for ventilation, mains and signal cables and access to the controls.
Do not install the subwoofer in a tightly enclosed cabinet or cover the amplifier's ventilation area.
Matching ATC Entry Series Loudspeakers
ATC identifies the C1 Sub Mk2 as an ideal partner for the SCM7, SCM11, SCM19 and SCM40 loudspeakers.
Suitable Audio T options include the
ATC SCM7
,
ATC SCM11
,
ATC SCM19
and
ATC SCM40
.
Read our
introduction to the ATC Entry Series
for an overview of the partnering loudspeakers.
ATC Home Cinema Matching
The C1 Sub Mk2 can form the low-frequency foundation of an ATC home cinema system using matching centre and surround speakers.
The
ATC C1C centre speaker
is a natural partner for systems based around the SCM7 or SCM11.
The larger
ATC C3C centre speaker
is designed to complement systems using the SCM11, SCM19 or SCM40.
ATC also identifies its HTS7, HTS11 and HTS40 on-wall loudspeakers as suitable partnering products.
C1 Sub Mk2 or C4 Sub Mk2?
ATC C1 Sub Mk2
- 12-inch or 314mm ATC driver
- 200W Class A/B amplifier
- 25Hz low-frequency cut-off
- 103dB maximum SPL
- RCA and high-level inputs
- Ideal for ATC Entry Series and HTS systems
- More compact cabinet
ATC C4 Sub Mk2
- Designed for larger and more demanding systems
- Greater output capability and low-frequency scale
- Suitable for larger rooms and higher playback levels
- More substantial cabinet and amplifier platform
- Best considered where the C1 Sub's output is insufficient
View the ATC C4 Sub Mk2
Finish Options
Cherry
A natural real-wood veneer designed to complement matching ATC loudspeakers and traditional furniture.
Black Ash
A darker real-wood veneer with visible grain and an understated appearance.
Satin Black
A discreet painted finish suited to both stereo and home cinema installations.
Satin White
A brighter alternative for light-coloured rooms and matching ATC speaker systems.
Real-wood veneer naturally varies in grain and shade, so individual cabinets may not match product photography exactly.
System Matching
Well Suited To
- Two-channel music systems
- Home cinema and multichannel systems
- ATC SCM7, SCM11, SCM19 and SCM40 speakers
- ATC C1C and C3C centre-channel systems
- ATC HTS on-wall loudspeakers
- Amplifiers with stereo pre-amplifier outputs
- AV receivers with a mono subwoofer output
- Stereo amplifiers requiring a high-level connection
- Single or dual-subwoofer installations
Check Before Buying
- The cabinet weighs 26.2kg
- The published depth includes the rear heatsink
- No balanced XLR input is listed
- Wireless audio and app control are not listed
- Automatic room correction is not listed
- Careful crossover and phase adjustment is required
- Larger rooms may require greater output
- Real-wood veneer naturally varies
Setup Guidance
- Use line-level or high-level inputs, not both
- Start with the gain near the middle
- Match the crossover to the main speakers
- Adjust polarity and phase from the listening seat
- Try more than one room position
- Use familiar music with clear bass information
- Keep the rear amplifier properly ventilated
- Reduce the level if protection activates regularly
Browse our complete range of
Hi-Fi subwoofers
,
home cinema subwoofers
,
stereo speakers
and
home cinema speakers
, or explore the complete
ATC range at Audio T
.
Key Features
- Active subwoofer for music and home cinema
- Hand-built ATC 12-inch or 314mm bass driver
- Massive motor assembly
- Ribbon voice-coil construction
- Fully discrete ATC 200W Class A/B MOSFET amplifier
- Grounded-source amplifier circuit
- Low-frequency cut-off of 25Hz at minus 6dB
- Maximum sound pressure level of 103dB
- Adjustable gain
- Continuously adjustable low-pass frequency
- Polarity switch
- Continuously adjustable phase
- Stereo RCA line-level inputs
- Stereo high-level binding-post inputs
- Summed mono RCA output
- Supports daisy-chained multiple-subwoofer systems
- Improved overload-protection circuitry
- Front-panel operating and limiter indicator
- Ideal partner for ATC Entry Series loudspeakers
- Suitable for ATC centre and HTS on-wall speakers
- Real-wood veneer and satin finish options
- Six-year ATC warranty, subject to current terms
Frequently Asked Questions
Is the ATC C1 Sub Mk2 suitable for music?
Yes. It is designed for accurate low-frequency extension in both two-channel music and home cinema systems.
How large is the bass driver?
It uses a hand-built ATC 12-inch or 314mm bass driver.
How powerful is the amplifier?
The internal discrete Class A/B MOSFET amplifier is rated at 200W.
How deep does the C1 Sub Mk2 play?
ATC specifies a low-frequency cut-off of 25Hz at the minus 6dB point.
Can it connect to an AV receiver?
Yes. A mono subwoofer output from an AV receiver can connect to either of the C1 Sub Mk2's RCA line inputs.
Can it connect to a stereo amplifier without a subwoofer output?
Yes. The high-level binding posts can receive a signal from suitable amplifier or loudspeaker terminals.
Can the high-level and RCA inputs be used together?
ATC advises using only one input type at a time.
Does it have an LFE input?
There is no separately labelled LFE socket. A mono AV receiver output can connect to either RCA line input.
Does it have balanced XLR inputs?
Balanced XLR inputs are not listed. Connections are provided through RCA line-level and high-level binding-post inputs.
Can two C1 subwoofers be connected?
Yes. The summed mono RCA output can feed another compatible subwoofer, with each unit adjusted independently.
Which controls are included?
The C1 Sub Mk2 provides gain, low-pass frequency, polarity and phase adjustment.
Where should the crossover be set?
Begin close to, or slightly above, the main speaker's published low-frequency cut-off and refine the setting by listening.
Where should the subwoofer be positioned?
Begin near the front speakers where practical, then experiment with distance from the walls and corners while listening from the main seating position.
Which ATC speakers suit the C1 Sub Mk2?
ATC identifies the SCM7, SCM11, SCM19, SCM40, C1C, C3C and HTS on-wall ranges as suitable partnering products.
How large and heavy is it?
It measures 450 x 360 x 400mm, including the feet and heatsink, and weighs 26.2kg.
What finishes are listed by ATC?
ATC lists Cherry, Black Ash, Satin Black and Satin White.
What warranty does ATC provide?
ATC lists a six-year warranty, subject to its current registration requirements, terms and conditions.
Why Buy From Audio T?
- Demonstrations with suitable stereo and home cinema systems
- ATC loudspeaker and subwoofer matching advice
- High-level and line-level connection guidance
- Crossover, gain and phase setup assistance
- Single and dual-subwoofer system advice
- AV receiver bass-management configuration
- Room-positioning and integration guidance
- Suitable interconnect and speaker-cable recommendations
- Home demonstrations may be available
- Part exchange available on suitable existing equipment
- Ongoing system and setup support
Contact your local Audio T store
to arrange a demonstration or discuss integrating the ATC C1 Sub Mk2 with your speakers, amplifier and room.