REL’s compact subwoofers, side by side. Here is the T/5x alongside the smaller Tzero MkIII below it and the T/7x above it, showing what your money buys at each step.

The T/5x is the successor to the T/5, the best-selling model in REL’s history, and it occupies the same place in the range: the point where a compact subwoofer becomes a serious one. It keeps the discreet footprint and full REL connectivity of the Tzero MkIII below it, but moves to an 8-inch driver and a Class A/B amplifier, which gives it more depth, more output and a larger room to work in. It is the REL we would point most two-channel listeners with standmounts towards first. It is a music subwoofer before it is a cinema one, and it makes no claim to shake a large room.

Brief product overview
A sealed, down-firing subwoofer with a 200mm (8-inch) long-throw FibreAlloy driver, a composite of paper and aluminium with an inverted alloy centre cap on a steel chassis. It is the same bass engine used in the T/7x, with greater excursion than the T/5i’s driver, so it plays louder, and an upgraded suspension. Power comes from a 125-watt Class A/B amplifier, a linear design where the Tzero uses Class D, and bass extends to 32Hz at −6dB in-room. The cabinet is laminated plywood with internal bracing, finished in five coats of piano black or gloss white lacquer, and because the driver fires into the floor there is no visible cone on any face. Inputs are REL’s high-level Neutrik Speakon connection from the amplifier’s speaker terminals, a low-level RCA input for active speakers or a pre-out, and a dedicated .1/LFE input with its own level control, so music and film levels are set independently. There is a phase switch and, on UK units, a standby switch. The optional Arrow wireless system removes the cable run. It measures 300mm wide, 307mm high and 313mm deep, and weighs 14.3kg.

How it sounds
Against the Tzero, the difference is scale. The larger cone and linear amplifier give the T/5x more weight and authority lower down, so double bass, organ pedal notes and kick drums gain physical presence rather than simply outline. The sealed alignment keeps it quick and tidy, and notes start and stop cleanly without the slight overhang that small ported subwoofers can add. Fed through the high-level connection, it takes on the tonal character of the main speakers and integrates so well that its main effect is on space: a deeper soundstage, more ambience in live recordings, and main speakers that sound larger and less effortful. The honest limits are output and room size. It is rated for rooms up to around 19 square metres, and in larger spaces or at cinema levels the T/7x or a Serie HT model will cope better.

What we’d partner it with
The Revival Audio Sprint 3 is a well-judged partner. It is a two-way standmount with a 180mm basalt-sandwich woofer and a soft-dome tweeter with Revival’s ARID anti-reflection dome, quoted to 55Hz from a rear-ported cabinet. The T/5x takes over below that and extends the system into the low 30s, while the Sprint 3’s 87dB sensitivity and 6-ohm load keep amplifier demands modest. The Sonus Faber Lumina II (86dB, 4 ohms, 55Hz) is a warmer alternative, and the Technics SB-C600 coaxial standmount is a more precise one; its 83dB sensitivity makes the T/5x’s support especially worthwhile.

For amplification, the Eversolo Play makes the three a complete system. It is a streaming integrated with 60 watts per channel into 8 ohms and 110 watts into 4 ohms from a Class D output stage, an AKM DAC, Roon Ready, Qobuz and Tidal Connect, an HDMI ARC input for a television, and room correction using an external measurement microphone. It also has a built-in phono stage for both moving-magnet and moving-coil cartridges, so a turntable plugs straight in. The Bluesound Powernode N331 is an alternative with more power and HDMI eARC but no phono stage, and the Technics SU-GX70 adds a moving-magnet phono input alongside streaming. All three use Class D or full-digital output stages, which affects how the high-level lead is wired (see Ownership), and although each offers a subwoofer output, the high-level connection is the one we’d use for music. The T/5x is supplied with a 10m Speakon lead for the high-level run. For the main speakers, use a well-made cable of appropriate gauge; AudioQuest and Chord are the cable brands we stock.

Who shouldn’t buy it
If your room is small, a study or bedroom around 14 square metres, and your speakers are compact, the Tzero MkIII does much of the same job for less and in less space. If your room is medium-sized or open-plan, or your main speakers are larger standmounts or floorstanders, the T/7x adds a 10-inch passive radiator and a 200-watt amplifier for more depth and control. If film is as important as music, the HT/1003 MkII puts a 10-inch driver and 300 watts behind the LFE channel and reaches 24Hz. And for a large room, a stereo pair of T/5x units, one near each speaker, is REL’s own suggestion before moving up the range.

Start with the T/5x in a corner behind one of the main speakers, on a firm floor with its feet in place, since the driver fires down and relies on the gap beneath the cabinet. Move it in small steps along the wall until the bass sounds even and the sub is hard to locate. Connect the Speakon lead to the amplifier: red to the left positive terminal, yellow to the right positive, and black to ground. With a Class D output stage such as the Eversolo Play’s, REL advises taking the black wire to the amplifier’s chassis ground rather than a negative speaker terminal. If there is no dedicated earth point, ask us or REL before connecting. Leave the main speakers running full range. Set the crossover close to where they roll off, then raise the high-level volume until the bass is felt rather than heard. Try both phase positions and keep the one that sounds fuller at the listening seat. If you use the Play’s room correction, set the T/5x by ear first and recheck its level afterwards. A television’s subwoofer signal can go to the .1/LFE input, which has its own level control and leaves the music settings untouched. On UK units, the standby switch sets whether the T/5x sleeps when idle. The optional Arrow wireless system replaces the cable if the run is impractical.