Audio T Verdict
The REL Carbon Special brings technology inspired by the company’s Reference subwoofers into a more manageable Serie S cabinet.
Its lightweight 300mm carbon-fibre active driver combines speed and fine pitch definition with the excursion required for substantial musical peaks and powerful film effects. A matching down-firing passive radiator extends the lowest frequencies without using a conventional reflex port.
The NextGen5 Class D amplifier provides 800W RMS of continuous output, while REL’s High Level connection allows the subwoofer to follow the tonal and timing characteristics of the main amplifier and loudspeakers.
Careful placement and tuning are essential. Properly integrated, the Carbon Special should add authority, space and low-frequency extension without drawing attention to itself as a separate source.
REL Carbon Special Subwoofer
The REL Carbon Special is a high-performance active subwoofer designed for ambitious two-channel music and home cinema systems.
A front-firing 300mm carbon-fibre active driver works with a matching 300mm down-firing passive radiator, powered by REL’s NextGen5 Class D amplifier.
The Carbon Special can operate individually, as part of a stereo pair or within a compatible three-high REL line array.
300mm Carbon-Fibre Active Driver
The front-firing long-throw driver uses a carbon-fibre cone with an inverted carbon-fibre centre cap.
Carbon fibre combines low moving mass with excellent rigidity. This allows the driver to respond rapidly to changes in the signal while resisting unwanted flex as output and excursion increase.
The driver is designed to reproduce fine changes in bass pitch and texture alongside the large dynamic contrasts found in orchestral music, rock, electronic recordings and film soundtracks.
Down-Firing Carbon Passive Radiator
A matching 300mm Carbon/Carbon passive radiator is mounted beneath the cabinet.
The flat-cone radiator supports the active driver through the deepest frequencies without introducing the airflow noise associated with a conventional open reflex port.
Its interaction with the floor also helps distribute low-frequency energy throughout the listening room.
The space beneath the cabinet must remain unobstructed so the passive radiator can operate freely.
19Hz Low-Frequency Extension
REL specifies in-room low-frequency extension to 19Hz at the stated minus 6dB point.
This allows the Carbon Special to reproduce deep musical fundamentals, recording-space ambience and low-frequency film effects that are felt physically as well as heard.
Extension alone does not determine successful integration. Room position, phase, crossover frequency and gain must all be considered alongside the behaviour of the main loudspeakers.
800W RMS NextGen5 Amplification
The Carbon Special uses REL’s NextGen5 Class D amplifier, rated at 800W RMS continuous output.
The amplifier is designed to provide the current delivery and control required by the long-throw active driver while maintaining efficiency and substantial dynamic headroom.
Electronic Set-Safe, DC fault and output-short protection help safeguard the amplifier and drive system during abnormal operating conditions.
CS PerfectFilter
REL’s CS PerfectFilter is designed to extend and control the lowest frequencies while preserving the speed and transparency of the complete system.
The filter operates within REL’s analogue signal path, avoiding the need to route the incoming High Level music signal through digital processing.
Its purpose is not simply to increase bass output, but to help the subwoofer improve scale, imaging and perceived clarity throughout the listening range.
REL High Level Connection
For most conventional two-channel systems, REL recommends connecting the Carbon Special to the main amplifier’s loudspeaker outputs through the Neutrik Speakon High Level input.
This allows the subwoofer to receive the same signal being sent to the main speakers, including the tonal and timing characteristics of the amplifier’s output stage.
The High Level input has a very high impedance and senses the signal without drawing meaningful power away from the loudspeakers.
A nominal ten-metre Neutrik Speakon cable is supplied. The
REL Bassline Blue High Level cable
provides a dedicated development option for compatible systems.
Confirm the Correct High Level Wiring
High Level wiring can differ between conventional Class A/B amplifiers, balanced designs, Class D amplifiers and monoblock systems.
Identify the amplifier’s output topology and follow the appropriate REL connection guidance before attaching the cable.
Stereo Low-Level RCA Inputs
Left and right RCA low-level inputs allow connection to a suitable pre-amplifier output, integrated-amplifier output or active loudspeaker system.
This provides an alternative where High Level connection is unavailable or unsuitable for the system architecture.
The low-level connection uses the same variable crossover and main level controls as the High Level input.
RCA and Balanced XLR LFE Inputs
Dedicated RCA and balanced XLR LFE inputs accommodate the subwoofer output from a compatible home cinema receiver or surround processor.
The LFE connection reproduces the dedicated low-frequency effects channel contained within film and multichannel soundtracks.
Balanced XLR can be particularly useful where a longer cable run is required between the processor and subwoofer.
Music and Home Cinema Together
The High Level connection and dedicated LFE input can operate simultaneously.
This allows the Carbon Special to integrate with the main loudspeakers during two-channel listening while also reproducing the dedicated effects channel during home cinema playback.
The High Level and LFE signal levels can be adjusted independently through the Carbon Special and connected surround processor.
Link Outputs for Additional REL Subwoofers
High Level, RCA LFE and balanced XLR LFE outputs allow the relevant signals to be passed to another compatible REL.
These connections support stereo-pair and line-array systems without requiring every subwoofer cable to return directly to the main equipment rack.
Each subwoofer retains its own amplifier and adjustment controls and should be tuned for its individual position within the room.
Airship II Wireless Compatibility
The Carbon Special is compatible with the optional
REL Airship II wireless system
.
Airship II can carry High Level and LFE signals together, allowing the Carbon Special to support music and home cinema without a long signal cable crossing the room.
Airship II should not be confused with the newer Airship Direct system used by the Carbon Special Black Label.
Room Positioning
Subwoofer position has a major influence on extension, output and integration.
Begin near a suitable corner behind the main loudspeakers, then move the Carbon Special gradually to find a position that provides strong and even bass without overexciting one room resonance.
The down-firing passive radiator and cabinet feet must remain unobstructed, and access should be retained to the rear connections and controls.
The final position should support the main loudspeakers without making the physical location of the subwoofer obvious.
Phase, Crossover and Gain Setup
Begin with conservative gain and crossover settings and establish the preferred 0 or 180-degree phase position.
The crossover is continuously adjustable between 20Hz and 120Hz. It should normally be set low enough to extend the main loudspeakers without thickening voices or upper bass.
Increase gain gradually until the system gains weight, scale and depth without allowing the Carbon Special to dominate.
When integration is correct, switching the REL off should make the system sound smaller and less complete rather than simply removing an obvious layer of bass.
Single Subwoofer, Stereo Pair or Line Array?
Single Carbon Special
- Supports both stereo channels from one cabinet
- Suitable for substantial music and cinema systems
- Requires one room position and mains connection
- Simplest installation and tuning arrangement
Stereo Pair
- One matching REL supports each loudspeaker channel
- Can improve clarity, width and room consistency
- Provides additional dynamic headroom
- Each subwoofer should be positioned and tuned separately
Three-High Line Array
- Up to three matching Carbon Specials per side
- Greater radiating area and vertical scale
- Requires correct couplers and safety restraints
- Uses High Level jumpers between stacked cabinets
View REL Bassline Blue Line Array Connectors
Plan Line Arrays Carefully
A stacked installation requires matching compatible subwoofers, the correct REL couplers, secure levelling and appropriate wall restraints.
Each cabinet weighs 38.7kg, so floor stability, access and safe lifting must be considered before installation.
Carbon Special or Carbon Special Black Label?
REL Carbon Special
- 300mm carbon-fibre active driver
- 300mm Carbon/Carbon passive radiator
- 800W RMS NextGen5 Class D amplifier
- Compatible with REL Airship II
- 430 x 455 x 539mm cabinet
- 38.7kg net weight
Carbon Special Black Label
- Re-engineered all-carbon-fibre active driver
- Revised passive radiator and suspension
- 900W Linear Class D amplifier
- Compatible with Airship Direct
- Wider and lower cabinet design
- Premium wood grille included
View the REL Carbon Special Black Label
Carbon Special or REL No.31?
REL Carbon Special
- Serie S medium-chassis design
- Active driver with passive radiator
- 19Hz low-frequency extension
- 800W RMS amplification
- Suitable for single, stereo and line-array systems
REL No.31
- Reference Series closed-box design
- Single pure carbon-fibre active driver
- 17Hz low-frequency extension
- 900W NextGen7 amplification
- Advanced Reference filtering and adjustment
View the REL No.31
Piano Black Cabinet
The cabinet is finished in eight coats of Gloss Piano Black lacquer, with polished metal handles and carbon-fibre detailing.
Use a soft microfibre cloth and a suitable non-abrasive polish intended for high-gloss finishes.
Avoid household sprays, abrasive cleaners and rough cloths that may mark the lacquer.
System Matching
Well Suited To
- High-performance two-channel music systems
- Medium-sized and larger listening rooms
- Large standmount and floorstanding loudspeakers
- High-output home cinema installations
- Single, stereo-pair and line-array systems
- Combined High Level and LFE operation
- Airship II wireless installations
Check Before Installation
- The cabinet weighs 38.7kg
- Do not obstruct the down-firing radiator
- Allow additional depth for the High Level connector
- High Level wiring depends on amplifier design
- Airship II is an optional separate system
- Line arrays require matching Carbon Specials
- Access to the rear controls should be retained
Setup Guidance
- Confirm amplifier compatibility before wiring
- Begin near a suitable room corner
- Establish phase before final adjustment
- Set crossover and gain conservatively
- Tune High Level and LFE operation separately
- Use appropriate assistance when moving the cabinet
- Follow REL instructions for stacked installations
Browse our
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,
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Key Features
- High-performance REL Serie S active subwoofer
- 300mm front-firing carbon-fibre active driver
- Inverted carbon-fibre centre cap
- 300mm down-firing Carbon/Carbon passive radiator
- 19Hz in-room low-frequency extension at minus 6dB
- 800W RMS NextGen5 Class D amplifier
- REL CS PerfectFilter technology
- Neutrik Speakon High Level input
- Stereo RCA low-level inputs
- RCA and balanced XLR LFE inputs
- High Level, RCA LFE and XLR LFE link outputs
- High Level and LFE inputs can operate together
- Variable 20Hz to 120Hz crossover
- 0 or 180-degree phase adjustment
- Compatible with REL Airship II
- Suitable for single, stereo-pair and line-array systems
- Electronic Set-Safe, DC fault and output-short protection
- Eight-coat Gloss Piano Black lacquer finish
- Nominal ten-metre High Level Speakon cable included
- Three-year REL warranty, subject to current terms
Frequently Asked Questions
Is the REL Carbon Special supplied individually?
Yes. One unit is a complete active subwoofer. A second matching Carbon Special can be added for stereo operation.
How powerful is its amplifier?
REL’s formal specification rates the NextGen5 Class D amplifier at 800W RMS continuous output.
Can it be used for music and home cinema?
Yes. The High Level connection can support stereo listening while the separate RCA or XLR LFE input handles the dedicated cinema effects channel.
Is a High Level cable included?
Yes. A nominal ten-metre Neutrik Speakon High Level cable is included.
Can it connect wirelessly?
Yes. It is compatible with the optional REL Airship II transmitter and receiver system.
Can Carbon Special subwoofers be stacked?
Yes. Up to three matching Carbon Specials can form each side of a compatible REL line array using the correct couplers, signal cables and safety restraints.
What is the difference from Carbon Special Black Label?
The Black Label has redesigned drivers, revised amplification, a wider and lower cabinet and Airship Direct compatibility. This original Carbon Special uses NextGen5 amplification and Airship II.
How large and heavy is it?
It measures approximately 430 x 455 x 539mm and weighs 38.7kg. Allow an additional 44.5mm of depth when the High Level connector is fitted.
Why Buy From Audio T?
- REL and loudspeaker system-matching advice
- High Level wiring guidance for different amplifiers
- Stereo and home cinema demonstrations
- Room-positioning and phase-setting assistance
- Gain and crossover tuning support
- Single, stereo-pair and line-array planning
- LFE, low-level and balanced XLR cable advice
- Airship II wireless integration guidance
- Access and safe installation planning
- Ongoing subwoofer and system-development support
Contact your local Audio T store
to discuss positioning, connecting and tuning the REL Carbon Special within your stereo or home cinema system.