REL 212/SX Serie S Subwoofer

The REL 212/SX is an active subwoofer designed for demanding two-channel music and home cinema systems.

Its tall cabinet contains two front-firing 300mm active drivers, one rear-firing 300mm passive radiator and one down-firing 300mm passive radiator.

This four-driver arrangement moves a substantial volume of air while using the room, rear boundary and floor to develop low-frequency scale in several directions.

Dual 12-Inch Active Drivers

The two front-firing long-throw active drivers use REL’s Continuous CastAlloy cone structure.

Lightweight carbon-fibre blades are bonded to the rear of each alloy cone to increase stiffness without introducing excessive moving mass.

Strengthening and damping the cones helps the drivers remain controlled during powerful effects while preserving the fine changes in pitch, texture and level contained within music.

Using two active drivers also spreads the workload, allowing substantial output without requiring one cone to provide all the necessary movement.

Rear and Down-Firing Passive Radiators

Two 300mm Carbon on Carbon passive radiators support the active drivers.

The down-firing radiator develops the deepest low-frequency energy through its interaction with the floor, while the rear radiator contributes to the sense of depth, height and atmosphere within the room.

REL’s SuperProgressive suspension is designed to provide substantial linear travel while increasing control as the radiator approaches the limits of its movement.

The passive-radiator arrangement provides low-frequency reinforcement without using a conventional open reflex port.

18Hz Low-Frequency Extension

REL specifies low-frequency extension to 18Hz at the stated minus 6dB point.

This allows the 212/SX to reproduce the lowest musical fundamentals, venue ambience and deep effects that are felt physically as well as heard.

Extension alone does not guarantee successful integration. The subwoofer’s room position, gain, crossover frequency and phase relationship with the main loudspeakers are equally important.

1,000W NextGen5 Class D Amplifier

A 1,000W RMS NextGen5 Class D amplifier powers the two active drivers.

Its high output provides the headroom needed for demanding cinema effects and large musical peaks while maintaining firm control through the lowest frequencies.

REL’s electronic Set-Safe system, DC fault protection and output-short protection help safeguard the amplifier and drivers during abnormal operating conditions.

REL PerfectFilter Technology

The 212/SX incorporates REL’s PerfectFilter system to extend and flatten the deepest bass while preserving the transition between upper bass and the main loudspeakers.

REL uses fast analogue filter circuits rather than placing the High Level music signal through a digital signal-processing stage.

The objective is to add scale, foundation and space without slowing the musical timing or making the subwoofer obvious as a separate source.

REL High Level Connection

In a conventional stereo system, REL normally recommends connecting the 212/SX to the main amplifier’s loudspeaker outputs through its Neutrik Speakon High Level input.

This input senses the same signal being delivered to the main loudspeakers, including the tonal and timing characteristics of the amplifier’s output stage.

The High Level connection has a very high input impedance and does not draw meaningful power from the main amplifier.

A nominal 10-metre High Level Speakon cable is supplied. The REL Bassline Blue provides a dedicated cable development option for compatible systems.

Stereo Low-Level Inputs

Left and right RCA low-level inputs allow connection to a suitable pre-amplifier output, integrated-amplifier output or active loudspeaker system.

The low-level connection uses the same variable crossover and main level control as the High Level input.

It provides an alternative where a High Level connection cannot be used or where the system architecture already supplies a suitable line-level subwoofer feed.

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 has its own level control and is intended to reproduce the dedicated low-frequency effects channel contained within a film soundtrack.

Balanced XLR can be useful where a longer signal cable is required between the processor and subwoofer.

Music and Cinema Connections Together

The High Level or stereo low-level music connection can operate alongside the dedicated LFE input.

This allows the 212/SX to integrate with the main loudspeakers during two-channel listening while also reproducing the dedicated effects channel during home cinema playback.

Separate Hi and Low Level and LFE gain controls allow the musical balance and cinema impact to be adjusted independently.

20Hz to 120Hz Variable Crossover

The crossover control for the High Level and low-level inputs is continuously adjustable between 20Hz and 120Hz.

It should normally be set low enough to extend the main loudspeakers without thickening voices or making upper bass sound heavy.

Small adjustments can make a significant difference, particularly with a subwoofer capable of this degree of output.

0 or 180-Degree Phase Adjustment

The phase switch provides 0-degree and 180-degree settings.

The correct setting is the one that produces the strongest, most coherent bass at the listening position without making the subwoofer easier to locate.

Phase should be established before final gain and crossover adjustments are completed.

Link Outputs for a Second 212/SX

High Level and LFE output connections allow signals to be passed to another compatible 212/SX.

A second subwoofer can improve room consistency, increase dynamic headroom and expand the perceived scale of the system.

Each cabinet should still be positioned and adjusted according to its relationship with the room and nearest main loudspeaker.

REL Airship Wireless Compatibility

The 212/SX is compatible with REL’s Airship wireless system.

Airship can carry the High Level music signal and dedicated LFE channel simultaneously, allowing both stereo and cinema operation without long signal cables across the room.

The REL Airship II is designed for compatible Serie S and Reference models, including the 212/SX.

Room Positioning

Subwoofer position has a major influence on output, extension and integration.

Begin near a suitable corner behind the main loudspeakers, then move the cabinet gradually to find a position that provides strong and even bass without exciting one room resonance excessively.

The rear passive radiator requires suitable clearance from the wall, while the down-firing radiator and cabinet feet must remain unobstructed.

The final position should support the main loudspeakers without drawing attention to the physical location of the subwoofer.

Gain, Crossover and Phase Setup

Begin with conservative gain and crossover settings, establish the preferred phase position and then adjust the controls in small steps.

Excessive crossover frequency can make voices and upper bass sound thick, while excessive gain can cause the subwoofer to dominate the system.

A well-integrated REL should add scale, space and authority while remaining difficult to identify as a separate loudspeaker.

When the correct settings are found, switching the subwoofer off should make the system sound smaller and less complete rather than simply removing an obvious layer of bass.

Single 212/SX or Stereo Pair?

212/SX or 212 Black Label?

212/SX or Carbon Special?

Piano Black Lacquer Cabinet

The cabinet is finished in eight coats of Piano Black lacquer and incorporates polished metal handles to assist with careful positioning.

The tall, relatively narrow form accommodates the vertically arranged active drivers while reducing the floor width required by a more conventional side-by-side arrangement.

Use a soft microfibre cloth and a suitable non-abrasive finish cleaner. Avoid household sprays or rough cloths that may mark the lacquer.

System Matching

Browse our Hi-Fi subwoofers , home cinema subwoofers , stereo speakers , home cinema speakers , home cinema amplifiers and subwoofer and system cables , or explore the REL range at Audio T .

Key Features

• High-output active subwoofer for music and home cinema
• Two front-firing 300mm active drivers
• Continuous CastAlloy active-cone construction
• Carbon-fibre reinforcement blades
• One rear-firing 300mm passive radiator
• One down-firing 300mm passive radiator
• Carbon on Carbon passive-radiator construction
• SuperProgressive passive-radiator suspension
• 18Hz low-frequency extension at minus 6dB
• 1,000W RMS NextGen5 Class D amplifier
• REL PerfectFilter technology
• Neutrik Speakon High Level input
• Stereo RCA low-level inputs
• RCA and balanced XLR LFE inputs
• High Level and LFE link outputs
• Separate music and LFE level controls
• Variable 20Hz to 120Hz crossover
• 0 or 180-degree phase adjustment
• Compatible with REL Airship wireless transmission
• Electronic Set-Safe, DC fault and short-circuit protection
• Eight-coat Piano Black lacquer finish
• Nominal 10-metre High Level Speakon cable included
• Three-year REL warranty, subject to current terms

Frequently Asked Questions