In 1953 Stig Carlsson designed the peculiar Coalscuttle, a cannon look-alike bass reflex object, with built-in tube amplifiers, 4 pcs Peerless cone tweeters, MT20HFC, mounted crosswise round the 8 inch midrange unit in the orifice, the broad band driver Philips 9710, and deepest down in the bottom, a Peerless 10 inch bass driver and the tube power amplifier. A specially designed pre-amplifier was also available.
This strange and today very much coveted speaker was sold in a shorter series 1959-62 by the name ”Elektronlund Ortho Acoustical System 1001”, abbreviated ”Lund LOAS 1001, commonly known as ”Kolboxen” (coalscuttle). In 1957 the “Elektrofon Tonträff” was introduced. It was a 24 litres omni directional, twoway bass reflex type with a midbass placed on a slanting baffle. The unit firing diagonally up into the roof. Little is today known about this speaker but the design principles were the same as used in the “coalscuttle”. .
The design from the coalscuttle was taken further which lead to the impressive “Lund OA-25” or “McProud”. An active, OTL tube powered, bi-amped, three way speaker. This speaker was introduced on the market in 1966 by the new company Sonab AB. The model was marketed as Sonab OA-6.
It was the first model with the classic “Carlsson-shape” like a matchbox standing upright. OA now stands for Orto Akustik (Ortho Acoustic) and the figure 6 stands for the number of speaker units used, One woofer, one midrange and four tweeters. Thanks to the built in power amplifiers only a preamplifier and the speakers were needed. Also for this speaker there was a specially designed pre-amplifier available. The design is today almost forty years but still it can compete with the best.
One Carlsson design that was not marketed by Sonab was immensely popular DIY version of OA-6. The woofer was dispersed of resulting in a very good design known as “POP BOXEN” (The pop box). It began with an article in the magazine “Radio & Television” about a cheap and well sounding Output Transformer Less, OTL with extraordinary data suitable for the DIYer. The design was an improvement of Philips standard OTL amplifier by Jon Idestam-Almqvist. To this amp a suitable speaker was needed.
J I-A then choose a design based on Stig Carlssons patent for the Coalscuttle and the speaker, then without name, was presented in “Radio & Television” no 4, 1964. This is rumoured to be the most stolen magazine in all Swedish libraries.
The Pop box was equipped with the same speaker units as the OA-5 but wider and standing on four legs, it also had a proper bass-reflex tube. The tweeters were set around the woofer.
The Pop box could be built in two versions.
One with 800 ohms speakers driven by the cheap OTL amplifier, the other using normal eight ohms units. Driven by the OTL tube amplifier Radio & Television meant that this sounds better than anything available at the market, no matter what price range!
In 1966 Sonab also introduced the speaker that would become the people’s choice. This was the OA-5. The 5 stood for four tweeters and one mid woofer. It was a downscaled version of the OA-6 where the separate woofer and the integrated power amplifiers had been removed.
The first version of OA-5 is distinguished by the baffle that is lowered 6 centimetres into the box. This leads to problems with reproduction of high frequencies. The high frequencies sounds “boxed in”. OA-5 and later OA-5 Mk II (Mk II had the baffle elevated 5 cm) became a great success for Sonab. Nobody knows how many were sold during the years 1966 – 1973 but there are figures of up to 500,000. A more reasonable figure is probably 100,000 but still, this is a very respectable figure.
Sonab brochure from 1966
Two other types were also available:
OA-4 which was a smaller version of the OA-5. It had a smaller box and only three tweeters:
V-1 the first Carlsson cube. The figure 1 stands for only one unit being used, the Philips 9710 Full range speaker used in all Sonab models as mid woofer, midrange or full range during the fifties and sixties. The V-1 had a very limited frequency response and couldn’t handle a lot of power but it was easy to place and available in a lot of colours.
In 1970 the follow-up to OA-6 was introduced, the Sonab OA-6 Mk II. It was a smaller and cheaper model where the 10-inch woofer has been replaced by the 8-inch broadband Philips 9710, the cabinet made from cheaper material and the tube amps replaced with a “bass-energizer”. This meant that the speaker needed to be driven by a power amplifier. The “bass-energizer” was only there to get some bass out of the 9710 used as a woofer.
The Oa-6 Mk II was sold 1970 – 1975. In the late sixties Sonab was in an economical crisis and was bought in 1969 by “Statsföretag”, a Swedish state owned business reconstruction company. “Statsföretag” gave Stig Carlsson ample rescores for research and after a few years the new series could be introduced. The first models to come were the replacements for OA-5 and OA-4 the new OA-14 and OA-12. The OA-14 had one woofer and four tweeters and the OA-12 of course had one woofer and two tweeters. Earlier models of Stig Carlssons designs had been designed for omni directional mono whereas the new models where proper stereo designs. Each pair consisted of one left and one right speaker with a much higher degree of direct sound. The mid bass used was
the new 6.5” SC 165 manufactured by Peerless. It was angled in towards the listener as were two of the four tweeters of the OA-14. The OA-12 had one tweeter facing the listener and one directed backwards over the speaker. The tweeters were still the Peerless MT 20 HFC. OA-12 and OA-14 were on the market 1973 – 1978.
In 1974 the smallest Carlssonspeaker ever was introduced, “the cube” OD-11. OD-11 logically meant one woofer and one tweeter. Filter and speakers were the same as in OA-12 and OA-14. The speakers on the OD-11 were also angled towards the listener. The difference was that the OD-11 could be placed differently than the others, it could also be placed hanging on the wall or used as a bookshelf speaker. The critics were overwhelmed and it was sold in tens of thousands. OD-11 was on the market during 1974 – 1978.
In 1975 the first large stereo speaker was introduced. It was the OA-116. The figure 116 logically meaning one woofer, one mid and six tweeters. Still the same units were being used the tweeters MT 20 HFC and woofer and mid range was SC165. The SC 165 was however slightly changed with different impedances. Critics meant that the OA-116 was second to none at the time.
On the OA-116 three of the six tweeters were facing the listener as well as the mid range, the woofer was placed under the speaker directed downwards. The OA-116 was set on wheels. A later version used an even better tweeter, the slightly larger conespeaker Peerless MT 24 HFC. OA-116 was on the market during 1975 – 1978.
In 1976 the masterpiece of the seventies was introduced, the OA-2212 equipped with two woofers, two midranges and no less than twelve tweeters, in total 16 speaker units per box! It was a professional model intended for use in studios and on the stage. The tweeters were Peerless MT 24 HFC and the SC 165 used as midrange in eight ohms version and woofer in 5.3 ohms version. OA-2212 was on the market during 1976 – 1978.
All the models designed in the seventies used baffles made of cast ABS plastic with mid bass / midrange angled towards the listener.
In 1978 “Statsföretag” shuts down Sonab due to bad investments from Sonabs management. Sonab tried to start making cell phones (too early!) and failed.
In 1983 the first new model in the new series is introduced. The new series is made up of three different two-way models made in Skillingaryd in Sweden under the name Carlsson. It is normally referred to as the OA-50 series. The first model was OA-51. A wallhanging strange lying down rectangular box with slanting sides facing the listener, it also featured an absorbent panel to dampen out early reflections. The speaker was meant to hang at the wall at least 60cm above the floor. It was equipped with a Scan-Speak 7” mid woofer and a Peerless tweeter.
Stig Carlsson meant that his earlier designs were obsolete and that he finally had managed to build the best speaker in the world for use in normal living rooms.
In 1984 the new OA-50 and OA-52 were introduced. They were floor standing designs and both models were boxes with the baffle placed raised above the box in the rear outer corner. Both had the same Peerless tweeter but the more expensive OA-52 used the same Scan-Speak 7” as OA-51 whereas the OA-50 used the now classical SC 165.
The surfaces near the speaker units on the OA-50 and OA-52 were clad with dampening material, in the cheaper OA-50 it was concealed under the wire mesh and on the OA-52 the dampening material was clad in cloth. There was dampening material in front of the speaker and standing alongside the rear side of the speaker. The design was made by Lars Lallerstedt, art professor and was a novelty in loudspeaker design. It was simple, functional and yet un-paralleled in its design.
Those who have seen (and heard) the OA-52 never forget it. It looks like small armchair for children and have an unforgettable sound. A number of leading sound-technicians in Sweden still owns upgraded pairs of OA-52 and use them as reference speakers.
Still less then 1,000 pairs were sold. Some reviews of the speakers in hi-fi magazines were unfairly critical, sometimes due to faulty speaker placing during listening sessions. This lead to bad sales figures for the speaker and this proved fatal for the economies of both the new loudspeaker company and Stig Carlsson. The new Carlsson Loudspeaker Company in Skillingaryd went bankrupt and the last speakers were sold in the shops in 1989.
The beginning of the nineties was a rough time for Stig Carlsson. He had to move up to the attic of his own house and let the rest out to get money and what little income he had was used to keep up his patent rights. Stig Carlsson still continued his design work, now with the measuring equipment in a cupboard and the speakers placed on both sides of the bed in the biggest room in the attic.
In the beginning of the nineties the perhaps worst chock of Stig Carlssons career came. A low budget loudspeaker company bought the rights to the name Sonab from Ericsson and started selling really cheap “Sonab Loudspeakers” that were made in Taiwan. They sold a lot of speakers, after some time they introduced their new brand: “Carlsson Loudspeakers” and used expressions like “A real Carlsson speaker” in their commercials, which was an insult to Stig Carlsson and his lifework. Stig Carlsson did not want to be associated with these speakers in any way, but the management for the “new Sonab” claimed that they together with the purchase of the Sonab brand also got the rights to use the “Carlsson” brand, in spite of the fact that Stig Carlsson manufactured speakers in his own name both prior to and after his time (since 1983) at Sonab. Sonab did not succeed in establishing this claim so they hired a loudspeaker designer with the name David Carlsson. Stig was in deep despair probably more over this than anything else. For more than a year it looked as the “Swedish Patent and Registration Office” were going to give “Sonab” the rights, but after an intervention from several prominent people in hi-fi and music circles the authority gave Stig Carlsson the right to use his own names for loudspeakers. But it was a close thing. In the same year 1996 the new “nineties series” was introduced. This was made up of heavily upgraded versions of OA-50 and OA-52, named OA-50.2 and OA-52.2. They both had a new metal dome tweeter from Vifa. The OA-50.2 used a new low distorsion version of SC-165 now with rubber surround, short circuit ring. The OA-52.2 had a new Scan-Speak woofer. They both had much upgraded crossovers. There was no OA-51.2 but there was a .2 upgrade kit available if you already had an OA-51. Critics called OA-50.2 “the perfect two-way speaker” and the OA-52.2 got even better reviews.
Stig Carlsson worked on completing “the three-way” for the remainder of his life. Little is known about this speaker outside the inner circle in the Carlsson trust. As ar as we know the speaker units are developed, the midrange and tweeter are placed in a strange hornlike construction and the woofer is mounted backwards at the floor. Ideas like these can be found in Stig Carlssons patent application for the OA-51. If and when the “tree-way” will come into production is not clear.
Despite these problems Stig Carlsson had a happy time as a professional for the last time of his life. Then he lost both his mother and only brother and now lived without family or close relatives. At this time Stig also inherited a million after his brother and could look forward towards a trouble free life. Perhaps all this was too much in a short period.
The eighth of march 1997 Stig Carlsson had a heart-attack during an evening stroll. He died at the “Södersjukhuset” hospital in Stockholm.
He was mourned by distant relatives and innumerable friends and colleagues. The funeral was held in Gustav Adolfs Church in Stockholm. It was a light and beautiful funeral with contemporary choir-music that Stig would have loved. The music was chosen by world leading choir conductor professor Eric Ericsson, today a member of the Stig Carlsson Trust.
The new millennium
After the death of Stig Carlsson the manufacturing of the two models OA-50.2 and OA-52.2 continued. In february 2002 the OA-50.2 was discontinued to make room for a new entry model.
In September 2002 The OA-52.3 was introduced with a new tweeter.
There are also upgrade kits available to upgrade speakers to OA-50.3 and OA-51.3.
In December 2003 the new OA-58 was introduced on the market. At this time (spring 2004) at least one new model is being developed by the Stig Carlsson trust.
The OA-60 (not officially named) has been shown, but not played, at exhibitions. You can read more about the trust on the CarlsonPlanet homepage in the section SSC.