Review: REL T/Zero Mkiii Subwoofer

REL T/Zero MK iii Subwoofer – Tiny but Mighty!
Review by David Neice


MSRP: $650 (Canadian)

Verdict: It looks like a toy and the cost is modest but it performs like a champ. In its favour – this subwoofer is lightning fast and is designed primarily for those audiophiles who generally hate subs but are inevitably faced with the need to use one (or two) at some point in their journey. 

The output from the T/Zero MK iii is subtle and not at all boomy. REL’s design idea is to gently lift the lowest octave of sound and enhance the mid-bass reproduction thus giving an extra dose of ‘realism’ to the sound field. Fortunately this particular sub is brilliant at that task.  

The modestly priced T/Zero MK iii is highly recommended for augmenting LS3/5a speakers and their clones, as well as Magnepan LRS or MMG speakers or other small speakers that need subtle bass reinforcement such as the DALI Spektor 1s and 2s, Unity Audio Inner Souls, or the Q Acoustic’s 3020i.  


How may times have we heard the words on audiophile forums – ‘I need a sub but I am skeptical of the genre and I need advice’. There are a whole class of audiophiles out there who are shy about subs and are worried about buying one and think that implementing one might lead to buyer’s regret. 

Let’s take those fans of the LS3/5a design as a case in point. Most owners love these speakers and realize that they have to live with a compromise – a very rapidly sliding bass performance. Eventually they come to ask themselves; ‘would a sub augment my overall experience?’. 

But there are caveats. Will the integration be seamless or faulty? Will the speed of the sub’s transient response match the speed of the mid-woofers? Will I get too much bass or too little? Will the quality of the bass and its tonal characteristics match the mains? And so anxiety builds. 

I was placed in this exact situation a few months ago when I wanted to supplement the bass for a pair of Unity Audio Inner Souls I reviewed here, as well as for my trusty DALI Spektor 1s. I had on hand an older eight inch reflex sub but it was nothing special so I went hunting. The ‘Audiophiliac’, Steve Guttenberg, sounded off about his recommendation to try the REL T/Zero. So I hunted for one and voila!  

Generally the audiophile population is divided into those who like subs and those who hate them. Fortunately this sub is designed for the latter group. So, let’s take a look at its design characteristics. 

REL Design

This fifteen pound subwoofer is so tiny that it initially looks almost like a toy. When I got it I worried for a while that it would not be up to the job. Silly me. The reason it is so compact, measuring just 8.5 X 9.5 X 10.5 inches, is that it utilizes a single driver (and no passive radiators) and this driver is only 6.5 inches in diameter and is located in a downward firing closed box. 

Most subwoofers are reflex ported and many sport passive radiators as well, and by the time you get all this gear into an enclosure with the goal of getting perhaps -3 db at 35 HZ, you will end up with a ten inch or even twelve inch main driver and a large plate amplifier.  

The design goal with the T/Zero is much more modest and the frequency response reflects this, and is stated in the specifications as – 6 db at 37 Hz. So this is not your standard boom-boom subwoofer where the goal is to add thundering bass while watching the T-Rex creatures on ‘Jurassic Park’. Home theatre enthusiasts need not apply. 

Instead the emphasis is on subtle reinforcment of the bass response for what are already excellent mini-monitors as well as bass-shy panel speakers such as the Magnepan LRS and its forebears. The emphasis is therefore on speed and resolution in order for the sub to ‘keep up’ with the mains. This leads to a sealed box acoustic suspension design, as this increases the potential speed and transparency. 

The REL T/Zero, like all REL subs, just oozes quality. The finish is gloss black (or white) and this is applied in multiple layers. The legs are steel, and the steel back plate is superbly finished, and is replete with multiple controls and inputs. 

The usual controls are available for selecting crossover frequency, the volume level, as well as a phase switch and power on/off. The power switch is selectable for either ‘always on’ or else it boots on start-up when the unit senses an input signal.  

Besides the hi-level Neutrik input discussed below, the unit also has an RCA low level input as well as a Low Frequency Effects (LFE) RCA input depending on the application. The T/Zero is equipped to allow you to take full advantage of Dolby Digital AC3, DTS, MPEG 2 and any other digital sound format that includes a dedicated Low Frequency Effects (LFE) channel. 

According to REL: the dedicated LFE input meets the tough specification laid down for digital 5/2.1 channels, usually known as 7.1. The output is nominally flat from 35 Hz – 90 Hz. It has a dedicated input level control which enables users to set the LFE level independently of the processor.

The controls are all very smooth and show evidence of high quality. The plate amplifier is Class D and the output is 100 Watts (RMS). Other specifications are found below. 


Connecting a REL Subwoofer

REL supplies an unusual hook-up system with all of its subs. Although it is possible to route RCA outputs from say your integrated amplifier to the sub, the better solution is to use the provided Neutrik Speakon connector as it is supplied with a 10 foot link of factory wiring. 

The bare end wires of the link are attached to your amplifier’s speaker jacks (follow the manual’s directions) and then a Neutrik socket is jacked into the back of the sub. This ensures that the cross-over function is fully completed thus taking a load off your main amplifier and turns the duties of driving the sub over to the sub’s plate amplifier. REL has arranged for this system of connection to apply to both single and double subwoofer installations.


The Ideal Subwoofer Experience

I am far from a subwoofer afficianado, but I do follow the audio forums closely and have gained a lot of useful information from them. I will pass it along here. Optimizing a sub installation is not for the faint of heart. It requires some real dedication. Experts say:  

  1. Until and unless you measure the output of your speakers, with and without the subwoofer, and at different crossover frequencies, and until you find the combination that produces the most linear frequency response in your room, it is said that you are just fishing around. 

This may seem a bit harsh but it is true and practically speaking very few audiophiles are likely to adhere to this rigid requirement. Essentially you would need to set up a microphone in the room and do an in-room frequency sweep to determine the best crossover point and volume level setting. That may involve running the mains full-range, or it may require cutting them off with a high-pass crossover. The measurements will tell you.

  1. Alternatively, experts say if your mains already have quite linear output to 30-45 Hz, the other approach would be to not use a subwoofer at all. All too frequently users think that a sub will add a lot of bass dimension even when they have floor standing speakers that reach quite low. All they are doing really is doubling the low end output. It may sound impressive initially but it is just wrong from a frequency response perspective and will become tiring with time. 
  2. Sub people also say that a sub-augmented system needs two subs, a left and a right as there is phase information even at the low end that ought to emanate from the correct location. 

These demands are probably asking too much of the average 2-channel audiophile and so let’s focus on less complex methods of sub integration, assuming also that only one sub is going to be the norm in most installations. 

Setting Practical Goals

Suppose we are committed to a single sub installation and we have some main speakers (likely book shelves) that drop off nicely at say somewhere between 50 to 80 Hz and so we know that a sub will help augment the lower and midbass response. But we are not technically prepared to go full tilt and microphone the room and perform a frequency sweep. What do we do? 

REL offers us some good advice. I have streamlined the steps they indicate but would refer all readers to their manual which elaborates each point. 

  1. Put the subwoofer tightly in a corner behind the main speakers initially. 
  2. Select some music that is bass driven with a repetitive bass line.
  3. Try to ignore the other music on the track and just listen to the bass line. 
  4. Set the crossover point at 12 oclock and the volume control at half way.
  5. Toggle the phase switch back and forth in order to detect the loudest sound coming from the bass line.  The loudest sound is the correct phase. 
  6. Pull the sub woofer gradually out of the corner, until once again the loudest bass sound is achieved. This may be a just few inches or a couple of feet. The sub should lock onto the room at some point by loading the room. 
  7. Now tweak the cross-over and volume control to taste. Generally speaking lower levels are preferred.  


Listening to the REL T/Zero MK iii

I tried the REL with two sets of bookshelf speakers; the DALI Spektor 1s, which really do need a sub because of their very limited bass, and a pair of Q Acoustics Concept 20s, which already have significant bass as standalones. In both instances I used my Unison Research ‘Simply Italy’ as the main amplifier as it drove the Q Acoustic speakers more delightfully. 

David, you didn’t test the pipe organ at Kings College?

From my large library of records and CDs I chose mostly tracks that were bass enhanced, although from time to time I played tracks that I think of as being a bit bass shy. Bass is not just about the electric or acoustic bass line of a track but also includes the effects of kick drums and in orchestral music, of kettle drums. Certain specialized performances such as Japanese drum orchestras also feature gargantuan amounts of bass drive that would simply overwhelm any electric bass line. 

In addition, some music tracks are intentionally developed in the studio to emphasize bass weight and the lowest frequencies are digitally enhanced to add weight and gravitas to the track. Examples would be found on tracks by Moby and other electronic music pioneers like Air. This of course is all a processing artifact, but can challenge any system that is bass light.  

First up for discussion is the signature track Pusherman from the classic movie soundtrack album by Curtis Mayfield, Superfly. I always return to this track to see what a system can do low down. Besides the exceptional bass lines, this track uses both a kick drum setup as well as conga drums, and the weaving of polyrhythmic flourishes between the drum sets is exceptional. From the very first few notes, the REL acquitted itself and the thrill of the track returned me to me as if I was hearing it for the first time.

Next up for examination is a heavy bass-driven track by Jenn Grant caled Paradise, on the CD of the same name. This track goes so low and is so heavy that it will strain the muscles of most reflex or ported subs. I used this track intentionally to test the REL T/Zero because it is a sealed enclosure without venting. Here we are up against the laws of physics as the little REL can only go so low and so loud. 

However, the bass was still satisfyingly opulent, even if the room was not vibrating in synch. Of more interest was the mid-bass reproduction which was full and vibrant. However, this track did indicate to me that if a buyer is after gobs of deep bass, then perhaps a larger sub from the REL line (such as the T/5) might be a good idea. After all, there are real limits to the power of a 6.5 inch woofer. 

Next up is the track Polly Come Home from the album Raising Sand by Robert Plant and Alison Krauss.  This track is also bass heavy, with a repeating bass line that stretches the limits of ported subs. It is not unusual to hear chuffing and huffing from a ported sub enclosure on this track. However, with the T/Zero the track was cleanly reproduced and the speed of the enclosed T/Zero sub was evident, particularly regarding its’ mid-bass performance. I played the track several times and was pleased with what I heard each time. 

Finally I will note that I listened carefully to a vinyl version of Andreas Vollenweider’s album White Winds. I was mostly curious about the mid-bass reproduction which is prominent on this album. The album contains lots of low notes on the harp, various low pitched female vocals, as well as piped instruments and large bells. These tracks proved to be very exciting and the T/Zeros provided gobs of midrange presence that kept up the overall excitement level. 

Of course in a review of this sort I have only touched on a select few of countless tracks I examined over a three month period, but I think the above examples do provide some flavour of the performance of the REL T T/Zero MK iii subwoofer. In a word or two: it’s a good one. 



Overall, the REL T/Zero MK iii can be firmly recommended for use with smaller speakers that need a subtle but not overwhelming bass boost. This would include various versions of the LS 3/5a as well as some single driver speakers like the Unity Audio ‘Inner Soul’. Small footprint planar designs like the Magnepan LRS and LRS+ would also benefit from the T/Zero.  

The speed of the enclosed driver is superior to small subs designed around reflex ports, and even though this subwoofer has a tiny footprint, it fulfills its design goals. However, bass addicts may want to look at larger models like the REL T/5 or T/7.  


MSRP: $650 (CDN)



Type – Closed Box, down-firing driver

Active Driver Size & Material – 6.5in. (165mm) long-throw, aluminum cone, steel chassis

Low Frequency Extension – -6dB at 37 Hz

Input Connectors – High Level Neutrik Speakon, Low Level (1) RCA, (1) LFE RCA

Power Output – 100 watts (RMS)

Amplifier Type – Class D

Wireless Capability – HT- Air MKII (sold separately)

Dual Parametric Filter – HT- Air MKII (sold separately)

Protection System – Yes

D.C. Fault – Yes

Output Short – Yes

Mains Input Voltage – 100-240 volts

Fuses – 2.00 Amp semi delay

Dimensions – W x H x D – 8.5 x 9.5 x 10.5 in. (216 x 241 x 260 mm)

Net Weight – 15 lbs. (6.8 kg)

Finish – Piano Black Lacquer, Gloss White Lacquer 5 coats

Supplied Accessories – Mains Lead  

Neutrik Speakon (Interconnect 10 Meters Nominal)

User Manual – Yes

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About David Neice (19 Articles)
David Neice is an audiophile hobbyist with more than fifty years experience at rotating audio components in and out of stereo systems. In the 1970s he was a founding member of the Toronto Audio Society. He writes extensively on fora at Canuck Audio Mart and has done so for nearly two decades while corresponding with fellow audiophiles world-wide. He holds a DPhil degree from the University of Sussex (UK) in the field of Science and Technology Policy and has taught at several universities and held successive posts as Director of Policy Research in government circles. Presently he is retired and listens to all sorts of music while living at 'chaos manor' in Stratford Ontario.

6 Comments on Review: REL T/Zero Mkiii Subwoofer

  1. Alan G Sanders // 2023/10/16 at 5:07 pm // Reply

    David! THANK YOU!!! I am (was) firmly in the “I hate subs” category because I have never found a sub that can match the speed of my Unity Audio Inner Soul or my LS3/5A style Linn Kan Mk.1.

    Once again, your review is both realistic and well presented without all of the hype and hyperbole that has spilled over into the audio world. Thank you for your honest and direct thoughts.

  2. David Neice // 2023/10/17 at 3:25 pm // Reply

    Hi Alan,

    Thanks for the kind comments. I do try to keep it real.

    David Neice

  3. David: Just recently enjoyed reading your review of the DALI Spektor 1s and thread(s). As an owner of 2 REL T/5x subs and long time owner of earlier REL models I can confirm the sound field improvements are more than just the bass. Properly set up a subwoofer (using high level inputs) can create a holographic sound field that helps a small speaker fill a much larger space than it otherwise could. I know you understand. As a result of your experience(s) with the Dali Spektor 1s, I ordered a pair to replace a pair of much smaller Gallo Acoustics A’Diva SE Spherical Loudspeakers. While the 3d holographic sound of the A’Diva-T/X5 combination has to be heard to be believed, there is a severe dip around 100hz that neither the A’Divas nor the REL’s can cover (eg: negatively impacts male voice). Over time this has become annoying to me (but not to the wife). Am looking forward to putting the much larger Dali Spektor 1s in the system with the 2 T/X5s.

    • Thanks for reading and commenting, Eric. The little Spektor 1 might be audio’s best kept secret. Oh, a little bird told me they’ll be on sale even cheaper tomorrow (1-Dec) here in Canada.


  4. Would you recommend the TZero over the CA Minx201? They are in same price category and size. The sub must sit on a shelf. It will be used with Q Acoustics 3020i with centre channel. The setup is also e-arced to my tv via the Denon S960.

  5. I bought a pair of these little T-Zero MKIII subs to use with my new Magnepan LRS+ speakers, and am incredibly impressed with what these little guys are doing. I did not use the speaker input, I used a Rolls SX45 active crossover to send 80ish hz +/- to the RELs via RCA cables, and the rest to the Maggies.

    This crossover really lit up the RELs and the Maggies, as the Maggies no longer have to deal with those lower frequencies and or stressing my amplifier. The sound is very holographic and the little RELs disappear in the room, as they should. The bass is nothing short of incredible out of these tiny units when paired with the Maggies using an active crossover. Ever hear a cello dig deep? The RELs are staying. 😉

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