The top of REL’s Serie T/x, side by side. Here is the T/9x alongside the smaller T/7x and the special-edition T/9x SE, showing what your money buys at each step.

The T/9x is the flagship of Serie T/x and the model where a compact REL becomes a partner for floorstanders and larger rooms. It keeps the layout of the T/7x, a front-firing active driver working with a down-firing passive radiator, but moves to a 10-inch active driver, a larger cabinet and a 300-watt amplifier. REL’s aim with the current version was more output without losing the speed and transparency the smaller models are known for. It is equally at home in a two-channel music system and under a television. In a large room it has limits, and REL’s answer there is a second unit rather than a bigger box.

Brief product overview
The T/9x uses a front-firing 250mm (10-inch) long-throw FibreAlloy driver, a paper and aluminium composite cone with an inverted alloy centre cap on a steel chassis. It is paired with a down-firing 250mm passive radiator of the same construction, an unpowered cone driven by the air inside the cabinet that extends the bass without port noise. A larger cabinet than the previous generation lets REL use a stiffer, better-controlled suspension for the same amplifier power. Power comes from a 300-watt MOSFET Class A/B amplifier with a large toroidal power supply, and bass extends to 27Hz at −6dB in-room. Inputs are REL’s high-level Neutrik Speakon connection from the amplifier’s speaker terminals, a low-level RCA input and a dedicated .1/LFE input with its own level control. There is a phase switch, a standby switch on UK units, and optional Arrow wireless. The cabinet is finished in five coats of lacquer, measures 370mm wide, 340mm high and 393mm deep, and weighs 20.6kg.

How it sounds
Against the T/7x, the T/9x adds scale. The larger active driver and extra power move more air, so organ pedals, large-scale orchestral works and electronic music gain real depth and physical impact, and the sub stays composed at levels where the smaller models would begin to strain. It keeps the Serie T/x character: bass lines stay quick and well defined rather than heavy, and fed through the high-level connection it takes on the tonal balance of the main speakers and blends in once set up. Much of its effect is spatial: a wider, deeper soundstage and floorstanders that sound more relaxed because their woofers are no longer working alone at the bottom of the range. With films it gives weight and realism to effects in a living room, though the deepest cinema effects at high level are the job of a Serie HT model.

What we’d partner it with
The Revival Audio Sprint 4 is a well-matched partner. It is a slim 2.5-way floorstander with two 180mm basalt-sandwich woofers, one working as a mid/bass driver and one for bass alone, and a 28mm soft dome tweeter with Revival’s ARID anti-reflection design. It is quoted to 45Hz with 89dB sensitivity and a 4-ohm load. The T/9x takes over below that range and gives the system real depth into the high 20s, while the Sprint 4 stays articulate through the midrange. The Sonus Faber Lumina III, a three-way floorstander quoted to 40Hz, is a warmer alternative. The Revival Audio Atalante 4, a larger three-way with twin 7-inch woofers, is the step up if the budget allows.

For amplification, the Arcam SA45 has the current a 4-ohm floorstander needs: 180 watts per channel into 8 ohms and 300 into 4 ohms from a Class G design that runs in Class A at low levels. It adds an ESS DAC, streaming via AirPlay 2, Google Cast, Spotify, Tidal and Qobuz Connect, an HDMI eARC input for a television, separate MM and MC phono inputs, and Dirac Live room correction with a supplied microphone. The Atoll SDA300 Signature is an alternative with 150 watts, streaming and a French build, but no phono stage. The T/9x 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. In the larger rooms the Sprint 4 is rated for, a second T/9x as a stereo pair, one near each speaker, is the natural next step.

Who shouldn’t buy it
If your room is small to medium and your speakers are standmounts, the T/7x gives most of the same integration for less money and in a smaller cabinet. If you want the T/9x’s size and power with carbon-fibre elements in the driver design, the T/9x SE is the step up within the same range. For a system built mainly around film, the HT/1205 MkII puts 500 watts behind a 12-inch driver for the lowest effects. And if your room is large and your speakers are substantial, it is worth comparing a pair of T/9x units with a single Serie S model before deciding.

Start with the T/9x in a corner behind one of the main speakers, the active driver facing into the room and the feet in place, since the passive radiator fires down and needs 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 a negative terminal. That is REL’s standard wiring for a conventional linear amplifier; confirm it for your amplifier 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 Dirac Live on the SA45, set the T/9x by ear first and recheck its level after the correction is applied, since the sub receives the corrected signal. 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/9x sleeps when idle. The optional Arrow wireless system replaces the cable if the run is impractical, and is REL’s suggested way to connect the second sub of a stereo pair.