KEF XIO review: High-end soundbar with Dolby Atmos & Uni-Q MX

STEREO GUIDE verdict

93%

93%

Highlight

The KEF XIO combines 12 active speakers, Uni-Q MX technology, VECO bass control, and streaming up to 384 kHz—a soundbar for authentic home theater sound and high-quality hi-fi playback. Only analog fans are left out.

Pros

1. Amazingly spacious and bass-heavy 5.1.2 playback from a single speaker
2. Natural stereo reproduction with a fairly wide soundstage
3. Support for all leading streaming services and DLNA servers
4. Expandable via subwoofer (including wireless)

Cons

1. No analog inputs

• Tonal balance / transparency

  9.4
• Bass / Dynamics

  9
• Spatial imaging

  9
• Usability / Connectivity

  9.5
• Price/Performance

  9.4

When you look at the classy-looking, flat KEF XIO soundbar, everything looks so professional and coherent that it’s hard to believe that the British brand hasn’t been represented in this area before. On STEREO GUIDE we have already reviewed two of the brand’s active speakers, which we gave a good report. The LSX II and the LS 50 Wireless II impressed both in terms of sound and functionality. However, the two compact wireless speakers were in a different weight class to the home cinema speakers. The weight of ten kilos is no coincidence: there is a lot of technology inside the over 1.20 meter wide AV device.

Speaker architecture: Twelve drivers, fully active control

KEF has designed this array of technology to be very flexible. This enables optimum sound performance regardless of whether the user wants to operate the XIO soundbar lying on a sideboard or hanging it on the wall under the TV. The position sensor controls the 12 integrated speakers with their 12 Class D power amplifiers with a total output of an impressive 820 watts to ensure optimum acoustic conditions.

Inside the new KEF XIO soundbar is an ingenious speaker architecture: two chassis take care of the left side, two the right; in the middle, two further units provide the center channel. There are also two side-firing modules for the surround effects. Four co-rotating woofers are installed for low bass support, which work together as a single subwoofer. This complex configuration allows true 5.1.2 operation in a single housing and raises the XIO above many classic soundbars.

This begs the question: Why does KEF use two center speakers? A look under the removable fabric covering provides clarity: only the center speaker that points towards the listening position (horizontally or vertically) is used.

Uni-Q MX & VECO: New technologies for precision and control

The XIO is the first to use KEF’s newly developed Uni-Q MX technology. This is a miniature version of the legendary coaxial principle that has been the British company’s trademark for decades. Instead of combining two separate drive units for midrange and treble, as in the large hi-fi models, KEF has opted for a clever single-driver approach: a central dome and a circumferential cone share the same drive unit, with a flexible ring mechanically coupling the two elements. This means that at low frequencies the entire diaphragm is responsible for sound transport, while at higher frequencies only the dome is active. This purely mechanical transfer between the mid and high frequencies eliminates the need for an electrical crossover. Incidentally, this is where the name “MX” for mechanical crossover comes from.

For the side surround effects, KEF also uses full-range drivers that expand the sound field via reflections on the walls and ceiling. The Uni-Q MX modules are used twice: The front-firing chassis serves the front channel, while the upward-facing one works as a treble driver for the 3D level. This creates a true surround sound experience from just one cabinet. The KEF XIO is not only compatible with Dolby Atmos and DTS:X, but also with Dolby Surround, 360 Reality Audio and MPEG-H Audio.

Acoustic concept and signal processing

Behind the elegant front of the KEF XIO lies a complex and sophisticated inner workings. Each of the twelve active loudspeaker chassis is controlled by its own power amplifier, so that the travel times, levels and phases are precisely coordinated. This allows the sound image of the XIO to be finely adjusted and reproduced stably in the room across all channels. This feature is otherwise more familiar from discrete multi-channel setups.

In addition to the newly developed Uni-Q MX coaxial drivers, KEF has also completely redesigned the woofer range. The four built-in woofers have an oval design (5 × 18 cm) and work as a closed, phase-corrected unit. Their folded surround allows large linear excursions, while the aluminum cone ensures high rigidity with minimal weight. The special feature, however, is in the voice coil: it measures the actual cone movement in real time via an integrated sensor. The system, known internally as VECO (short for Velocity Control), uses this data for active negative feedback to increase precision and control.

As a practical result, the bass of the XIO remains exceptionally clean even at higher levels because the system intelligently limits the excursion before distortion occurs. This does mean that the very last low bass component is cut in favor of a controlled, impulse-free reproduction. But this is exactly what ensures the tight, defined bass reproduction you expect from KEF. All four woofers receive the sum signal of all channels and thus act like four small subwoofers that carry the bass foundation evenly into the room.

Acoustic concept: DSP, Music Integrity Engine 2.0 and active sound control

Signal processing is carried out by a powerful DSP, which coordinates the control of the chassis with millisecond precision and perfects the interaction between the front, treble and surround channels. The in-house Music Integrity Engine 2.0 ensures frequency and delay corrections across all channels. This technology provides the foundation for precise spatial imaging even in compact dimensions.

The sophisticated technical concept makes the KEF XIO one of the rare soundbars that not only fulfills home cinema but also hi-fi requirements. And all without the need for an external subwoofer or rear speakers.

Connectivity & features: HDMI eARC, streaming up to 384 kHz and wireless bass

The XIO is also fully equipped in terms of connectivity, at least for users with a purely digital focus: In addition to HDMI eARC for current televisions with Dolby Atmos and DTS:X support, there is an optical digital input for older devices, USB for firmware updates and a LAN port for stable network connections. Apple AirPlay 2 and Google Cast can also be used with the XIO for audio streaming. WLAN 6 and Bluetooth 5.3 are invisibly integrated. And if you still prefer additional low bass, you can integrate an external subwoofer via an RCA socket.

However, if you don’t want to compromise the elegant appearance of the XIO with additional cables, you can also bring the bass into play wirelessly. KEF offers the wireless subwoofer output via the optional KW2 system. The small KW2 RX receiver is simply attached to the back of a compatible KEF subwoofer and receives the signal wirelessly from the soundbar. This allows the subwoofer to be positioned freely in the room – without any tripping hazards and without compromising on sound quality. The connection remains stable and delay-free, ensuring seamless interaction between the soundbar and woofer module even in wireless mode.

App & calibration: KEF Connect between convenience and teething troubles

As usual with soundbar reviews, I tested the KEF XIO together with my esteemed colleague Raphael Vogt from the German audio magazine LowBeats in the editorial team’s home cinema listening room in Worms. Together we were able to try and solve the numerous little pitfalls of the KEF Connect app . I also didn’t feel alone with my criticism. While the app, which is available to download free of charge for iOS and Android, has received a lot of praise in the scene, we were really annoyed at times. The obligation to register with the manufacturer via an account that has yet to be created was the least annoying factor. Many competitors also require this in order to use their apps. At least we were able to solve the setup problems together.

The problems also affected the automatic calibration function, which is a welcome feature in itself. After the calibration failed several times, we discovered after some online research that the function had not even been implemented in firmware version 1.0 of the XIO at the time of testing. The problem has since been overcome, as we finally found newer software after a targeted search and were then able to optimize the soundbar very practically for the room using the two integrated measurement microphones. In this respect, this part is not relevant, but it ultimately shows that, despite all the good ingredients, an eye was turned here and there when operating the XIO. Because plug & play somehow looks different, especially as it should not be forgotten that the problem described was not the only operating obstacle.

What we really liked was the care taken with data protection, as KEF has designed the microphones so that they can be deactivated with a switch on the back of the housing.

Impressive automatic calibration and sound effects

Also well done: The sound presets that can be used based on the calibration are an interesting feature of the British soundbar. The KEF XIO offers six preset sound programs based on the automatic calibration of the room. In “Direct” mode, the soundbar plays the input signal completely unadulterated – ideal for purists who want to do without additional signal processing. The “Standard” setting, on the other hand, activates KEF’s upmixer and virtualization, which allows the sound to unfold more broadly and voices to emerge more clearly from the center. The “Music” mode has a very similar profile, with a slightly more open and lively effect, while “Film” emphasizes the bass range and brings out the surround effects more strongly.

If you want to be considerate of roommates or neighbors in the evening, choose “Night”. Here, the lowest bass frequencies are specifically reduced without impairing intelligibility. The “Dialogue” mode, on the other hand, focuses more on speech intelligibility by emphasizing the center channel and slightly reducing the lower frequencies. Overall, the six presets cover a wide range of applications. It ranges from sober studio sound to a dynamic home theater atmosphere.

Streaming services & hi-res support: from Spotify to HIGHRESAUDIO

The XIO is also uncompromisingly versatile when it comes to streaming. The soundbar supports Spotify Connect and Tidal Connect, allowing music to be streamed directly from the respective apps in full quality – without any detours via Bluetooth. Amazon Music, Qobuz, Deezer and HIGHRESAUDIO are also supported, so that even lovers of high-resolution studio master files get their money’s worth. The QQ Music service, which is popular in Asia, is also integrated via QPlay. The range is complemented by Internet radio and podcasts, which can be conveniently selected via the KEF Connect app. As always, the actual availability of the individual services depends on the country in question, but the XIO’s platform coverage is already one of the most comprehensive in the soundbar segment.

If you prefer to store your sound files on a local hard disk in the network, you also have the option of streaming via a DLNA server. The list of processed formats leaves nothing to be desired. Neither does the maximum possible resolution. It is 24 bit/384 kilohertz.

Sound test: The XIO amazes in stereo and surround

What amazed my colleague and me the most was the wide stereo stage, which even in normal direct mode without sound effects enabled a very decent stereo image. And the very good result could even be improved by using virtualization or upmixing. The immersive feeling is well suited to live concerts, although such effects are always a matter of taste. In any case, I found the bass reproduction from the LFE channel astonishing in view of the four relatively compact, integrated woofers. We really enjoyed the special effects in films such as Top Gun Maverick in the LowBeats listening room. And we mustn’t forget that we’re talking about an above-average ceiling height and a floor area estimated at around 40 square meters.

Also very good: Despite the powerful bass, which should make a subwoofer superfluous in most apartment buildings, voices could still be heard very clearly. Dialogue intelligibility was really excellent and very natural.

Stereo width, precise bass and real treble graduation

Also great: while many so-called Dolby Atmos soundbars had their problems with the ceiling height, with the KEF you could really notice an increase in the height of the imaginary sound stage. And the placement of sounds far to the side of the 1.21 meter wide soundbar also worked amazingly well. Colleague Vogt even connected another subwoofer, the Velodyne Acoustic DB 15, for his review the next day and was delighted with it.

When using subwoofers, the switchable high-pass filter does a good job: it relieves the integrated woofers and passes on low frequencies below the crossover frequency to the external subwoofer. This useful addition puts the KEF XIO in a completely different league, of course, but also increases the price and space requirements. And in many cases, the extra bass would be more of a problem in terms of conflicts with the neighborhood. However, for dedicated home cinemas, possibly in the basement of your own home, this is a thoroughly recommendable option. What is then possible in terms of sound would require a significantly larger budget with an armada of discrete speakers in order to be able to enjoy movies or concert videos in this quality.

KEF XIO: Conclusion and alternatives

If you disregard the somewhat hairy operation at the time of the reviewt, which was a while ago, the very stylishly designed KEF with its high-quality surface really delivers a great deal of home cinema enjoyment for the money. Thanks to its ingenious design, with the position sensor and the speakers that work perfectly both hanging and lying down, the English soundbar can be integrated very well into a variety of interiors. It is perfectly suited for flat screens from 55-65 inches. From a purely musical point of view, the similarly priced Nubert nuPro XS 8500 RC would be a good alternative, especially in terms of powerful, deep bass without an additional subwoofer. However, the Swabian power bar cannot keep up in terms of connectivity, immersive audio and format diversity.

Technical specifications: KEF XIO

• Manufacturer’s recommended retail price: 2,300 euros
• Dimensions (W x H x D): 121 x 7 x 16.5 cm
• Weight: 10.5 kg
• Special features: AirPlay 2, Google Cast, UPnP, Bluetooth 5.3, KEF Connect, HDMI (eARC), USB-C (service), TOSLINK, RJ45 Ethernet (network), supported audio codecs: Dolby Atmos, DTS:X, 360 Reality Audio, MPEG-H, FLAC, WAV, AIFF, ALAC, AAC, WMA, MP3, M4A, LPCM and Ogg Vorbis.
• More at www.kef.com

• KEF LS 50 Wireless II review
• Review: KEF LSX II with HDMI and USB