Loudspeaker/Source Spherical Coordinate System

We should decide on a PHI/THETA convention to use for spherical loudspeaker coordinate systems. There's no particular standard that is currently used. See below for what the CLF format uses (hopefully it makes sense, it's tough to draw this):


The positive X, Y, and Z axes come out of the front, right(when viewed from front), and top of the loudspeaker, respectively. The azimuthal angle phi is defined 0 degrees at the top of the loudspeaker (the +z axis), and rotates clockwise in the yz plane when viewed from the front of the loudspeaker. The polar angle theta is defined from 0 degrees on-axis to 180 degrees in the back of the loudspeaker. The polar angle half-circle always rotates so that it goes through the selected phi.

I'm open to using another convention, but as for the CLF parser, I will probably stick to this so we don't get lost in coordinate system conversions just yet.

No file, test, or entry point is named in the issue. Review the CLF spherical-coordinate convention and the repository's existing loudspeaker/source coordinate handling, then document and apply one consistent PHI/THETA convention; done means the convention is decided and coordinate conversions no longer remain ambiguous.

Written by the indexing model from the issue text.