I've done a bit of experimenting, and implemented some VOPs which can be used to generate and evaluate spherical harmonics inside a VOP net. I've written up some info on what this is all about here: http://mattebb.com/weblog/spherical-harmonics-in-vops/ [mattebb.com] and you can download the OTL and a hip here: http://mattebb.com/projects/houdini/houdini_sh_otl_hipnc.v001.zip [mattebb.com]

Or just check the video - hope it's understandable!

https://vimeo.com/40133531 [vimeo.com]

I have ideas for some more more practical usage for these tools in mind, will update here if I can get time to do it

that's amazing stuff, thanks!
I always love your work, hope you have more time with Houdini and tutorials