In Praise of a Classic: the BBC LS3/5A
Such factors as the mathematical modeling of woofer tuning by Neville Thiele and Richard Small, FFT-based testing pioneered by Laurie Fincham of KEF in the 1970s, the introduction of PC-based measurement equipment such as DRA Labs' MLSSA system, and such computerized tools as Finite Element Analysis, as well as great leaps forward in materials science, mean that typical 21st-century speakers such as the Dynaudio Special 25 or the Paradigm Signature S2, which I reviewed in June 2005 and July 2005, respectively, are better in almost every way than a typical design from even 20 years ago, let alone 40.
As is my usual practice, around the time I was measuring the Bozak I dragged out my longtime reference speaker, a 1978 sample of a BBC LS3/5a, manufactured by Rogers, to perform a set of acoustic measurements. I do this to ensure that a systematic error has not crept into my speaker measurements. If the LS3/5a continues to measure identically, then I can be sure that nothing has gone wrong with my test gearmicrophone, mike preamp, power amplifier, etc.
This latest set of measurements checked out, so I returned the LS3/5a to the closet. But then it struck me: this British speaker will celebrate its 40th anniversary in 2015, yet in many ways it is still competitive with modern designs. (You can find Stereophile's complete review coverage of the loudspeaker, starting with J. Gordon Holt's March 1977 review and continuing through to my review of the 1993 version manufactured by Harbeth and my 2007 review of the Stirling LS3.5A v.2, at www.stereophile.com/standloudspeakers/361/index.html.) Yes, there's a touch of nasality in the upper midrange, the treble is less smooth than, say, the Paradigm or Dynaudio, and the upper bass is less well defined than audiophiles now expect from even inexpensive speakers. But when it comes to accuracy and stability of stereo imaging and sheer purity of midrange reproduction, the tiny BBC-designed speaker is still a contender.
How could this be? A touch of history is in order, courtesy the LS3/5a Enthusiasts website:
Back in the early 1970s, the BBC in the UK needed a small location monitor that would provide consistent reproduction in small, suboptimal environments, such as a recording truck. A team led by T. Sommerville and D.E. Shorter, of the BBC's Research Department, developed the LS3/5, based on a small monitor they had designed for acoustic scaling experiments. That monitor used a B110 woofer with a doped Bextrene cone and a T27 SP1032 Mylar-dome tweeter, both sourced from British manufacturer KEF. The speaker showed much promise, but problems with the drive-units led to a detailed redesign carried out by H.D. (Dudley) Harwood of the BBC's Research Department, and Maurice E. Whatton and R.W. Mills of the Designs Department. (I was surprised to learn that one change was to move the tweeter to the top of the baffle.)
The design was licensed to a number of commercial manufacturers: Rogers and Chartwell at first, then Harbeth (formed by Dudley Harwood), Spendor (formed by ex-BBC engineer Spencer Hughes, who had been the chief engineer on the acoustic scaling speaker), Goodmans, and Audiomaster (whose chief engineer, Robin Marshall, had also worked in the BBC's Research Department before going on to form Epos and eventually ending up at Harman). Since then it has seen just two reworkings. The first, in 1988, was to bring the speaker back in line with its original specificationsthere had been inevitable drifts in the drive-unit parameters since 1976and the most recent, as reported by Ken Kessler in our April 2005 e-newsletter, performed by Stirling Broadcast, was because the original KEF drive-units were long out of production. Stirling's v2 LS3/5a costs from $1410/pair to $1542/pair, a far but inevitable cry from the mid-1970s price of 52 pounds each! More than 60,000 pairs of LS3/5as were manufactured up to 1988, 43,000 by Rogers alone (footnote 1).
So why is that almost all speakers from the 1960s and 1970s sound as dated as you'd expect, whereas the LS3/5a remains a competitive design? Perhaps it was the fact that the LS3/5a was intended to be a monitor (though many professional monitors are even more colored than good domestic designs). Perhaps it was the unique assembly of speaker engineering talent at the BBC in the early 1970s, which I don't think has been matched since. Perhaps it was the fact that the design was thoroughly and unusally worked outa BBC white paper by Harwood, Whatton, and Mills, "The design of the miniature monitoring loudspeaker type LS3/5a," report RD 1976-29, is available at the BBC's website. Perhaps it was just serendipity.
But whatever the reason, I thought it worth recognizing the LS3/5a's longevity. John Atkinson
Footnote 1: A comparison between the on-axis responses of the Stirling variant, the 1996 KEF example, and my original 1978 sample can be found in fig.3 here.