Over the years there has been much confusion about the LS3/6, the Spendor BC1, and the Rogers Export Monitor. One of the things that immediately muddies the waters is the fact the LS3/6 was never labelled nor marketed as such - instead, it was simply known as the "BBC Studio Monitor"! Also, there doesn't seem to be a BBC design report for the LS3/6 - if anyone knows differently, please let me know.
Contents
Overview
The (really!) short version of the story:
- The Spendor BC1 came first
- The BBC LS3/6 is a development of the BC1 - not the other way around
- The Rogers Export Monitor came a few years later, and is not a BBC design, despite the obvious visual similarities
The Export Monitor was replaced by the Studio 1 in the late 1970s. I was in two minds about including it on this page, but as it uses the same form factor and is a 3-way design based around the Celestion HF-1300, it feels logical to include it in this story.
Unpicking the details
Let's start with some useful evidence that will help us to build up the full picture.
My first source of information about these models came from Allen Edelstein, which was posted during a discussion on the Spendor mailing list (formerly a Yahoo Group, but now hosted on Groups.io). This was posted many years ago - about 2 decades back - but as I haven't yet located the original message in the archive, I can't provide a more accurate date or direct link to the message.
The Export Monitors were a mod of the LS3/6 by Rogers on their own to make the speaker a better home product. This was especially to increase the power handling which was low on the LS3/6 partially due to a light voice coil structure with a paper former. I recall (over 25 years ago) that the LS3/6 had the most beautiful, slightly lush midrange of any speaker I had ever heard and I'm not sure if this still would not be true.
The BC1 was a pre-derivative of the LS3/6, but not a BBC model. Spencer Hughes had worked on the 3 way LS5/5. The BBC thought they could use the 8 inch mid of the LS5/5 to make a 2 way smaller monitor and they started to work on it. They stopped mid-stream and Spencer used the research to develop the BC1 on his own. It was originally a 2 way with just an HF1300. The STC super tweeter was added later. Meanwhile the BBC started the LS3/6 work again and finished it. Rogers took on the manufacture and they proposed adding the HF2000 super tweeter which the BBC approved.
Allen Edelstein
So, quite complicated!
Next, a detailed letter from the late Spencer Hughes that helps enormously. This can be found in several places, but I'm indebted to Derek Hughes for allowing me to include it here. It was written in 1980, and naturally, is written from Spendor's point of view, so doesn't go into much detail about Rogers.
Dear Sir,
The Spendor BC1 was not, as it has so many times been described, a development of the BBC loudspeaker type LS3/6. Perhaps a short history of the lead into, and the development, of the two systems may be of interest.
From the very early days, even before hi-fi, the BBC has designed its own monitor loudspeaker systems as commercial systems were not, and most are still not, accurate enough for broadcast work. These designs were based on available units matched by, what were in those days, very complex crossover networks and mounted in custom designed cabinets.
During the mid-1960s, 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. It was assumed that plastic would be a consistent material unlike paper pulp, which to some degree seemed to depend on the mood of pulp stirrer. Over the years it has been found that it was not quite that easy.
The section of the BBC Research Department involved in this operation was headed by Mr. Del Shorter, now retired, with Mr. H.D. Harwood now of Harbeth Acoustics, second in command and myself completing the investigating team.
Some two years were spent making 12in 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. This loudspeaker was described in an article written by Mr. H.D. Harwood in the March 1968 issue of Wireless World.
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 8in unit was produced. This unit turned out to be almost certainly the first commercial 8in Bextrene driver and still arguably the best.
The first pair of BC1s was constructed using these units and Celestion HF1300 units. The cabinets were smaller than the current model and initial listening tests indicted that the performance could be improved by an increase in size, hence the present design. At this point it was all being done for fun.
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 used an 8in unit made by Research Department, the Celestion HF1300 and a redesigned crossover. The main change in the crossover 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 BC1s were fitted with an amplifier mounted in the back panel and the 4001G super tweeter added. This addition was for purchase tax reasons, but it did have two extra gains. Firstly, it improved the overall dispersion characteristics, secondly, from the broadcasting angle, it made any 625-line breakthrough to be more easily detected.
Now the LS3/6 was offered to a number of commercial companies and eventually taken by Rogers, then under the control of Jim Rogers. With approval, and a little assistance from the BBC, Rogers added the Celestion HF2000.
As Spendor was now a commercial company it was agreed that a royalty should be paid to the BBC for each BC1 produced. This was in recognition of the work I had done on the loudspeaker whilst still employed by the BBC.
To perhaps prove the order of development of the two systems, it is of note that out of over two thousand BC1s supplied to the professional market there are over six hundred in operation with the BBC and as far as I know very few, if any, LS3/6 speakers.
In addition to the above, the name Spendor is derived from the first names of myself and my wife Dorothy. Mrs. Hughes provided practical assistance in the early days with her coil winding expertise and now as Managing Director is responsible for all accounting, sales and general management. Derek Hughes, the son, another ex-BBC employee, deals with an amplifier design and assists me with research and development and general running of the factory.
Yours,
Spencer Hughes
So at this point we can understand that the BC1 was the first to appear - developed by Spencer Hughes in his own time, and leading to him ultimately leaving the BBC to run Spendor. Before leaving, however, there was a request for something very much like the BC1, so the BC1 was adapted by Spencer and became the BBC LS3/6.
Just as an aside, I think it's amazing that the request was for just one pair - you wouldn't necessarily have thought that 1 request would be sufficient to set the R&D loudspeaker machine into operation, but perhaps the fact the BC1 was already a successful commercial design was sufficient to tip the scales? And presumably the BBC believed other departments would find a use for the speaker once it had been produced. And in a way, they were correct. However, as Spencer notes above, it was the BC1 that most chose. I'm not sure why, but suspect that price was a factor. It's also possible that the BC1, having been in production for some time before the LS3/6, was the one that everyone knew about.
The LS3/6 was manufactured under licence by Rogers Developments, as the company was originally called when it was owned by Jim Rogers (there's another story!).
In the transition from the BC1 to the LS3/6, some changes were made - most obviously the addition of a large auto-transformer to allow the relative sensitivities of the drive units to be adjusted.
As noted, the Coles 4001 super-tweeter was added to the BC1, turning it into the familiar 3-way unit that we know today. Meanwhile, and quite separately, the LS3/6 also morphed into a 3-way design; but this was at the suggestion of Rogers, who used the Celestion HF2000.
Unfortunately for Rogers, the LS3/6 was a notoriously difficult loudspeaker to manufacture - especially the bass driver. To make matters worse, this drive unit proved to be very unreliable in service - no-doubt the paper voice coil former was at least part of the problem. This is what ultimately led to the development of the Export Monitor.
Essential reading for events surrounding Rogers: a historical account written by Brian Pook, who was the MD of Rogers between 1976 and 1982. I'll attempt to summarise the key points:
In 1975, having just got the company back on an even keel - now trading as "Swisstone Electronics", it was decided to "sort out" the LS3/6. These had established a reputation, and there was a steady (if gentle) demand for them. But as noted, they had a lot of problems - reliability and manufacturing cost being among them.
A bass driver was commissioned from Yorkshire company Dalesford which increased the power handling somewhat, and the required specification of the HF1300 was changed to greatly reduce the rejection rate. The model was very successful, even though the new bass driver didn't sound quite as good as the original BBC drive unit.
Having discussed the history, let's look at the loudspeakers themselves:
The LS3/6
I am indebted to Keith Garratt for sending me these pictures many years ago. Initially they were something of a mystery because while they look like an Export Monitor, the rear label says "Rogers BBC Studio Monitor Speaker", and also proclaims that they are "produced under license from the British Broadcasting Corporation". Clearly these are the LS3/6, but as mentioned above, they were never marketed as such. I don't know why, but that was presumably a commercial decision by Rogers.
Note the unusual grille cloth colour - this is original, but it's certainly different to the usual black that Rogers usually employed. Like earlier BC1s, but unlike the Export Monitor, this grille is fixed from behind the baffle.
Here is a picture of the rear label. The low power rating is futher confirmation that this is an LS3/6. And note the high impedance of 15Ω.
It should be noted that this speaker was also available in 8Ω and 25Ω versions. A small paper label is placed over the screen-printed default impedance of 15Ω - this label has the same background colour and printing style as the main label.
The differing impedances are acheived by selecting different taps on the auto-transformer - no other changes were necessary. My documentation suggests that the 25Ω option was added later, when an additional tap was added to the transformer.
Here are two views of the woofers, which unfortunately (but not surprisingly) were faulty. I understand they were going to be sent for repair, but I don't recall hearing an update on that.
And this is a close-up of the crossover - as you can see, it's a serious piece of engineering! Those large inductors must have been incredibly expensive, not to mention heavy! The autotransformer is the largest one, and the smaller units are conventional inductors. The triangular PCB is for the super-tweeter, and appears to be an afterthought - because that's exactly what it was!
Some more information can be found on the Spendor group - have a rummage in the Files area. Here are a couple of direct links, which should work for signed in members:
- LS3/6 brochure, instructions, BBC test specification RL/L/165, and schematics
- Another brochure
- Photo of a prototype LS3/6, with no super-tweeter
Servicing the LS3/6
Unfortunately, the original BBC-designed woofer has proved to be rather fragile, and working originals are very rare indeed. In the unlikely event that you have a set, please keep the volume down! Nearly all remaining examples of the BBC LS3/6 contain replacement woofers.
Official repairs
As you'll see below, the Export Monitor uses a Dalesford woofer that was custom-made for Rogers. It is likely that Rogers used this as an in-service repair for the LS3/6 (along with some extra crossover components to correct for differences between the original and replacement woofers). These woofers are much more reliable than the original, but won't sound exactly the same as the original BBC design. I don't believe the BBC approved of this, so examples repaired this way probably don't meet the official BBC spec, but as they hardly used the LS3/6, it probably didn't matter to them. The subjective differences are likely to be relatively small in practice.
I wonder if Rogers offered people with faulty LS3/6s the choice of the original BBC drive unit or the cheaper - to Rogers, at least - and more reliable Dalesford? If so, I guess that the majority would quite understandibly choose to trade the BBC specification for long-term reliability. Or perhaps the Dalesford was the only option that Rogers offered? If anyone knows, I'd love to hear from you.
Unofficial repairs
It is possible that you'll find other woofers fitted to these speakers, but none of these will have been approved by Rogers (and definitely not the BBC!). Unfortunately, there are plenty of repair workshops who don't really understand loudspeaker design and will throw in whatever they can find that physically fits!
Be aware that there are other Dalesford woofers that look identical to the part used by Rogers. But as mentioned, the woofer used by Rogers was a special design for them to use in the Export Monitor. As far as I know, you won't be able to tell them apart by looking - you would have to measure the performance, and have an example of the correct Dalesford part to compare it to. That's not easy! So while it might be tempting to salvage a outwardly similar woofer from a loudspeaker from another different manufacturer, bear in mind it might not work as well as the original. Obviously, that might still be preferable to nothing at all - it's a judgement call, but at least make an informed choice.
One helpful factor might be the label on the magnet. On this page you'll see pictures of the Dalesford woofer wearing both Rogers and Dalesford labels. When an OEM drive unit manufacturer supplies a loudspeaker to a speaker manufacturer, they usually don't apply their usual branding, leaving that to the customer. After all, not all manufacturers like to advertise where they get their drivers from - indeed many don't like people to know that they weren't made in-house. So this raises an obvious question: if you find a Dalesford woofer with a Dalesford sticker, have these come from some other (not Rogers) speaker?
Another official repair!
It has just come to light (May 2020) that another option might have been available from Rogers. At this point in time, I only have information about this from one source, so if anyone else can help me to verify this, I would be extremely grateful.
I am indebted to John Elliot for getting in touch to tell me about his LS3/6s, which he inhereted from his father.
At first glance the woofers fitted to his examples look exactly like the unit used in the Studio 1, which is what replaced the Export Monitor, so my first thought was that a well-meaning engineer had repaired them using parts from a Studio 1. That sort of thing is not uncommon, and you can forgive a non-specialist for not appreciating the distinction between the various models over the years...
But when I looked more closely, I spotted that the impedance of the replacement woofer was 11Ω, not the expected 8Ω of the Studio 1 woofer. This obviously changes things - a lot.
By the time of the Studio 1 - about 1980 - Rogers had the ability to produce woofers in-house, so didn't need to rely on third parties like Dalesford. And as Brian Pook describes, they weren't completely happy with the Dalesford unit because of the steel chassis and diaphragm profile - they considered the unit developed for the Studio 1 to be better in every respect. So it's perhaps not surprising that they appear to have done a version to suit the LS3/6 - it would have been a relatively easy project for them.
With this replacement woofer, there is a series RC network in parallel with the woofer, and I'm sure that Rogers would have specified the components used (and probably supplied them along with the replacement drive units if the repairs were not being done at the factory) to ensure the correct response.
As mentioned, I would love to hear from anyone who might know more about this - this is the first time I've come across later Studio 1-style drivers in an LS3/6, and I've been researching these speakers for some 20 years! There's always something new to discover...
The Stirling Broadcast LS3/6
In 2011, the LS3/6 was re-launched by Stirling Broadcast. The design work for this was done by Derek Hughes, son of Spencer and Dorothy Hughes - and who today would be better-placed to do this? These are one of my favourite loudspeakers today - I can confirm that they are rather special.
The Rogers Export Monitor
The Export monitor was released in the mid-1970s. Many thanks to Chris Self for sending me this flyer...
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It's interesting to read that each Export Monitor is compared to a BBC LS3/6, confirming the link between these models.
Chris also sent me these internal pictures of his early Export Monitors, which uses a crossover that looks identical to the BBC LS3/6. Given how expensive these must have been, I wonder if Rogers decided to use up stocks of components bought originally for the LS3/6? Or perhaps reusing the BBC design was just the quickest way to get the product to market?
There are some extra components mounted off the crossover PCB - they are quite hard to see on these pictures, but I did find another picture on an eBay listing (which I won't include, as the seller didn't respond to my messages asking for permission). This picture showed that the components are a capacitor and inductor wired in parallel, and that combination is placed in series with the woofer. They are soldered to some old-school tagstrip, which is screwed to the baffle. As mentioned above, they are required because of differences between the original LS3/6 woofer and the Dalesford replacement.
Note the Dalesford label on the woofer. Are these replacements from another speaker that used the standard Dalesford offering, or did the Rogers label come later?
The baffle is birch ply, and the rest of the cabinet likely is too. Indeed, I wouldn't be surprised if the cabinet is identical to the original LS3/6 - again, there might have been stocks that needed using up, or perhaps it was easier and quicker to not attempt to revise the cabinet design given that the priority was getting the speaker to market as quickly as possible. That said, note that the grille is held on with plastic pegs so is now much easier to remove - which means at least this much changed from the LS3/6 cabinet. Though that's a minor change, of course.
Revised Export Monitor
I was sent these pictures of a mid-run Export Monitor but I haven't been able to track down the original e-mail, so please contact me if you recognise these images as yours.
As you can see, the crossover is quite different, and must have been much cheaper to manufacture - apparently this revision happened in spring 1977.
This baffle is still made from birch ply, and it's probably fair to assume that the rest of the cabinet is also still ply. The internal walls are lined with bitumen damping and foam pads.
As above, the bass driver is the Daleford unit, albeit with a Rogers label this time. I confess to initally being confused by the super-tweeter, as it looks somewhat like a KEF T27 from the front, but nothing like one from behind. That's because, as mentioned above, it's actually a Celestion HF2000; remember, that's the tweeter that donated its grille to the T27 fitted to the LS3/5A!
One way to tell if you have the earliest Export Monitor is by looking at the baffle. Notice how the area beneath the bass driver is free from fixings? That's because the new crossover is a much lighter affair than the earlier BBC-designed crossover used in the the LS3/6 and the earliest Export Monitors, and is simply held in place with wood screws. But those earlier crossovers require a rather more secure fixing method, so that area is peppered with bolts and T-nuts that carry the weight of that massive autotransformer. Unfortunately, I don't have permission to use the only photos I have that show these fixings, but a Google image search for "Rogers Export Monitor" will find lots.
All the photos I can find also show that rear panel is no longer screwed in place, and is now permanently attached. At this stage I don't know if this is the case with all Export Monitors, or if this came in with this revised version. Of course, as soon as the grille became removeable from the front, there was no need to retain the removable rear panel, but as I speculated earlier, if they were using up old stocks of LS3/6 cabinets, perhaps the very earliest examples of the Export Monitor did retain the removeable rear panel?
Another change: look again at the pictures of the LS3/6 and note how the two tweeters are retained with metal brackets attached to the rear of them. But in the pictures of the Export Monitor, you'll see that both tweeters are screwed to the baffle from the front in the usual way. I don't know if this is a change that happened with the Export Monitor, or if it happened part-way through the life of the Export Monitor, but it's worth being aware of these physical differences when seeking replacement parts (though that's only part of the equation, as I mention on the Service/Spares page).
Late Export Monitor
I'm grateful to Matthew Gregory for sending me details of his Export Monitors, which are quite different again. At first, I thought that they had been modified - albeit to a very high standard - but as they have been in his family all of their life, he was able to confirm that the only work to them was a pair of replacement woofers and latterly a crossover component upgrade which was done by Wilmslow Audio.
I have since found a set of pictures of a pair of late Export Monitor that confirms the details I've seen in Matthew's pictures. Thank you to John at Retrotech Audio for allowing me to include a photo here:
The tweeter is now a KEF T27. The Studio 1 (below) uses the T27, and until I learnt about this later version, I had assumed that the T27 came in with this model change. Like in the LS3/5A, the T27 is wearing the protective grille which originally came from the Celestion HF2000 seen above in the earlier Export Monitor and LS3/6.
Incidently, the easy way to tell at a glance between a HF2000 and a T27 wearing the same grille: solder tags!
Also, the bass reflex port has changed from a simple square hole to a more conventional round opening with a short cardboard tube behind. It is in the same place as the original square port, and I initially assumed that someone had retro-fitted this by drilling with a hole-saw where the square opening was - but it does look original. Because the port is larger, the crossover PCB has been rotated through 90 degrees.
I was also sent a picture of one of the original bass drivers, and it looks very much like the original steel-framed Daleford unit, but there is no label on the rear of the magnet. It is slightly different, in that the terminals are on opposite sides of the chassis, instead of emerging together on the same side.
The Rogers Studio 1
Launched in 1980, this is a development of the Export Monitor, and as you can see, it retains the large 3 way format. I'm grateful to many people for helping me with this model, but special mention must be made of Leonard Hicken for sending through a detailed document with lots of additional details (see also the Rogers history that he compliled).
The bass driver is now made in-house by Rogers, and uses a diecast aluminium chassis. It continues to use Bextrene for the cone material. The tweeter remains a Celestion HF1300, but the super-tweeter is now a KEF (SP1032) - although as discussed above, it appears that change happened towards the end of the Export Monitor's run. Note how the bass driver is rear-mounted, with the opening rounded over to reduce diffraction effects. The two tweeters are flush-mounted for the same reason.
The cabinet is made from 9mm MDF rather than the birch ply of earlier models, but as before the panels are damped with bitumen pads in the classic "BBC thinwall" tradition. The baffle is no longer removable, but the rear panel is still held on with screws. Note the centrally mounted round port with the short length of plastic pipe behind it - a quick and easy way to distinguish this model from most examples of the Export Monitor. All but the earliest models had the opening rounded over to reduce turbulence.
The input terminals varied over the life of the model - early examples used a male XLR socket, then 4mm binding posts were added in parallel with the XLR. After that, the XLR sockets were dropped. While I don't know for sure, I wonder if there was an option to choose? Knowing that Rogers made the LS3/5A (and later on the LS5/9) with either 4mm terminals or XLR sockets, depending on whether they were selling to domestic or professional users, it's not much of a stretch to imagine they might have done the same thing for this model.
In contrast to the LS3/6 and Export Monitor, these have a much higher power rating of 200-300W. While I don't disbelieve this, it seems incredible when comparing the bass driver to that found in my ATC's. Click here for a review of the Studio 1.
This is a close-up of the crossover.
This crop of the rear of the PCB shows that it was designed in 1980 by Richard W Ross.
Leonard Hicken traced out the circuit diagram, and I've re-drawn it to match my usual style. As is the norm, the inductors are not marked, so we don't know their values. There's no silk-screen either, so we don't know what the component designations should be.
As you can see, it follows the usual layout, as seen in the original LS3/6 (minus autotransformer) of 3rd-order electrical with the HF1300 connected in reverse phase - a topology that was commonly used by the BBC and Rogers.
The Studio 1 was followed by several other models, but as they no longer use the HF1300-plus-supertweeter layout established by the original BC1 and LS3/6, they appear on the other Rogers models page.