Audio T Verdict
The REL S/850 is the flagship of the standard Serie S range, combining considerable scale and output with the speed and control required for serious music systems.
Its front-firing 305mm CarbonAlloy active driver, matching 305mm down-firing passive radiator and 850W amplifier allow it to deliver powerful, physical bass without losing the precision needed to blend naturally with high-quality loudspeakers.
It is equally comfortable supporting a stereo system or reproducing the dedicated LFE channel in a home cinema. High Level, stereo low-level, RCA LFE and balanced XLR LFE connections make it suitable for a wide range of systems.
The S/850 is not simply intended to make bass louder. Properly positioned and adjusted, it can increase the scale, clarity and spaciousness of the entire system while remaining difficult to identify as a separate sound source.
Airship Direct compatibility, stereo-pair operation and support for full REL line arrays also allow the system to grow considerably over time.
REL S/850 Serie S Subwoofer
The REL S/850 is a high-performance active subwoofer developed for premium music systems, home cinema and installations requiring deep extension with substantial dynamic headroom.
It combines a front-firing 305mm CarbonAlloy active driver with a matching 305mm down-firing passive radiator, 850W RMS Linear Class D amplification and low-frequency extension reaching 19Hz at the stated minus 6dB point.
The S/850 can operate as a single subwoofer, as part of a stereo pair or within a vertically stacked REL Serie S line array using up to three matching units per channel.
The Benchmark of REL Serie S
The S/850 is the model around which the latest generation of REL Serie S was developed.
Its driver materials, amplifier, cabinet proportions, internal construction and line-array hardware informed the design of the other models within the range.
Serie S sits above REL’s compact Serie T/x models and is intended for systems requiring greater scale, output and low-frequency authority while preserving musical speed and integration.
The S/850 is particularly well suited to medium-sized and larger listening rooms, powerful floorstanding speakers and systems expected to handle both music and home cinema.
305mm CarbonAlloy Active Driver
The front-firing active driver uses REL’s 305mm CarbonAlloy cone structure.
A lightweight primary cone is reinforced by a pure carbon-fibre centre cap, increasing rigidity without adding unnecessary moving mass.
The lower moving mass helps the driver react quickly to sudden musical and cinematic information, while the reinforced cone remains controlled during large low-frequency movement.
The driver is mounted within a rigid die-cast alloy chassis that provides a stable mechanical foundation for the cone, suspension, voice coil and motor system.
Pure Carbon-Fibre Centre Cap
The latest S/850 replaces the heavier solid aluminium centre structure used by some earlier REL driver designs with a lightweight pure carbon-fibre cap.
This cap braces the main cone while reducing moving mass, helping the S/850 combine explosive dynamics with the ability to reproduce quieter bass detail and subtle changes in texture.
The benefit is not limited to extremely deep notes. A faster and more controlled bass system can improve the perceived timing, clarity and scale of the entire musical presentation.
305mm Down-Firing Passive Radiator
A matching 305mm passive radiator is positioned beneath the cabinet and works alongside the front-firing active driver.
Its flat Carbon and Carbon cone structure combines carbon fibre, glass fibre and lightweight closed-cell material to provide high stiffness with relatively low moving mass.
REL states that the redesigned passive radiator is approximately 40 per cent stiffer and significantly lighter than the previous generation.
It is engineered to accommodate more than 60mm of movement in each direction, allowing the S/850 to reproduce substantial low-frequency output without relying on an open reflex port.
Front-Firing Active and Down-Firing Passive Design
The combination of a front-firing active driver and down-firing passive radiator allows the S/850 to move a considerable volume of air from a comparatively manageable cabinet.
The active driver provides speed, control and direct output into the room, while the passive radiator supports the deepest frequencies and largest dynamic changes.
The cabinet must remain upright on a firm and stable surface so that the passive radiator has the correct operating clearance beneath it.
Keep the Passive Radiator Clear
Do not place the S/850 on its side, obstruct the space beneath the cabinet or allow loose cables and objects to contact the down-firing passive radiator.
Thick or uneven floor coverings should not prevent the cabinet from standing securely or reduce the intended clearance beneath the subwoofer.
19Hz Low-Frequency Extension
REL specifies low-frequency extension to 19Hz at minus 6dB.
This allows the S/850 to reproduce extremely deep musical information, organ notes, electronic bass and demanding home cinema effects.
The additional extension can also improve the perceived scale, atmosphere and spaciousness of recordings where obvious deep bass is not present.
Room dimensions, placement, floor construction and the listening position will all influence the extension and output achieved in practice.
850W Linear Class D Amplifier
An 850W RMS Linear Class D amplifier powers the CarbonAlloy active driver.
The amplifier combines the efficiency of a Class D output stage with a substantial traditional power supply designed to provide strong current delivery and dynamic headroom.
REL states that the amplifier can deliver approximately 1,000W during demanding peaks while providing 850W of continuous rated output.
This reserve allows the S/850 to reproduce sudden musical transients and film effects without immediately sounding compressed or strained.
Reference-Inspired Input Filtering
The S/850 uses upgraded analogue input filters fitted with premium thin-film capacitors derived from REL’s flagship designs.
REL keeps the principal filtering within the analogue domain, avoiding unnecessary digital conversion within the normal signal path.
Fast analogue filters help preserve the timing, tonal character and dynamic expression required for the subwoofer to blend naturally with the main loudspeakers.
The S/850 does not provide the dual parametric filter system fitted to REL’s No.31 and No.32 Reference models.
Fully Electronic Protection
REL’s electronic Set-Safe system monitors the amplifier during operation.
Additional protection is provided against DC faults and output short circuits.
These systems operate automatically but do not replace correct connection, ventilation and installation practices.
REL High Level Connection
REL’s preferred connection for many conventional stereo systems is the supplied High Level Neutrik Speakon cable.
This receives the same signal and sonic character being delivered by the main amplifier to the loudspeakers.
The main speakers remain connected directly to the amplifier and continue to receive their normal full-range signal. The S/850 is added alongside them and adjusted to support their natural low-frequency roll-off.
A nominal 10-metre Neutrik Speakon High Level cable is supplied with the S/850.
Check High Level Amplifier Compatibility
The correct High Level wiring arrangement depends on the design of the connected amplifier.
Balanced, bridged, differential, Class D and certain specialist amplifier designs may require a different grounding arrangement from a conventional stereo amplifier.
Do not assume that a wiring method used with one amplifier will be suitable for another. Check the amplifier instructions or contact Audio T before connecting the High Level cable whenever there is uncertainty.
Stereo Low-Level RCA Inputs
Two RCA inputs allow the S/850 to receive a stereo low-level signal from a suitable pre-amplifier, integrated amplifier, processor or active loudspeaker system.
The source must provide variable outputs that follow the main system volume.
Low-level connection can be particularly useful with active loudspeakers and equipment that does not permit a suitable High Level connection.
Dedicated RCA LFE Input
A dedicated RCA LFE input connects to the subwoofer output of a compatible AV receiver or surround processor.
This carries the separate low-frequency effects channel used by film, television, concert and multichannel game soundtracks.
Bass management, loudspeaker crossover points, delay and channel level can normally be configured from the connected home cinema processor.
Balanced XLR LFE Input
A balanced XLR LFE input is provided for compatible surround processors and professionally planned installations.
Balanced connection can be useful where the processor is positioned a considerable distance from the S/850 or where the cable route passes close to other electrical equipment.
The connected processor must provide a suitable variable balanced subwoofer output.
Simultaneous Music and Cinema Connection
The S/850 can use its High Level or stereo low-level connection for music while also remaining connected to the dedicated LFE output of a home cinema processor.
The High Level and .1/LFE signal paths provide separate gain adjustment, allowing the subwoofer to integrate naturally with the main loudspeakers during music while reproducing the dedicated effects channel during films.
This arrangement is particularly useful where the same main loudspeakers and power amplifier are shared between stereo and home cinema systems.
Signal Output Connections
The S/850 provides High Level Speakon, low-level RCA and LFE output connections.
These can be used to pass the appropriate signal to another compatible REL when building a stereo pair, multiple-subwoofer system or Serie S line array.
Every connected S/850 remains independently powered and retains its own gain, crossover and phase controls.
Airship Direct Wireless Compatibility
The S/850 is compatible with REL’s optional Airship Direct wireless system.
Airship Direct can transmit High Level and .1/LFE signals simultaneously, preserving the S/850’s separate music and home cinema operating modes.
Its receiver module connects directly to a dedicated socket on the S/850 amplifier panel, removing the separate receiver enclosure, RCA interconnects and receiver power adaptor required by earlier Airship systems.
The Airship Direct transmitter remains connected to the amplifier or processor and requires its supplied power adaptor.
Use Airship Direct with the New Serie S
The S/850 is designed for REL Airship Direct rather than the older Airship II receiver arrangement.
Airship Direct is an optional accessory and is not included with the subwoofer. Please check current UK availability with your local Audio T store.
Bassline Blue High Level Cable
A standard 10-metre High Level cable is supplied with the S/850.
The optional
REL Bassline Blue High Level cable
provides an upgraded connection for compatible amplifiers and REL subwoofers.
Bassline Blue is available in different versions and lengths, including configurations developed for compatible Naim amplifiers.
Confirm the correct cable version and amplifier wiring arrangement before ordering.
Positioning the REL S/850
Begin with the S/850 positioned along the same wall as the main loudspeakers.
A corner position can increase output and low-frequency extension, while moving the cabinet away from the corner may reduce excessive room-related bass.
Avoid enclosing the subwoofer tightly within furniture or positioning it where the front driver, passive radiator, controls or ventilation can be obstructed.
Final placement should be determined by listening or room measurement rather than appearance alone.
Plan the Installation
The S/850 measures approximately 488mm wide, 410mm high and 540mm deep and weighs approximately 42.5kg.
Allow additional space behind the cabinet for plugs, cable bends and access to the amplifier panel.
Suitable lifting assistance should be used when unpacking, moving or repositioning the subwoofer.
Initial Stereo Setup
- Place the S/850 along the same wall as the main loudspeakers.
- Switch off the complete system before making any connections.
- Connect the supplied High Level cable or suitable stereo low-level interconnect.
- Begin with conservative crossover and gain settings.
- Select the phase setting that produces the strongest and most coherent bass at the listening position.
- Adjust the crossover so the S/850 supports the natural roll-off of the main loudspeakers.
- Increase the gain until the additional bass is clearly audible.
- Reduce the gain slightly until the subwoofer no longer draws attention to itself.
- Complete the setup using familiar music from the normal listening position.
Initial Home Cinema Setup
- Connect the AV receiver or processor’s subwoofer output to the RCA or balanced XLR LFE input.
- Set the S/850’s dedicated .1/LFE gain conservatively.
- Configure suitable loudspeaker crossover points within the processor.
- Run the processor’s measurement and room-correction procedure where provided.
- Review the measured subwoofer level, distance and crossover settings.
- Check that bass effects do not overpower dialogue or the main loudspeakers.
- Complete the setup using familiar film, concert and music material.
Single S/850, Stereo Pair or Line Array?
Single S/850
- Substantial extension and output from one cabinet
- Simplest positioning and connection arrangement
- Well suited to medium-sized and larger rooms
- Supports both music and home cinema systems
- Provides a foundation for future expansion
Stereo Pair
- One S/850 supports each main loudspeaker
- Can improve left-to-right low-frequency balance
- Provides greater combined dynamic headroom
- May improve bass consistency within the room
- Each subwoofer requires individual adjustment
Serie S Line Array
- Uses up to three matching S/850 units per channel
- Can be developed gradually from a stereo pair
- Increases vertical scale and effortless output
- Every subwoofer retains individual adjustment
- Requires substantial space and careful planning
REL Serie S Line Arrays
The S/850 is designed to support vertically stacked Serie S line-array installations.
A system can begin with a stereo pair, expand to two units per channel and ultimately use three matching S/850 subwoofers on each side.
The aim is not simply to produce more bass. A correctly designed line array can increase the height, scale and physical presence of the reproduced soundstage while providing greater dynamic ease.
Each subwoofer retains its own gain and crossover adjustment, allowing individual units to be configured according to their position within the stack.
Line-Array Levelling Adjustment
A precision-milled knurled aluminium adjustment control is integrated into the front rail structure.
This allows the lower cabinet in a line array to be levelled on uneven floors, thick carpet or padded flooring before additional S/850 units are stacked above it.
The adjustment is intended specifically to provide a safer and more stable foundation for an approved REL line array.
Supplied Line-Array Mounting Hardware
REL includes line-array mounting hardware with the S/850.
The supplied hardware is intended to secure matching Serie S cabinets when installed in an approved vertical arrangement.
The combined height and weight of a complete stack mean that installation should be planned carefully and completed in accordance with REL’s instructions.
Do not improvise alternative brackets, fixings or supports.
Bassline Blue Line Array Connectors
The
REL Bassline Blue Line Array Connectors
can pass the High Level signal between compatible REL subwoofers within a vertical stack.
This allows one main High Level cable to run from the amplifier to the lower subwoofer, with shorter connectors carrying the signal to the units above.
The number of connectors and mounting components required should be confirmed as part of the complete line-array design.
REL S/550, S/850 or Carbon Special Black Label?
REL S/550
- 250mm CarbonAlloy active driver
- 305mm down-firing passive radiator
- 550W RMS Linear Class D amplifier
- 19Hz extension at minus 6dB
- Approximately 445 x 372 x 500mm
- Approximately 31kg net weight
- More manageable Serie S cabinet
View the REL S/550
REL S/850
- 305mm CarbonAlloy active driver
- 305mm down-firing passive radiator
- 850W RMS Linear Class D amplifier
- 19Hz extension at minus 6dB
- Approximately 488 x 410 x 540mm
- Approximately 42.5kg net weight
- Flagship standard Serie S model
Carbon Special Black Label
- Advanced carbon-fibre active-driver construction
- 305mm down-firing passive radiator
- Higher-output Linear Class D amplification
- Larger and deeper cabinet
- Greater dynamic authority and refinement
- Airship Direct and line-array compatibility
- Positioned above the S/850
View the REL Carbon Special Black Label
All three models provide High Level, low-level and LFE connectivity, Airship Direct compatibility and support for stereo-pair operation.
The choice should be based on the room, main loudspeakers, desired scale and available floor space rather than low-frequency extension alone.
Wider, Lower and Deeper Cabinet
The S/850 cabinet uses wider, lower and deeper proportions than the previous generation.
The additional internal volume gives the active driver and passive radiator greater operating freedom while allowing the amplifier to work more efficiently.
Clean cabinet creases catch the light without adding unnecessary decoration, helping the large subwoofer appear more integrated within a contemporary room.
Recessed Stainless-Steel Handles
Stainless-steel handles are recessed into elliptical sections of the cabinet to provide secure gripping points when the S/850 must be moved.
Thick internal aluminium sections reinforce the handle mountings and contribute to the cabinet structure used for approved line arrays.
The approximately 42.5kg weight means suitable care and lifting assistance should still be used when unpacking or repositioning the subwoofer.
Piano Black and Gloss White Finishes
The S/850 is available in Piano Black Lacquer or Gloss White Lacquer.
REL applies eight coats of lacquer to create a deep gloss surface intended to complement contemporary loudspeakers, furniture and system components.
Warm silver-gold detailing provides a subtle contrast against both cabinet finishes.
Use a clean, soft microfibre cloth for routine care and avoid abrasive household cleaners that could mark the lacquer.
Cloth Grille and Optional Premium Wood Grille
A matching cloth grille is supplied as standard.
An optional sculpted Premium Wood Grille can be added for customers who prefer a warmer and more individual appearance.
The wood grille uses natural material, so grain pattern and colour will vary between individual examples.
The Premium Wood Grille is not included with the standard S/850. Please check current UK availability and cabinet-finish compatibility with your local Audio T store.
System Matching
Well Suited To
- High-performance stereo systems
- Medium-sized and larger listening rooms
- Premium floorstanding loudspeakers
- Active speakers with suitable variable outputs
- High-performance AV receivers and processors
- Combined stereo and home cinema systems
- Single and stereo-pair installations
- REL Serie S line arrays
- Airship Direct wireless systems
Check Before Installation
- Allow clearance beneath the passive radiator
- The cabinet weighs approximately 42.5kg
- Allow additional space behind the stated depth
- Confirm the correct High Level amplifier wiring
- RCA and XLR interconnects are not supplied
- Airship Direct is an optional accessory
- The Premium Wood Grille is optional
- Do not obstruct the front driver or amplifier panel
- Line arrays require significant vertical space
- Suitable lifting assistance will be required
Setup Guidance
- Begin along the same wall as the main speakers
- Establish phase before final crossover adjustment
- Keep the initial gain setting conservative
- Blend the S/850 rather than making it obvious
- Use the dedicated LFE connection for home cinema
- Review automated room-correction results
- Adjust from the normal listening position
- Test with familiar music and film material
- Recheck setup after the system has been used
Browse our
home cinema subwoofers
,
home cinema amplifiers
,
home cinema speakers
,
wireless accessories
and
subwoofer and system cables
, or explore the
REL range at Audio T
.
Key Features
- Flagship standard REL Serie S active subwoofer
- Front-firing active driver and down-firing passive radiator
- 305mm long-throw CarbonAlloy active driver
- Pure carbon-fibre centre cap
- Die-cast alloy active-driver chassis
- 305mm Carbon and Carbon flat-cone passive radiator
- Steel passive-radiator chassis
- More than 60mm passive-radiator travel in each direction
- 19Hz low-frequency extension at minus 6dB
- 850W RMS Linear Class D amplifier
- Approximately 1,000W available during demanding peaks
- Reference-inspired thin-film input-filter components
- Fully analogue REL input filtering
- High Level Neutrik Speakon input
- Two stereo low-level RCA inputs
- Dedicated RCA LFE input
- Balanced XLR LFE input
- High Level Speakon signal output
- Low-level RCA signal output
- RCA and balanced XLR LFE output options
- Simultaneous High Level and LFE operation
- Compatible with REL Airship Direct
- Suitable for single and stereo-pair systems
- Supports Serie S line arrays with up to three units per channel
- Integrated line-array levelling adjustment
- Line-array mounting hardware supplied
- Wider, lower and deeper cabinet design
- Recessed stainless-steel handles
- Piano Black or Gloss White finish
- Eight-coat lacquer finish
- Matching cloth grille supplied
- Optional Premium Wood Grille
- Fully electronic Set-Safe protection
- DC fault and output-short protection
- Three-year REL warranty, subject to current terms
Frequently Asked Questions
Is the REL S/850 intended mainly for music or home cinema?
It is designed for both. High Level and stereo low-level inputs support music systems, while RCA and balanced XLR LFE inputs provide dedicated home cinema connection.
What is the difference between the S/550 and S/850?
The S/550 uses a 250mm active driver and 550W amplifier within a 31kg cabinet. The S/850 uses a larger 305mm active driver, 850W amplifier and 42.5kg cabinet for greater scale and output.
Does the S/850 include a High Level cable?
Yes. A Neutrik Speakon High Level cable measuring approximately 10 metres is supplied.
Can the S/850 connect to active loudspeakers?
Yes, provided the active system offers suitable variable low-level outputs. The left and right RCA low-level inputs can then be used.
Can High Level and LFE connections be used together?
Yes. This allows the S/850 to support the main loudspeakers during music while also reproducing the dedicated .1 channel from a home cinema processor.
Can the S/850 connect using balanced XLR?
Yes. It provides a balanced XLR LFE input for a compatible AV receiver or surround processor.
Can the S/850 operate wirelessly?
Yes. It is compatible with the optional REL Airship Direct system, which can transmit High Level and LFE signals simultaneously.
Is Airship Direct included?
No. Airship Direct is an optional wireless accessory and should be purchased separately.
Can the older Airship II be connected directly?
The S/850 is designed around the new Airship Direct receiver module. Check with Audio T before attempting to use an earlier wireless system.
Does the S/850 have parametric room adjustment?
No. The dual parametric filters fitted to REL’s Reference models are not provided on the S/850.
Can two S/850 subwoofers be used as a stereo pair?
Yes. One S/850 can be positioned beside each main loudspeaker, with every subwoofer independently adjusted for its channel and room position.
Can S/850 subwoofers be vertically stacked?
Yes. The S/850 supports approved Serie S line arrays using up to three matching units per channel with the correct REL mounting hardware.
Is the line-array mounting hardware included?
Yes. REL lists line-array mounting hardware among the supplied S/850 accessories. Additional signal connectors may be required for a complete installation.
Is the Premium Wood Grille included?
No. A matching cloth grille is included, while the sculpted Premium Wood Grille is an optional accessory.
How large and heavy is the S/850?
It measures approximately 488 x 410 x 540mm and weighs 42.5kg. Additional room should be allowed behind and beneath the cabinet for connections and the passive radiator.
Why Buy From Audio T?
- REL subwoofer and loudspeaker-matching advice
- Comparison with the S/550 and Carbon Special Black Label
- High Level amplifier-compatibility guidance
- Low-level, RCA LFE and balanced XLR connection advice
- Combined stereo and home cinema system planning
- Single and stereo-pair setup assistance
- REL Serie S line-array planning
- Room-positioning and phase-setting guidance
- Crossover and gain setup support
- Airship Direct wireless compatibility advice
- Bassline Blue cable recommendations
- Premium Wood Grille availability guidance
- Delivery and installation planning
- Ongoing system and after-sales support
Contact your local Audio T store
to discuss demonstrating, positioning and integrating the REL S/850 within your music or home cinema system.