Ambisonics
A way of recording and storing the entire sound field around a point, independent of how many speakers it is eventually played through.
Rather than one channel per speaker, ambisonics describes sound as directional components. First-order B-format has four channels: W for omnidirectional pressure, and X, Y and Z for front–back, left–right and up–down. Higher orders add more spherical harmonics and sharpen the directionality. A decoder renders the result to any speaker layout you like — or to headphones via HRTF.
Michael Gerzon and colleagues developed the technique in Britain in the 1970s, right in the middle of quadraphonic sound's commercial flop, and it remained an academic curiosity for thirty years. What rescued it was VR and 360° video: when the listener can turn their head, the sound field has to rotate with it, and that is exactly what the format handles with simple maths.