March 2019

KEF LSX Wireless Music System
The greatest thing since sliced bread!
Review By Phil Gold

  What a pleasure to find an inexpensive component that excites a high-end reviewer. And a product from KEF! KEF Chorales were the first decent speakers I owned. Modestly priced, high performance, utterly reliable, what's not to like? I owned them fresh out of university until I traded them in for the even more remarkable Spendor BC1 - more extended, lively and open, but with a habit of eating through woofers at the volume level I preferred.

Chorale (1970-79) According To KEF
The introduction in 1970 of the B200 class of bass drivers with an 8" doped Bextrene cone allowed a useful expansion of the KEF speaker range, being used straight away in the C-Series models Chorale, Cadenza and Cantor. The Chorale paired a B200 with the established T27 tweeter in a 20 liter closed box design, which became an instant success and KEF's new best-selling product. It combined an extended high frequency response with a natural, uncolored midrange and a full round, bass - quiet and delicate or complex and heavy music being handled with equal ease. The success of the Chorale ensured that it remained in production until 1979.

First Time Reviewing KEF
I haven't owned or reviewed any KEF products since then, but I've been very impressed with the spectacular and uber-expensive Muon speakers, the Blade and the LS50, all of which are based on KEF's Uni-Q dual concentric driver technology. Dual concentric means the tweeter sits at the center of the woofer. KEF is not the only company to have developed dual concentric technology – think of early pioneers Altec and Tannoy. KEF's major advance in 1988 was to bring the acoustic centers of the tweeter and midrange together in all three dimensions, thereby enhancing the time coherency of the drivers. Currently Cabasse, ELAC and TAD are also following this difficult path. Let's face it, it's hard enough to design a high-performance tweeter, let alone to mount one within a high-performance woofer.

Uni-Q According To KEF
It is not easy to produce a convincing and realistic illusion of a live performance because the sound from a high-quality loudspeaker does not come from a single source or drive unit. Two or more units are required to faithfully reproduce the entire audio spectrum from the low bass produced by a concert organ or a cinema explosion, to the delicate nuances of the human voice in the midrange right up to the shimmering treble of cymbals. Most loudspeakers have the midrange and treble drive units mounted one above the other, so the sound is coming from two different places, causing audio 'confusion' and losing the chance of achieving a truly natural sound. With Uni-Q, the midrange and treble units are mounted at precisely the same point in space - allowing them to integrate perfectly and create the ideal sound field for the listener to experience a convincingly natural sound.

What I Like About...
What I like best about the LSX is that KEF has developed it on a firm sound foundation, the Uni-Q driver, adding wireless streaming and control, active bi-amp'ing and reducing the size of the Uni-Q driver. All this without losing sight of the superb sound with which the bigger and more expensive models have seduced the audiophile world. The LSX derives most immediately from the very successful LS50 Wireless speaker, which in turn was based on the more conventional LS50 speaker. The LS50, introduced in 2012, was KEF's modern-day answer to the famous BBC designed LS3/5A from 1975, whose drivers it supplied, but based on a version of the thoroughly refined Uni-Q design. With a 5.25" Magnesium/Aluminum alloy cone woofer and a 1" vented aluminum-dome tweeter, the LS50 was specified at 79Hz to 28kHz (+/-3dB), with a maximum SPL of 106dB. All this in a box measuring 11.9" x 7.9" x 10.9" (HxWxD), weighing 15.8 lbs and priced at $1499.99 per pair.

The LS50 Wireless appeared in 2016, with the addition of two amplifiers, DACs and wireless streaming. Digital inputs arrive at one speaker, which is linked to the second by an Ethernet cable. Wireless, USB and TosLink optical inputs are available in addition to Bluetooth 4. Tidal, Qobuz and Spotify support is built right in. There's even an analog input, which is immediately converted to a 24-bit/192kHz bitstream. The woofer is directly driven by a 200 Wpc Class D amp, and the tweeter by a 30 Wpc Class A/B amp. The DSP based crossover works before the amplification stage and can compensate for the natural response curve of each driver in the box, so the LS50 Wireless can gain the full benefits of active amplification in terms of direct connection of amps to drivers and superior bass output compared to the standard LS50. How they ultimately compare depends on what amps you use to drive the standard LS50, what speaker cable you use to connect them and the quality of your DAC. Press reviews have been very favorable. The weight is up a little over the LS50 with 22.5 lbs for the primary speaker and 20 lbs. for the secondary, while the depth of each speaker increases to 12". the LS50 Wireless is specified at 45Hz to 28kHz (+/-3dB), with a maximum SPL of 106dB. Note the significant bandwidth extension achieved by active amplification and DSP. The price is a very reasonable $2,199.99.

So now KEF has shrunk the LS50 Wireless to create the LSX. The new box measures just 9.5" x 6.1" x 7.1 (HxWxD), the weight drops to under 8 lbs., while the price drops to $1099.99, just half the price of its bigger brother. There are other changes too. The woofer is now 4.5", the tweeter 0.75", while the woofer amp outputs 70 Watts to the tweeter amp's 30watts. Both amps now operate in Class D, a move necessary to avoid the need for bulky heatsinks. The frequency range is now specified at 54Hz to 28kHz (+/-3dB) and the max SPL is 102dB. To make sure it fits into your décor, you can choose between Gloss White, Maroon, Olive, Blue and Black finishes. The test units are Gloss White.

We can see from the specs that the diminutive LSX has superb bass reach for its size, easily beating the original LS50 and approaching the LS50 Wireless. As an audiophile, the combination of a metal dome tweeter and Class D amplification raises questions – would the treble be harsh and fatiguing, or has KEF perfected its secret sauce?

The LSX comes with a simple eight-button remote control, but I rarely used it. Instead I controlled the speakers from my iPhone. KEF provides two apps – KEF Control and KEF Stream. You can stream from your PC or smart phone to the LSX over Bluetooth, but the preferred path is to use your home Wi-Fi, which enables you to control the speakers from any room in your house. I did most of my listening through Tidal HiFi, since KEF provides a free six-month subscription. But I also used the LSX pair, to excellent effect, as speakers for my flat screen TV, and they performed very well in this role, connected by an optical cable. I never felt the need for a subwoofer.

You use KEF Control to setup the connection and to configure the LSX for the best sound in your room. You can use BASIC or EXPERT mode for sound shaping. BASIC asks if your speaker is on a stand or a desk. Then you enter the distance to the wall, and if you are using a desk you also give the distance from the front edge. Then you tell it how lively your room is, and how large.  You can also configure a subwoofer. Then you can save that as a named configuration and set up more configurations that you can switch between on the fly.

For more control you can select the EXPERT mode. It offers independent selection of desk mode and wall mode, with a slider for each allowing 6dB of adjustment, plus a 4dB range for treble trim. You can select Phase correction (on, off), bass extension (less, standard, extra). If you are using a subwoofer (which I wasn't) you can select high pass mode and frequency, sub out low-pass frequency, sub gain and sub polarity.

The settings tab allows you to select Cable mode or Wireless mode for passing the signal from the Master to the Slave speaker, and you can also select whether the Master should sit on the right or the left. I tried both and couldn't tell the difference. There are options for when to switch into Standby (20m, 60m, never), volume setting (turn on and off the hardware buttons, volume button sensitivity, maximum volume limitation and a balance control. The CONTROL app also allows you to update the firmware in the speaker.

To play music from your phone you select the button "Open KEF Stream", which puts you into the second KEF app. Here you select which device you want to connect to. From here you can connect to any Media Server you may have, or to TIDAL or Spotify, which stream directly from your internet provider, not through your smartphone or computer. Once connected to Tidal, KEF Stream just works as a remote control, and once you set a playlist or an album going, you can turn off your phone and the music continues through its direct streaming. If you do close the apps or turn off your phone, that's when you'll need the small remote control, so you can pause, adjust volume, switch tracks and so on.

Does all this work as advertised? Mostly yes, but not perfectly. Networking is rarely perfect. I ran into the occasional operational glitch, where the speakers would fail to respond to KEF Stream. I spoke to KEF's Jack Sharkey about this and he told me this is a known issue, and we can expect it to be addressed in a future firmware update. Until then, try turning it off and turning it on again. Worked for me. A second problem for me is the range of the remote control. Rated for 33', I had some trouble at 20'. Your mileage may vary, or your room may not be so large, so you may never run into this issue. In any event, I used the remote control so rarely this was rarely an issue. I also found the LSX would often react slowly to commands, but this is most likely TIDAL's responsibility, not KEF's.

Now I'm not thrilled about there being two apps (KEF Control and KEF Stream) that you need to use on your iPhone or Android device. But iPhone users can relax. The next firmware update (free of course) will allow you to use iTunes or whatever music app you like to speak directly to the LSX using AirPlay 2, so you won't need KEF Stream any more.

OK, OK. Enough about the logistics.

Q. How does it sound?

A. Simply remarkable.

Nothing shows the LSX in better light than a Nina Simone playlist in Tidal HiFi. There is real excitement generated by these miniature speakers, out of all proportion to their size. You can turn up the wick and it gets louder but it doesn't bloat or strain. Nina's in the room, and her voice is magical. No, you don't get the dynamic range of bigger separates, you don't get the black background or the inner detail of high-end audio, you don't get the amazing reflexes and long sustain of megabuck speakers, but it's what you do get that counts. You get a real sense of scale, a beautiful tone, a non-fatiguing treble, a punchy bass and most of all… you get amazing imaging by any standards, courtesy of the coincident drivers. Mood Indigo gives us Simone's superb pianism (streets ahead of pretty much all rivals) plus her inimitable voice. Miss Simone is in the room. Don't Smoke in Bed, Do Nothing ‘Till you Hear from me, and my all-time favorite Cotton Eyed Joe take me back decades.

The LSX tackles the concert grand piano in style. You get a good feeling for the color and weight of the instrument in the hands of Richter in Handel, or Kissin in Chopin, and you can easily distinguish the touch of each artist. The sound is consistently warm, forward and engaging with a variety of genre, folk, rock, Spanish guitar, orchestral music, jazz. The excellent imaging makes up for omissions in other areas by bringing performers into the room with you. There are no hard edges to the sound, despite the use of Class D amplifiers, but I do miss some of the transient attack and especially the massive dynamics I hear in the concert hall or through my reference system. Let's be realistic here. While they exceed my expectations and offer remarkable value for the price and performance for their size, KEF has the Blade, Muon and other models aimed directly at the audiophile. The LSX is designed to bring a new level of performance to this price range and size class, way ahead of the various smart speakers from Apple, Google, Sonos and Amazon, and competitive with similarly priced speakers that lack the wireless streaming abilities. KEF's aim is true. They have achieved just what they set out to do, and the LSX is justifiably screaming off the shelves.

The LSX has a punch and liveliness that reminds me of small speakers from Totem Acoustics. This sound is quite forward, although given the DSP options you can tame this quite a bit. I didn't find the settings in the KEF Control app to work like traditional tone controls so much as fine tuning within a limited range. This is fine by me. The sound is neutral and well balanced at its central settings, and the DSP just helps to optimize the speakers to your room and your taste. However even at the central settings, DSP is already working its magic to get an enhanced bass extension from the small woofer, with the aid of the rear port. Few conventional speakers offer any such adjustments, so they are often much more critical about room placement. The LSX can work its magic just about anywhere.

Now how does the LSX compare with its big brother, the LS50 Wireless? I don't have them here, so I can't do any AB testing, but from the specifications, I would expect the LS50 Wireless to dig deeper (3dB down at 45Hz vs 54Hz) and play louder (106dB versus 102dB). I would expect other aspects of the sound to be quite similar, given the commonality in design elements.

So pound for pound, and dollar for dollar, the LSX is a class act, beautifully constructed, attractive to look at, and glorious to audition. A winner in my book. I can't wait to see what else KEF may have up their sleeve.

Specifications
Type: Powered speakers with DAC and music streaming capability
Woofer: 4.5" magnesium/aluminum alloy cone
Tweeter: 0.75" aluminum dome in Uni-Q drive array
Woofer Amp: 70 Watts Class D
Tweeter Amp: 30 Watts Class D
Maximum Sound Output: 102dB
Frequency Response: 54Hz to 28kHz (+/-3dB more bass extension)
59Hz to 28kHz (+/-3dB standard)
55Hz to 47kHz (+/-3dB less bass extension)
Analog Input: 3.5mm AUX
Wireless Inputs: Bluetooth 4.2 with aptX codec 
2.4GHz/5GHz 802.11a/b/g/n
Digital Inputs: TosLink optical and RJ45 Ethernet
L/R Speaker Connection: 2.4GHz Wireless (up to 48kHz/24bit)
RJ45 Ethernet (up to 96kHz/24-bit) 
Bluetooth Range: 33'
Digital Input Resolution: Up to 192kHz/24-bit. 
Streaming Support: Tidal, Qobuz and Spotify built in
KEF Apps: KEF Control, KEF Stream (IOS, Android)
Dimensions: 9.5" x 6.1" x 7.1"
Weight: 7.9 lbs (primary) and 7.7lbs (secondary)
Finishes: White Gloss, Blue, Green, Maroon, and Black.
Price: $1099.99 per pair

Company Information
KEF USA
GP Acoustics (US), Inc.
10 Timber Lane
Marlboro, New Jersey 07746

Voice USA: (732) 683-2356
E-mail: info.us@kef.com
Website: www.KEF.com