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R400b Subwoofer

At just 14 inches square, the KEF R400b high performance subwoofer is compact, yet packs an incredible punch. Only a serious subwoofer could keep up with KEF's R-Series, and the R400b makes an awe-inspiring addition to any listening room or home theater set-up.

• Click here to read the latest R Series review from High-Def Digest!

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The R400b's reinforced and solidly braced cabinet houses twin 9in. LF drivers powered by twin 250W Class-D amplifiers. The drivers are mounted back-to-back: This ‘force cancelling' arrangement nullifies opposing reactive forces. The result is virtually no cabinet agitation and therefore a clean, fast, powerful bass performance.

Legendary KEF R Series
Featuring many of KEF’s latest innovations in premium hi-fi and home theatre loudspeaker technology, the R Series makes genuine audiophile standards of entertainment more affordable than ever before. Stunningly fluent Uni-Q driver arrays combine with potent new bass drivers and many ingenious refinements to create a rich, spacious sound image of such accuracy that it approaches the benchmark standards of KEF’s legendary Reference Series.

  • Click here to learn more about the KEF R400b subwoofer at
  • Customer Reviews

    Outstanding Review by Baskette
    Build Quality
    Sound Quality
    Would you recommend?
    Very accurate sub...a must have! (Posted on 7/6/2017)
    R400b - perfect match for Video and Music Review by Matthias
    Build Quality
    Sound Quality
    Would you recommend?
    After a few years with my KEF system , I finally added the R400b to complement the setup.
    I have been running the XQ5, XQ2, and XQ1 on an Denon AVR4308 for a few years. Listening to music was the major duty of the system. However, after a while watching movies became more frequent. Optic is just as important as build quality to me. So, I added the R400b to system. My expectations were high, as I LOVE my XQs in every aspect. And the R400b met every little bit of my expectations. The build quality is outstanding. It matches nicely the high gloss finish of my speakers. The setup was as easy as I had hoped for. The sound support when listening to movies is outstanding. The sub adds exactly what I was hoping for: crisp, powerful deep ends without ever being overwhelmed with the performance of the XQ5s. I keep changing the set up when listening to pure music. Most songs eg Jack Johnson in between dreams nicely work with the sub. However, more rock genres, I prefer w/o the sub.
    All in all , I absolutely enjoy this sub. Perfect match to a higher end set up, especially if you enjoy a high build quality and finish to show off in your living space. I recommend this product. (Posted on 12/11/2016)
    Holly Cow, What Phenomenal Sound Review by Rene
    Build Quality
    Sound Quality
    Would you recommend?
    I am of course the very very lucky winner of the HT-Guys 10th year anniversary grand prize – the Kef R-Series 5.1.2 Dolby Atmos Speaker System: 4 x R100, 1 x R200c, 1 x R400b, 2 x R50. I am so grateful to you guys, and to Dippin from KEF for this amazing prize.

    I apologise for the delay of this long overdue email, but with work, travel and other engagements, I did not have the time to fully test out the speaker system before now. Holly cow what phenomenal sound.

    First thing I wanted to point out is that I never bought individual speakers in the past. I have a limited budget for my home ‘entertainment’ setup, and I always put more of an emphasis on the television itself than the audio equipment attached to it. I did have ambiophonic setups in the past, but I’ve always had all-in-one systems with the inexpensive speakers that came with it. I always thought that the quality was decent, that I could experience all the audio mixes available correctly and that the speakers were fine for my needs in a small apartment. My last setup was an Onkyo HT-S5500, 7.1 Channel Home Theater Package. The Onkyo HT-R591 receiver that came with it does have the height input, so I was able to plug in the R50 speakers, even though it is not an Atmos enabled receiver.

    Wow, what a jump, I feel like I went straight from from preschool to postdoctoral studies. The first thing that is apparent is the shear power of the R-series set of speakers, which most certainly is due to the bigger drivers. Prior to receiving the R-400b subwoofer, I had done a calibration with the rest of the speakers. I was surprised how well these small speakers could handle low-end sounds.

    After a kerfuffle with U.S. / Canada customs (basically they destroyed the subwoofer and sent it back to KEF), I received the R400b. I did a proper three-position calibration using the Audyssey microphone. Well wow … what can I say.


    I am so used to listening to mp3s or streams on the go, that I didn’t think that it would matter much to me listening to music on such a system. Boy was I wrong … all of a sudden you rediscover new elements in music you thought you knew extremely well. I pay for the Rdio music service, which basically allows me access to a seemingly limitless catalogue of albums from a browser. There is also a Roku app for this service and this is the main source of streaming music to my audio setup. I realise this is not an ideal source, but the 192 kbps streams are good enough for me. There is a 320 kbps version, but I don’t really hear a difference. I would love for someone to point out a piece of music where they actually hear the difference between a 192 kbps vs 320 kbps bitrate, and what to look out for.

    I decided to use music I am quite familiar with to test out the system.

    “David Bowie: Earthling” – I’m Afraid of Americans (Rdio)

    There are such a variety of tones in this track and the speakers render all superbly.

    I’ve never felt the low tones this way; not a wash, just exactly the tones as they are supposed to be … but with such power that after 1 min I had to stop it in fear of forever ruining my reputation as good neighbor. This is going to be tricky … I’m going to need to spy on my neighbours to find out when they are not home so I can fully enjoy my setup.

    “Miles Davis: Ascenceur pour l’échafaud” soundtrack (CD & Rdio)

    I have listened to this music for such a long time on various formats (tape, CD, streaming), so I figured this would be a good test case.

    The first thing that was obvious was the hiss in the 1998 CD release of the 1958 recording. I never noticed this before, not that I was paying attention to it, but this is a testament to the quality of the speakers that I can notice it. On the re-mastered version, which was available on Rdio, the hiss was absent as expected, however I did notice a bit of gating (is that the correct term?). Basically I felt that the removal of the noise signature took a little away from the original elements, especially noticeable on the tenor sax. But this was very slight and obviously has nothing to do with the speakers, but the mastering itself. What a wonderful experience to listen to this piece on these speakers. After twiddling around with the different modes of the receiver, I stopped on the Dolby Pro Logic IIz – Height setting, since it seem to provide more ‘presence’ … the effect of which gave the impression of having the musicians in the room with me. For the first time I was aware of each individual player with all there expressiveness. This was absolutely clear when I could hear each individual brush stroke on the snare and the subtle accents. It gave me a whole new appreciation of the musicianship and the timeless quality of this recording. For those of you thinking of getting the R50s to enhance your sound, I strongly recommend it as it gives more breadth and more frontal power, which enhance the illusion of having the musicians there with you.

    Actually I'd like to know what do you guys recommend as audio mode when listening to music ?

    "Gyorgy Ligeti" – Continuum / Atmospheres / Ramifications

    There are recordings that just beg for a multi channel aural space, anything by Gyorgy Ligeti for instance. For those not familiar with this composer, just think of any memorable moment in a Stanley Kubrick film and chances are it’s enhanced by music by Ligeti. It’s a music that requires precise speakers, because his compositions often play with rhythmic layers that create phasing, where every note is important. If the sound is muddled, the effect is lost. The KEF speakers render these effects perfectly, since again, the individual voices can clearly be heard.

    Everything I put through it (Jazz, Rock, Folk, Classical, Electronic) sounded phenomenal to me. I never thought that surrounding myself with sound would be so pleasant, but also heighten my awareness of the musicianship by hearing very precisely the contribution of each player. This was only made possible because of the dynamics and accurateness of these R-Series speakers.

    Movies & TV:

    I have very few 7.1 mixed films in my collection, as I tend to purchase more foreign classics in ‘full glorious mono’ (as a friend would put it), but I did have "Prometheus" by Ridley Scott, which I used to test out the speakers. Right from the start, with the rolling military snare drums of the 20th Century Fox Fanfare and thunderous thump of the bass drum, I was transported into the theater. In the introductory scene, there is a waterfall … the roar of it was quite phenomenal and then a massive alien ship hovers into the frame with substantial low tones passing overhead. In the past, I’ve had systems that could deliver a good rumble to the room, but this is the first time I can say I could distinguish the tones of these two low hums … and even though there was absolutely no denying the power of these tones, I didn’t feel that it was simply just making the walls shake … it was clearly connected to what I was seeing on screen and totally engulfed me into the experience of being there. Granted, this has to do with good sound design, but I think I would not have gotten this if it weren’t for these speakers. With regards to the R50s, I have the impression they were also quite active during this sequence, because I did have the impression that the low tones of the ship were coming somewhat above me (though I realise that probably all speakers are involved to achieve this specialization).

    I’ve also been listening lately to the Daredevil series on Netflix. Having a Roku, I do get the Dolby Digital + mix. In light of the fact that this character is blind and has an enhanced auditory sense, the sound mix is used quite effectively to convey this ability, especially during fight sequences. All the thumps and positioning effects are quite vivid with these speakers and dialogue very clear in the center channel.

    Sincerely, KEF literally brought the theater into my home and now I understand why you guys (Braden & Ara) sometime say how much nicer it is to have this experience in your own home. As you often pointed out, the speakers make all the difference … and now I fully agree, speakers should be the number one priority of any enthusiast.

    When I’ll have the budget for it (in the new year), I will get a full blown Atmos enabled receiver and let you guys know of my impressions. For now I’ll just be enjoying the speakers thoroughly on a daily basis.

    Thank you HTGuys and KEF… you rocked my world!

    Now for the tricky part: Avoiding Eviction.

    Off to watch some HDTV.

    Rene (Posted on 7/15/2015)
    Kef 400b is a must subwoofer Review by apesfan
    Build Quality
    Sound Quality
    Would you recommend?
    The Kef r400b is an enginering feat and an audio delight. It compliments my mainspeaker in reaching the depths of sound and is and exciting participant in reaching the thunderous bass of Rock and pop and instrumental/classical music is a natural get out of the way effort.
    Agreat sub and highly recommended. Buying a second one for evening out some bass nulls. Take care, a customer for life, John M. (Posted on 7/12/2015)
    Good things come in a small package Review by Franche`
    Build Quality
    Sound Quality
    Would you recommend?
    The R400b subwoofer by far blows away its competition in such a small tight package. It drives anything that is thrown at it effortlessly. The sound it produces you would think you had a monster subwoofer or two. I have this in a 18'x18' room. Do not be afraid of this with two 9" drivers. You will be blown away what you hear. It pairs very well with the R series of speakers. Great Job KEF... (Posted on 5/20/2015)
    R400B The Perfect Match for R900s Review by Chris72174
    Sound Quality
    Would you recommend?
    Build Quality
    Accurate, tight and musical are just a few words I would use to describe the KEF R400B subwoofer. The identity of every low end source is obvious and spectacular through these subs. Hidden details on otherwise familiar songs are revealed like sonic jewels. I am currently running 2 of these paired with KEF R900s crossed over at 40hz rounding out my 2 channel set up. This combination is a match made in audio heaven. (Posted on 3/2/2014)


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    Model R400b
    Design Powered Subwoofer (Sealed)
    Drive Units Bass units:
    LF: 2 x 225mm (9in.)
    Frequency range (-6dB) 26Hz - 140Hz
    Maximum output 111dB
    Amplifier 2 x 250W (500W)
    built-in Class-D
    Low pass filter Variable 40Hz - 140Hz, 4th-order
    Low level signal inputs RCA phono sockets
    Speaker level inputs
    Internal volume 22 litres
    Power requirements 100V - 120V / 220V - 240V

    ~ 50 / 60Hz
    Power consumption 600VA
    Weight 21.5kg (47.4lbs.)
    Dimension (H x W x D)
    (with terminal & plinth)
    365 x 330 x 351 mm
    (14.4 x 13 x 13.8 in.)
    ** KEF reserves the right, in line with continuing research and development, to amend or change specifications. E&OE. **

    "If you're looking for premium speakers to fill your home theatre and handle a variety of musical genres, you can't do much better than the KEF R Series. Transparent. Well-rounded. Superb rendering and imaging at all volume levels. A powerful-yet-compact subwoofer. Fantastic in pieces, but as a complete sysem your home will sound better than your local movie theatre."
    Year: 2016
    Magazine / Issuing Body: High-Def Digest
    Country: United States
    Product: R900, R700, R500, R600c, R400b
    Click here to read the full review!
    Everything Audio Network R900 Review
    Subwoofer highly commended over $2,000
    Year: 2012
    Magazine / Issuing Body: Sound+Image Awards 2013
    Country: Australia 
    Product: R400b
    Home Theater Top Picks
    Year: 2012
    Magazine / Issuing Body: Home Theater
    Country: USA
    Product: R400b
     • Download full review
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