The first model to be introduced in the Stig Carlssons series of the eighties was the OA-51. The brand Sonab was now gone and the new series was named after Stig Carlsson himself as Carlsson OA-51. This was the first model produced at the new Carlsson-factory in Skillingaryd.
This model looked like nothing else. A strange wall-hanging (or standmounted) and horizontally positioned rectangle, as a speaker still unique in its form. The speakers were massively braced inside, provided in reversed pairs where the left respectively the right upper corner was cut away. The backward-slanting baffle embraced the whole front. Close to the elements a large removable absorbent-panel, slightly angled outwards that was attached at the inner short side of the speaker. This was in order to reduce early reflections. The woofer was equipped with a strong magnet, a wide voice-coil and very small cone-area. It shared baffle with a high-class omni-directional dome-tweeter from Peerless, with, for it’s time, very low distortion.
Stig Carlsson considered that his earlier designs was out of date and that he at last had designed the best speakers in the world for living-rooms.
BEST OF THE 50-SERIES
Still a lot of people consider the OA-51 to be the most excellent model in the 50-series. The high position (it should be placed at least 60 cm above the floor, on a wall) eliminates the necessity to reduce floor-reflections as minutely as for for the OA-50/52. The sound perspective is also higher for OA-51 than for OA-50/52.
All the speakers in the series from the eighties had the not so good textile-dome-tweeter Peerless 115DT26. This element was often blamed for the less favourable reviews of the 50-series through the eighties. This in turn ruined Stig Carlsson and he thereafter lived in poverty for twenty years.
But this tweeter was very carefully selected for its low distortion, because it was the most omni-directional tweeter at that time and it tolerated high currents. The woofer, ScanSpeak (18W/8542) was then a smashing new element and probably the best available. It is still on the market, but today it sounds not so good compared to what is available and is really not worth the SEK 1.300, that is still demanded for new items. The woofers problem is it´s midrange distorton.
Sonab OA-51 was sold during the years 1982 to 1989.
This model was not, unlike OA-50/52, produced during the nineties in a .2-version. Instead a kit for owners of OA-51 to upgrade to 51.2 status was available from 1997 to 2002. You got the Vifa metal-dome tweeters and the much better 7-inch ScanSpeak woofer, 18W/8545, with rubber surrounds and carbon-fibre sprayed paper-cone (the same as for OA52.2). The sound-improvement was as great as the step from OA52 to OA52.2.
UPGRADING KITS TO OA-51.3
There are two versions of this upgrade kit, one absolutely top quality and a somewhat cheaper version that gives most of the sound improvements:
Top quality version includes:
+ new Carlsson T-11oa silk dome tweeters with practically immeasurable distortion. This element is the same as in OA-52 and in the new 60-series.
+ new ScanSpeak carbon fibre reinforced 7-inch woofer 18W8545 – the same as in the top model OA-52.3
+ a new design crossover
+ teflon-insulated solid cable
Budget version includes:
+ same elements as the top quality version above but with
+ standard crossover components and wiring. Includes the amazingly transparent SCR/MKP conductors and will please 9 out of 10 owners enough!
Upgrading from OA-51.2 to 51.3
There is also a .3-kit for those who have already upgraded to OA-51.2.
It contains new tweeters and crossovers.
TECHNICAL DATA Carlsson OA-51
Box volume: 16 litres
Measures W x H x D: 43 x 30 x 25 cm
Width including panel: 72cm
Weight: 11 Kg
Principle: Two way bass reflex type. Direct/ omnidirectional with absorbent panel.
Impedance: 8 ohms
Frequency range: 32-20.000 Hz
Frequency response: 40-17.000 Hz ± 2dB when the loudspeaker is mounted on a wall far from the other room boundaries.
Crossover frequency: Approx. 2.500 – 3.000 Hz
Roll off point -3db, relative to 100Hz: 42Hz.
Mid-bass: 1pc 7 inch 8 ohms Scan-Speak 18W/8542.
Tweeter: 1 pc 8 ohms Peerless 115DT26
Finishes: Rosewood, walnut and black ash in matched pairs, white lacquer. Other finishes on request
The OA-51 was also marketed in Great Britain.
Prices: 1984: 6000:- SEK per pair (white laquer/special order 6500:-)
Second hand: From 500 SEK per pair depending on the finish. Upgraded : 2500 SEK up to 18000 SEK depending on finish and level of upgrading.