Jecklin disk

A Jecklin disk is a sound-absorbing disk placed between two microphones to create an acoustic "shadow" from one microphone to the other. The resulting two signals can produce a pleasing stereo effect on headphones and loudspeakers but are sometimes not fully mono-compatible. A matching pair of small-diaphragm omnidirectional microphones is generally used for this technique, although it is possible to use other kinds of microphones resulting in more subtle effects.

This technique was invented by Jürg Jecklin, the former chief sound engineer of Swiss Radio and teacher at the University for Music and Performing Arts in Vienna. He referred to the technique as an "Optimal Stereo Signal" (OSS).

It is a refinement of the baffled microphone technique for stereo initially described by Alan Blumlein in his 1931 patent on binaural sound.