The OA-50's After Flodd Redesign Saga

[AldoSaniJr]

I am a Brazilian, living in Porto Alegre, South of Brazil. I was a happy owner of 4 Carlsson OA-50 speakers bought in Finland in 1984 and upgraded to OA-50.3 back in 2005-2006. I also have imported the last 4 OA-52.3 produced by Larsen, just before he started producing his own design OA's. Two of those I sold to a friend of mine. All 6 were just destroyed by the worst flood ever here. I had all my furniture, including the speakers stored in a garage box in one of the local yacht clubs. The garages were built in the early 50's and have never since being flooded. In early May the water reached 1.65m level inside the box. The speakers were completely under muddy waters for about 2 weeks and partially covered without reach for another 3 weeks.
The MDF boxes were of course destroyed. The bass/midrange speakers, after careful cleaning with brushes, clean water and isopropyl alcohol surprisingly became as good as new. All the tweeters had their domes wrinkled. After cleaning, 4 resumed their original shape. 2 are still a bit wrinkled. I suppose this is due to water inside. I will take the magnets out and clean the coil gap. Afterwards I'll recenter them. i have already accomplished that on the old tweeters before the upgrade.
I have been designing minimalist furniture as a hobby since the early 80's. In 1989 I started using AutoCad. From 1998 to 1999 I designed my 55' aluminum sailing boat. I have been designing sailing boats ever since as a hobby. In 2002 I moved from AutoCad to Rhino 3D. I now design and build 40'+ aluminum sailing boats as an active retirement work. We use a lot of CNC (Computerized Numeric Control) cutting and machining.
So I decided to draw the MDF speaker boxes in order to have them CNC cut and rebuild them. When I started doing so I set myself a challenge: To redesign the boxes in order to keep their sonic signature and have a sculpture look as spectacular as they sound. Stig Carlsson have some very nice looking speakers design. I love the sculptured early works (ET/Tonträff, Kolboxen). Then he started a minimalist phase that culminated with the genius OD-11. After Sonab the Carlsson OA-50 is clearly derived from the minimalist phase while OA-51 and 52 are more sculptural pieces. I like the OA-50 and OA-51 looks but I always felt that the OA-52 is somewhat didactic: The Ortho Acoustics principles are very clear but there is something aesthetically wrong with its proportions. They look a bit too heavy. The OA-50's quite disappear in a room decor. The OA-52's don't. Worse they are hard to fit. They sound great, but my wife hates them because of their looks.
Just two days ago I thought it would be quite hard to design something that would look much nicer with the following constraints: Same volume, same speakers positioning, same box material, thickness and structure and the same early reflection absorption characteristics. I suppose I succeeded! With very minimal changes the redesigned speakers look much better. My OA-50's metal screens are completely rusted. I will use the same mesh screen but made of polished stainless steel. The MDF box will be epoxy base automotive spray painted.
I include virtual CAD pictures on the attachments, as well as some pictures of the dismantled speakers after they were recovered from the flooded storage.
Due to the high complexity of the speakers structure I divide them into some parts:
- Speakers and crossover (not shown).
- Stainless steel screen grate
- Early reflection absorption frames
- Box composed of:
- Resonance box split into:
- Base and Structure
- Side Walls and resonance tube
- Speaker box
The OA-50, have a simplified construction to be cheaper. It has the same volume as the OA-52 though. It is easier to build all the same. But in order to differentiate them I chose to just change the grate and back absorption panel as the speaker hole size, and the cable connectors, of course. In this way, using the same box, the speaker get a more boxy (like the OA-50) aspect.
I include perspective and exploded views of the whole and the parts.
If anyone decide to build a DIY speaker like that I can send the cutting plan files as well as the border angles for machining before assembling.