Sonab OA-5 is, without competition, the most widespread speaker in Sweden, ever. In the end of the sixties everybody in Sweden wanted a pair of the strange and wellsounding speakers. The standing matchbox design struck well with the pure design trends and the omnidirectional sound suited the modern man who mingled in couches, floors and on beds.
OA-5 Typ 2 (Mk II) is a development of OA-5 Typ 1 (Mk I). It was equipped with 1 of the cheap but well sounding fullrangespeakers, Philips 9710 and 4 inward facing/omnidirectional conetweeters of the same type that made the Kolboxen (Coalscuttle) and OA6 Typ 1 (Mk I) successful, the Peerless MT20HFC. The filter components were aircored inductors and standard capacitors.
“OA-5 Type 2” differs from its predecessor in one major area: The baffle has been elevated up to level with the topside of the speaker. This leads to sonic advantages: The tweeters can now radiate freely in all directions, the mid-range radiates more freely also. This makes the sound clearer and airier. Furthermore the stereo-image becomes clearer, although the width is not a strong area in any of Stig Carlssons models from the sixties (they were actually mono-designs). The increased boxsize should also allow for a deeper bass-response. For now there is no technical data available for “OA5 Typ I” and therefore it is not possible to say how much deeper it goes. (If you have a manual please scan it and mail it to Carlsson Planet to be published in the future.) The downside of the simplified design without port tube is something that MkII has inherited from its predecessor. This is a cheap solution to save costs in the production. Apart from this the speaker is well designed with good-quality crossover components, braced boxes etc. This results in good soundreproduction for its era. OA5 Typ II (MkII) was on the market from approx. 1970-1973.
RESTORATION AND UPGRADING
The important thing with all the models from the sixties (V-1, OA-4 and OA-5) is not to touch the screws fixing the acoustic damping device behind the mid-bass woofers. This acoustic damping device has been impedance adjusted at the Sonab factory to give each speaker correct bass-reproduction and the correct transient response. Therefore these screws should not be touched. However the mid-bass woofers should be removed and re-conditioned according to Restoration and upgrading.
One problem with these models is how to mount goldplated terminals neatly on the lower backside when there are vertical dampingbraces on the inside of the cabinet walls? Normally we recommend using a circular cutter and using countersunk round terminals. With use of this method you loose the stabilising effect of internal bracing in the lower backside of the speaker. This effect is however acceptable. An alternate method is to mount the terminals off-centre on the lower backside. This does not look quite as nice but you do not need to cut the braces.
Another problem is how to access to the crossover and internal wiring due to the fact that the cabinets are glued together. There are two ways to access the inside, both unsatisfactory. One way is to remove the acoustic damping device under the mid-bass and poke about that way. When using this method the factory tuned bassresponse is lost and this can not be reset without the use of measuring equipment. The other way is to saw the baffle or bottom open and risk ruining much of the speaker. Also there are great difficulties in restoring the cabinet to airtight original condition. Our advice is therefore: Let the crossover and internal wiring remain in the original way, except for the capacitor that needs to be replaced by now. Note: On some models the baffle is screwed into the cabinet, in that case the above mentioned problems do not apply.
Apart from this OA-5 Type 2(Mk II) is restored according to Restoration and upgrading.
TECHNICAL DATA Sonab OA-5 Type 2
According to Sonabs handbook and/or ”Hifihandboken”
Box volume: 47 liters
Measures: B x W x D: 24 x 61 x 43 cm
Weight: 10 Kg
Principle: Omnidirectional, bass reflex type.
It is not a tradional bass reflex box due to the fact that there are no port tubes, just two tuned ports in the bottom of the cabinet similar to Dynaudios “Variovent”.
Impedance: Approx 7 Ohms
Frequency range: (DIN 45500): 37-18.000 Hz
Frequency response: 42-15.000 Hz ± 4dB
Crossover frequency: 2700 Hz
Mid-bass: 1pc 22 cm 8 Ohms Philips 9710 fullrangespeaker
Tweeters: 4 pcs 5 cm 8 Ohms Peerless MT20HFC
Finishes: Rosewood, walnut, teak, oak, natural pine and white laquer.
Also availeble in red, blue or green stain.
Prices: 1973: 745 SEK per pair.
Second hand: 100 up to 1.500 SEK.
Restored: If well restored up to 2.800 SEK.
Restored and upgraded with new tweeters (Peerless 62CT13 Prices ranging up even up to 5.000 SEK.
They can well be worth this if one is not too critical regarding the musicians’ lateral placement in the soundimage.