Veteran UK speaker manufacturers Rogers have just restarted production of the legendary LS3/5A, alongside that of its bigger brother, the LS5/9 (pictured below). As well as making 'Classic' models (built to the exacting specifications of the originals), both speakers will also be available in 'SE' (Studio Edition) versions, which are fitted with Panzerholz (a hardwood/resin compound) baffles and upgraded crossovers, “for the most demanding of studio applications”.
The revival is being headed by Andy Whittle, who was Rogers' Technical Director back in the '90s, when the company were still making the 'original' LS3/5A. To find out what makes that speaker's design so special (and why second-hand models are still so highly sought after), we'll let SOS speaker guru Phil Ward's fascinating history lesson (originally published in SOS June 2016) do the talking...
History Of The LS3/5A
The LS3/5A originated in the mid-’70s, at a time when the BBC designed a fair proportion of their own broadcast and studio equipment. The whole idea of state-owned broadcasters designing and building their own kit is all but unthinkable now, but right up until relatively recently, if the BBC found themselves needing a specific tool that wasn’t available commercially, their Kingswood Warren research labs were tasked to come up with the goods.
The genesis of the LS3/5A was not as straightforward, however, as the Kingswood Warren boffins simply being asked to design a compact monitor and dutifully delivering. Although there was a need at the BBC for a ‘Grade II’ compact monitor for use in outside broadcast trucks, the development of the speaker that became the LS3/5A didn’t kick off in direct response to such a request. In fact the progenitor was a speaker designed for one-eighth-scale acoustic modelling of concert halls...
Long before ‘virtual’ computer-based acoustic modelling of performance spaces was possible, such work was done using literal modelling techniques. A physical scale model of the space would be built and miniature speakers and microphones placed appropriately within it to analyse its internal acoustic characteristics.
Now, there is no record (well, not in any document I’ve found) of who the engineer was to whom it first occurred that the acoustic modelling speaker used at Kingswood Warren actually sounded pretty good and might form the basis of a compact monitor. But whoever it was, I’d wager they had no idea at the time how significant a lightbulb moment they’d had.
In the early 1970s, when our story begins, speakers, whether for domestic or professional applications, were on the whole pretty big. Stereo hadn’t really been around all that long, and neither had powerful transistor amplifiers, so a single, large speaker was still the norm. Now, even if it’s on the large side, positioning one speaker is far easier than positioning a pair, as is required to create a stereo image, so the physical size of the speaker wasn’t so much of an issue. With stereo, however, came the problem of speaker positioning, and with that not only came the need for speakers to be smaller, but also for pairs of speakers to be closely matched in terms of performance.
It hardly seems believable now, but back then, there were very few commercially available small speakers that would satisfy the BBC’s needs. One of those few speakers that was available to the BBC was the original Goodmans Maxim, and a 1965 internal Kingswood Warren report describes its performance and assesses its potential. The report was written by Dudley Harwood, who went on to found Harbeth Audio (the company name being a conjunction of Harwood’s name and that of his wife, Elizabeth). The Goodmans Maxim itself was designed by a young Laurie Fincham, who went on to become Technical Director of KEF, manufacturers of the drive units eventually used in the LS3/5A. There’s none of that ‘six degrees of separation’ stuff in the British loudspeaker business; one or two degrees will usually suffice.
Harwood’s Maxim report, which can be found at http://downloads.bbc.co.uk/rd/pu..., makes interesting reading (well, it does if, like me, you’re irrationally interested in the history of speaker design). Even without converting the archaic imperial measurements of the test results, it’s obvious that the Maxim, by today’s standards, was inefficient, had restricted bandwidth at both ends of the spectrum, and displayed precious little power handling. However, those shortcomings weren’t issues that Harwood expressed much concern over; in fact he was generally satisfied with the Maxim’s performance. The issue that was of most concern to Harwood was sample consistency.
Along with the basic requirement for a small speaker that performed adequately for broadcast quality monitoring, the BBC needed the speaker to be consistent from sample to sample. If, say, a single speaker in an OB truck failed, it would be decidedly inconvenient if the pair had to be replaced, and equally unsatisfactory if the second pair didn’t sound the same as the first. So each individual speaker was required to perform within response limits that, even today, are a challenge. If the Goodmans Maxim report revealed one thing, it was that this degree of consistency would not likely be found in an existing commercial speaker. So, with a concept on the table for a design inspired by the acoustic modelling speaker, the Kingswood Warren engineers turned to KEF Electronics for help.
KEF got the call partly because, now under Laurie Fincham’s engineering leadership, the company were by some distance the most technologically advanced in the field, and partly because there was already an established relationship with the BBC. An earlier research project at Kingswood Warren into thermoplastic diaphragm materials had resulted in driver cones made from Bextrene (a polystyrene-based sheet material most often used in packaging and plastic consumables), and KEF were the first speaker manufacturers to commercialise the development, with their B110 five-inch bass/mid driver. Coincidentally, a five-inch bass/mid driver was also just about the right size for the speaker Kingswood Warren had in mind. And just as conveniently, KEF had developed an advanced (for the time) 27mm-diameter high-frequency driver, called the T27.
The Kingswood Warren speaker engineers believed that drivers with thermoplastic diaphragms were, along with their fundamental performance advantages, likely to offer better consistency than drivers with traditional ‘paper’ diaphragms. They were, of course, correct in general terms: sheets of plastic do tend to be more consistent in physical characteristics than sheets of paper. However, the diaphragm is just one among many potential sources of inconsistency in a driver, and the B110 had a couple that particularly caused headaches. Firstly, sample differences in the mechanical properties of the driver’s neoprene diaphragm surround resulted in variable frequency-response anomalies, and secondly, in order to perform optimally, that Bextrene diaphragm required a coat of tacky gunk, called Plastiflex (a book-binding adhesive closely related to PVA wood glue), applied to its surface to provide extra damping. The problem with the layer of Plastiflex was its application — by hand with a paint brush — which meant that the mass of the diaphragms would vary, and changes in the baseline sensitivity of individual drivers would result.
Despite these potential consistency issues, the B110 and T27 were chosen for the LS3/5, and the remainder of the development just required an enclosure and passive crossover. Remarkably, there’s no need for me to spend too many words going into the detail of the design of the enclosure or crossover, because it’s all documented in another BBC Research Department report, again by Dudley Harwood: http://downloads.bbc.co.uk/rd/pu....
Harwood’s LS3/5A report is fascinating throughout, but a couple of things stick out for me. Firstly, significant effort was clearly expended on fine-tuning the LS3/5A cabinet — even to the extent that the variety of wood used for the internal batons was driven by the influence this had on subjective sound quality. The cabinets also were built from a tightly specified grade of birch plywood, and incorporated not only elaborate internal panel damping but even constructional techniques designed to ensure that screw holes were guaranteed airtight. Secondly, the sample variation of the B110 mass/mid driver meant that an unusual tapped inductor was used in the crossover network, so that the effective sensitivity of the tweeter could be adjusted to compensate for the sensitivity of individual bass/mid drivers. The crossover network is a complex one also, with as many elements dedicated to equalising the pass-band frequency response of the drivers as there are dedicated to low- and high-pass crossover filtering.
If you’ve read Harwood’s LS3/5A report, you’ll know that the project hit a snag after the first 20 prototype pairs were made. The snag was that KEF had modified both the B110 bass/mid driver and T27 tweeter for their own needs, and so the LS3/5 design had to be revised to compensate for the changes. This is the point at which the LS3/5 became the LS3/5A.
While the original LS3/5 became a small historical footnote, the LS3/5A was a huge success, and as well as building units in-house, the BBC took the decision to offer licences for its commercial manufacture and sale to the general public. There were two motivations behind the licence decision; firstly it meant that in-house demand for the monitor could also be more easily satisfied (by the mid ‘80s, it’s said that around 3500 were in use by the BBC), and secondly, selling licences was an effective way of recovering the speaker’s development costs. These were estimated at well over £100,000 — a very significant sum back in the mid 1970s.
New For Old
And that brings us neatly back to Rogers, the first ever company to manufacture the LS3/5A commercially, and thus the name most commonly associated with it. The resumption of production is clearly excellent news for anyone who's been coveting an LS3/5A without the decades' worth of wear and tear, but it'll also be of interest to anyone who owns a vintage example: because Rogers will also be offering full re-cones and services to a range of classic Rogers/BBC speakers.
The LS3/5A Classic and SE editions are on sale now, priced at £2899 and £3499, respectively. To find out more, head over to the Rogers website at the link below.
