The BBC LS3/5a – Revisiting a Classic - g4dcv.co.uk

1 The BBC LS3/5a . Revisiting a Classic MARTIN COLLOMS LOOKS AT THE BACKGROUND TO THE BBC LS3/5a , RE-ASSESSES ITS RELEVANCE TO TODAY'S HI-FI SCENE, AND ALSO CHECKS. OUT ITS STIRLING BROADCAST V2 SUCCESSOR. MARTIN COLLOMS. History Jim Rogers called the JR149. I still have that original The story of the LS3/5a begins in what many regard as Audiomaster LS3/5a , frequently used as a long term the golden years of the BBC, in the days when it ran a reference 30 years on, plus a middle period version from substantial Engineering Department. The loudspeaker Rogers, and thought a 21st century reassessment might be division ourished under the stewardship of such interesting.

2 Legendary engineers as Shorter, and subsequently Rumour has it that once this unlikely candidate Dudley Harwood, to develop broadcast quality (originally knocked together for a scale model studio monitoring speakers that were good enough to assess experiment) o cially entered the BBC development programme quality. Existing commercial models, which programme, it proved really hard to nalise, partly due had largely been designed through trial and error, had to variations in driver response. Furthermore, design proved too inconsistent, and also su ered from excessive precepts which had proved e ective with larger speakers coloration.

3 Turned out not to apply to such a small model. The 3/5a In the late 1950s and the 1960s, research was had to be largely voiced by ear, with extended reference to undertaken to track down the various problems, and live sound, since its small dimensions and consequently several speaker designs were created, from the large LS5/ wide directivity gave unexpected results when compared 1A two-way, based on a big 15-inch paper cone bass/mid with the usual expectations based on the axial frequency with two paralleled 38mm Celestion HF1300 hard dome response. tweeters (in this case from GEC and labelled BCS1852) This is why the frequency response is not at; the strapped across its face, to the smallest of them all, the speaker was critically voiced octave-by-octave, so that The test panel for the unsighted live versus miniature LS3/5a with its 5inch (110mm) bass/mid and the whole radiated sound, driver and cabinet e ects recorded test for the LS3/5a .

4 19mm dome tweeter, both KEF-sourced. Engineers who included, sounded most lifelike. Some years later Laurie The drummer was Barry Fox, played a major role in the 3/5 and 3/5a development Fincham, then Engineering Director at KEF Electronics the panel was from left to included Derek Mathers , Maurice Whatton and Spencer and an exacting perfectionist, was determined to right Stewart Tyler (ProAc) , Hughes. (Spencer later went on to found Spendor. His better the 3/5a, probably piqued by the BBC's success David Weymss (BBC), Derek Scotland (Lentek, Audiolab), famous 2 cubic foot BC1 model was privately developed using KEF drivers.)

5 He created a high tech miniature Stephen Liebmann while he was still at the BBC, to which his contract called the Reference 101 with an almost perfectly at (student), Marianne Colloms, conferred intellectual property rights, which is why the frequency response. While its technical neutrality was Martin Colloms, Julian speaker also subsequently appeared as the Rogers built unquestionable, it neither sounded as lifelike, nor did Vereker (Naim Audio). LS3/6.). Writing under the pseudonym Hughes, I rst assessed the miniature BBC LS3/5a for Hi Fi For Pleasure in 1976, in a 30-speaker group test. That particular sample was made by KJ, later branded Audiomaster, under the direction of Robin Marshall, an ex-BBC.

6 Engineer who subsequently founded Epos, though a number of other manufacturers also took out licences to make the 3/5a. For this ambitious assessment, live versus recorded judgments complemented stereo listening and laboratory testing (see contemporary photo by HFP. editor Trevor Preece). I subsequently tried versions from KEF, Chartwell, Rogers, and Spendor, and an idiomatic but very successful non-BBC cylindrical rival from HIFICRITIC MAY / JUNE 2007 29. HFC3 29 7/8/08 8:43:33 am HIFICRITIC. Vol1 | No3 May | June 2007. Because these it really better the musical performance of the standard material, build and damping of the enclosure, still sets speakers are quite 3/5a.

7 (Laurie's e orts should not be dismissed, however, this speaker apart in terms of low panel resonance and without mentioning that he had previously designed an absence of spurious re ections. The enclosure itself easily damaged the best selling quality bookcase miniature ever, the is built from 12mm birch plywood, lined with bitumen by excess power Goodmans Maxim, not to mention the similarly pads to control panel resonances, while the use of solid input, do check successful Celestion Ditton15.) beech as corner llets is also a critical element in the before buying a The most famous clone must be the Linn Kan which overall sound.

8 Secondhand pair. borrowed the 3/5a enclosure and major parts, threw With low coloration a speci c engineering target, the Even better, try away the crossover and its monitor equalisation, and nal requirement was an electrical network that would created one of the fastest and most involving wall mount shape and balance the system sound energy, provide an and get some sort miniatures ever. Blatantly inaccurate and decidedly accurate blend for the two drivers, and a very natural of guarantee on coloured, it proved both the strengths and the weaknesses overall sound quality suitable for programme monitoring. condition. of the BBC design.

9 Linn fans were being kind when they The very complex 13-element crossover includes a treble described the BBC model as too polite! network inductor that also operates as a level-matching More than 60,000 pairs of the original LS3/5as were auto-transformer. Components include high quality made, so there should still be plenty around! screened air-gap inductors and lm capacitors, and equalisation is applied in both high and low frequency Engineering details sections. The level-adjusting transformer taps allow the The LS3/5a is a sealed box with an internal volume of precise matching of mid to treble, and the whole thing is about 5 litres.

10 It does not use re ex loading, due to the hard-wired, fed from a single terminal pair. additional coloration and distortion this could introduce Hardly any component in either enclosure or driver with a small box. The KEF SP1003 long throw bass/mid may be substituted without the blend su ering audible driver has a strong 110mm pressed-steel, Dorma chassis, disturbance. This is because the 3/5a sets such a high and an 85mm vacuum-formed Bextrene cone, heavily standard for tonal balance that errors which would pass coated with Plasti ex (a PVA adhesive used in book unnoticed in an ordinary speaker are readily exposed. binding) for damping.