That LS3/5A Phenomenon

A new Rogers LS3/5A alongside
its contemporary equivalent – the KEF LS50

Now, I appreciate that I’m describing a niche category within a niche category, but among audiophiles, the BBC LS3/5A is perhaps the most widely celebrated loudspeaker. And now I’m about to perpetuate the hullabaloo by blogging about it for a second time (my first Music & Miscellany post was entitled, Not The LS3/5A – you might like to read it for a bit of background). I do however have reasonable grounds I think for revisiting the subject in this post because I’ve recently been fortunate to spend some time with a loaned pair of new Rogers Classic 15 Ohm LS3/5As.

The background to the LS3/5A loan is that I was working on a magazine review of a monitor that is not only intended to play similar role as the LS3/5A, but also engineered by its designer (a big LS3/5A fan) to have a comparable set of electro-acoustic and subjective qualities (At the time of publishing this post, the monitor review isn’t yet published, so I can’t reveal its identity). So I felt it would be interesting to get hold of a pair of LS3/5As and compare the two monitors. It turned out that the designer of the review monitor has done a pretty good job of meeting his design aims, but the comparison also reminded me just what an unusual and exceptional little speaker is the LS3/5A – especially considering that it was designed in the mid 1970s. For the truly committed, a contemporaneous BBC R&D technical paper is available for download that describes the development of the LS3/5A. It can be found here.

Just as fascinating as the LS3/5A itself however is the story of its contemporary rebirth following the end of the initial, mid 1970s to mid 1990s, period of manufacture. During that time, the BBC granted manufacturing licences to Rogers, Chartwell, Spendor, Audiomaster, RAM, Goodmans, Harbeth and KEF. It’s estimated that upwards of 100,000 pairs of LS3/5A were made in total (the majority by Rogers). Among a particular niche in the audiophile community however, the end of that first phase of manufacture didn’t diminish interest in the LS3/5A, and the prices that used pairs in good condition could command began to rise alarmingly. So beginning in around 2008, a number of both established and start-up speaker manufactures took out new licences to begin manufacture again. One of the more recent new licensees and manufacturers is the present incarnation of the original Rogers company, now under different ownership, but lead technically by Andy Whittle, who was the last technical head of the original Rogers company. It was Andy who kindly loaned me the pair of new LS3/5As, and I took the opportunity on returning them to quiz him about what’s involved in accurately recreating an iconic product that was designed in 1975 and last manufactured around 1993.

The biggest issue that any new manufacture of LS3/5As has to face is that KEF no longer manufactures the B110 bass/mid driver or T27 tweeter, or anything like them (KEF, furthermore, no longer sell individual drivers). The materials, components, electro-acoustic parameters and manufacturing techniques required for both drivers are relatively well known however, so armed with component and material sources and a suitable manufacturing line, remanufacture of both drivers is perfectly feasible. And that’s what Andy has set up for his new LS3/5A. Both drivers are manufactured in Asia with components and materials carefully sourced to be as close to the originals as possible. There are however unavoidable elements of uncertainty inherent to recreating the drivers because the fine detail of their original electro-acoustic performance is all but impossible to establish with complete certainty. For example, any original bass/mid driver will be at least 25 years old, so the mechanical properties of its thermo-plastic and rubber parts (diaphragm and surround) will have drifted away from their original values. Similarly, it’s known that diaphragms for the T27 tweeter were vacuum moulded at KEF in white mylar sheet and subsequently spray painted black. Unfortunately, spray painting introduced variability between diaphragm batches, so the typical performance the original tweeter is hard to tie-down. The result of these and other variables is that contemporary characterisation of any original driver’s electro-acoustic performance, doesn’t reveal exactly how it would have performed when it was new. The only option for Andy and the other current remanufactures of the original drivers is to incorporate every snippet of historical knowledge to inform ideas on exactly how the original drivers performed in order to steer manufacture of new ones. Previously being technical head of Rogers is pretty useful in that respect.

With new drivers in production, Andy’s next challenge was the crossover assembly and cabinet. Fortunately, both are rather more straightforward to recreate than the KEF drivers. The crossover assemblies in new Rogers LS3/5As are manufactured to be as close as is possible to the originals, complete with the characteristic BBC style tapped transformer inductors. Capacitors and resistors are specifically selected to offer equivalent performance to original LS3/5A items and are mounted on a glass-fibre substrate printed circuit board using the same layout and spacing.

A new Rogers LS3/5A with its grille removed.

New LS3/5A cabinets are produced, as were the original items, in birch ply with beech corner fillets. Damping panels are attached to the inner surfaces. As with the original, the cabinet architecture incorporates a removable front panel to which the bass/mid driver is rear mounted and the tweeter is front mounted (with its well known, diffraction suppressing foam strips). The crossover assembly is mounted on stand-off pillars behind the tweeter.

The results of all this effort is a speaker that subjectively has all the magic for which the LS3/5A is so well known. In particular, its character through the midrange is extraordinarily natural and immensely seductive. The intention of the BBC designers who created the LS3/5A was to provide broadcast engineers with an accurate and reliable reference for radio and TV shows that, back in the 1970s, were predominantly inhabited by simply recorded voices and acoustic instruments – and it shows. If there’s something awry with the sound of a voice or instrument it’s immediately obvious. It’s this I think that most resonates with the audio enthusiasts who value the LS3/5A so highly; it speaks of the original, purist aims of hi-fi to reproduce music with such convincing accuracy that it transports the consciousness of the listener to the time and place of the recording.

The interesting question that’s left however is why? What is it, in electro-acoustic engineering terms, that makes the 46 year old LS3/5A such an extraordinary performer? To my mind it’s a list of things; closed-box format, skilful driver design and integration, and clever tonal voicing, but at the top of the list I’d put the LS3/5A’s immensely rigid but properly damped cabinet structure. Along with writing previously in this blog about the LS3/5A, I’ve also written before about how cabinets contribute to the sound of loudspeakers and how I think the phenomenon is no longer given the attention it deserves. My recent experience of a new LS3/5A does nothing at all to change that opinion.

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