KEF LS50 Loudspeaker Review 
Home Theater Loudspeakers Bookshelf/Monitor Loudspeakers
Written by Andre Marc   
Thursday, 07 November 2013

KEF, based in the U.K., enjoys status as one of the most respected, and long-lived, speaker manufacturers in high-end audio. The company has designed and sold some of the best-known speakers in the history of the hobby. They have multiple lines they sell direct and through an extensive worldwide dealer network. Their products range from statement, reference level speakers, to more modest home theater applications. Their economies of scale and engineering resources allow them to cover all bases.

KEF is famously associated with the development of the British Broadcasting Corporations’ iconic LS3/5a two-way mini monitor. The BBC used KEF drivers to develop a compact speaker for location monitoring that could stand the rigors of professional use. The design was later licensed to a number of manufacturers including Rogers, Spendor, Harbeth, and others. I owned two pairs of Rogers LS3/5As; I currently own a pair Spendor S3/5Rs. Variations of the design are still manufactured by a few companies, including Stirling Broadcast, Harbeth, Spendor, and My Audio Design.

KEF decided to commemorate their 50th anniversary with the LS50 monitors, which sell for $1500 a pair. They were designed in the U.K. and are manufactured in their own group factory in Asia. According to KEF, “the LS50 is a two-way loudspeaker system, inspired by the LS3/5A and conceived to celebrate the 50th anniversary of KEF. Like the LS3/5A, the LS50 has been developed with the extensive application of the latest engineering techniques, along with meticulous attention to detail. It uses KEF's latest 5” mid-range and 1” high-frequency driver units in a compact two-way system. Extensive listening tests were performed to ensure the right engineering choices were made to achieve the best possible balance. Both systems could be described as “Engineers loudspeakers”, where the design has been determined by engineering parameters and sonic performance, rather than marketing requirements.”

KEF says they used all of their engineering muscle to develop the LS50 as a “statement” product, despite its affordable price. Starting from the ground up, they paid attention to very specific parameters such as enclosure design, bracing and resonance control, front baffle diffraction, and port design.

In KEF’s own words, “the development of the LS50 was based on a highly technological approach. Simulation and measurement is used wherever possible to identify, quantify and resolve performance shortcomings. This philosophy is classic KEF and is one which has been consistently applied over the company’s 50 year history. The recent maturity of numerical techniques, such as FEA and BEA, make the approach more effective than ever – especially when guided by critical listening and engineering intuition. Recent products such as the Blade, the R-series and now the LS50 are testament to the efficacy of this process.

The LS50 uses a central driver position and computer optimised acoustical damping to avoid
exciting resonances due to standing waves. A combination of bracing on the symmetry planes and constrained layer damping within the enclosure construction is extremely effective at absorbing the driver vibration and effectively eliminates cabinet colouration due to wall radiation. The baffle design provides a smooth response over the entire forward region, reducing tonal variation in different listener positions and ensuring the most spacious sound with precise stereo imaging. The port design has a profile optimised to avoid turbulence with the accompanying distortion and bass compression. A flexible section in the port reduces resonant midrange output from the port
.”

The LS50s secret weapon is KEF’s proprietary Uni-Q driver. Variations on this coaxial driver design are used throughout KEF’s lines, including on their flagship, $30,000 Blade floorstanders. I am a big fan of speakers with coaxial drivers, which includes Thiel and the recently reviewed Bogdan Audio Creations Art Deco. This type of design brings an unmistakable coherence and singular voice to the table. The KS50 uses a 5.25” Uni-Q driver, finished in a very distinctive orange-gold melange. KEF hyper-engineered the Uni-Q driver to address linearity, distortion, and dispersion. This allows the driver to essentially act as a point source. 




Set Up & Listening

I used the LS50s in two separate systems, and with three separate amplifiers. KEF told me to make sure the speakers get 100 hours of break in, and to provide them with decent power. I used the McIntosh MA6600, 200 wpc and the Electrocompaniet ECI-3 70 wpc integrated amplifiers in system one. The speakers were installed on 26-inch Sound Anchors stands, with Transparent speaker cable. In system two, they were put on 26-inch sand-filled Atacama stands driven by the new Rogue ST 100, 100 wpc tube amp, with a CIAudio PLC-1 MKII passive linestage.

KEF’s break-in advice turned out to be spot on as, out of the box, the speakers were a bit reticent. This is very common for speakers outfitted with drivers made of advanced materials.  Once the driver relaxed a bit, I heard the same spectacular coherence experienced at various trade shows (as driven by Parasound electronics). I also heard dynamics that were simply thrilling for speakers this size. And the icing on the proverbial cake? The LS50s’ dynamic capabilities seemed effortless.

KEF LS50Contemporaneous with the review period for the for LS50s, I received my copy of the Deluxe Edition remaster of Van Morrison’s monumental 1970 album, Moondance. Through the LS50s, horn lines were perfectly brassy, bass lines were amazingly precise, and Morrison’s vocal gyrations were startling at times. It almost seems like the LS50s were designed for music made from this era, with vibrant tonal colors and an analog soulfulness.

The LS50s were also a perfect match for classic, well-recorded jazz. Wayne Shorter’s Night Dreamer -- 192 Khz, 24 bit download, HDTracks -- was a sheer joy to listen to, especially with the Rogue ST 100 driving the LS50s. It was hard to believe this recording was nearly fifty years old. The KEFs exhibited the best vibrancy and midrange purity I have heard at this price point. The Shorter recording also illustrated the way the KEF produced the natural timbre of acoustic instruments.

A newer recording that I have really taken to, Sting’s The Last Ship, is a very pure sounding production. Sting’s voice is recorded very naturally, and the mix on this interesting song cycle is very dynamic and warm. This was a case of feeling drawn into the music by the LS50s, and not being able to listen while multi-tasking. These speakers demand a listener’s attention because of the organic musical presentation they provide.

On the other side of the spectrum, Paul McCartney’s musically excellent NEW, his first album of originals since 2007’s Memory Almost Full, is not a great recording. It suffers from a Pro Tools sheen, which is a shame since the songs are great fun. The LS50s did the album no favors in exposing its brittle production, but nonetheless, the music rose above, and the speakers’ coherence made the sound tolerable. The LS50 was able to contrast these two recordings, which showed its transparency to sources.

Speaking of transparency to sources, the LS50s sounded slightly different with each amplifier I used them with. The McIntosh MA6600 was evenly balanced, if a bit polite. The Electrocompaniet was a bit warmer, and offered up a soundstage that was a bit wider. My favorite pairing was with the tubed Rogue ST 100. This combo was the most holographic, tonally rich, and musically satisfying for me. 



Half way through the review period, I came to the realization that the LS50s were difficult to evaluate by breaking down multiple performance parameters. This is because they speak with one voice, unlike some other speakers at this price point with multiple drivers. I ended up really enjoying every album I listened to as a music lover and a reviewer. I can’t imagine the LS50s would be difficult to integrate into any system, within its limitations.

As fantastic as the LS50s are, in my opinion, they perform best when used within certain guidelines. First, they need an amplifier with more than a few watts. None of the amps I used put out less than 70 watts per channel. Secondly, they exhibit virtually no weakness in a smaller room, but their relatively limited low frequency output would preclude use in a very large room. I also think using a subwoofer would very much defeat the purpose of the LS50, which is voiced so seamlessly. Subwoofer integration is possible, but a task for those with endless patience.

I also believe the LS50s perform best in a relatively near field listening set up, with a maximum listening distance of eight feet, give or take. Even though the speakers produce a larger soundstage than their size would indicate, physics come into play. Bear in my mind, with all of my caveats above, your mileage will vary.

I did manage to compare the LS50 to my Spendor S3/5R, which sold for approximately the same price as the LS50. It is a classic two-way BBC style monitor, with similar specifications and dimensions. The Spendor, surprisingly, held its own despite being a decades old design, with a delightfully musical balance. The LS50 offered up more resolution, a bit more recorded detail and more overall impact. But it was not at all a blow out. I found the comparison interesting in that it really highlighted what advanced driver materials and enclosure design can accomplish.

KEF LS50

Conclusion

KEF 50th Anniversary LS50 monitors are a smashing success in every category: sound, appearance, design, and value. LS50s can be dropped into a system with far more expensive components without out anyone blinking an eye. KEF feels confident enough about this that they list under their “flagship” products, alongside the twenty times more expensive floorstanding Blades. I can add the LS50s will rise to the task with high quality speaker cables, stands, and optimized placement.

The only conceivable way the LS50s could disappoint would be in an inappropriate set up. This means in a room too large, with an underpowered amplifier, and at unreasonable listening levels. Audiophiles with common sense will not fall into these traps. In the proper context, KEF LS50s earn my very highest recommendation. In the areas of coherence, tonal accuracy, and overall balance, they set new standards.


Specifications


KEF LS50: $1499.99/pair.
www.kef.com

Specifications

  • Frequency range (–6dB): 47Hz–45kHz.
  • Frequency response: 79Hz–28kHz, ±3dB.
  • Sensitivity: 85dB/2.83V/m. Nominal impedance: 8 ohms.
  • Dimensions:11.9" (302mm) H by 7.9" (200mm) W by 10.9" (278mm) D.
  • Weight: 15.8 lbs (7.2kg).

 

Review System 1


CD Transport: Musical Fidelity M1 CDT
Server: Squeezebox Touch w/ CIA VDC-SB power supply
via Ethernet to MAC Mini w/ Western Digital & Seagate
external drives.
DAC: Bryston BDA-1, John Kenny Ciunas USB DAC
Headphone Amp: Pro-Ject Head Box II
Headphones: Grado SR60
Preamp: Audio Research SP16
Amplifier: Audio Research VS55, Rogue ST 100
Speaker: Thiel CS2.4
Cables:  Stager Silver Solids, Darwin Ascension (IC), Transparent  MM2 Super (IC), Transparent Plus (Speaker) Acoustic Zen Tsunami II (AC),Transparent (AC).Shunyata Venom (AC) Element Cable Red Storm (Digital AC), DH Labs TosLink, DH Labs AES/EBU, Audioquest, Forest, WireWorld Ultraviolet, DH Labs USB(USB) DH Labs (USB)
Accessories: Symposium Rollerblocks, Shakti Stone, Audience Adept Response aR6 power conditioner,Salamander rack

Review System 2


CD Player: Onkyo C7000R
Music Server: Squeezebox Touch via Ethernet to
MAC Mini w/ Western Digital & Seagate external drives.
DAC: Musical Fidelity V-DAC II, Burson Conductor
Integrated Amplifier: McIntosh  MA6600, Electrocompaniet ECI-3
Tape Deck: Revox A77
Speaker: Harbeth Compact 7ES3, Spendor S3/5R
Cables: Darwin Cables Silver IC, Kimber Hero HB,  DH Labs White Lightning (IC),QED Transparent MusicWave (Speaker),PS Audio (AC), Mojo Audio (AC), DH Labs TosLink, Audioquest Forest USB, Wireworld Ultraviolet USB
Accessories:Cable Pro Noisetrapper, Sound Anchors Stands, Wiremold, KECES XPS






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