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10.06.13
Stirling Broadcast
BBC LS3/6 loudspeakers

History hints

BBC, British Broadcasting Corporation, also called "auntie" or "Beeb" by the Brits, is the biggest and most prestigious UK broadcaster based in London, founded on October 18, 1922. Talking about British Sound is remembering the monitor series designed in the '60s and '70s by the great auntie. Among them, and emblem of timbric excellence, the BBC LS3/5a nicknamed "shoe box". A small bookshelf loved by the most and opposed by those audiophiles who had forgotten the reasons of its existence, i.e. soundproofing the mobile workstations. Notwithstanding the poor extension on the low frequencies and the scarce dynamic performances, this mini speaker had a formidable detail inside a great tonal balance frame and a legendary mid range outcome.

 

The figure of Harold Lister Kirke has an important role in the history of BBC epic: head of Research Department at its inception for the first all-important twenty years, he applied a scientific method and shared it first with the industry, then with the public.

If we consider that the unity designed in 1924 by the pioneers Chester W. Rice and Edward W. Kellogg, actually the first speaker in history, was made available for BBC, we understand how its historical path is strictly connected to the dawn of electroacoustics. The unity was mounted on a big floorstander refined in a polished Black Piano, codified LB/3, while the entire system was called LSU/7.

 

What came out, after the tests run between 1945 and 1947, was the LSU/10, a big monitor destined to the recording studios for more than thirty years. A huge pro system with an oak cabinet of 280 liters that could go down till 40 Hz and up only to 6 kHz, but enough for AM radio stations broadcasting music recorded at 78 rpm and reproduced by Shellac gramophones. Always in 1947 H.D. Harwood joined the BBC R.D. coming from the National Physical Laboratory, where he had worked on earpieces designing and loudspeakers calibration. In 1948 the tests on a loudspeakers system begin through the listening of the spoken parts in the middle of a field, far from any reflecting surface and with their comparison with the original voice, although it was known that a correct reproduction of the word doesn't necessarily give the same result for the music, which deploys itself on a wider frequency range.

 

We have to wait till the 60's and the 70's for the noble stock of the BBC monitors which have been later catalogued under four classifications:

  • LS/1 Loudspeaker assemblies, miscellaneous use
  • LS/2 Chassis units
  • LS/3 Loudspeaker assemblies, outside broadcast use
  • LS/4 Loudspeaker assemblies, studio use

All of them had a very neutral sound and a great articulation. At BBC the certainty was that the type of material used for the membrane had a marked effect on the overall sound. Therefore they changed over, from the initial material - the paper -to the Bextrene, a kind of polystyrene. Its major advantage, besides the sound qualities, was the ease by which more consistent and repeatable results could be obtained. The cones were got with a vacuum forming process, then they have to be coated with a damping compound to remove colorations in the region between 1.500 and 2.000 Hz. Unfortunately, this process has never successfully been automated and the compound was applied by hand onto every membrane. In the '70s starts the use of plastics - notably polypropylene - again with pioneering work at Research Department. Polypropylene did not need to be coated, as the material was inherently self-damping. Because of its lower density, polypropylene yields greater efficiency than Bextrene.

 

Among the glorious BBC monitors, besides the mythic LS3/5a, are the LS3/1, LS3/4, LS3/7, LS5/1, LS5/2, LS5/4, LS5/5, LS5/6, LS5/8, LS5/9, and the LS7.

 

BBC LS3/6: genesis of a success

To understand the complex gestation of the BBC LS3/6 is necessary to go back with memory to two historical models: the Spendor BC1 and the Rogers Export Monitor speakers. The BBC original design had a low power handling due to the light structure of the moving coil made of paper, although the mid range was defined as "luxuriant". The purpose of the following Export Monitor was to improve substantially the Power Handling without undermining the timbric qualities. The target was reached thanks to five years of designing experience in making the BBC Rogers LS3/6 Studio Monitor.

 

The Spendor BC1 were a pre-derivative of the LS3/6 but not a BBC model, since this last one was oriented to manufacture a small two-way monitor using the 8" mid of the LS5/5 speaker, that Spencer Hughes was making at that time. Successively Hughes still worked on his own on the BC1, originally thought as a two-way with a Celestion HF1300 tweeter and only in a second moment he decided to add a STC 4001 supertweeter.

In the meantime the BBC completed the project of the LS3/6. Rogers took on the production and proposed to add the Celestion HF2000 supertweeter. BBC agreed.

Let's quote Hughes himself: "During the mid nineteen sixties the development work carried out by the BBC had advanced to a stage which was beyond the capabilities of the available paper pulp cone bass units. The decision was taking to investigate the possibilities of using some form of plastic as a cone and surround material. Some two years were spent making 12-inch unit cones in a variety of shapes and from a range of plastics; this could be a story on its own. The first successful unit was made from the now well-known Bextrene and used in the development of the BBC studio monitor type LS5/5. My part, as a laboratory technician, in the operation was to do most of the actual work both on the plastic investigation and the development of the LS5/5. With that experience I decided that it should be possible to make a loudspeaker from scratch in the home environment. With the aid of our electric fire, a compressor working in reverse and an iron bedstead the first vacuum former was built. Bins full of malformed cones were produced before any measure of success was achieved and the first eight inch unit was produced. This unit turned out to be almost certainly the first commercial eight-inch Bextrene driver and still arguably the best.

The first pair of BC1s was constructed using these units and the Celestion HF1300 units. The second pair of BC1s was made for a friend who took them to Merrow Sound of Guildford. The third pair was sold to Merrow Sound and Spendor was on the way to a small niche in the audio world. Now some difficulties were beginning to arise as under the terms of my contract with the BBC, the design had to be offered to them. Fortunately the "Pop" era had just started and the main request was for more power, so the BC1 was turned down. Around about this time there was a special requirement within the BBC for one pair of speakers about the size of the BC1s. Being a kind soul I suggested that my design could be used, so I was given the task of producing an official version of the BC1, later designated the LS3/6".

 

This design considered an 8" unit made by Research Department, the Celestion HF1300 tweeter and a redesigned crossover. The main change in the filter was the addition of a large multi-tap autotransformer to allow adjustment of levels between the two units, normal BBC practice at that time.

Some months later, the BC1 was fitted with an amplifier mounted in the back panel and the STG4001G super tweeter added. The addition of the third transducer was for purchase/tax reasons, but it actually improved the overall dispersion characteristics.

 

Now it's time to turn to the present where the difficult task of retracing the splendors of the BBC LS3/6 is in the hands of three champions: the Harbeth Super HL5 A, the Spendor SP1/2R2 and the most recent Stirling Broadcast BBC LS3/6 Reference Loudspeaker, protagonist of our test.

 

As with the smaller LS3/5a, also the LS3/6 was thought as a monitoring loudspeaker for outside broadcast use. The British Rogers was one of the first companies to produce it. The BBC monitor event has shown how can be useful for the "home" systems to gleaned from the pro, an intelligent behavior still profitable today.

Stirling Broadcast has restored with authority an old glory like the LS3/6 and at BBC people are not very "comprehensive" towards who wants to revive one of their glorious speakers: the license can be obtained only after a rigorous exam which assures the strict adherence to the original specs.

 

On the Stirling Official website is stated that a very high quality crossover is used to mesh custom made drive units, including a super-tweeter, into thin-wall, birch plywood (9mm ply) cabinets with double thickness rubber damping pads and screw-on, removable front and rear panels, as per the BBC "lossy" cabinet design ideal, as also seen in the Stirling version of the LS3/5a V2.

I have to say that very "laconic" was Doug Stirling's contribute to my request of further info. With traditional British confidentiality he declared that in the LS3/6 the mid-woofer crossover is of the second order, while on the high sections is of the third order. The crossover utilizes prime passive components with air-wound inductances and polypropylene capacitors that produce a negligible distortion. The filter is directly connected to the input terminals for the maximum signal transfer. All the connections to the drivers are Hard Wired. Doug apologized but, due to the restrictions of the BBC license, he could not give me more detailed info on the crossover circuit layout or on the transducers.

 

Technically the Stirling can be defined as a 2 way bass reflex system with supertweeter or a 3 way, if we consider the SB-4436 as three way instead of a "simple" gregarious of refinement of the extreme high range. The designer of the Stirling Broadcast is Derek Hughes. He tried to follow the BBC original model by creating a loudspeaker which looks to the past but is modern in its performances thanks to high quality components, tougher transducers and a more linear conduct. So we have better power handling, more regular frequency response, good angular dispersion and very low coloration.

 

In a cold morning I received a pair of Stirling LS3/6 in the walnut finish that shows a sober Brit elegance.

The other available Editions/Veneers are :Cherry, Zebrano, "Limited Edition Gold Label", Ebony "Limited Edition Gold Label", Rosewood "Limited Edition Gold Label. The huge bookshelf was a must in the '70/'80s and I personally wish for its revival because of its great adaptability in the domestic environment. It could be the right way between a mini speaker, with limited dynamics and extension of the low frequencies, and a tower which usually offers a generous bass, even though unsuitable to avoid the resonances.

 

Therefore the Stirling are neither a mini nor a slim tower, but they are mounted in a 45litre reflex loaded cabinet and, despite all the studies on the diffractions of the sound waves on the edges, they stand out for their sharp edges. Moreover the front baffle is "framed", I mean it is rearward of a couple of mm to leave room to the grill. To remove this last one, without damaging the wood, I suggest to use a small spatula covered with some soft cloth and carefully lever on the borders.

 

Speaking of eccentricity the mid-woofer has the flange toward the inside, while in the 99,99% of the speakers it is toward the outside. This SB-4432 unit measures 16 cm effective from centre to centre of the suspension, which is linked to the surface through a wide rounded milling that creates a step of about one cm.

 

The transducer of the mid-low range is atypical also in the rubber external border, which is overturned, while in the middle there is a classic anti dust dome. In the low portion of the baffle is the reflex port, which is 8 cm deep and 7 cm wide.

 

Given the absolute ban of opening the cabinet, I couldn't explore inside the speaker to take some pictures or remove the drivers. The reason is that the rear panel is tuned to the chassis and when you disassemble and reassemble it, the tuning would be compromise and the manufacturer has to intervene to "retune" the whole thing. We are dealing with a "Resonance Control" cabinet, which technique does not damp the vibrations but calibrate them in order to contribute to the amazing spatial reconstruction given by this loudspeaker. The target has been reached by using a 9 mm birch plywood multilayer and not a deaf MDF, so to enable the sound to "breath" through the six panels. A brave choice.

 

I suggest to place the speakers onto stands, at least 40 cm tall. The multifunction screw terminals allow the Bi-Wiring/Bi-Amping and accept both 4mm plugs and bare wires up to 4mm cross sectional area. For the monowiring, two metal golden rods are provided and they have to be bridged between the terminals.

 

The listening session

A brush up on my system, composed by Trends Audio TA 10.2 integrated amp, Rotel RC 06 preamplifier, Rotel RB 1070 power amp, EAM Lab HP 01 preamplifier, EAM Lab TO 3.8 power amp, Rotel RCD 1070 CD player, HP G62 Personal Computer with Foobar 2000 player and E-MU Creative Pre Tracker Pre USB 2.0 sound card, Pro-ject Debut II SE turntable with Denon DL 160 cartridge, Fluxus 2*70 S signal cables, Fluxus LTZ 900 power cables and Fluxus "Alimentami" main cables.

 

No sex, Please, We're British

I do not mean to ape the comedic play written by Alistair Foot and Anthony Marriott, but the title seems significant of the personality of such systems, far from the "luxurious" excesses and typical clamors of a certain too much extroverted Hi-Fi.

For the listening test I wanted to wander in the meanders of my record collection into the unknown, since it happens that of an album that you have listened to many times, you can say "I know it well" with self-confidence and then you find out that something has never been detected, that some nuances have never come out. Hence, I can say that the LS3/6 are like X-rays, without comparing this adjective to others like coldness or lack of musicality.

 

Before soaking into music I suggest to have on hand an adequate amplification in order to let the Stirling express themselves at best. I use my Trends Audio TA 10.2 to test the easy drivability: it is a small "T" class amp provided with the Tripath TA2024 chip, very valuable for the timbric and spatial characteristics, enough analytic to catch all the nuances, unfortunately of low power, only 6+6 watts on 8 ohms, and quite weak in the loads below 3 ohms. Too low power, so I turned to the Rotel RC 06 preamp and to the Rotel RB 1070: an amp with 135 watts per channel, honest and sufficiently performing with a certain level of power but you have to keep the volume not very high, otherwise the sound comes out slightly degraded. In this case there was power but not enough refinement. The masterstroke comes with a real High-End match: EAM Lab HP 01 preamp and the EAM Lab TO 3.8 power amp with 200 watts per channel, with a beautiful "tube-like" voice and the sinew of the solid state amps. As I said in the technical notes, the low sensitivity, 86 dB/W/m, the quite high impedance and a well damped reflex system, need enough power and my suggestion is to avoid going down below 100 watts per channel on 8 ohms.

 

I start with the Complete Lute Works by John Dowland in the splendid performance of Paul O'Dette. Enthusiastic are the timbric chisel of lute and Orpharion, the nuance richness on the entire range and a valuable balance. The supertweeter gives great openness and air to the reproduction. Impressive is the extremely natural acoustic of the instrument, its breathing in the space without any effort or colorations. The notes flow unflappable, without any connotation that can distract the listener by deviating or better disturbing the course of music.

 

It's time for the vinyl with Sei sonate per archi by Gioacchino Rossini, performed by the Solisti Veneti under the direction of Claudio Scimone. There's a lot of balance between violins, violoncellos and double basses, a nice sensation of air that makes the timbre particularly clean, realist, without any harmonic limitation which tends to make opaque the timbric shine.

 

Still on the acoustic music with the strings instruments. The baritone guitar by Pat Metheny in the solo album of 2003 One Quiet Night: a work recorded in just one night that offers sparks of great artistic and technical interest. This record is a good test on control and linearity in the low range. The Stirling perform well showing high quality in articulation, control and damping of the low range, a healthy character trait present in every recording. I can hear subtleties never heard before. The extreme rigor in the low range of the audio bandwidth can be excessive in some occasions but it can be tempered with the right amplification, that is with a good low supply. I have reached a good balance with the EAM Lab and I repeat that it's important to have a good current in order to fully exploit the dynamic potentialities of the Stirling. Then, a listening at high volume of the brutal Rage Against the Machine of the homonymous American alternative metal/rapcore group, made me understand that the LS3/6 can be effective also in these occasions.

 

After an excursion on the well tempered Johann Sebastian Bach's harpsichord, proposed by the supreme pianistic art of Glenn Gould, I adventure myself in the most demanding symphonic literature, where I can appreciate how the Stirling can treat the full orchestra, the scansion of the soundstages and more easily the width of the margins of the three-dimensional soundstage. I go on with the Symphonie fantastique by Hector Berlioz in the interpretation of Andre Vandernoot with the Orchestre National at 24 bit/96 kHz, rich of details and intact in the demanding dynamics leaps and the album Britten's Orchestra with Michael Stern directing the Kansas City Symphony, in high resolution too, at 24bit/88kHz. The LS376 acts like a champion also in the spatial recreation with a precise scansion of the sound stages, a correct sizing of the stage without any imbalance among width, height and depth but, most of all, a fantastic air which makes magnificent the timbre transparence, and no veil on the brasses lustre. The devastating timpani in the incipit of the Requiem Symphony could make anyone jumping from the armchair if reproduced at high SPL.

 

To catch the strength of the SB-4432, I just listened at a not very high volume, but enough high though. The Brit speakers teach us that more than strength what it's beneficial is the velocity of the response to transients and the damping which the sound comes to the listener's ears with: two qualities often combined. Both Jaco Pastorius' fretless bass and Billy Cobham's drums are empty without such qualities.

 

At BBC they know that power is nothing without control, a principle applicable also in the electroacoustic field.

The elegant jazz atmosphere of Brad Mehldau & Rossy Trio in When I Fall in Love, emerges with gauzy delicacy with Jordi Rossy's drums showing a silvery cymbal in the enthralling swing background and harsh brushes on the snare drum. The atmosphere a la Blue Note is giving back with sure feeling thanks to the convincing micro and macrodynamics output, within a neutral ground color. The same feelings, although more intense, awaken in the Conférence de Presse Vol 1 e 2 by Petrucciani where the pitied great pianist duets with Eddy Louis in a series of involving standards enriched with original improvised embroideries. The atmosphere is more incisive, sometimes more sanguineous, in this limpid recording.

 

The test on the voices is passed brilliantly. Always controlled the male voices, not projected in the very first row though. The great Fabrizio De André, always present in my sessions, is here very civil, with a timbre under surveillance, maybe less involving but with an exemplar precision. The female voices are very classy, mostly in the high range where they are dazzling and vivid. In this convincing performance the high part of the tweeter and the supertweeter has a good game and the vocal brilliance is intact thanks to the great harmonic completeness, opening and airiness. A brilliance that fades a bit with the mids when protagonist is the mid-woofer. Nothing dramatic though. The sound stays on high levels of naturalness but a certain step between the SB-4432 and the SB-4434 is considerable. The last test is with Eight Basque Songs by Jesús Arámbarri, Naxos edition. The easy brilliance of these orchestra pages appears intact. The punctualism of the small instruments is given back with great accuracy, homogenously with the remaining orchestra fabric. The image is sculptural in its plasticity, spreading with good openness in the entire listening environment.

 

Conclusions

The Stirling Broadcast BBC LS3/6 are speakers that make think about what is very important in the High-Fi reproduction. During the time, I believe that the audiophile has leaven the starting point: giving back the sound in a less interpretative way in favour of something neutral and inflexible that gives back the sound as it is. With the Stirling you embrace an important piece of the Hi-Fi story, you benefit of a philosophy based on the maximum adherence on the naturalness of the real sound. They were made as monitor of good dimensions, without any dynamic and extensive limitations on the low frequencies, with a power handling also overabundant if considered in the economy of a normal domestic environment. That the LS3/6 is prevalently an home system is proven by the exemplar behavior on the low frequencies, always limpid, controlled, with a perfect British aplomb. They are not only chic, they are not just nice and cozy: if driven with a good quantity of watts they do their job also with more aggressive music revealing an unthinkable grit. In such conditions the sound becomes tense, compact and electrifying.

Considering the accuracy of the finish, the quality of the making and of the transducers, the price of 3,490.00 euro is proper.


Warm thanks to Giuseppe Castelli, Doug Stirling and Gerardo Ventura of PlayStereo for giving me permission to realize this review.

 

 

Official technical specifications:

Manufacturer: Bridgefoot Lodge, Lydford on Fosse, Somerset TA11 7DP UK

Power Handling: 90w continuous,150w short term, IEC268

Max Sound Level: 107dB, pair @2m

Input Impedance: 8ohm nominal

Input connections: Bi-wire, 4mm terminals

Frequency Response: 45Hz to 17kHz +/-3dB(On HF axis @1m)

Sensitivity: 87dB/1watt/1m

Cabinet Dimensions: 30cm (12") wide x 30cm (12") deep x 63cm (24") high

LF Drive Unit: SB-4432

HF Drive Unit: SB-4434

SHF Drive Unit: SB-4436

Crossover frequencies: 3kHz, 13kHz

Weight: 18.5kg

Official Italian dealer: to Audioazimuth website

Official current price in Italy: 3,490.00 EUR





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