The baby of REL’s subwoofer range, the Tzero III is truly tiny at only 22x24x24 cm (WHD). So much so that you wonder if it can produce decent bass, particularly from a single 6.5” driver. £450/$499 /€499 is hardly beer-money either. 

The headline spec of -6dB at 37Hz is decent though, low enough to augment most standmounts a HiFi Starter will use. Some floorstanders too. And the Tzero III’s size makes it easier to accommodate, it won’t dominate a room visually.

So is the Tzero III a ‘proper’ subwoofer, or do you really need something bigger for low bass? We tried it with several speakers during its time here. Let’s see how it got on.

What you get

It’s small, but with a 100W NextGen Class D amplifier and REL’s filter network, crossovers and limiters sitting alongside the 6.5” aluminium-coned driver the Tzero III packs a lot in. 

The driver fires downwards. On the rear are REL’s familiar controls; High & Low level inputs for music, a separate .1/LFE input for AV, the crossover control and separate gain controls for music and AV (connect both, use them separately).

Available in Gloss White or Black, the Tzero III rests on four square aluminium feet. A REL logo sits atop the speaker. Overall the look is discrete. Build quality is very nice.


If present, a subwoofer filter on your amplifier makes life easier, sending bass to the Tzero III’s Low-Level input, the rest to the main speakers. Leaving you just position and gain to set. 

REL recommends High Level connection though – the subwoofer receiving the same signal as the speakers, aiding integration. A 10m Neutrik lead is provided. Run it from subwoofer to speaker terminals or to the speaker outputs on the amplifier. You then have position, crossover point and gain to set. Not always easy. I covered it previously (here), but to recap: –

    • Corner placement maximises boundary reinforcement (= more bass). If the subwoofer is against a wall (or freestanding) increase the gain.  
    • Initially set the gain to 40%, then increase the crossover point until you hear the subwoofer contributing. 
    • Listen for some time – don’t fiddle. Muddy, ill-defined bass means the subwoofer and mains are overlapping. Reduce the crossover point slightly, listen again. 
    • With the crossover set, assess the balance between bass and the rest of the sound. If bass is prominent reduce the gain (and vice versa). 
    • Repeat the process (probably several times), listening carefully between changes until everything sounds right. Be methodical. Over time you’ll make smaller changes until you’re satisfied.  

The lack of a scale on the gain or crossover knobs doesn’t help. The adjustments are also slightly imprecise (my T/7x is the same). Oh to be able to adjust everything from the listening position. The process does get easier though once you get a feel for what’s happening, there’s just a learning curve. Setup aside, the REL is fairly straightforward. Can it deliver though?

Listening – Marantz & Elac

Combining the Tzero III with a Marantz PM6006 amplifier and Elac DB6.2 speakers made sense price-wise. And the Elac’s spec of -6dB @ 44Hz said the REL should help. Without subwoofer the amp and speakers sounded clean and open. The sound wasn’t neutral, shining a spotlight on music rather than emphasising texture and richness. It was engaging though.

Playing the vinyl of Hans Theessink’s Slow Train on a Pro-ject Debut Carbon EVO demonstrated the point. It’s a superb recording. Without the REL there was plenty of detail, a great sense of the acoustic (no reverb was used) and really taut bass. But…..was something missing?

In went the TZero III  to elevate the sound quality quite notably. Bass went lower and gained weight. Not much, it’s not on the recording. What was there filled out though and was slightly warmer, the REL giving it room to breathe without sounding remotely loose or ill-defined. 

The bigger differences were further up the spectrum, the Tzero III fleshing out the sound and enriching tonality to just the right degree. A hint of etching was replaced with refinement. And the soundstage was notably more open; it was easier to place the musicians and sense the interplay between them. The Tzero III brought everything more together. 

Which highlights a key aspect of REL subwoofers. Yes, bass goes deeper. They also open up the soundstage, even on music with little bass. That’s counterintuitive – how can they impact things when there’s no bass – but I’ve heard it many times now.

Same speakers, better electronics

In came an Ayre AX-7e amplifier with Pro-ject streamer (Stream Box S2 Ultra) and Mytek Liberty II DAC. The Elacs remained. I’d not played the Ayre recently, it’s really accomplished. Mellifluous maybe, particularly against today’s clarity champions. Musically it’s very satisfying though.  

On went Other Doors, Soft Machine’s new album, which nods strongly to the 60s when the band was formed. Think grown-up psychedelia, prog-not-prog. Yet it sounded fresh. 

Without a subwoofer the quality of the recording was clear. ‘Penny Hitch’ had an immediate sound. Drums were prominent but not overpowering. Synths & guitar provided a bedrock over which the bass player riffed (sounding very Weather Report-ish). The various strands of the mix melded into a collective whole. 

Darn me if the REL didn’t pull its soundstage trick again; wider, deeper, musicians more clearly laid out within the acoustic space. The different elements were easier to hear yet the band was also tighter in the musical sense. The sense of live music was greater. Bass also dug deeper, although its qualitative improvements were more noticeable. 

It wasn’t chalk and cheese. Reverting to a sub-less setup wasn’t a disappointment. The impact of the Tzero III was noticeable though, refining a £300 speaker beyond its norm. More than spending the £750 of the REL plus Elacs on main speakers? Possibly – I wished I still had Monitor Audio’s Silver 100 (£750) for comparison.

Yes but what about the bass?

Time to plumb the depths (what you’ve been waiting for!) Sticking with the better electronics and Elacs I played the OST to Kiss My Wounds. It’s classic Kanding Ray – haunting electronica underpinned by low synths that threaten your speaker drivers at every turn. In his hands gratuitous bass transforms into beautifully eerie music. 

The Ayre coaxed the Elacs impressively low without a subwoofer. Would the REL help? Answer: yes, and then some. Yet again the soundstage opened up but this time bass took centre stage. Deeper, much deeper. More forceful too, the sense of menace from greater heft almost palpable. Bass was better defined too, with more texture coming through. 

Schiller’s ‘Empire of Light’ from Illuminate was equally good, the signature synth line much punchier with the REL. The music gained bounce, the sound was more anthemic than before. And yes, everything sounded bigger again. 

Switching to classical, Jaap van Zweden’s ‘Dies Irae’ from Britten’s War Requiem is a superlative recording. The REL weaved its magic on the soundstage as usual. Deeper bass, particularly from the huge kettle drums, also added notable gravitas to proceedings. 

Overall it’s clear; the Tzero III digs deeper than you think for its size. It’s no ersatz subwoofer

With active speakers

The REL overlapped with several active speakers being reviewed, three of which it had a run out with. First up were PSB’s Alpha iQ all-in-ones (£1,299), a complete system within two speakers. Like the Tzero II they’re ridiculously small, making them kindred spirits. The Alpha iQs use the BluOS streaming platform, which includes a subwoofer filter. Hallelujah – easier setup.

Despite its 10cm driver the Alpha iQs dig amazingly deep. They don’t really need a subwoofer. The REL did make a difference though, expanding the soundstage. Bass also went lower, words like ‘rumbling menace’ and ‘majestic’ peppering the review. Overall the improvement wasn’t revolutionary but did justify the extra outlay.

With the REL T/7x, itself no giant

Triangle’s AIO Twin is another, lower cost, all-in-one (£699). Its Linkplay streaming platform is stable, intuitive and looks good, but doesn’t have a subwoofer filter.

Midrange is the AIO Twin’s strength. Both treble and bass are slightly curtailed, although the speaker still sounds unfeasibly big for its size. The REL enhanced that further, opening out the soundstage. And the improvement to bass was step-change. Only try the REL with the AIO Twin’s if you can afford it, you’ll struggle to go back to them running solo.  

Finally Q Acoustics’ M20 HD (£399); add a WiiM Mini streamer for a £500 system that blows your socks off. Again there’s no subwoofer filter, so setup is fiddlier. Persist and you’ll be rewarded with a beautifully balanced sound that elevates the M20 HD’s performance even higher. Improvements aren’t quite as big as with the Triangles. But, bass depth was still lower, and the soundstage grew in stature. This is one sub-£1,000 setup we’d recommend without hesitation.


The Tzero III acquitted itself really well. It’s tiny, but that doesn’t stop it adding useful low-end grunt to speakers up to, say, £1,000. It also opens up their soundstage notably, a benefit that shouldn’t be underestimated. 

If possible try a Tzero III with your own speakers. That way you’ll hear the benefits it brings to you, which does vary speaker by speaker. It also depends on your room, even REL saying the Tzero III is best in smaller rooms. Got a bigger room? Consider the excellent T/5x (or similar). At £699 it doesn’t cost that much more.

Whichever, the benefits of a good subwoofer are significant. The Tzero III manages to deliver in spades. And it’s tiny size minimises the amount it intrudes on everyday life. Against which its £450 price tag starts to look decidedly good value. Dinky powerhouse it is then!