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FEATURE REVIEW

Metamaterial on test
KEF’s classic LS50 versus theinnovative LS50 Meta

• OPINION 12 pages of letters & views • VINYL RELEASE Warren Zevon’s Stand In The Fire on 180g LP• CLASSICAL COMPANION Zubin Mehta, Conductor • STUDIO TOURS Visiting Third Man, Nashville• VINTAGE REVIEW B&O Beovox CX50 loudspeaker • READERS’ CLASSIFIEDS Hi-Fi bargains galore

UK £5.50 Aus $13.99

L ICOWNYVI

Two-way, dual-concentric loudspeaker
Made by: GP Acoustics (UK) Ltd, Maidstone, Kent
Supplied by: GP Acoustics (UK) Ltd
Telephone: 01622 672 261
Web: www.kef.com
Price: £1000

LOUDSPEAKERKEF LS50 Meta

METAMATERIAL

After nearly a decade in production, KEF’s iconic LS50 compact monitor has been
comprehensively updated. We compare the original with the latest ‘Meta’ variant
Review: Ken Kessler & Paul Miller Lab: Paul Miller

Hardly a curse, but it’s still a
massive challenge for any
manufacturer to improve on asmash hit. I don’t care if you’retalking about cars, cameras or cookers– whatever the classic, the follow-up ismetaphorically referred to as ‘that difficult
second album’. KEF faced this with theLS50 which (terrifyingly) will be ten years
old in 2022. In the interim, there havebeen active and wireless versions of thespeaker, but the passive original [HFN Jul’12] is a much-loved default purchase inthe under-£1000 sector. The new LS50
with the Meta suffix (£999) is KEF’s The
Godfather Part II. Yes, it’s really that good.

STILL MAGNIFICENTMany of you read these reviews in theorder they are printed but I would ask
you, instead, to pause here. Please go
directly to PM’s technical description of‘Metamaterial’ [p59], then the interview
with design prodigy Jack Oclee-Brown[p61], followed by the Lab Report [p63].
This foreknowledge is the only way one caneven begin to appreciate precisely what
KEF has achieved here, and there is also
the £200 price differential
between the outgoing LS50
and the LS50 Meta to address.
I emphasise here thatthe original remains both amagnificent and affordable
speaker, while pointing outthat an additional £200 in this
sector is a huge percentage
increase for an entry-level or financiallyrestricted customer. I say this so as not tocreate anxiety in those audiophiles who
think their lives have been diminishedbecause a new model ‘something’ hasarrived, and there are tens of thousands ofowners of passive LS50s. While I’ve used

LS50s since they first appeared, they are
one of many speakers I have for reference.

SIDE EFFECTS
To prepare for this test, I set up thestandard LS50s in a system of components
relative in their value andlived with the speakers fora week and nothing else
before the review samplesof the LS50 Meta arrived.
I won’t say I had forgotten
how good they are, but it
had been a few months
since I had last fired up
the LS50s for review purposes. That Uni-Q
concentric driver is something special.
Dual- and tri-concentric units had
been around for years, not least theTannoy and later Thiel designs, when KEF
first unleashed its version in 1988. The
company’s long-serving chief engineer
Laurie Fincham,
now with THX,explained, ‘When
you were making
a regular two- or
three-way speaker,
there was always
a spacing between
the drivers, whichmeant you had to‘Undeterred, I
found myself
cranking up
the volume’

LEFT: Original LS50
[far left] featured arose gold-coloured
130mm Uni-Q
array with 25mm
tweeter mounted at
the centre. A 12thgeneration Uni-Q isfitted to the LS50
Meta [near left] withchanges to the motorsystem, suspension,
surround and cone of
the midrange driver.
The rear tweeter duct
has also been enlarged asa ‘waveguide’ back to themetamaterial absorber

Reprinted from Hi-Fi News for global distribution | www.hifinews.co.uk

on wave propagation throughthe material and require a
depth comparable to thewavelengths involved –impractical when dealing with afinite cabinet space like the LS50’s.
By contrast, KEF’s metamaterial
is a 100mm-diameter ABS discthat hosts an array of quarterwave
resonators, each tuned to a specificfrequency and harmonics. By
controlling the size and tuning of eachresonator, KEF claims to smoothly
absorb sound over a usefully wide range.
In practice these resonators take theform of 2mm square-section channels,
realised as a computer-modelled maze,each exiting at the centre of the disc via
a series of ducts. The rear output of theUni-Q tweeter is guided directly toward
these ducts and into the sound-killing
resonator channels [see illustration,opposite]. Working in concert, theseresonators deliver an effective absorption
bandwidth of ~600Hz-5kHz beyond which
traditional foam attenuation takes over. PMThe headline differences
between the LS50 and new‘Meta’ version are driven as
much by the re-engineered
crossover and evolution of theUni-Q driver as they are by KEF’s
novel metamaterial insert, ensuring
the new speaker enjoys a smoother,cleaner response at low and mid/presence frequencies [see Lab Report,p63]. However, the application ofAMG’s (Acoustic Metamaterials Group)sound absorbing matrix – attachedbehind the Uni-Q tweeter – has an audibleand measurable impact across the vital
midrange and presence bands [see CSD
waterfalls, below].
The term ‘metamaterial’ is potentiallyconfusing because its application here has
nothing to do with a material. Instead it’sa method of achieving a property – in thiscase sound absorption – that could nototherwise be achieved using common
porous damping materials such as longhaired wool, foam or bonded-acetate fibre.
These traditional damping techniques rely

0 dB-80.0-16
1.7-24
3.3-32-40500

1k2kFrequency in Hz >>3k4k5.0msec
5k

make a compromise, either vertically orhorizontally. So you had the problem withbookshelf speakers – were they on theirside or were they standing up? They could
only work well in one orientation’.

FORMING A Q
Fincham credits the arrival of rare-earthmagnet technology as the enabler, crucial
as KEF was not considering coaxial speakers
the size of Tannoy’s drivers. ‘A dealer told
me about this new magnetic material…
composed of neodymium, iron and boron.
It was very small and had ten times theenergy, so I was intrigued. I said, “It’s sosmall that we can make a coaxial speaker”.’
Size wasn’t the only benefit. ‘I also
realised that with the Uni-Q, I could make aloudspeaker system that didn’t have a box.
What I mean by that, if you’d ever seen theearlier ones, the crossover was on the back

ABOVE: Metamaterial disc absorbs
rear-radition from the Uni-Q tweeter via
a matrix of 30 tuned radiators.
LEFT: Cumulative spectral decay fromthe LS50 between 500Hz-5kHz (5msec)
RIGHT: The same test applied to theLS50 Meta – note reduction in spurious
output, particularly from 1-3kHz

0 dBof the driver so you could test the wholething separately. Much more importantly,
when you put it into a cabinet, it’s just fourscrews to connect it up and the job’s done.
You don’t have to put a crossover in – lotsof different things – all in one go.’
KEF has now used Uni-Q drivers in all
manner of loudspeakers, including the Egg
lifestyle mini-speaker, but one insider tellsme the technology’s evolution into the‘tangerine’ drivers, seen first in models likethe Blade (2009), had its greatest impact
in the original LS50. For the LS50 Meta,
irrespective of the attention deservedly
being paid to the labyrinthine metamaterial disc, the drive unit itself has beenrevised extensively, as has the cabinet. As
PM explained, this is effectively the ‘12thgeneration’ Uni-Q in just over 30 years.
Side-by-side, it’s almost impossible totell the difference, beyond the change of-8
0.0-16
1.7-24
3.3-32-40
500

1k

2k
Frequency in Hz >>3k

4k

5.0msec5k

the driver’s colour from orange/copper toa more muted hue. I prefer this less bling-ychoice, but the LS50 Black would be mypreferred look. Here’s where a cutaway anda view of the back help [see p61 and p63]
to reveal the interior changes, as well as
revisions to the back panel.
The port opening is now flush to further
reduce turbulence, and the cavities in
the corners for the baffle retention bolts
have been eliminated. I’m not sure if thesehave impact on the sound, but the rearsurface is now slightly domed, while a step
between the rear panel and the cabinet
sides has been introduced.

RISE AND SHINE
While PM measured a slight difference
in sensitivity, it wasn’t noticed whenswitching between the two, so I wasable to treat the LS50 and the LS50 Meta

www.hifinews.co.uk | Reprinted from Hi-Fi News for global distribution

LOUDSPEAKERJACK OCLEE-BROWNRIGHT: 3D renderingshows the substantial
cross-bracing, coupled
to the low-diffraction
cabinet via a ‘lossy’layer – all part of KEF’s
constrained layer
damping. Note also
the soft reflex port,
flared inside and out

equally in that
respect. Stands
were 24in tall, andthe positioning
was as per theinstructions, firing
straight ahead. I
also experimented
with toe-in andfound that had its
own virtues, butfor the remarks that
follow here, I stuck with
KEF’s preferences.
Most of the heavy
listening was with open-reeltapes but vinyl and CD wereused, too, and I avoided pairing
these loudspeakers with crazily-priced
high-end ancillaries as I do not expect
anyone to spend £50k on a record deckand listen to it through a pair of speakers
at £999. Those days of unbalanced
stupidity in funds allocation are over.
However, as I found, the LS50 Metas are
so good that they will end up not just with
£500-£1000 integrated amplifiers but with
far more ambitious powerhouses because
they will rise to the occasion.

HUNGRY FOR POWER
My main set-up consisted of the Technics
RS1500 tape deck fed directly into a Bob
Carver Crimson 275 power amp, as well asbouts with a PMC Cor integrated amplifier
and an EAT E-Glo i Integrated [HFN Oct ’20].
Vinyl playback was via an EAT B-Sharp deck
[HFN Jul ’20] with Jo No5 cartridge [HFN
Dec ’18] with the EAR-Yoshino 834P phono
stage [HFN Jun ’94] and CDs through theMarantz CD12/DA12. Wires came fromYTER and Max Townshend. Note, however,that whatever you expect for sensitivity in asub-£1000 speaker, the LS50 Meta, like its
predecessor, is power-hungry. This will not
be happy with a 30W/ch integrated.
Spending a week to ‘re-learn’ theoriginal LS50’s sound proved crucial. I
had grown accustomed to the surprising
amounts of bass, the wide and deepsoundstage, and a not-unpleasant ‘bloom’to the sound that gave an illusion ofadded weight or warmth. They certainly

do not sound like speakers measuring
only 302x200x280mm (hwd) and withessentially a 5.25in woofer. It accounts
for the loudspeaker’s success if the best
selling-point a small speaker can have isthat it sounds huge.
Of course, KEF retained all of the LS50’svirtues in making the transition to LS50
Meta, and the initial exposure to the latteris one of familiarity mixed with surprise.
It’s like seeing a friend for the first timeafter a few years have passed, who, inthe interim, lost a stone or spent time ina gym. Recognition is compounded withpuzzlement; in this case, it was all positive,and I wisely chose my definitive bass-withcool-vocals tester to start the proceedings.

Another day in lockdown, andanother Zoom call, this time withEditor PM ‘meeting’ KEF’s Headof Acoustics, Jack Oclee-Brown.
Metamaterial is the buzzword [seeboxout, p59], but it doesn’t define
the latest LS50 – that honour stillgoes to the Uni-Q coincident driverarray with its distinctive ‘Tangerine’
waveguide. For example, the centraltweeter is composed of aluminium
alloy, not beryllium or ‘diamond’,and yet its breakup mode is deferred
to a high 40kHz (~30kHz is typical).
‘This all stems from our workon the Muon project’, reveals
Jack, ‘a spherical dome is required
to optimally load the Tangerine
waveguide, but an elliptical crosssection yields greater stiffness. We
combined both in the Uni-Q tweeter,
and a very stiff triangular section isformed where the two parts join.
‘We’ve evolved the Uni-Q driverand motor over its long lifetime, butone big change in the Meta is ournew crossover design. The transfer
function/slopes are 4th-orderelectrical/acoustic (combined) andyield much improved on- and off-axissmoothness.’ [See Lab Report, p63.]
Will we see metamaterials inother KEF speakers? ‘The timescaleis uncertain but, yes, “mets” willundoubtedly move out to ourother speakers’, says Jack. ‘More
importantly, the new streaming
platform used in the LS50 Wireless
II will be a big part of our productstory in the coming year. We are also
very keen to do more than simply
make a passive speaker active, andour little KC62 subwoofer gives aglimpse of what is possible.’ PMUTTERLY UNEXPECTED
Though I do not claim to understandhow sounds are chosen to be sampled
by hip-hop producers and engineers,surely Levon Helm’s drumming on ‘Up On
Cripple Creek’ on The Band’s eponymous
second LP from 1969 [Mobile Fidelity MFSL
1-419] deserves to be ripped off by any
musicians who want to inject so much funkinto their tracks that the beat becomes
irresistible. Abetted by Rick Danko’s equallycommanding bass playing, the track neverfails to excite any listener eager to extract
every single millisecond of joy. The original
LS50 delivered enough of that to tell its
www.hifinews.co.uk | Reprinted from Hi-Fi News for global distributionLABREPORTKEF LS50 & LS50 METAABOVE: Put fingers gently inside theport and you’ll feel a flexible tube
fabricated from a closed-cell foam
and flared inside and out to reduceturbulence. The port profile wasupdated for the LS50 Meta [right]

audience that this was a recordingof peerless worth on every level.
What swapping to the LS50 Meta
yielded was utterly unexpected.
Keep in mind I remained unsureof what to anticipate, even after
reading PM’s and KEF’s material.
Within no more than ten seconds,
I had identified a drier, more open
upper-bass and airier percussion
across the spectrum, a trace more
realism in the vocals and somethingeven harder to comprehend, forthere was no loss of the warm,
ear-cosseting bloom that made theoriginal LS50 undeniably more-ish.

KILLER TEST
So convincing is the LS50 Meta that I
found myself cranking up the volume
to levels well above my comfort
zone to find that it can fill a room far
beyond any expectancy associatedwith size. Because the bottom
octaves of ‘Up On Cripple Creek’
drive the track as much as anythingelse, turning up the levels increased
the realism. And here I detected
another unexpected gain when thedecibels increased: the LS50 Meta
appears to recreate greater image
height than the LS50.
Whether or not that’s anillusion, what sold me on the LS50
Meta even more was the curious
behaviour from the upper midband
through to the top end. Although
the track is nauseatingly twee and I
would normally fast-forward throughit, I was caught unawares by theauthenticity of the xylophone on‘Talk To The Animals’ from Herb
Alpert & The Tijuana Brass’ The
Beat Of The Brass [A&M AMC146
open-reel tape]. Ordinarily, I listen
to Alpert’s superb recordings
because the punch of his trumpet
is a killer test for transient attack,treble smoothness and otherqualities. So explain this one to me...
how is the LS50 Meta faster, withcrisper transients, smoother in its
decay, yet even less likely to show
signs of sibilance than the alreadysweet-sounding LS50?
On to something less cluttered,
the luscious-sounding Julie London
on Julie Is Her Name [Analogue
Productions APP-3006-45], every
track sounding ‘in the room’. Gears
into reverse for the pounding ‘GladAll Over’ from The Dave Clark Five –All the Hits [BMG BMGCAT408DLP].
No shortage of attack, scale or sheer
power. The bottleneck guitar inKeb’ Mo’s Peace... Back By Popular
Demand [Pure Pleasure/Epic/Okeh
PPAN92687] as fluid and serpentine
as it should be. As you might havegathered, I love this speaker.

To ensure the validity of our comparisons, new samples of boththe LS50 and LS50 Meta were tested ‘back-to-back’ underidentical lab conditions. So, while the LS50’s pair matchingis within 1.3dB and response uniformity good to ±2.9dB and±4.0dB [grey/orange traces, Graph 1] the new ‘Meta’ delivers
an improved response flatness of ±2.1dB and ±2.2dB [black/redtraces] with even tighter 0.5dB pair matching (all 20Hz-20kHz).
The sharp Uni-Q tweeter breakup mode at 40.2kHz (+22dB re.
1kHz) cannot be avoided but this is still impressively out-of-band
for an alloy dome [see interview sidebar, p61].
Sensitivity is rated at 85dB for both models but the LS50’s
boosted 2-6kHz band gives it an edge here, yielding 85.0dB
versus 84.5dB for the LS50 Meta (averaged, 500Hz-8kHz). The
new crossover also sees a change in the Meta’s impedance/
phase trend above 200Hz where there’s a slightly tougher
upper bass/midrange load. The LS50’s modulus is <8ohm over anarrow 125Hz-630Hz [min. 4.09ohm/213Hz; grey trace, Graph2], while the Meta is <8ohm over a broader 115Hz-980Hz [min.
3.65ohm/242Hz; black trace, Graph 2]. Swings in phase angle
are largely unchanged at circa –60o/+50o but the Meta’s load
[red trace, Graph 2] is more reactive at midrange than bass freqs.
The –6dB bandpass of the LS50’s mid/bass cone is 80-650Hz,that of the Meta a wider 72Hz-900Hz, though both ports remain
tuned to a sharp and clean 50Hz (–6dB bandpass of 38-80Hz,
LS50; 38-85Hz, Meta). This yields a steep 4th-order roll-off but
usefully low extension of 42Hz for the ‘standard’ LS50 and aslightly deeper 40Hz for the Meta (both –6dB re. 200Hz). Notealso the generally ‘flatter’ more uniform bass output of the Meta
[green shaded area, Graph 1]. PM

ABOVE: Response inc. nearfield summed driver/port[green], corrected to 1m at 2.83V [yellow], ultrasonic[pink]. LS50 Meta, black/red; LS50 grey/orange

HI-FI NEWS VERDICT
Shocking is not a word to bandy
about lightly but the gains over
the original LS50 are so obvious,
so immediately perceived thatone can only shake one’s head indisbelief that this was achieved,in part, by a passive internal
tweak. The LS50 Meta – especiallywhen you consider its ~£1000
price – ticks every box for asmall speaker: huge soundstage,generous bass, terrific imaging.
Satisfying? Try ‘supernatural’.

Sensitivity (SPL/1m/2.83V – 1kHz/Mean/IEC)

84.6dB / 84.6dB / 82.4dB

Impedance modulus: minimum& maximum (20Hz–20kHz)

3.65ohm @ 220Hz
31ohm @ 93Hz

Impedance phase: minimum& maximum (20Hz–20kHz)–62o @ 110Hz+48o @ 860Hz

Sound Quality: 89%

THD 100Hz/1kHz/10kHz (for 90dB SPL/1m)

1.2% / 0.2% / 0.7%

Dimensions (HWD) / Weight (each)302x200x280mm / 7.8kg

0-------- 100

ABOVE: Impedance magnitude (black/grey) and phase(red/orange) for LS50 Meta and LS50, respectively

HI-FI NEWS SPECIFICATIONSHI-FI NEWS SPECIFICATIONSPair matching/Resp. error (200Hz–20kHz)

0.5dB/ ±2.2dB/±2.1dB

LF/HF extension (–6dB ref 200Hz/10kHz)

40Hz / 54kHz/59kHz

www.hifinews.co.uk | Reprinted from Hi-Fi News for global distribution