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KEF LS50 (tloo)In celebrating its 5Oth anniversary, KEF has produced a mini monitor reflecting itsaudio engineering heritage and with details trickled down from its Blade flagshipReview: John Bamford Lab: Keith Howard

hile KEF - together withCelestion - has been ownedbythe Hong Kong-based ColdPeak multinational group

however. the LS50 bears about as muchresemblance to its suggested forebearas does today's BMW-era Mini to Sir Aleclssigonis's iconic design introduced in 1959by the Brit ish Motor Corporation.

.POII{T SOURCE'To casual viewers the LS50 wil l look l ike aminimalist, single-driver loudspeaker. Ofcourse, audiophiles wil l appreciate thatthis single driver is one of KEF's two-wayUni-Q coincident arrays with its tweetermounted at the acoustic centre of themid/woofer's voice coil - pioneered in the1980s to provide a nominally ideal pointsource. This latest

design innovation. For example, whilethere might be l itt le new in flaring a portat both ends to avoid 'chuffing', the factthat the port's tube is formed of closed-cellfoam and is actually flexible and porousis indeed novel. KEF says it aids clarity byallowing midrange frequencies to escapeinto the cabinet and prevents longitudinalresonances causinQ midband coloration.

A two-way such as this, with a singleUni-Q driver, makes for an ideal front-centrespeaker - the 'dialogue channel' in an AVsystem - something that was not lost onKEF in the early 1990s when it introducedReference Series centre sDeakers aimed

since 1993, and today has a massivemanufacturing plant in southern China, CPAcoustics is rightly proud of the brand'sBrit ish heritage. lt maintains UK rootswith offices based in Tovil, Maidstone - onthe site of the original Kent EngineeringFoundry where the late Raymond Cookefirst started his KEF Electronics company.

KEF was founded in the autumn of1961. So th is d iminut ive LS50 'bookshel f '

proudly sports 50th Anniversary Modellegends on its baffle and rear panel.Handsomely finished in piano gloss black,and with KEF s logo mark etched subtlyinto the top of the cabinet, it 's a compactmini monitor measuring around 300mmin height. The enclosure is reflex loaded,a flared ell iptical port venting at therear. Befitting its price the enclosure issturdily constructed with constrained layerdamping between its walls, internal cross-brace and front baffle. The baffle is curvedboth to minimise diffraction and furtherincrease the rigidity of the structure.

BBC CONNECTIONIt was, of course, in ' l 966 that KEFintroduced the world's f irst commerciallyavailable drive unit that featured a coneformed of Bextrene: its famous B 1 1 0 driver.Along with the company's T27 tweeter theB1 10 was to be employed by the BBC inthe LS3/5 Monitor, a small speaker just 12inhigh that was used in outside broadcastvehicles. Subsequently the speaker wasrefined to become the BBC LS3/5a,manufactured under l icence and madeavailable to consumers worldwide [seeboxout, opposite pagel.

In employing 'LS' nomenclature in thisAnniversary Model it 's clear that KEF is keento remind consumers of the important roleit played in early audio engineering andthe emerging development of hi-f i soundreproduction, implying that the LS50 is anLS3/5a for the 21st century. Other thanthe fact that it's a very compact monitor,

iteration, colouredrose gold for thissumptuous 1S50,features a 130mm(5.25in) midrangecone formed ofa magnesium/aluminium al loywith a ribbed long-throw surround thatKEF dubs 'Z-Flex'.

It crosses over at2.2kHz to its 25mmvented aluminiumdome tweeter.In today's Uni-Qdesign the tweetersports a 'tangerine'

waveguide tomaximise dispersion.

Thanks to moderncomputer-aideddesign methodsemployed by KEF forambitious projectssuch as its f 20kBlade floorstander.the LS50 includessome patent-pending

RIGIIT: Rosegoldcolourcd 130mmUniQ coincident arraywith 25mmtweetermounted at the centre

52 | www.hifinews.co.uk I tUlV ZOtZ

at videoohiles with LaserDisc-drivenmult ichannel systems. Being so ultra-compact, f ive or more LS50s would makefor an ideal surround sound set-up in manyhomes. What's the bett ing that a cost-down 'non-Anniversary' LS50 is already onthe CAD screens of KEF's desiqn team?

1&|, MINI MARVELSKEF recommends placement on 45-60cmtal l stands, posit ioneda metre from sidewalls to enjoy thespeakers' abi l i ty tocreate wide, out-of-the-box images, andaround 50cm from arear wall .

'The thought "Where

no protective gri l les provided with theseAnniversary Model LS50s, by the way.

I had in residence a pair of Track Audio'sexquisitely-made speaker supports thatproved a lovely match with the LS50s- albeit more costly that the speakersthemselves! Given that I si t around f ivemetres away from compact standmountersin my 7m-long l istening room, the LS50smade surprisingly easy work of loading

the room. Andthey soundedsubstantially largerthan I expected.

It 's somethingo fac l i ch6 , l know,but the thought'Where is all thatbass information and

The Iate Raymond Cooke, OBE,worked alongside Dudley Harwood(who later founded Harbeth! inthe BBC's Engineering DesignDepartment in the 1950s beforejoining Wharfedale and laterforming KEF. His relationship withAuntie Beeb blossomed as KEFpioneered new technologies. Itwas the first company to beginproduction of drivers with conesmade of materials other than paperand was first to apply Fast FourierTransform analysis to the measuringof speakers. As well as producingfinished speakers in its Maidstonefactory it was selling drivers toother companies: not least itsBextrene-coned 811O bass/mid unitand Melinex-domed T27 tweeterfor the BBC-designed tS3/5a,manufactured under licence by thelikes of Rogers, Chartwell, Harbethand Spendor... to name but four.More than 100,000 LS3/5as weresold worldwide. At one point KEFwas making around lO,OOO driversof various types per week and,reportedly, half of the UK's speakermakers were using KEF drivers.

is all that bass weightcoming from?"

crossed my mind'I l istened to the

1550s in their au naturel state in my larger-than-average l istening room, although afoam bung is provided to modify the port 'soutput i f ideal placement is constrainedby room layout/dimensions. Actual ly, i t 's abung within a bung: you can 'half restr ict 'the ports or ful ly block them. There are

weight coming from?' crossed my mindtime and t ime again as I put them throughtheir paces.

Wi th Madonna 's g rand iose 'Frozen 'from | 998's Ray Of Light album [Maverick/Warner 9362-46847-21 the sound waseasy-on-the-ear and commendably

luxurious, notwithstanding the'electronicedge' of the recording created by theart i f ic ial production techniques employedby Wil l iam Orbit and Patr ick Leonard. TheLS50 created a wonderful ly wide, deepand 'open' image of a musical event thatnever real ly happened (Orbit worked withsamples, synthesizer sounds and Pro Toolsra ther than l i ve mus ic ians . . . ) and thespeaker al lowed expl ici t detai ls of myriadsound-effects to cut easi ly through the mix.The presentation was al l-embracing - andamazingly r ich and ful l-bodied.

There are thunderous, air-moving basseffects in 'Frozen'that can create mayhemwhen played through huge f loorstanders orsubwoofers. A mini monitor won't ratt le therafters, of course. Nonetheless, the l i t t leLS50 more than hinted at the scale of thetrack, serving up a cavernous soundstage.The bass end was terr i f ic. l t was vividand concise, reasonably punchy whenthe occasion demanded, and remarkablyweighty considering the LS50's size.

This speaker's abi l i ty to showcasetransparently the superiori ty of hi-ressources compared with'standard' CDresolut ion 16-bit l44.|kHz f i les was e>

JULY2012 i www.hif inews.co.uk !53

RIGHT: At the rear is just

one set of high quality inputterminals for single wiring. Putfingers gently inside the portand you'lf feel a flexibletube

more than evident whenplayed the often-mentionedrecording by Channel Classicsof the Budaoest FestivalOrchestra performingStravinsky's Fi re b i rd Suite(our June c lass ica l a lbumchoice). 'Test ' samples at44 . '1 .96 and 192kHz can bedownloaded at no cost fromwww. c h a n n e I c I a ss i cs.co m.

Where with 44.1kHzplayback the sound wasclearly good enough toshow that this is a splendidrecording, balanced to soundopen and spacious whilepossessing suff icient 'oomph'to make the sound appearlarge-scale (never ceasingto cause visi tors to remark, 'Wow

- this l i t t le speaker has amazingbass capabil i ty.. . ' ) the markedimprovement when playing the96kHz version of the piece was asclear as night and day. The orchestrasounded less't ight ' and constr icted,the image scale increased in widthand depth, and the str ings andpercussion became smoother, morel iqu id , w i thout the sound appear ingto lose lead ing-edge 'b i te ' .

MIDBAND SUPERIORIIYTruly surprising was theimorovement observed when'upgrad ing ' to the 192kHz vers ionof the track. Via my monoli thicTownshend Audio Sir Calahadspeakers the dif ference betweenthe 96 and-1 92kHz f i les i s sub t le a tbest, while the improvement in tonalcolour was more readi ly obvious viathe diminutive KEF - testament tothe LS50's fabulous midband clari ty.Perhaps I should describe thedifference between the two sourcefi les as more 'vi tal 'via the 1S50. inthat i t appeared to further open upthe image and h igh l igh t th is babymonitor 's abi l i ty to sound wa-aybigger than i t is. With top-drawerrecordings i t truly can sing.

I can't cr i t ic ise the voicing ofthe 1550. Roger Water 's 1992epic Amused To Death [Columbia468761-21 sounded nothing shorto f sub l ime on th is KEF min ia tu re .

KEF LS50 (rgoo)KEF claims 85dB sensitivity for the 1550, only about 1dBoptimistic according to our.measurements which finds thepink noise figure, averaged for the review pair, at 84.1 dB(2O0Hz-20kHz). This performance requires that the LS50 be a4ohm design, with a minimum measured modulus of 3.8ohm.KEF inexplicably accords the LS50 an Sohm nominal ratiagwhile claiming a minimum modulus of 3.2ohm - but at leastour results show that minimum figure to be conservative.lmpedance phase angles are quite large, as a result of whichthe EPDR (equivalent peak dissipation resistance) falls to aminimum of l.9ohm at 25H2, with a similar dip at 132Hz..

The payoff for the LS50's below average sensitivity andmoderately testing load comes in the form of good bassextension for so small a cabinet, our diffraction-correctednear-field measurement recording 42Hz (-6dB re. 200H2). Inthe manner of the new Q Series, this roll-off is rapid when itcomes, so transient capability may have been compromised toachieve this. The near-field testing confirmed that KEF s cleverflexible reflex tube justifies the claims made for it by doing agood job of preventing unwanted midrange output from theport. The on-axis frequency response [Craph 1, below] isn't flatbut follows a mostly flat trend, within error limits of 13.6d8and t3.5dB respectively, 2OOHz-zOkHz. Pair matching, ovef thesame frequency range, was in the very top drawer at 10.6d8.The cumulative spectral decay waterfall [Graph 2] shows fastinitial decay and implies the low cabinet output you'd expectof the LS50's exacting construction, although some lowlevelupper-midrange/lower-treble hash is,still visible. KH

FElroo

93

90wi th the a lbum's in t imate lyrecorded vocals and space-creatingsound effects melding to del ivera del iciously invit ing three-d imens iona l 'aud io a tmosphere ' .

I t rs possible to push the speakerbeyond i ts comfort zone, of course.During the cataclysmical ly dynamiccrescendos of ' l t 's A Miracle', late onin the a lbum ( th is was around 95dBat the l istening seat), I detected theLS50 introducing a hardening toWaters' tortured declarat ions andvaledict ions, which he howls at thetop of his voice.

Public address i t wi l l not do.But the LS50 did prove capable ofshocking me with i ts abi l i ty to let r ipup to a po in t , a l l the wh i le sound ingfresh, open and very very ref ined. O

This is a cracking l itt le speakerof which KEF's design engineersmust be most proud. Sweetlyvoiced yet highly revealing ofsource quality, it surprises anddelights in equal measure. Andboy does it sound big, defyingits compact dimensions. ltdeserves to be a runaway successfor KEF worldwide, especially ifthe company follows up with acheaper, less elaborately-f inishedversion for a wider market.

Sound 0uatity: 86%r0r . : : ; : J:r]:ti l:i;=.,.-r:{t i.*i i:r::,,,= f OO

a 8 s€

200 1k 10k ,OkFrequency>> @]

ABOVE: On-axi3 response shows a flat trend with finepair matching. Uni-Q notch is pushed out to 30kHz

Frequenq in Hz >>

ABOVE: Solid cabinet construction ensures lowcoloration, while Uni-Q resonances are well controlled

s€n:::'v'ty{sPflln{rj.ui':,::"1lt.lt":l.l IImpedance modulus min,/max (2oqz-2okHzl

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lmpedance phase min/max (2oHz-20kHz)

84:7dBi84:1 181841

dB

3.8ohm @ 1 95Hz35.5ohm @ 90Hz

-58" @ 1 05Hz

?o: @76H1r0 .6dB

42Hz I >4okqzl>4jkHz

;;;,;;|;i*302x200x278mm

54 j www.hifinews.co.uk ! JULY 2012