I found a very interesting paper on omni directional sound sources.
Paper title is: “An experimental evaluation of regular polyhedron loudspeakers as omni directional sources of sound” from T.M. Leishman e.a.
The paper can be downloaded from: https://scholar.google.nl/scholar?q...sound+pdf&hl=nl&as_sdt=0&as_vis=1&oi=scholart
Tests were done in an anechoic chamber with an circular microphone array on regular polyhedra with 4 to 20 drivers. The sound sources were meant for acoustic room measurements but I think that some results are also valid for sound reproduction applications.
Especially, the “balloon” presentation of the results was an eye-opener for me.
For me, the measurements at 2 and 4 kHz suggest the following:
Paper title is: “An experimental evaluation of regular polyhedron loudspeakers as omni directional sources of sound” from T.M. Leishman e.a.
The paper can be downloaded from: https://scholar.google.nl/scholar?q...sound+pdf&hl=nl&as_sdt=0&as_vis=1&oi=scholart
Tests were done in an anechoic chamber with an circular microphone array on regular polyhedra with 4 to 20 drivers. The sound sources were meant for acoustic room measurements but I think that some results are also valid for sound reproduction applications.
Especially, the “balloon” presentation of the results was an eye-opener for me.
For me, the measurements at 2 and 4 kHz suggest the following:
- The radiation pattern continuously changes when frequency changes. I suppose we don’t notice this because the many room reflections will cancel out these effects.
- The prickly shape of the radiation patterns are caused by diffraction on the polyhedral edges. I assume that the different (truncated) polyhedra will all have different patterns. The size act as a scale factor. These diffraction effects are not always taken into account in theoretical analysis.
- The differences between the different polyhedrons, and with that the number of drivers, are not significant. All are appr. equal good (or bad).
- The diffraction effects cannot be eliminated by EQ methods. At the most, the spl can be make more or less flat in one direction.
It is already established that EQ can do nothing about diffraction.
If you consider that a polyhedron is an approximation of a sphere with flat bits “glued” together. Use smaller panels, and add as much roudnover as you can. A sphere with flat spots only to mount the driver would be the resulkt if you took the concept to the limit. Edge diffraction would then be one driver interfering with another.
Now i’ll go read the paper, you make it seem quite enticing.
dave