Also called a Henry. A disc usually made of plywood, typically 10″-12″ in diameter. There is a mounting for the microphone on one edge, and the disc is covered in an absorbent material. The concept is that the microphone spacing matches that of human ears and the disc provides the sound-shadowing effects of the head, so the ensemble should be able to capture sounds in the microphones which will most closely match what a person would hear, effectively transporting the listener to the recording venue. Results are variable.
See also ambisonic.