Hi Jesse,

With Ambisonics, ideally your loudspeakers should discretize perfectly a sphere, you should have your head at the exact center of this sphere, etc. and perhaps if you forget that your head interferes and the loudspeakers don't generate plane waves you'll be able to reconstruct a coherent sound field... But to avoid these restrictions (because very few people have a full sphere of loudspeakers - or want to ask the audience to be completely crushed at the center of the sphere) there are several techniques : optimizations of the energy and/or velocity vectors, optimizations of the decoding, etc. The problem is that none of the solutions are completely generic. Your choice must be driven by your approach and your goal.The advantage of Ambisonics lies in its intermediary representation of the sound field that allows to apply transformations (rotation or whatever) and to decode for different loudspeakers configurations. But if you just want to spatialize individuals point sources, you can also use VBAP that is perhaps much more accessible. Nevertheless yes, you can surely find a way to decode the sound field for two ring of loudspeakers with Ambisonics (we can discuss it if you want). And one good rule is just to avoid placing sources where the loudspeakers are missing. I don't know if I really answer the question, I hope a bit :)

Cheers,

Pierre

Date: Fri, 23 Jun 2017 16:19:29 -0600
From: jmejia@anestheticaudio.com
To: pd-list@lists.iem.at
Subject: [PD] HOA / spatialization approaches for a hemisphere
Message-ID: <3149263781acf8439b762eef943d60e5@anestheticaudio.com>
Content-Type: text/plain; charset="utf-8"

Hi List,

I'm putting together a 32 channel HDLA and looking for spatialization
advice. The configuration will be two rings, one higher than the other,
and I've been thinking a bit smaller/closer to approximate a hemisphere.
But that's flexible - they could be parallel rings if it simplifies
things.

I have some (limited) experience using HoaLibrary + PD for 2D ambisonics
- so my initial thought was to try the 3d externals there - however I'm
not sure if it actually makes sense to build an abstraction setup for a
sphere of twice as many channels while limiting access to the upper
hemisphere only. I'm assuming there would be some problems with that
approach.

I found a few papers on mixed-order ambisonics - by Chris Travis and
also the AmbiX crew - but I'm not sure if there's away to implement that
stuff with HoaLibrary. I'm also open to using different software if
something else is recommended instead.

Thanks for any advice!

-Jesse