The LS3/5A (each element pronounced separately, without the stroke) is a small studio monitor loudspeaker originated by the BBC for use by outside broadcast vans to ensure quality of their broadcasts. The speaker concept set out transparent and natural sound as the goal, and the achievement of the result is widely acknowledged.
The BBC granted licences to a small number of British firms, which first manufactured the product in 1975. The product underwent a change in 1987 due to consistency issues in manufacturing, and again in around 2003 when original parts from KEF ran out. Upwards of 60,000 pairs of the speaker have been sold. Reviewers have recognised its enormous importance as a bookshelf design.
History The LS3/5A is a commercially produced loudspeaker driven by the need of the BBC to monitor and assess broadcast programme quality. It was derived from the LS3/5, which was conceived and developed by the BBC Engineering Department in the early 1970s, when it was under the stewardship of Dudley Harwood. Having found no commercially produced small loudspeaker that met the requirement for naturalness and sonic neutrality, the BBC specifically set out to design a speaker to achieve natural overall sound quality and good dynamic range for monitoring broadcasts in tightly confined spaces.
As the BBC broadcasting unit was about to order another batch of the monitor, it was found that the supplier had modified the drive units, meaning the LS3/5 design had to be fundamentally revised. The BBC's Designs Department was called upon to adapt the product in light of the supply changes. Modifications were made to adapt to the new drive units and deal with the altered resonance pattern, and the LS3/5 became the LS3/5A.
The BBC then licensed the product to a small number of private sector companies. Production began in 1975. In 1987, as a result of reassessment of the product due to consistency issues in the manufacture of the mid–bass driver, the drivers were modified and the crossover changed. The overall impedance of the crossover fell to 11 ohms from the original 15 ohms.
The various official versions of the LS3/5A from various licensees sold in significant numbers in its life of over a quarter of a century. Sales estimates range from 60,000 to 100,000 pairs.
In the tail end of the 1990s, due to the parts being discontinued, the 3/5 had technically reached the end of the road. Some licensees continued to make small numbers of speakers, for a while, using re-manufactured parts. However, Stirling Broadcast, one of the last batch of licensees, completely redesigned the product based on the audio signature of the original, and launched the LS3/5A v2 with the full endorsement of the broadcaster in early 2006.
In 2014, production of the 15 ohm version of the LS3/5a with a full BBC Licence was re-commenced by Falcon Acoustics using re-engineered versions of the original drive units and the original design BBC crossover all produced in-house.
Speaker Name The product name is derived from BBC naming convention: the "LS3" designation meant it was a loudspeaker intended for outside broadcasting, as opposed to the "LS5" loudspeaker, intended for studio monitoring. The number after the stroke is the model number, the LS3/5 is "number 5" outside-broadcasting loudspeaker. The letter that follows denotes alterations to the original specification, of which there was only one in this instance after the LS3/5, thus the "A".
Design For its outside broadcasting monitoring, the BBC required a small studio monitor suitable for near-field monitoring of the frequency range from 400 Hz to about 20 kHz. The principal constraints were space and situations where using headphones is unsatisfactory, such as in mobile broadcasting vans. There were no commercial constraints. The BBC Research Department, then situated at Kingswood Warren, were responsible for development work, and commenced scaling tests in 1968. They were able to answer a request for a prototype in under a week because it resembled an experimental loudspeaker that the department had already developed for some preliminary acoustic scaling tests. The speaker had to be voiced by ear an octave at a time, because scale test results were inapplicable to a model of this size. Engineers took measurements; comparisons were performed against the LS5/8 – a large "Grade I monitor" already in use at the time – and with live sources. In 1970 engineers came up with the LS3/5, built using the KEF B110 (A6362) and the KEF T27 (A6340) drive units, and a 9-ohm crossover filter. Estimated development costs of the order of £100,000 were said to have been incurred at the time. Approximately 20 units of the LS3/5 were produced in-house.
The BBC had initiated tendering to have the LS3/5 made under licence. As the broadcasting unit was about to order another batch of the monitor, it was found that KEF had discontinued the B110 (A6362) and the T27 (A6340) in favour of the B110 (SP1003) and T27 (SP1032) specification, and was already using them in the Coda, one of their own-brand commercial loudspeakers. Thus the design had to be revised because these new units had different impedances, technical characteristics and altered resonance patterns. The tweeter was considered potentially fragile because it now had an exposed dome, so a suitable protection grille was found to cover and protect the dome. The tweeter was also surrounded by a thick felt rectangle to prevent interference pattern effects being created by the edge of the cabinet. The crossover also had to undergo change, and the LS3/5 became the LS3/5A in the early summer of 1974.
The KEF B110 SP1003 is a 110 mm speaker with a doped Bextrene (a proprietary type of polystyrene copolymer) cone and a neoprene surround. The KEF T27 SP1032 has a 19 mm mylar dome fitted and is with a perforated protection grille. The loudspeaker has an internal volume of approximately 5 litres. The speaker cabinet (loudspeaker enclosure) measuring , is made using birch plywood strengthened at every joint with beech braces, and heavily damped. Although there was no specification for the wood of the original LS3/5 cabinets, the BBC closely specified wood types in defining the LS3/5A due to concerns that other hard woods – specifically Parana pine, with which the BBC conducted tests – would cause noticeable colouration (i.e. detract from sonic neutrality) due to interaction with a resonance of the bass drivers.
Martin Colloms notes in Hi-Fi Critic that: "Hardly any component in either enclosure or driver may be substituted without the blend suffering audible disturbance. This is because the 3/5A sets such a high standard for tonal balance that errors which would pass unnoticed in an ordinary speaker are readily exposed". The BBC then licensed the product to a small number of private sector companies.
In a review in Stereophile, John Atkinson remarked on how it was "virtually unknown for a speaker to be still available, virtually unchanged, 14 years after [its introduction]".
Construction J. Gordon Holt indicates in Stereophile that most of the cost lay inside the case, having been spent on a complex equaliser and phase-corrected crossover. However, Holt's colleague, John Atkinson, notes that the cabinet alone "costs the manufacturer the same as the retail price of a typical speaker". Only specific speaker drivers manufactured to strict tolerances may be used. There were other measures to control diffraction and ensure tonal neutrality.
The circuitry provides equalisation in both high and low frequency sections. The 13-element crossover includes an inductor for the treble section with seven positions that allows adjustment to match level of mid to treble sensitivities. The design also specifies high quality screened air-gap inductors and film capacitors. David Prakel in Hi-Fi Answers suggests it was a costlier speaker to build than imagined because tight specifications meant a high failure rate in production – the BBC had specified "the finest, most expensive ingredients and representing an investment of hours of skilled labour".
Signature sound Similar to sealed-box speakers of similar size, the 3/5A has little or no low bass, but the design reinforced its lower register by a boost at around 160 Hz, giving the subjective impression that the speaker is more bass-rich. It has a gently rising frequency response above 5kHz, leading reviewers to notice the sound being a little bright at the treble registers, or that the speakers "reproduce the high-end roughness of solid-state amplifiers mercilessly" thus suggested partnering with valve amplification would be advantageous. A slight nasal quality in the midrange has also been noted in the earlier versions. The accuracy and stability of its stereo imaging and its clean midrange reproduction are also appreciated qualities. J. Gordon Holt suggests that the quality was "comparable to that from Quad Electrostatics, at far lower cost and with added bonuses of slightly smoother high end, better stereo imaging, a broader listening area". John Atkinson suggests in Stereophile that the LS3/5A is ideally suited to the reproduction of program having a limited dynamic-range requirement, for example chamber music; he said that the LS3/5A "has never boogied and never will; it's just too polite ever to cut the mustard on rock, or even straightahead jazz".
Constructors A total of 11 companies were ever granted licences by the BBC to manufacture the model, a maximum of 3 at any given time. The product proved highly challenging to manufacture, if for no other reason than tight specifications and consistency of parts, and many of these companies would have a chequered corporate history. Audible differences could result from the mounting screws, grille fabric, or the origin of the wool.
Rogers Audio was the earliest licensee, but went out of business before producing a single unit. The Rogers name was bought by Swisstone, who started manufacturing the 3/5A under licence in 1975. Rogers' production accounted for the majority, of around 43,000 pairs by 1988, and 50,000 pairs in total. Of the other main manufacturers, Spendor produced about 11I have one of the last pairs made and they are numbered 217x4 and 217x3,000 pairs, and Audiomaster 10,000. Dudley Harwood, the BBC engineer instrumental in the creation of the 3/5A, started Harbeth and obtained a licence in 1977, but the company produced no LS3/5As for a decade. Eventually, Harbeth accounted for 7,000 pairs. KEF, who obtained its licence in 1993 (and at which point there were 4 concurrent manufacturer licensees), claims approximately 4,000 pairs were made from 1994 to 1998. Other licensees included Chartwell, RAM, Goodmans, Graham Audio and Stirling Broadcast.A current licence for the 15 ohm LS3/5a is held by Falcon Acoustics
Reception Despite not being a "commercial product" at the outset, the LS3/5A was commercially successful in its twenty-something-year life, from 1975 until approximately 2000, when the availability of KEF drive units came to an end. The speaker has amassed an "enthusiastic, focused, and loyal [...] following, and none so large or vocal", according to Paul Seydor in The Absolute Sound.
Estimates of their sales differ, possibly due to scope and cut-off: when it ceased production in 1998, "some 100,000 pairs were in circulation, with 3000 pairs sold in its last year alone", according to Seydor; in 2001, Ken Kessler similarly estimated in Hi-fi News that 100,000 pairs had been produced. In 2007, Martin Colloms reported "more than 60,000 pairs of the original LS3/5As were made". John Atkinson noted that it had sold in excess of 60,000 up to 1988, of which Rogers represented two-thirds.