Rogers LS5/9 Classic SE

The LS5/9 has been voiced with the grille in place, but removing it exposes the re‑engineered LS2/14 bass/mid driver, and the Audax HD34 tweeter. The solder points along the left‑hand side of the baffle allow the tweeter’s level to be factory‑tuned in 0.5dB increments.

Despite its decades‑old design, the Rogers LS5/9 can still compete with some of the best monitors around today. We put this faithful recreation to the test.

Going back over half a century, high‑quality, professional audio equipment simply wasn’t available ‘off the shelf’, and so most of the major record companies and broadcast organisations had to design and build their own bespoke equipment. Nowhere was this truer than at the BBC, which established phenomenally innovative ‘R&D’ and ‘Equipment’ departments to design and build, respectively, pretty much everything that was required, often setting world‑class benchmark standards.

When it came to monitor loudspeakers the BBC evolved over many decades a particular approach to the design of both bass drive units and loudspeaker cabinets. The acme of the BBC’s in‑house loudspeaker heritage was undoubtedly the LS5/8, which was developed at the end of the 1970s to address a growing requirement for higher control‑room monitoring levels. The Beeb’s quirky naming scheme used LS to indicate that the product was a loudspeaker, ‘5’ to signify a ‘grade‑1’ monitor speaker for studio applications, and the ‘8’ simply meant it was the eighth‑generation design.

Excellent though the LS5/8 was, its physically large cabinet (110 litres) was simply too big for some of the BBC’s more compact control rooms. At the time, outside broadcast (OB) vehicles often used another well‑known and highly regarded compact BBC monitor speaker, the LS3/5A, but that was considered too small for a studio control room (and was officially classed as a ‘grade‑2’ monitor, anyway). So a few years after the LS5/8’s introduction the BBC boffins set about developing a more modestly sized grade‑1 studio monitor to bridge the capability gap and, logically, that was assigned the product label LS5/9.

Its design goal was to match the tonal accuracy, midrange transparency and production consistency of the LS5/8, while accepting the inevitably reduced bass‑extension and SPL capabilities of a more compact (28‑litre) cabinet. The prototype LS5/9 was trialled in 1983, and there’s a typically detailed BBC design report available online at http://downloads.bbc.co.uk/rd/pubs/reports/1983-10.pdf. Production LS5/9 monitor speakers were initially built under licence for the BBC by Rogers, although later on other manufacturers were also licensed to build it.

By the mid‑1990s, high‑quality, consistent monitor loudspeakers were available off the shelf from a number of manufacturers, and it became uneconomic and unnecessary for the BBC to continue developing its own speakers and drive units. Consequently the LS5/9 was the last monitor speaker to have a BBC‑designed bass driver, and also the last to be developed exclusively by the BBC’s R&D department at Kingswood Warren in Surrey.

LS5/9 Renewed

Given its unique pedigree and domestically acceptable size, the LS5/9 developed a strong following as a hi‑fi speaker, particularly in the Far East, and in recent years there seems to have been something of a resurgence of interest leading to the LS5/9 being reincarnated by several UK manufacturers — notably Rogers, whose LS5/9 Classic SE is reviewed here.

Although originally a UK manufacturer, Rogers were sold to a Chinese company in the early ’90s and their speaker production subsequently moved to the Far East. However, a few years ago the owner was persuaded to build the revered LS3/5A and the LS5/9 speakers under BBC licence back in the UK. As a result, the cabinets and passive crossovers circuit boards are made entirely in the UK and to the original BBC design specifications, and the whole speaker is assembled and tested in the UK too.

The fairly elaborate passive crossover is mounted alongside the tweeter behind the front baffle, and uses 27 elements — 17 resistors and 10 reactive components (capacitors and high‑power dust‑iron‑cored inductors) — to create third‑order (18dB/oct) slopes. The crossover frequency is 3kHz (the original design was 2.4kHz, a change presumably due to the revised bass driver’s characteristics), and the speaker presents an easy 8Ω nominal load (with a minimum impedance of 6Ω). With a low‑ish sensitivity of 87dB/W/m, Rogers recommend using power amps of 30‑100 Watts, connected via a single pair of silver‑plated 4mm ‘banana’ sockets (XLR/Neutrik connectors are available as an option).

Compared to many modern project studio monitor speakers, the LS5/9’s cabinet is still quite large, at 275 x 460 x 285 mm (WHD), and each unit weighs 12kg. In contrast to the modern vogue of exposed drive units, the LS5/9’s front baffle is recessed slightly to allow for a front grille covered with black tygan fabric. This grille is held in place by Velcro around the edges, and a fabric tab at the bottom aids its removal if necessary — although the speaker is voiced with the grille in place, and the nude baffle isn’t the most attractive anyway!

Cabinet Meeting

The design goal of any speaker cabinet is that it should be acoustically inert, of course, and the usual solution is to make it as solid and rigid as possible. However, that typically also makes it heavy and expensive, and any panel resonances tend to be high‑Q and thus ‘ring’ for a relatively long time, which is not helpful. The BBC’s boffins took a completely different approach: based on their research from the 1960s, and driven by the need to reduce both manufacturing cost and weight, they applied good engineering principles to come up with the idea of the ‘thin‑walled cabinet’.

Thin panels obviously tend to vibrate — just as the body of a violin or cello does — so this was prevented by gluing on bitumous pads to provide ‘critical damping’. In technical terms, these bitumous pads both lower the panels’ resonant frequencies and broaden the resonance peak to have a low Q (shortening the duration of any ringing) — both being Good Things in the context of a loudspeaker. In addition, internal acoustic damping was added, originally in the form of 40mm‑thick rockwool slabs in porous fabric bags stapled to the cabinet walls.

Of course, different speaker designers have different opinions of the ‘thin‑wall cabinet’ concept, but the BBC employed it on many very successful speaker designs over the years, and it seems to me an elegant, practical, engineering solution.

Rogers have maintained the BBC’s design in their reincarnated LS5/9, using 9mm‑thick Russian birch plywood for the panels, with beech hardwood battens to strengthen the joints. The outside is veneered with either walnut, rosewood or olive as standard finishes, but the review model is the upgraded SE version which features amazaque wood veneer.

The cabinet is ported, with a 90mm‑deep tube (tuned to around 40Hz) opening at the top right‑hand corner of the front baffle above the tweeter. Modern bitumous damping pads are affixed to each panel, as in the original, while modern acoustic foams are used instead of the mineral wool — but the results are exactly the same. While the standard models use 9mm birch ply for the front baffle as well, the SE version reviewed here uses a 9mm‑thick Panzerholz baffle (see 'Panzerholz' box), which is claimed to improve the bass response — presumably because of its greater stiffness.

Drive Units

Dating from the 1960s, the BBC’s R&D department researched extensively to find a bass driver cone material that gave more consistent results than the traditional doped paper, and it was instrumental in the development of plastics in this role. An early success was a thermo‑formed rubberised polystyrene material called Bextrene, which produced less distortion than paper‑pulp cones. One well‑known application of Bextrene was in the infamous KEF B110 bass‑mid driver employed in the LS3/5A (and many other similar drivers of the age). Further research through the ’70s led to the BBC developing a translucent polypropylene material which could be formed easily into any desired cone profile, and the first BBC loudspeaker to use this kind of bass driver was the LS5/8. For the LS5/9, the BBC built a scaled‑down version of this polypropylene bass driver, resulting in an 8‑inch (210mm) bass unit codified as the LS2/14.

Perhaps not surprisingly, this bass‑mid unit is no longer available and, sadly, most original bass drivers have deteriorated badly over the years due to weak spiders and decayed PVC surrounds. This could have been a big problem as the specific plastic and the critical flare of the cone were fundamental to the performance and sound character of the speaker as a whole. Fortunately, the man charged with overseeing Rogers’ recreations of their classic BBC monitors, Head of Design Andy Whittle, was able to reverse‑engineer the BBC designs to create modern replacement drivers with virtually identical performance. A key element of the design of the LS2/14 was the inverted half‑roll PVC surround cone termination, which is absolutely critical to the mid‑band performance and that has been re‑engineered to match the BBC’s original specs. Rogers’ revamp of this unique bass driver is now built in the company’s facility in China, but is hand‑finished in the UK.

A few years ago, the original tweeter was unavailable too: the LS5/9 used the same 34mm fabric dome unit as its big brother the LS5/8, but commercial production of this tweeter ceased for many years. Thankfully, French manufacturers Audax recently restarted manufacturing their HD34 drive unit, although the frequency response is slightly different to original models. To achieve the required performance parameters for the LS5/9, Rogers fit an additional damping layer, as well as a perforated dispersion plate.

To ensure accurate HF balance and stereo pair matching, the original LS5/9’s crossover included a resistor ladder connected to solder terminals on the front baffle, which allowed the precise tweeter output level to be set in 0.5dB increments during the final QC process. This facility has been retained in Rogers’ reissue and it can be seen alongside the tweeter through the front grille. However, this is a factory setting; there are no user user‑adjustable options or controls on the LS5/9.

Listening

Rogers market the LS5/9 Classic SE as being built using the same techniques and specifications as the originals, matching the BBC’s exacting standards. However, in some small ways it actually improves upon the original, most obviously in its higher power handling and slightly greater SPL capability (106dBA). I partnered the review speakers with either a pair of Bryston PP120 Monoblock amplifiers, or a Bryston 4B stereo power amp, depending on which listening room I was using at the time. Both configurations worked very well and the speakers actually seemed to benefit from the tight control of a powerful amp. Rogers recommends a ‘break‑in’ period of around 50 hours, mostly to allow the PVC surround on the bass driver to reach its optimum condition, so I ran the speakers in the background for a couple of days before starting serious auditioning.

My memories of the LS5/9 from back in my BBC days were that it could be a bit fussy about placement, and I think that’s still true of these recreations. The spacing between the speakers is critical to optimise the stereo imaging, and proximity to the rear wall affects the bass response more obviously than in some designs. However, with good positioning the LS5/9s deliver a vast and realistic soundstage that extends well beyond the speakers, and I soon forgot the sound was actually coming from those physical boxes! That said, the stereo imaging is not as precise and sharply focused as many modern monitors can manage, almost certainly due to the old‑school design of relatively broad front baffles with sharp edges.

The clarity of voices and midrange detail was reliably consistent and, frankly, quite sublime.

Tonal accuracy was always the primary goal of the LS5/9, and particularly in respect of speech, of course. I’m pleased to report that Rogers’ LS5/9 reincarnation achieves that in spades! I always use a reference speech recording as a first test when evaluating any monitor speaker as it is such a revealing signal. Subtle colorations or distortions instantly become obvious when listening to speech, just because our brains are well tuned to spotting anything ‘unnatural’ — but the LS5/9 Classic SE passed that test with flying colours! Spoken words and singing voices both enjoy a vivid clarity and naturalness that many so‑called monitors fail to achieve. The LS5/9 could fairly be described as precisely analytical in this respect, and I’d opine that the midrange resolution and detail are easily benchmark‑standard, revealing the subtlest elements of complex mixes with great clarity.

A common criticism levelled at classic BBC monitor speaker designs like the LS5/9 is known as the ‘BBC Dip’ — a built‑in, broad and shallow (2‑3 dB) depression through the midrange, centred around 2kHz. The Rogers LS5/9 Classic SE seems to exhibit this characteristic too, although I can’t say it bothered me at all, and it certainly doesn’t detract from the transparency of the midrange. In comparison to some more modern monitors with a slightly forward midrange character, the LS5/9 could come across as less informative, but it’s really not at all — and it’s actually a lot less fatiguing to work with over extended sessions.

With such a large tweeter I was expecting a little less ‘air’ extension than smaller designs, but I didn’t hear any obvious limitations and the LS5/9 delivered a smooth and detailed high end, while the upper‑mid region was free of sibilance.

However, I did find the speaker’s low‑frequency performance oddly variable. As I mentioned earlier, room placement is critical and I spent considerable effort, in two different listening rooms, optimising things as far as possible. Nevertheless, some very familiar test tracks exhibited great depth and solidity, while others sounded unexpectedly anaemic. The published specifications suggest a frequency response of 50Hz‑16kHz (±3dB), although listening to my test track of descending bass notes my impression was of a slightly higher roll‑off frequency. And yet these speakers were still putting out very audible content down in the 30Hz area on some of my test tracks — low frequencies that many monitor speakers fail to reproduce at all. But despite the context‑sensitive variability I experienced in the low‑end, when the music suited the LS5/9s I found them exceptionally good and genuinely revealing monitors, and the clarity of voices and midrange detail was reliably consistent and, frankly, quite sublime.

So, despite being a 40‑year‑old design, the Rogers’ LS5/9s can definitely still challenge more modern alternatives, especially in showing how vocal clarity should be done! The elephant in the room, though, is that these are £5000 speakers, to which must be added the cost of a high‑quality power amplifier. It goes without saying that in the pro‑audio market there is some very strong competition from quite a lot of extremely capable active studio monitors at and below that price range.

So while it’s difficult to recommend the Rogers LS5/9 Classic SE purely on a cost/performance basis, it does have some impressive strengths. If I was setting up a spoken‑word studio these monitors would certainly be on my shortlist.