There is, truly, no substitute for stereo reproduction when it comes to delivering music the way it was designed to be heard. The first stereo demonstration was made in 1881, with Clément Ader’s stereo telephone headsets delivering sound direct from the Paris Opera. British engineer Alan Blumlein at EMI extended the idea to speakers in the 1930s after watching early talkies movies where the sound didn’t follow the on-screen movements of the actor. Stereo went via tape to the LP in 1957, and has been the mainstay of hi-fi ever since. And yet today the trend towards smaller wireless speakers has led to a regression back to mono, or at least one-box stereo, which is not much better.

So we applaud KEF’s marketing slogan for the LSX — “Give your music the space it deserves.” While some one-box wireless speakers can be paired with a second unit, KEF’s LSX is a true stereo system from the start. You get one master speaker and one slave, requiring a mains cable each but no other connector between; they will connect and share music at 24-bit/48kHz. Or you can use the supplied Ethernet cable between them and they will then share music at 24-bit/96kHz.

You can plug sources into them — the master speaker has a full-size optical input, and a minijack analogue input. One of these might serve to take the sound from your TV, for example, while their wireless abilities can serve your musical needs.

The speakers can network via Ethernet or dual-band Wi-Fi, along with Bluetooth direct streaming that supports the aptX near-CD-quality codec for Android users whose phones support aptX. While Bluetooth will limit quality (see below), the network connection will allow streaming of files up to 24-bit/192kHz, though subject to the 48kHz or 96kHz transmission limit between speakers as noted above.

We had a dream set-up experience, with everything working first time. There is a KEF Connect app which walks you through the initial connection, then it hands over to a KEF Stream app which gives you access to Spotify Connect and Tidal directly, and to files via DLNA from home shares. The imminent arrival of Apple’s AirPlay 2 will allow a degree of multiroom use and voice control via Siri, and of course there’s Bluetooth streaming which includes the aptX codec if your Android phone supports it (no AAC codec for Apple users, perhaps because AirPlay 2 is on the way).

We had them playing within five minutes of unpacking the speakers. They really are small — just 24cm high, though reassuringly weighty with all the technology within — the networking circuits, the power modules providing a quoted though unspecified 100W to each speaker, split 30W to the tweeter and 70W to the woofer. They port to the rear, with the port matching your choice of colour on all but the white and grey finishes, which both boast a startlingly scarlet port. All but the white version come wrapped in fabric from Danish textile manufacturer Kvadrat (white fabric would get too dirty too quickly, KEF explains), while the ribbed backplate is not a heatsink; the ribs merely provide a design link to the company’s larger LS50 wireless speakers, we gather, while the real heatsink is internal. If you look closely you’ll see that the backplate leaves a small gap at top and bottom, creating an airflow which allows internal heat to rise and exit.


Coaxial Uni-Q
If you’re wondering about us mentioning woofers and tweeters when only one drive unit is on show, this is KEF’s fondest piece of technology — the Uni-Q driver, which places the tweeter inside the larger driver. This is neat both aesthetically and sonically, since with coaxial drivers you avoid the time alignment issues of separately placed drivers. Coaxials go back a long way — one of the other brands in this group, Altec Lansing, had coaxial studio monitors as early as 1943. But KEF’s Uni-Q drivers are not only coaxial but coincident, delivering a time-aligned point source of sound. The effect is to allow a wider sweet spot, or at least a wider area without ill effects to the frequency response. The LSX’s version of KEF’s Uni-Q driver combines a 19mm aluminium-dome tweeter within a 115mm magnesium/aluminium-alloy mid/bass cone, compared with the 25mm/130mm combo in the LS50W.

But the LSX is “not simply a baby LS50W”, we were informed by KEF’s Ben Hagens when we were first introduced to the speaker. He says this is more about KEF changing what hi-fi can be — a product for the 95%, not the 5%, he said.

That’s partly about making it simple to use, but we wonder if it also explains the sonic balance of the LSX. It was immediately apparent that their bass response had been significantly loaded by the use of DSP (digital signal processing — KEF refers to it as a ‘Music Integrity Engine’). The effect on their frequency balance is especially impressive at casual listening levels. Most systems lose relative bass strength as level drops, but the LSX keeps the balance tilted for a powerful and musical presentation. The deep three bass notes under BjÖrk’s Hyperballad rolled out of the LSX pair and energised the room even at medium listening levels, but didn’t then overly drown the vocal when we turned things up. More than that, there is hi-fi magic in the Uni-Q drivers; Neil Finn’s vocal on the ‘Afterglow’ version of Private Universe was rich and real in a truly presented acoustic space.

In this, however, we would strongly point you to using the Wi-Fi input path (see panel), rather than Bluetooth, which simply stripped a little joy out of everything — less fizz to BjÖrk’s bass, less acoustic around Neil’s vocal; it’s simply a loss of information when streaming via Bluetooth. (Those with aptX-compatible Android phones may enjoy better results.) Also we noted that in Wi-Fi mode, the side buttons of our iPad Pro fully controlled volume, whereas in Bluetooth mode these only controlled the level within Apple’s Music app; we had to return to KEF Control to turn it up further, a messy solution, more so as the physical remote was glitchy in this situation. KEF Control should just get out of the volume path when using Bluetooth (as it does for Spotify).
In our first week of casual use we had decided that the LSX’s DSP made the bass too lumpy when you turn them up loud. This is true — via Bluetooth. From Wi-Fi the bass is more solid, tighter, even with tracks below CD quality. Since the Wi-Fi connection could be used to play tracks and iTunes playlists direct from our iPad Pro (despite Apple supposedly closing off this option for others, including Bluesound), we stuck with this for the rest of our time with the LSX, and loved them ever thereafter.

The apps
There are two apps — ‘KEF Control’ gets you connected and also acts as a remote control, useful if you find the supplied physical remote with its red-on-black markings as difficult to read in anything other than bright daylight as did we. If you select the Wi-Fi input, you are shifted to the ‘KEF Stream’ app, which offers the highest quality path for music to the KEFs. The menu of KEF Stream (inset on the screen above) distractingly offers ‘News’, which turns out to be KEF news, and news about the LS50s at that... Rather more useful is ‘Playlists’ and ‘Library’, which show music stored on your device (other manufacturers say Apple is now preventing this, which would seriously hamper playback for iOS users of the LSX if they did). Below those are Tidal, Spotify (the KEFs use Spotify Direct under the control of your Spotify app), and ‘Media Servers’ for UPnP network streaming — we played high-res FLAC, WAV, AIFF and AL this way, though a 24/192 WAV file proved too much for something in the chain.

While the best of the single-box wireless speakers in our group this issue (Vol 32#3, Apr/May 2019) achieve musical and sometimes powerful results, the true stereo KEFs with their coaxial drivers deliver a higher level of hi-fi, effective at medium listening levels from Bluetooth, but far better using the Wi-Fi connection, where they can be entrancingly effective music-makers from such attractive and compact cabinets.