OA-1

“OA-1” Omni directional loudspeaker for mounting on a wall

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A wall mounted omni directional bass reflex speaker using a full range driver. This design has never been put in production. The design principles are similar to the ones used for the Coalscuttle (Kolboxen). The speaker uses one full range driver firing upwards into a cone distributing the higher frequencies.

The design idea
The general object is to give optimum projection of the audio spectrum in the listening room Design goals:
1. Generating enough acoustic power without distortion
2. Generated acoustic power distributed evenly to the listeners in the room, which is difficult at low and high frequencies
3. Obtaining the above two in an enclosure that is not bulky by using the characteristics of the room efficiently.
Also to increase the acoustic efficiency at low frequencies

Measures, estimated
Box height 28cm
Diameter 31 cm
Bass reflex tube length 13 cm
Bass reflex tube diameter 8 cm
Cone diameter 27 cm
Cone height 19 cm
Supports for cone 19 cm
Volume 15 – 20 litres
Distance to wall 19 cm

Drive units, estimated
Full range unit: Most likely the Philips 9710

Crossovers
None

Explanations to figure
10. Cylindrical casing
11. Baffle
12. Bottom
13. Loudspeaker opening
14. Reflector
15. Rods
16. Bass reflex port
17. Bass reflex tube, integrated in the wall bracket
18. Wall

The cone (reflector) placed above the upwards firing loudspeaker is a device that is used in todays advanced products. Bang & Olufsen uses a lens in their Beolab speakers and Mirage also uses this technique in their speakers. Stig Carlsson did this in the fifties, well ahead of the competion.

Written by Martin Dellstig

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