Sonab OD-11

HISTORY
OD11 also known as the ”Carlsson-cube” is the smallest and easiest to place Carlsson-speaker of all. At its introduction in the seventies it struck all the hi-fi reviewers with awe. How could such a small speaker go so low? The reason was of course Stig Carlssons thorough bass-reflex design and the fine speaker units, the 6.5 inch Peerless mid-woofer and the Peerless conetweeter MT20HFC. These conetweeters can be found in all the Carlssonspeakers from the sixties and seventies. The models from the seventies all have high quality crossovers and innovative boxdesigns with recessed and angled speakers in a cast baffle made from ABS-plastic. The speakers are set in a very uncommon way in baffle of the OD11. The speakers are pointed out of the box in a way that so far is not equalled by any speaker manufacturer in the world. The direction of the speakers is diagonally upward and outward! The direction of the sound goes out from the corner of the cabinet. This gives several possibilities for placing the speakers. In the original manual several listening position for the speakers are mentioned. Unusual examples: Wallhanging, diagonally downwards or wallhanging diagonally upwards or standing on the floor against the wall firing into the wall. Feel free to test the different ways. The speakers came with wallbrackets and a template for drilling the holes in the wall. The four feet gives the OD11 the correct distance to the wall / floor for the port tube. The use of wallbrackets does not affect the distance for the portholes. A smart idea that results in the OD11 sounding its best in almost any position.

LISTENING IMPRESSIONS
The OD11 is a two-way monitor sounding as good standing in a bookshelf as on the floor. Even today the sound from a pair of OD11 is integrated and relaxed. You will find yourself forgetting that the speakers are both small and old, instead you will find your self to be spirited away by the good reproduction of the music. There is something very comfortable and right about the sound of the OD11. Perhaps the phase-problem from the other designs from the seventies that are using several tweeters in different directions is missing in the OD11. You might find that a pair of restored OD11 is all you will ever need for the rest of your life. The only missing item is the bass-response for the very lowest frequencies but if you live in a flat this might actually be an advantage.

RESTORATION
Most items according to Restoration and upgrading
The OD11 is easy to restore. There are a few things worth mentioning that are specific for the OD11. Mid-bass
The mid-bass is fixed according to Restoration and upgrading. The tweeter must be removed prior to the mid-bass. One of the screws for the mid-bass is located under the tweeter. Take care and use both hands when unscrewing the speaker to avoid putting the screwdriver through the cone of the speaker.
Tweeters
The tweeters are more frequently damaged on the OD11 compared to other Carlsson designs. This is due to the fact that there is only one tweeter to carry the load. However you should regard this as an opportunity to upgrade the speaker with the new Peerless 62CT conetweeter, see Restoration and upgrading.
Crossovers
The crossovers should also be seen to according to Restoration and upgrading. The crossover for the OD11 is the same as for OA12 and OA14. The only difference is that the OA12 uses two 16 Ohms tweeters in parallel, The OA14 uses four 8 Ohms in series-paralell whereas the OD11 only uses one tweeter in 8 Ohms.

UPGRADING
Tweeters
The biggest improvement on the speaker is to replace the tweeter with the new Peerless CT62. On the OD11 the tweeter is located in a small recess on the highest part of the baffle above the mid-bass. The 62CT is bigger then the old MT20HFC so in order to be able to mount the new tweeter you must make new grooves for the bigger tweeter. Start by removing the old tweeter. After the old tweeter is removed place the new one on the same place and use a marker to indicate where new grooves needs to be located, cut with a sharp knife on booth sides. The ABS-plastic is rather thick but see to that you do not cut through it. An alternate method is to cut a piece of metal to the same size as the frontplate of the speaker. Heat the metal-piece on the stove and use it to melt new groves of the right size in the plastic. Watch out as the plastic melts rather quickly. Afterwards fill in the old holes with glue or similar making the box airtight.
Put the new tweeters in, lean back and enjoy.
The new tweeters might need some breaking in before giving their best.
Terminals
We recommend that you change the terminals to goldplated ones instead of the old DIN terminals. On the OD11 it’s fairly easy. Drill holes in the ABS plastic in the bottom, countersink the holes a bit allowing the screws of the posts to reach through. Pull the posts tight. A good example for terminals / binding posts is the ANP8 from Hifikit (www.hifikit.se)
After that you take some single strand wire and solder between the crossover and bindingposts
Internal wiring
According to Restoration and upgrading

TECHNICAL DATA
According to Sonabs handbook and/or ”Hifihandboken”

Box volume: 10 litres
Measures: B x W x D: 26 x 26 x 26 cm
Weight: 6 Kg
Principle: Omnidirectional, bass reflex type. Diagonally facing speaker-
elements for frontfacing wall or bookshelf placement or upwardsfacing floor-position
Impedance: 8 ohms
Frequency range: 45-18.000 Hz
Frequency response: 52-15.000 Hz ± 4dB
Crossover frequency: 1800 Hz
Mid-bass: 1pc 6.5 inch 8 ohms Peerless SC165.
Tweeters: 1 pc 5 cm 8 ohms Peerless MT20HFC
Finishes: Rosewood, walnut, teak and black or white lacquer.
Prices:
1978: 1300 SEK per pair.
Second hand: From 50 for ugly up to 1200 SEK for perfect but unrestored pairs.
Restored and upgraded: With new tweeters (Peerless CT62) prices ranging up to 4.000 SEK.
They are well worth this.

Martin Dellstig – Co-Editor