This is a review written by Terry Ellis April 2026.

For my video review please see my YouTube channel link here

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Long wait

I had been patiently waiting all year to get my hands on the new REL Acoustics Serie S/850 and that is because I love subwoofers and what they add to an audio system because it’s very obvious because bass is so tangible and tactile and important. l do I love really good subwoofers.

Good looking

The Serie S is a very popular subwoofer range from REL and I can say this because of how many systems I have calibrated with them. I think that is because it’s always been a sweet spot subwoofer range, not just in terms of performance but also the styling and connections. I think REL get it, a subwoofer is so often a giant black box manufacturers are expecting people to have multiples of in their home. The nicer that box looks the easier having it in the home is and that does matter and I very much appreciate it.

I am sure REL used to say S stood for serious but I actually think the S should now stand for style because well look at it. REL have managed to find another way to reinvent the box to make it look even nicer and more stylish than before. I think it’s the combination of the handles and their colour and how they are set off by the recess areas for your hands, but its also the grooves and how clean they have been cut. It looks familiar to whats come before from REL but only from the much more expensive No.31 and 32. I lived with a pair of N0.31 for around a year so maybe that is this why this visual detail really stands out to me but it does make a difference.

I like the attentions to detail for the REL plaque on the top and how nice the finish is on it and how this nice finish is mirrored with the S/850 plaque that sits on top of the grill. Extra touches of quality like this we will inevitably take for granted very quickly but I think they will make a difference to how you feel about spending a premium amount of money on a subwoofer as is being asked by REL.

In detail

While I am speaking about the grills you may have seen some images of the new REL S series subwoofers with a wood grill and I really wanted to see one in the flesh. The wood grill is an additional extra purchase with the 850 and smaller 550 that costs about £450, so it’s a lot of money extra being asked. If you are looking to pair these subwoofers with any of the retro designed speakers and there are loads of them the extra cost might be worth it to you for a better visual match. I normally prefer to go “commando” with my speakers and subwoofers anyway because I like to see the drivers moving, I think its cool. Modern speaker drivers don’t move that much anymore whereas subwoofers are much more fun to watch because they still go at it at times when you get greedy with the volume.

I can many being happy with the included grills because they are very heavy well made things that definitely help to soften the look and that could be what you want. I do have to question if with this white finish 850 would look better if the lugs that hold the grills were also white and not black, I think maybe it would.

Lets talk specifics the S/850 uses a front firing active 12 inch woofer being driven by an 850 watt RMS Class D amplifier, with a 12 inch down firing passive radiator. The front firing driver cone is made from what REL call a carbon alloy material and it has a pure carbon fibre centre cap instead of aluminium and REL say these changes make the driver lighter and stiffer. Lifting the over 40kg lump up so you can see the passive radiator its cone is made from carbon glass fibre that REL say is 40% stiffer and lighter than previous range and it has 60mm of travel in each direction.

From the back there is the expected REL amplifier plate and the colour may have changed but the suite of connections and controls has not changed since as far back as I can remember so if you know REL subwoofers everything will be familiar. If you are new it’s all pretty self explanatory but fair play to REL they publish a lot of setup guides and make a lot of videos so kudos to them for helping their customers better understand their subwoofers. One thing I noticed was that the clicks on the controls were very obviously stepped with very obvious individual points and that seemed better than some REL’s I have setup in the past.

More interesting is the power supply for the Class D amplifier. REL say they are using a traditional power supply, to me that means a toroidal transformer and not a switching power supply which is much bigger heavier and more expensive to implement. Maybe only a few people will care about this but if that is you, same as me this will make you happy and is especially impressive at this power level of 850 watts RMS and 1000 watts peak. I am sure you need a big power supply for that.

REL say the crossover filters used in the 850 are using better quality components than before, such as higher quality film capacitors taken from the flagship subwoofers, trickle down tech we all love that. These filters are one of the reasons HiFi enthusiasts buy REL subwoofers as these are make REL’s high level connection work as it does.

Who is it for

So who is the REL S/850 for, for starters is the costs £3599  and with the wood grill, £4048. This is a serious amount of money for a subwoofer especially when you consider potentially buying a stereo pair or going all in for a six pack line array. That is an over 20 grand investment. All of the options are a lot of money so clearly the S/850 is for a very serious passionate music and or movie lover. I think the S/850 is more likely to be someone’s second subwoofer where they have started with a smaller T3, 5, 7 or 9 maybe and they want to step up to a bigger and beefier and more capable subwoofer without going too big and keeping the nice styling they are accustomed to.

Before you commit it might make sense to visit the REL suggested pairing tool that is free to use on their website. This tool will suggest what REL thinks will work best with your speakers and if your new and unsure then some free advice cannot hurt.

Before moving on I think its important to define what is a very good subwoofer because it will not be the same answer for everyone.  Some people care mostly about the raw numbers from ground plane measurements taken in a field and I appreciate how useful that information can be. I care more about what happens when I put the subwoofer in my room and how easy is it for me to get the bass result I am looking for as part of a two channel music only system. Unlike in cinema where maybe the focus is on raw output to what low frequency for music the demands are different and much more difficult to standardise. I judge a subwoofers performance very similar to a speaker and have to use all of my years of experience because I know what I am looking for.

Sound quality

For reviews I always like to have a reference product as a metric to judge others against.  I was hoping to have the S/812 here at the same time to see how much improvement there was in thwe S/850 but sadly I couldn’t get one. I  don’t have a reference subwoofer setup currently because of the lack of space in my home so i could not follow my usual review process.  I am happy to be honest about this and let you decide how you feel about it and how you judge the quality of this review as a result. I have been judging the S/850 quality based on my expectations and experience of having setup many subwoofers for many people and having had a lot of different subwoofers in this exact same room over the last 15+ years. That includes a lot of REL subwoofers.

I did all my testing for two channel music only using a high level connection, which is a speaker level connection straight from the back of my Esoteric S03 class A/B power amplifier, using a REL Bassline Blue high level cable. In my recent subwoofer reviews I have placed the subwoofer more in the middle of the room to try and better remove my rooms acoustics from what I hear. I did test the S/850 like this but I spent more time with it placed in a more user typical spot in the room with it sat next to the speakers. To be honest I did hear that much difference between the placements which proved to me this is a very transparent subwoofer even playing louder than was sensible for the speakers.

One my key subwoofer dislikes is when you can audibly locate where the bass is coming from and I did not have that issue here at all.  That does not mean every bass note was pitch perfect, I still have a room that even as extensively acoustically treated as it is still effects the bass due to the rooms small size. I listened through a ton of different music from stupid bass heavy tracks like Bass I love you and some drum and bass, electronic and reggae where you expect a subwoofer to make a big improvement from adding more bass. I also listened to a variety of non bass heavy music from commercial tracks to some light jazz and audiophile types of tracks where the subwoofers benefit might not be so obvious and there was a number of things I noticed.

Firstly there is a lot of heavy bass in a lot of modern produced music, like the 2020’s is making up for the lack bass in 80’s music. With the S/850 in the system all music new and old sounded more lively and energetic with a greater sense of occasion by a noticeable amount. I have been struggling try understand this to  explain it because I think about adding subwoofers to “flesh out” the music, to make it sound more full, bold and better balanced adding a greater sense of scale and presence in the room. The S/850 did that but to also make the music sound livelier and more energetic I can only put this down to the fact that bass is the musics foundation and the beats leads the way.

REL explain how the drivers in the S/850 are lighter and stiffer and having better filters this made it sound different to what I expected. It is a very fast and agile subwoofer but that I expected but is also a bit of a caged animal aspect to how it sounds too where it seems like its always just waiting to give you a bass hammering with the right music. This  has been hard to describe because for the majority of the time the S/850 sounds quite delicate with bass notes up to that point where it wants to go harder on you when the music demands it  and calling a subwoofers sound delicate feels like a huge misnomer doesn’t it.

It reminded me more of a muscular and dramatic T9X subwoofer more than I remember Serie S subwoofers sounding which is a comparison just from memory do take that into account. I am saying this because my memory of  Serie S subwoofers was they are a little heavier sounding with a more voluptuous sounding bass, the S/850 is not like that at all. It sounds more tight and pistonic in its bass delivery and maybe then comes over a touch dryer as a result, but you don’t get any obvious bass lingering or heaviness in the music even at lower volumes. At loud volumes the room can cause bass ringing of course but the S/850 transitions between higher and lower bass notes more like a T9X so very light on its feet. Always with this sense of I can hammer you with bass at any time which is a hard one to explain but trust me when you listen to it I think you will see what I mean, and this does all feels a little different for a REL S suboofer.

I tested with the crossover set higher and lower and the volume set high and low and there didn’t seem to be any limitation there within reason. This is important to know if you are looking to pair the S/850 with small stand mount speakers that might really benefit from a higher crossover and letting the 850 pick up a lot of the bass duties. I am a fan of higher crossovers on good subwoofers aynway even with some larger speakers because I understand human hearing and our perception of bass and HiFi systems that are setup or voiced too “neutral” up sounding too lean. I dont enjoy music sounding lean, it’s not realistic either to me so avoid this sound presentation as much as I can.

On off testing

I know there will be people that think I am wrong about this and that is fine but I find a higher crossover on a REL gets you closer to the sound of a six pack because it audibly raises the bass effect higher up the sound stage. The S/850 had no problem playing with the crossover set to around 12 o’clock I didn’t test any higher than that, but it was fast and clean playing notes in that frequency region which is great to know. I can’t say all music was 100% perfect all the time, I am not sure it ever is, especially for for bass when you scale it up big but it was very good overall for the majority of music I listened to. The S/850 sounded well integrated with the speakers where it was adding a lot to the music in all the usual REL ways and it was impossible to tell what bass was coming from the speakers or the subwoofer even at louder volumes, within reason of course.

I did a number of sub on and off tests and I always missed the REL when it was turned off. The bass it delivered added scale and dynamics, fleshed out the vocals nicely and aided with a greater sense of sound stage in the room where the individual music elements felt better knitted together or more cohesive.  There was that extra energy to the music as I mentioned before so of course anyone would miss all of this if it was taken away. The S/850 also made the low frequencies becomes it’s own vivid dynamic and vibrant part to the music, this is what I mean by the added energy to the music.

I could control this to some degree with the subwoofer placement and also the volume level. Listening at very low volumes late at night I could raise the bass volume a little a bit and the system still sounded very full, dynamic and lively. This is one of the great benefits of having subwoofers in a system the extra level of control to the sonic balance of the system. In terms of the output the S/850 seemed like a lot of sub for my small room size. The output from one S/850 was more than enough but I still think having two would have allowed to set things up better for a better result overall and but I did wonder if two of the smaller 550’s would be right for this room. They probably would but I did enjoy how the S/850 could play deeper notes without stressing hardly at all and that is often driver size influenced I have found

In saying all of this do I think the S/850 will be the best subwoofer for the money if all you listen to is Bass I love you, probably not, but for those who listen to other music I think the articulation and tight control of its bass delivery will impress you. How it delivers fast bass notes with a clean authority, is definitely a little different to what I expected and was still adjusting to and that is where a comparison would have been perfect and I can only apologise for not being able to do one.

Final Thoughts

Getting bass nailed for any audio system in a room is the hardest thing you can ever do, but it’s probably the most important thing to work on. Bass is so important because it adds so much to the experience and any subwoofer that makes the setup process easier gets a tick in my book. I do  think the modern REL’s have been making HiFi integration system easier.  The T9X has been the easiest subwoofer to setup in my room if that information helps anyone but they don’t do as much in terms of raw bass output and I think is partly why they are easier to setup. The S/850 has felt similar to the T9X to setup so if you moved up to one you will have a massive head start.

That is where I do have the same complaint as with all REL subwoofers below the flagship range. I don’t care about having an app control, a remote control would be nice but I can get off my ass to change the settings that is fine. I do think as REL’s are getting more powerful and capable having some EQ adjustment built into them like what you get with the No.31 could be really helpful to trim the bass where the room does too much. This is still on my wish list and sadly not delivered this time around but we can keep asking because if you don’t ask you don’t get.

The S/850 looks great, sounds great and will add a lot to the systems that it is used in making it an easy one to recommend.

An Essential Audition Award is granted in recognition of a products high performance but with a certain uniqueness that makes auditioning even more essential.

For the full specification of the REL Acoustics website here