On 03/28/2018 04:23 AM, Len Moskowitz wrote:
Stefan Schreiber wrote:
At first sight I could not tell anything about the difference between
an OctaThingy and Octomic capsule mount.
Even not at second...
Could you give me/us some hint?
Eric's OctaThingy is based on a tetragonal trapezohedron.
OctoMic is not. It's based on another geometric solid.
Which one exactly?
The angles are different.
I presume you mean the elevation angles, right? I don't think Eric's
paper includes the actual elevation angle he used for his design. What
is the elevation angle in the Octomic?
Aaron (Heller) did 3D print some Octathingy arrays and his code
(https://bitbucket.org/ajheller/mic-arrays/, predates mine) uses
atan(sqrt(1/2)) for the elevation (same as a tetrahedral microphone).
Eric writes that the design is based on the tetragonal trapezohedron,
but I always found it easier to visualize it using its dual, the square
antiprism (with the capsules mounted in its vertices):
https://en.wikipedia.org/wiki/Square_antiprism
Changing the side triangles from equilateral to isosceles (ie:
stretching it vertically) creates a family of shapes, most interesting
among them would be the equilateral square antiprism (equal angles
between capsules) and the one where the vertical elevation angles match
the ones of a tetrahedral design. I always had both choices in my 3d
models, but others are possible. Different vertical elevation angles
will optimize the array differently, but the underlying geometric solid
is the same.
-- Fernando
PS: I first asked about what could be done with eight capsules in July 2015:
On 07/24/2015 09:34 AM, Aaron Heller wrote:
If you want to try something, there's what we've been calling "the octathingy".
Four capsules up, four down, with the down facing ones rotated 45 degrees. See
attached photos.
I 3d printed my first "proof of concept" in November 2015 (see picture)
but it took a long time to get a full working prototype (I did the
tetrahedral design first). Always working on too many projects... :-)
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