REL T/7x Subwoofer - Listening and Set Up


BOB’s Review Series - No 40 – REL Acoustics Serie T/7x Subwoofer – x 2

Introduction – Dyson started with vacuum cleaners but now also make fans and hairdryers, BMW make cars and motorbikes, Saab made cars and bizarrely Jet Fighters, Yamaha make pretty much everything hi-fi, and they also make pianos and motorbikes. Hopefully you can see where I am going with this because REL concentrate all their efforts into only making subwoofers. There is a good business here because REL make such good products they simply don’t need to diversify and are happy and profitable doing what they know best – designing and building some of the very best Sub-Bass Systems available for audio and Cinema setups.

I don’t have an AV Cinema system at home, preferring two channel audio, so why am I reviewing REL subwoofers, why do I have two of them and am I the right person therefore to write a subwoofer review? Good questions and ones that I asked myself before taking them home to try. I have little previous experience of running subs at home and if I’m honest I have never really seen the attraction of them for anything other than a home cinema setup where sound reinforcement rather than sound enhancement is the desired outcome. In a roundabout way this makes me the best candidate to review a subwoofer because having little previous home experience I come with no expectations, biased viewpoint, or opinions.

One of REL’s most important actions way back in 1990 was the adoption of the High-Level connection that takes its input directly from the output speaker terminals on your amplifier and thus sending exactly the same signals in the same timeframe to the sub as the signals being sent to your main front two channel stereo speakers. This is the preferred way to connect a sub to a two-channel system and it’s the way I used them for this review. For AV systems its best to use the low level .1/LFF RCA connection which takes a dedicated sub channel output from a dedicated AV amplifier acting as the point one, two or four channel in your 5.1 or 7.4 system etc. REL have been making subs for a very long time at their base in Bridgend in the UK and today have a range covering almost every conceivable need for the domestic or professional user.

Technology – The T7/x has a 200w class AB amp built in to power the drivers from the signals sent to it from your main amps speaker outputs. They have an active 8” long throw drive facing forward and a 10” passive down firing driver. The grills can be removed but I found them to be acoustically transparent enough that I left them in place. They are 356mm wide, 320mm high and 363mm deep and weigh 17.5kg each. They come supplied with a 10m Neutrik Speakon cable for High-Level connection. They have a low frequency response of -6dB at 30Hz. The T/7x Sub comes in at £999 (at the time of writing) It is possible to run these subs with a REL Arrow wireless device which does away with the Speakon lead connections but at a cost of £199 per sub. The Arrow has a wireless range up to 13.7m.

REL also make a range of better connection cables, the Baseline Blue and the Baseline Blue Array. These come in 3, 6 and 10m lengths but for me and I suspect many others a 1 or 1.5m option would be of interest. They start at around £299 each. I used the supplied leads for this review.

System Components used in this Review:

Preamp: Gryphon Essence Preamp

Power Amplifier: Gryphon Essence Stereo Power Amp

Digital Sources: Innuos Statement Streamer – Meridian 201 CD Transport

DAC: PS Audio Perfect Wave DS DAC

Analogue Sources: Meridian 204 Tuner and Revox B77 MKII Reel to Reel

Streaming Sources: Tidal HiFi and Qobuz Hi-Res – Innuos Statement Hard Drive

Streamer Management: Roon – Innuos Statement acting as Roon Core and Storage

Speakers: Marten Mingus Quintet – now with new Marten/IsoAcoustic Isolator Feet

Performance – I didn’t really want a large box in my listening room (I have a better half to consider) and although I should probably use a REL S Series or bigger Sub in my room I looked instead at the new Tx range and plumbed for the middle sub, the T7/x. For me it was the Goldilocks option, not too big, not too small, just right. The new Tx series recently replace the Ti series, and the T7/x comes in piano black or white finish. The main external difference between the older model and the new one is the rounded edges and corners of the new Tx rather than the sharp-edged cuboid format of the Ti. Internally the new Tx range has larger internal volume, redesigned driver and passive driver suspension, revamped damping, and some changes to the built-in amp. They have used trickle down technology and lessons learned from the Serie S range into the new Tx ranges. These significant changes to the cabinets and drivers are such that I feel they are definitely worth considering as an upgrade should you already have the earlier Ti version.

Armed with the knowledge that two-channel audio needs a sub capable of speed and fidelity whereas an AV sub needs punch and slam for those dynamic cinema moments I set about installing them into my two-channel system. I used the Hi-Level connection and set about the lengthy process of dialling them in. Integration is the key word here and something anyone setting up a sub should try to understand and take time to get right, the process as described by REL is roughly as follows for an audio rather than AV setup:

  • Connections for Class AB Amps – For an audio set up always use the Hi-Level connection. For a single sub the red lead goes to the red right positive main amp speaker output and the yellow lead goes to the red left positive speaker output. The black lead can be connected to either black terminal but not to both black negative speaker terminals on your amp. For a stereo pair twist the red and yellow leads from the same Sub together and connect the twisted pair for the right sub to the right red positive terminal and the left twisted pair of the left sub to the left red positive speaker terminal. The black lead for the right sub goes to the right negative speaker terminal and the left black lead goes to the left negative speaker terminal. Alternatively, they can be connected instead directly to your actual speaker terminals to reduce the need for running long leads back to your amp when using two subs.
  • Connecting to a Class D or Differential Balanced Amp – all as above but don’t connect the black leads, just leave them floating free. As my Class A Gryphon is described as a Differential Balanced amp, I didn’t connect the black leads to the speaker terminals. They can be connected to a ground tag if your amp has one but only if you get a hum without them connected. Just to be safe I taped up the redundant black leads to prevent them touching anything else.
  • Location - First decide on location in your room. For maximum room loading REL suggest placing one or two subs in the corners of the room behind the main speakers. But their website also suggests placing two of them next to the main speakers and in larger rooms they should be on the outside and just behind the front of the main speakers and in smaller rooms they can be placed inside and just behind the main speakers with them toed in to point at your listening position. I liked them best set inside the main speakers but for aesthetic and sound quality reasons I preferred them firing straight down the room without toe in. What is a large room anyway? No one ever really says what constitutes a large or small room but I’ll stick my neck out here and suggest anything in the UK less than 25sq m is small.
  • Phase - Turn the Crossover knob to zero
  • Turn the Volume knob up quite high
  • Play a bass heavy track
  • Switch the phase setting between 180 and 0 and decide which one sounds louder. The louder one is the right one. I couldn’t hear much difference but ended up at 180 deg.
  • Crossover and Volume - Set the Crossover to 10 clicks and the Volume at 10 clicks or about the 10 o’clock setting.
  • The sub or subs should not sound boomy or dominating and should enhance the sound from the main speakers not overpower them. Try reducing the Crossover a couple of click and listen again. At this point increase the volume by a couple of clicks.
  • Do this many times until you are satisfied that the subs are working well. You should be able to hear the RELs even with your main speakers playing but they shouldn’t overpower them.
  • Listen – leave the sub or subs alone for two weeks and then fine tune them again as they run in and you get used to them in your system.
  • Seen But Not Heard – There is a myth that a correctly set up sub should be seen and not heard or in other words they should be set at a point where you can’t really hear them. But this kind of defeats the purpose in my opinion. Correctly set up subs should be heard but not be set so loud that they overwhelm the main speakers in a stereo system, just don’t overdo it, they should not be boomy or dominant. In an AV Cinema set up subs do something very different and should definitely be heard or even felt! Remember an audio set up requires a sub with speed and fidelity whereas an AV set up needs slam. It’s a fine a subtle art that should enhance not overwhelm your main system.

REL suggest that in most systems the Crossover setting should be set somewhere between 10 and 15 clicks on the rear control knob and the Volume setting should be between 11 and 16 clicks for a single sub. It is important not to set the Crossover point too high otherwise the sub will start competing with your main speakers and this won’t result in happiness. The lower the Crossover setting the higher the Volume setting can be. When first using just one T7/x sub I eventually settled on Crossover at 10 clicks and Volume on 14 clicks. When adding a second sub the combined volume can increase by 3db so in theory you should turn the volume down a bit, and I settled on Crossover at 8 clicks and Volume at 13. At all times I had both subs set identically and on 180-degree phase shift, which seemed just a little louder than 0-degree phase shift.

Incorporating one REL T7/x into my system added extra bass as one would hope and did appear to open the soundstage a little. I tried it in a corner and then next to my main speakers and preferred the latter position. On ‘Hey You’ from The Wall by Pink Floyd the drums were more detailed with added weight and substance, but you do need to experiment with the settings on the T7/x otherwise it’s too easy to have them dominate the main speakers. With these REL Subs I did need to turn the volume on the preamp up before they really came to life and at lower evening listening volume levels their impact was less noticeable.

Playing more bass heavy tracks at good volume levels I chose ‘The Expert’ from Yello’s Touch Yello album and the RELs added considerable substance and weight to the performance and even Heidi Happy’s vocals seemed livelier and more vibrant.

Adding the second Sub wired as a stereo pair via the Hi-Level connection wasn’t of course twice as good as one Sub, I’d say it added a further 15% to the sound quality of using just one Sub but that elusive 15% is the Holy Grail for us audiophiles looking to improve our systems and, in this context, I would have to say two is definitely better than one.

The second Sub added even more depth but also increased the soundstage. ‘Run Like Hell’ also from The Wall now had an almost holographic Phil Spector-esc wall of sound imaging with drums panning left to right better than I had heard them before.

Conclusion – I had these Subs for an extended period, rarely turning them off as I grew used to what they were doing. Like many devices that are designed to enhance your system it’s not until you take them out that you realise just what they were adding and now I miss them greatly. I never thought I’d say that about Sub Woofers or as REL call them Sub Bass Systems, but there you are, I liked them – a lot. For those of us not wanting cinema levels of bass reinforcement in our two channel systems I would always go for the two small subs route unless you have a large listening room and/or don’t mind a big box or two sitting on the floor. REL of course may disagree and they did suggest a single Carbon Special sub would be the best fit in my system, perhaps another day.

Dislikes – just the rear blue light which is I felt was unnecessarily bright, and could be especially annoying if you are using them for cinema purposes in a darkened room.

Bob – Team Reference Audio