KEF LS 50 Review
If you had asked me which (passive) test speaker of the still young LowBeats history the manufacturer should activate, the answer would not have been difficult for me, the KEF LS 50, of course! This small compact loudspeaker with a coaxial mid-range tweeter (known as “Uni-Q” at KEF) sounds much larger than it is and surprises with naturalness and precise reproduction that would also look good on much more expensive loudspeakers. I love the KEF. LowBeat’s sound engineer Jürgen Schröder paid her perhaps the greatest compliment, “You can even master with it in the recording studio.”
And we were by no means the only ones who were so enthusiastic about the LS 50; the hi-fi press worldwide gave it outstanding reviews. Therefore, the idea of activation was obvious – at least the English have now taken exactly this step. The active LS 50 Wireless is an LS 50 that has grown somewhat in-depth, which requires the space gained for two power amplifiers and heat sinks plus processors and DACs.
About the basis for this all-in-one package, the passive LS 50, we have already reported in detail, which is why I would like to keep this point as short as possible. The striking shape of the LS 50 with the baffle sloping on all sides with the 13-centimeter Uni-Q driver in the middle is acoustically sophisticated and perfected in endless simulations, just like the flawless, multi-braced cabinet.
- Complete HiFi system with streaming, Bluetooth, Chromecast, etc.
- Excellent sound also on the TV via eARC
- Sound adjustment to set up and room via app
- Pretty high price
- Operation via sensor buttons is sometimes a bit sluggish
Furthermore, the KEF-typical coaxial driver with integrated tweeter is now in its 11th generation and, unlike many other coaxes, can be described as sounding mature. So, no nagging, no restriction in the high-frequency range, only the advantages of the coax. An exemplary spatial representation and uniform sound radiation of the entire mid-high range.
So it’s no wonder that the LS 50 Wireless is based on this housing construction and this excellent coaxial driver. And KEF didn’t have to do big pull-ups to activate the passive LS 50.
From a purely visual point of view, the increase in the volume of the housing and the closure to the rear with the heat sinks for the power amplifiers are even good; the already very successful exterior gets an additional attraction.
The digital signal processing of the LS 50 Wireless works with a HiRes resolution of 24Bit/192 kHz. This means that every incoming signal (including the analog ones) is first raised to this 24-bit/192-kilohertz level.
All sound corrections occur digitally before the signal is reconverted digitally/analog by the D/A converters (DACs) before the power amplifiers (AMPs). The power amplifiers are a classic (analog) A/B power amplifier for the high-frequency range and a powerful Class-D switching power amplifier for the low-frequency range.
The diagram shows the signal path into the LS 50 Wireless. Because there is a master and a slave speaker, the left and right speakers differ in the input area (diagram: KEF)
As the diagram also shows, the KEF LS 50 Wireless opens up a comparatively large number of connection options for the user:
- USB (asynchronous) for music from the computer
- A network input, an optical digital, and an analog cinch input
- Bluetooth 4.0 aptX is the currently best wireless connection to disposal
In practice, the LS 50 Wireless is set up quickly. We let the stopwatch run while unpacking the boxes and setting up with the app in the WLAN, less than five minutes. That’s great.
The practical and listening test of KEF LS 50
Once the two loudspeakers are connected with the included, 5-meter long CAT6 cable (not wireless) and the LS-50 app is loaded from the App Store; phase 2 can start. The smartphone or tablet recognizes this Network of the LS 50 Wireless – the extensive acoustic adjustments are already open to the user. By the way, the Expert mode only sounds demanding in the name; in reality, neither Basic nor Expert modes are difficult to understand.
For me, the modern KEFs always have a touch of too much bass. However, with a little trial and error in Expert mode, I had “my” perfect LS 50 sound in no time, thanks to the many setting options. That’s the advantage of active loudspeakers. You can’t achieve such a precise adjustment to the room acoustics or personal taste with passive speakers. Activation has another easy-to-hear benefit. Also, in Expert mode, you can switch “Time Correction,” i.e., the group delay of the tweeter and mid-bass speaker, on or off. This is a qualitative advantage that passive solutions cannot offer – not even with coaxial drivers optimized for it.
The measurements show how the “Time Correction” works. The output signal is a rectangle (left) distorted by the playback chain of woofers and tweeters plus the crossover (middle). The digital correction on the time domain (right) makes the signal much more similar to its original form. Our tip: Always listen with “Time Correction”!
The advantage of the system is that you can switch the “Time Correction” on and off. “Without” the room image is similar to the passive LS 50 – so already extremely good, but the sound snaps in even better. Everything is sharper contours. That’s impressive.
On the other hand, the operation is not as smooth as the setup. Using the pretty remote control, the processor takes an unusual time to implement the commands. For example, the restless tester pressed the volume for the third time until something happened. But even if you enter settings directly on the speaker or in the app menu, the processor takes an unusually long time to implement them. These are little things that you get used to quickly and will certainly be improved with the next upgrade.
We have already let the passive LS 50 run in partly absurd combinations – simply because it works out the differences even between the most expensive components very precisely.
For example, it was a lot of fun testing them with our Octave V 80 SE tube reference to let it run, what a representation of space, what an “authenticity” in the reproduction of voices. But the upstream amplifier can be as good as it wants. Activation with built-in power amplifiers for each branch and digital signal routing with the (ultimately necessary) D/A conversion only directly in front of the tweeter or woofer has unmistakable advantages.
Moreover, the power amplifiers are more or less closely connected to the drivers because you can improve the sound much more effectively with good signal processing than with a passive crossover. You can also adjust them much better to the room and your taste.
We first played the LS 50 Wireless wirelessly in the listening test. It runs smoothly and with “normal” resolution music at CD-level via Bluetooth and WLAN without any difficulty. HiRes streaming (up to 24Bit/192kHz) also works largely without problems in the WLAN. However, our WLAN sometimes has fluctuations, so there were sometimes dropouts. So I switched to cable – and then stuck with it. Because wired, the LS 50 Wireless sounded even more effortless. And with this control, the wiring between the two KEFs makes sense again.
The tonal characteristics of the KEF LS 50 are already known. It is a very full, natural tone, paired with a fantastic spatial representation and a very fine, never aggressive treble. The active LS 50 Wireless loses none of these fascinating properties. On the contrary, the very good power amplifiers and the precisely tuned tuning sharpens the contours models the individual instruments or voices even more believably in the listening room. This lets low-frequency waves roll through the recordings in an equally more lively, unfathomable, and precise manner as on the new Yello Toy. The experience factor with the passive LS 50 is great; with the active wireless version, everything becomes even more manageable.
The LS 50 Wireless is relatively small, and you would think it would quickly run out of breath, especially at higher volumes and deep bass. But, think, if you don’t demand too much bass from it in the settings (extended), it will amaze you with its extraordinary level of stability. If that is still not enough for you, you will find a subwoofer output (cinch) on the back, via which the LS 50 Wireless (by cable) can control an additional active bass.
With a subwoofer – we used the Velodyne SPL 1000 Ultra, which is ideally suited for this – completely new possibilities arise. Because you can spare the KEF with a subwoofer almost the entire (power-intensive) bass range, it plays much louder and with less distortion overall.
What do we have? A very pretty speaker with no flaws in quality and is available in three highly attractive color variants. For better differentiation, the LS 50 Wireless is available in subtly different color combinations than the passive LS 50.