Audio T Verdict
The REL S/550 brings the speed, build quality and flexible connectivity of REL’s Serie S range into a cabinet that is easier to accommodate than the larger S/850.
Its front-firing 250mm CarbonAlloy active driver, down-firing 305mm passive radiator and 550W amplifier produce deep, controlled bass that can support serious stereo systems as convincingly as home cinema.
The S/550 is not designed simply to add boom or make bass effects louder. Properly positioned and adjusted, it can increase the scale, openness and physical presence of the complete system while remaining difficult to identify as a separate sound source.
High Level, stereo low-level and dedicated LFE connections make it highly flexible, while Airship Direct compatibility, stereo-pair operation and REL line-array capability allow the system to be expanded over time.
REL S/550 Serie S Subwoofer
The REL S/550 is a high-performance active subwoofer developed for music systems, home cinema and installations requiring deep extension without the physical size of REL’s larger Serie S models.
It combines a front-firing 250mm CarbonAlloy active driver with a larger 305mm down-firing passive radiator, 550W RMS amplification and low-frequency extension reaching 19Hz at the stated minus 6dB point.
The S/550 can operate as a single subwoofer, as part of a stereo pair or within an advanced REL line-array installation using up to three matching units per channel.
A New Generation of REL Serie S
The S/550 forms part of REL’s redesigned Serie S range and replaces the previous S/510.
Its cabinet is wider, lower and deeper, providing additional internal volume while creating a less vertically imposing shape within the listening room.
Revised drivers, increased amplifier output, updated internal bracing and the new Airship Direct connection distinguish the S/550 from the previous generation.
Serie S sits above REL’s compact Serie T/x models and is designed for systems requiring greater scale, dynamic range and low-frequency control.
250mm CarbonAlloy Active Driver
The front-firing active driver uses REL’s 250mm CarbonAlloy cone construction.
A lightweight primary cone is reinforced by a pure carbon-fibre centre cap, increasing rigidity while helping to keep moving mass under control.
The revised suspension permits greater controlled movement than the previous-generation driver, allowing the S/550 to reproduce demanding bass information without immediately sounding strained.
The driver is mounted within a rigid die-cast alloy chassis that provides a stable mechanical foundation for the cone, suspension and motor assembly.
305mm Down-Firing Passive Radiator
A 305mm passive radiator is positioned beneath the cabinet and works alongside the front-firing active driver.
Its flat Carbon and Carbon cone structure uses carbon fibre, glass fibre and lightweight closed-cell material to combine stiffness with low moving mass.
REL states that the redesigned passive radiator is considerably stiffer and lighter than the previous version, allowing it to respond more quickly while handling greater movement.
The passive radiator extends the S/550’s low-frequency output without requiring a conventional open reflex port.
Front-Firing Active and Down-Firing Passive Design
The combination of front-firing active driver and down-firing passive radiator allows the S/550 to move a substantial volume of air from a relatively manageable cabinet.
The active driver provides speed, control and direct output into the room, while the passive radiator supports the deepest frequencies and larger dynamic changes.
The cabinet must stand 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/550 on its side, obstruct the space beneath the cabinet or allow loose cables and objects to contact the down-firing passive radiator.
A thick or uneven floor covering 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/550 to reproduce extremely deep musical information and home cinema effects while adding weight and scale to the complete system.
Room dimensions, placement, floor construction and the listening position will all influence the extension and output achieved in practice.
Correct setup should allow the S/550 to extend the main speakers naturally rather than making every recording sound artificially bass-heavy.
550W Class D Amplifier
A 550W RMS Class D amplifier powers the CarbonAlloy active driver.
The amplifier is designed to provide the speed, current delivery and dynamic headroom required for sudden musical transients and demanding cinema effects.
REL states that the amplifier can deliver sustained output beyond its formal rating under controlled test conditions, rather than relying solely on a brief peak-power figure.
Premium polypropylene components are used within the input filtering, following principles developed for REL’s Reference models.
Analogue PerfectFilter Technology
The S/550 uses REL’s second-generation PerfectFilter circuitry to shape and extend its useful low-frequency response.
REL keeps the input filtering within the analogue domain, avoiding unnecessary conversion or digital signal processing within the normal signal path.
Fast analogue filtering helps preserve the timing and tonal character needed for the S/550 to blend with the main loudspeakers.
The S/550 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/550 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/550.
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/550 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/550 or 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/550 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/550 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/550 remains independently powered and retains its own gain, crossover and phase controls.
Airship Direct Wireless Compatibility
The S/550 is compatible with REL’s optional Airship Direct wireless system.
Airship Direct can transmit High Level and .1/LFE signals simultaneously, preserving the S/550’s separate music and home cinema operating modes.
The receiver module connects directly to a dedicated socket on the S/550 amplifier panel, removing the separate receiver box, RCA leads and receiver power adaptor required by earlier Airship systems.
The transmitter remains connected to the amplifier or processor and requires its supplied power adaptor.
Use Airship Direct with the New Serie S
The S/550 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/550.
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/550
Begin with the S/550 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 an excessive room-related bass peak.
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.
Initial Stereo Setup
- Place the S/550 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/550 supports the natural roll-off of the main loudspeakers.
- Increase the gain until the added 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/550’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/550, Stereo Pair or Line Array?
Single S/550
- Deep extension and strong output from one cabinet
- Simplest positioning and connection arrangement
- Suitable for many medium-sized rooms
- Supports both music and home cinema systems
- Provides a foundation for future expansion
Stereo Pair
- One S/550 can support 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/550 units per channel
- Can be developed gradually from a stereo pair
- Increases vertical scale and dynamic authority
- Every subwoofer retains individual adjustment
- Requires significant space and careful planning
REL Serie S Line Arrays
The S/550 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/550 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 effortless output.
Each subwoofer retains its own gain and crossover adjustment, allowing the individual units to be configured for their positions within the stack.
Line Array Levelling Adjustment
A precision-milled adjustment control is integrated into the front rail structure for use when the S/550 forms the base of a line array.
This allows the lower cabinet to be levelled on an uneven floor, thick carpet or padded floor covering before additional subwoofers 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/550.
The 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 or S/850?
REL S/550
- 250mm CarbonAlloy active driver
- 305mm down-firing passive radiator
- 550W RMS Class D amplifier
- 19Hz extension at minus 6dB
- Approximately 445 x 372 x 500mm
- Approximately 31kg net weight
- Suited to many medium-sized rooms
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
- Greater scale and output for larger systems
View the REL S/850
Both models provide High Level, low-level and LFE connectivity, Airship Direct compatibility, stereo-pair operation and Serie S line-array capability.
The choice should be based on room size, main loudspeakers, required output and available floor space rather than low-frequency extension alone.
Wider and Lower Cabinet Design
The S/550 cabinet uses lower, wider and deeper proportions than the previous S/510.
The additional internal volume gives the active driver and passive radiator greater operating freedom while allowing the amplifier to work more efficiently.
Updated internal bracing helps control cabinet resonance while the lower profile reduces the impression of a tall, conventional subwoofer box.
Integrated Handles and Front Rails
Recessed handles are incorporated into elliptical sections of the cabinet to provide more secure gripping points when the S/550 must be moved.
The front rails form part of the visual design and also support the levelling arrangement used when the S/550 sits at the bottom of a line array.
The approximately 31kg 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/550 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.
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 is produced from natural material, so grain pattern and colour will vary between individual examples.
The Premium Wood Grille is not included with the standard S/550. Please check current UK availability and finish compatibility with your local Audio T store.
System Matching
Well Suited To
- High-performance stereo systems
- Medium-sized listening rooms
- Standmount and floorstanding loudspeakers
- Active speakers with suitable variable outputs
- Premium AV receivers and surround 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 31kg
- 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 vertical space and careful planning
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/550 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
- High-performance REL Serie S active subwoofer
- Front-firing active driver and down-firing passive radiator
- 250mm 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
- 19Hz low-frequency extension at minus 6dB
- 550W RMS Class D amplifier
- Second-generation REL PerfectFilter circuitry
- Fully analogue 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 cabinet 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/550 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/550 include a High Level cable?
Yes. A Neutrik Speakon High Level cable measuring approximately 10 metres is supplied.
Can the S/550 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/550 to support the main loudspeakers during music while also reproducing the dedicated .1 channel from a home cinema processor.
Can the S/550 connect using balanced XLR?
Yes. It provides a balanced XLR LFE input for a compatible AV receiver or surround processor.
Can the S/550 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/550 is designed around the new Airship Direct receiver module. Check with Audio T before attempting to use an earlier wireless system.
Does the S/550 have parametric room adjustment?
No. The dual parametric filters found on REL’s Reference models are not provided on the S/550.
Can two S/550 subwoofers be used as a stereo pair?
Yes. One S/550 can be positioned beside each main loudspeaker, with every subwoofer independently adjusted for its channel and room position.
Can S/550 subwoofers be vertically stacked?
Yes. The S/550 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?
REL lists line-array mounting hardware among the supplied S/550 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/550?
It measures approximately 445 x 372 x 500mm and weighs 31kg. 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 larger REL S/850
- 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
- Ongoing system and after-sales support
Contact your local Audio T store
to discuss demonstrating, positioning and integrating the REL S/550 within your music or home cinema system.