Images created by the Quantum
Chemistry Group, Universidad de Oviedo, Spain
The colour convention is that red lobes are in-phase (positive) and green lobes are out-of-phase (negative).
In Ambisonics, the convention is for the x-axis to be pointing away from the viewer and the y-axis to be pointing left. As depicted here, they are pointing towards the viewer and right; this rotation just toggles the colours of some of the lobes.
With Ambisonics, a sound field is decomposed into spherical harmonic components, termed W, X, Y and Z. These are collectively called B-Format. The responses look like this:
The zero- and first-order components can be augmented by second- and third-order spherical harmonic components. To date, because of the need for an impractical number of transmission channels, little work has been carried out on higher-order Ambisonic systems. However, work has started on the development of the necessary microphones and decoders.
Second-order Ambisonics requires five transmission channels for horizontal surround sound and nine for full-sphere. Third-order Ambisonics requires seven channels for horizontal and sixteen for full-sphere. It is also possible to mix a high-order horizontal with a lower-order full-sphere; this would require an intermediate number of transmission channels, as listed in the following table:
The second-order spherical harmonic responses look like this:
The third-order spherical harmonic responses look like this: