KEF LSX Smart Active Loudspeaker Review

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Woolly cabinets, not woolly sound

by Ed Selley Apr 17, 2019 at 8:06 AM

  • Hi-Fi review


    KEF LSX Smart Active Loudspeaker Review
    SRP: £1,000.00

    What is the KEF LSX?

    The KEF LSX is a two way active speaker with decoding on board. Until comparatively recently, KEF was, barring a subwoofer amp here and there, content to solely focus on the business of making speakers - no great limitation given that they make plenty of them and do so very well. Even though speakers have not seen the upheaval that electronics have, KEF has still decided to be proactive about the changes going on in the industry at the moment. As well as the ‘normal’ areas that speaker brands have taken a look at like Bluetooth speakers and headphones, KEF has taken the plunge and started to make active speakers.

    What is notable about their first effort, the LS50 Active and now the LSX is that KEF’s take is that the best course of action is that their active speakers should be a self-contained system rather than something that you attach to a preamp. To do this, it means that housing both the electronics needed to make this work and the control system to make using it a practical proposition is quite a challenge and one that has to be done on top of the ‘standard’ challenges of making an active speaker.

    Of course, this means that the LSX has to be looked at a little differently to most speakers. This isn’t so much a pair of speakers as it is a complete system. Does the LSX do enough, and with enough aplomb to be all the system you need? Read on to find out.

    Specification and Design

    Kef LSX Specification and Design
    The LSX is slightly different to KEF’s more conventional speaker offerings in many ways but in one important regard, it is business as usual. Around the front, you’ll find an example of the company’s long-standing Uni-Q driver. Absolutely central to KEF’s design thinking and philosophy, it places the tweeter in the throat of the mid bass driver. This ensures that the dispersion of both can be controlled correctly and they will work on axis with one another. KEF has been beavering away on Uni-Q for over twenty years now and the version in the LSX has all of the refinements we’ve seen over the last few years including the ‘Tangerine’ waveguide on the tweeter to further help dispersion and the textured surround we’ve seen on other recent ranges.

    Like the LS50 and the Q350, KEF has moved this driver to the centre of the front panel. As well as some aesthetic benefits, which we’ll come to in due course, this ensures that driver acts uniformally on the front panel and that the cabinet can be designed to take this into account. A rear port helps to augment the low frequency response further. As such, the trad bits of the LSX are in keeping with the things we recognise from KEF.

    To make it active, the LSX uses a 70 watt amp for the mid bass and a 30 watt one for the tweeter. The design of the speaker is a true active design too. The crossover is in front of the amplification and is augmented by a DSP system. KEF calls this a ‘Musical Integrity Engine’ and says that it helps to shape the high and low frequency output of the LSX. This is not something that can be tweaked by the user - it goes about its business along predetermined lines.
    Kef LSX Specification and Design
    If the KEF was like the Acoustic Energy AE1 Active, this would be it. There would be an XLR on the back of each cabinet and away you’d go. KEF has decided that the best use of an active speaker is as a complete system though. This is how the LS50 Active is designed and they have done the same with the LSX. This means that the right hand ‘Master’ speaker contains a network module that works both wirelessly and wired, along with an optical input, a standard line level connection and aptX capable Bluetooth. There is additionally a subwoofer output for some 2.1 based fun.

    As well as conventional network audio, the LSX also supports Spotify and Tidal internally. There is no Tidal Masters support, which is a bit of a shame given they are included in the price of the basic subscription. One reason for this is that if you make a wireless connection to the LSX, it will downconvert incoming signals greater than 24/48 to this figure anyway. AirPlay 2 has been announced but wasn’t present on the review samples yet.

    If you do use a wired connection this cap is raised to 24/96 but I don’t think that many LSXs will be used in this fashion. One innovation over the LS50 is that the connection between the ‘Master’ speaker with the input board and the ‘Slave’ is a wireless connection protocol. KEF hasn’t been so rash as to remove the ability to wire them together though should you require. This is done via CAT5 rather than conventional speaker cable and a long example is provided in the box.

    Kef LSX
    This is a useful spread of features but there is a catch. At the time of writing (March 2019), the app that controls these functions simply isn’t very good. For starters, there are actually two apps - one that sets the LSX up and one that controls it. As you might imagine, this doesn’t result in the most joined up control experience possible. The ‘KEF Stream’ app that does day to day music selection from your library and Tidal, is sluggish in operation, awkward to browse and - on Android in particular - seems to lose contact with the speakers from time to time. I was recently slightly uncomplimentary about the DTS Play implementation in the SVS Prime Wireless but, on balance, I think KEF might have been better served going third party.

    This is a shame because the physical aspects of the LSX are beautifully realised. The LSX is recognisably a KEF speaker - that driver means that it could be little else - but it brings some design touches that are all new to the table. The first of these is that the cabinet is covered in an industrial fabric from Danish company Kvadrat. This is available in five finishes but really, the ones that grab the attention are the Blue, Green and Red options. In any of these, the LSX becomes more than electronics and takes on a character of its own. The Blue review samples look absolutely brilliant.

    They are also extremely well made. Each speaker feels hefty and carefully assembled, and little details like the point where the cloth meets the front baffle are done to an exceptional standard. This is not a large product for £1,000 but get it out of the box and you can see where the money has gone. It also comes with a remote which is a useful extra item as it allows for quick input selection and control when you can’t be bothered to fire up the app.

    Kef LSX
    The physical aspects of the LSX are beautifully realised

    How was the LSX tested?

    The KEF was placed on pair of Soundstyle Z60 stands and connected to an IsoTek Evo 3 Aquarius for power and a Melco N1A for a music library. An LG 55B7 OLED was connected via optical and a limited section of testing was carried out with an SOtM SMS 200 Neo Streamer and Chord Hugo2 running into the analogue input for a test of the absolute abilities of the speaker section of the LSX. The apps were installed on an Essential PH-1 and an iPad Pro and Bluetooth testing was undertaken from the Essential. Material used has included FLAC, ALAC, Tidal, Spotify and Deezer with some Netflix, Amazon and broadcast TV.

    Sound Quality

    Kef LSX Sound Quality
    Traditionally, I launch into the music capabilities of products in this section but I’m going to break the habit of a lifetime and start with using the LSX as external speakers for a TV. The reason for this is simple enough - the KEF is genuinely outstanding as a sound bar alternative. I know that Steve Withers has been working his way through a selection of products that do everything short of hoovering and that cost about £6.75 but I assure you that the LSX is a bit special in this regard.

    The reason for this is that the traditional virtues of three dimensionality and soundstaging are incredibly effective at contextualising the image on screen. The recent episode of The Grand Tour with the history of the Porsche 917 demonstrates this to excellent effect. The movement of the car across the screen is perfectly handled and the effect is far more immersive than you might reasonably expect from a pair of speakers. Dialogue stays intelligible and little details - not least the symphony of fury that is that flat 12 engine are superbly handled. I wouldn’t consider buying the LSX solely for augmenting a TV but if it is something you will need a system to do it does perform this role superbly.

    Happily, it’s no slouch musically either. The DSP functionality in the KEF might not be user adjustable but it works superbly to make this relatively compact speaker - it stands just 24cm tall - sound bigger and more assured than you might expect. What I like about this is that it has been achieved without that weirdly boosted and unnatural sound that can result from over zealous use of processing. Enjoying the joyously ballistic Doko Mien by Ibibio Sound System, the KEF manages to deliver enough bass to hit hard and be felt as much as heard but it integrates well with the rest of the frequency response and never sounds sluggish or disjointed even with this splendid homage to African dance hall greatness.
    Kef LSX Sound Quality
    The other real development for me is that in engineering their own relationship between the amps and drivers, KEF has made a speaker that sounds sweeter than some of my experiences with their passive products. With something a little on the sharp side like UNKLE’s War Stories, the LSX does a great job of keeping the intensity and energy of the album intact but managing to tame the worst excesses at the same time. It’s really beautifully judged and it ensures that the KEF will sound very engaging across a real world collection, rather than simply the edited highlights. It’s forgiving too - Deezer via aptX Bluetooth sounds more than reasonable too.

    That this has been achieved without affecting any of the existing virtues of KEF’s design practise is the really clever bit. As noted, the soundstage is truly outstanding and this is joined by excellent detail retrieval, tonal realism and a general togetherness that really benefits everything from the simplest acoustic work to complex massed instrumental work. It’s an extremely easy speaker to spend a very long time listening to.

    Kef LSX
    The KEF manages to deliver enough bass to hit hard and be felt as much as heard but it integrates well with the rest of the frequency response and never sounds sluggish or disjointed


    OUT OF


    • Sounds absolutely superb
    • Great piece of industrial design
    • Useful spread of inputs


    • App is sluggish and unresponsive
    • Sample rates restricted over wireless
    • Might benefit from Tidal Masters support
    You own this Total 1
    You want this Total 0
    You had this Total 0

    KEF LSX Smart Active Loudspeaker Review

    Every aspect of the design and engineering of the KEF LSX needs to be seen as a bit of a slam dunk. It looks fantastic and had the build quality to match. The decision to use a material coating for the cabinet is a great one, giving a point of differentiation that isn’t different for different’s sake. While part of me wants to see more ‘classic’ active speakers that can front a selection of electronics, the fitment of the LSX makes for an excellent alternative to a more conventional all-in-one system.

    Critically, it sounds great too. Across music and AV use, this is a barnstorming product that engages, cossets and delights in a way that isn’t always the case for something that might be seen to be very slightly 'lifestyle' in its design and implementation. There have been more than a few occasions where I’ve found myself totally emotionally invested in what these little speakers are doing.

    The catch is that I’ve also spent a fair bit of time swearing at the control app. KEF has done all the bits of the LSX where they are traditionally strong with their standard skill and attention to detail. The problem is that the software that ties this together is currently not up to the same standard. Of course, while a hardware issue will blight a product for its production life, software is a fixable area. I believe that KEF will make further improvements to the control interface to give this sublime little speaker the app it deserves and for that reason, it still earns our Recommendation.

    Suggested retail price when reviewed: £1,000.00

    The Rundown

    Build Quality




    Sound Quality


    Ease of Use




    Value for Money




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