Sonab OA12 clones

[JoelRiehl]

Supposing a person - being unable to find any on the used market - decided to build a pair of OA12 clones. Assuming access to the information on this site, what are the obstacles and challenges you would see?

[lennartj]

The baffle for the bass/midrange must be very difficult to make by hand to achieve the correct angle for the element.

[JoelRiehl]

I feel like I can handle most of the fabrication. What I wonder about are certain subtleties to the design:

- The "expanded ABS": is the density of the material critical to the sound? Or could I use a substitute: MDF, fiberglass, solid surfacing (Corian) or other?
- The thickness, density and shape of the internal webs - does it affect the sound? Could I just build dividers out of particle board, plywood, or MDF?
- The midbass mounting, via Z clips with rubber gasket: I think I read somewhere that the tension on the screws pressing the speaker down on the gasket is "tuned" at the factory. Is that true?
- The bass port tube: I read that this is tapered to avoid a puffing sound at the outlet (the ones on my OA116s appear straight - maybe the taper is very subtle?) What is the degree of taper, and how to fabricate it
- The material of the cabinet body itself: particle board of a certain density is used. Is that critical? What would happen if I substituted plywood or MDF?
- The matching of the crossover with available speaker elements: the 6.5" Silver Flute from Madisound and the Peerless CT62 tweeter. I have no grasp of the electronics.

I would hate to spend hundreds of hours on a pair and have them not sound good.......

[momus]

The OA 12 is a beautiful little speaker, both estetically and soundwise, but remember that the construction is over 40 years of age. There are speakers that have less distortion and sound "better". But some people just like these speakers - they can give a modern speaker a match for the money ,although i´ve heard some old british speakers 50 years of age that sounded really "modern". I have also listened to an old AR 3 from 1958 that sounded very nice, so modern doesn´t always mean "better sound".
If you like the very special "airy" sound from the OA 12, then go for it. Just remember that Stig Carlsson himself gave up the idea with multiple tweeters with the next generation of speakers (OA 50, OA 51 and OA 52).
Maybee I´m wrong, but i don´t think a clone made of MDF should sound very different from the original. But remember that it is nearly impossible to obtain the Peerless CT 62. They don´t make them any more. The Silver Flute is perhaps not the ideal match for this enclosure. It would be better to use a Carlsson B 65 oa instead (Tymphany/Peerless) . There are also a new cone-tweeter (Obi T 22) that betters the perfomance from the older ones, but then you have to change the filter. The woofer and the tweeter you can buy from http://www.hifikit.se, and you can also read about this speaker at http://www.carlssonkult.se. Let google translate.

[JoelRiehl]

Momus,
Thank you for the reply. I understand the shortcomings of the speakers. The "airy" quality you mention is what I remember most strongly, and the thing that I loved most about the OA12 (and 14). That, and the surprisingly large sound for their size. Your post inspires me to try it - but maybe an updated version rather than a perfect reproduction.

[JoelRiehl]

Curiosity question: What patents, if any, are the 1970s designs covered under?

[JoelRiehl]

Well I went and done it. I bought a pair of OA-12s on e-bay. The bass elements in them are shot - and were themselves earlier replacements of unknown provenance. I looked up the Carlsson B 65 oa at hifikit.se. $123.43 US each if I'm reading correctly. The discussion on carlssonkult.se seems to indicate that even this speaker has compromises (e.g. peakiness at around 1,000 hz) compared to the original. Since the Silver Flute is $29.80 US each, and since I am not made of solid gold, please expand if you don't mind, on what sorts of compromises you would expect from the Silver Flute. Meantime I suppose I'll start looking for a restored or restorable pair of Peerless CT 62 or somebody parting out an old pair of speakers. Thank you as always for sage advice.