MBHO OSS Schneider Disc - Stereo Microphone Mount

What you are looking at is not an extraterrestrial spacecraft but a "Schneider disc". The Schneider disc is a variation of the Jecklin disc developed by Jürgen Jecklin for his stereo microphone technique known as Optimal Stereo Signal (OSS). The idea behind OSS is to use a pair of spaced omnidirectional microphones approximately 6 inches apart (roughly the distance between the human ears) with a disc placed in between the spaced pair. The disc is covered with a thin layer of foam intended to absorb high frequencies - thus improving stereo separation between the microphones.

The difference between the two types of discs is the foam sphere at the center of the Schneider disc, which reduces the amount of high-frequency energy reflected from the disc, and results in an increase of stereo separation. Below approximately 200 Hz, the Schneider disc has little (if any) effect on the stereo signal because the audio wavelength is large enough to bend around the disc, equally reaching both microphones. However as frequency increases above 200 Hz, the Schneider disc's foam sphere increases stereo separation between the spaced pair.

The Schneider disc may be used in OSS technique for stereo recordings of orchestral or chamber music, as well as for stereo micing of solo instruments. In order to properly implement OSS, the microphones should be identical, omnidirectional and should be set for equal output to avoid unbalancing of the stereo image (this can be checked using headphones). For the best balance between direct and room sound, the Schneider disc should be located at the distance from the source where the direct sound and the diffuse sound from the room are at equal strength. This distance is known as the diffuse field distance and can be located by careful listening.