Photo of a Jecklin-type disk made by MB Electronics in the mid 1980s. The central plate is about 8 mm (a little less than 3/8") thick, covered on both sides with 8 mm thick foam. The foam is probably too thin; there is still too much high frequency energy reflected from the disk. The Jecklin-type disks supplied by Josephson Engineering since about 1995 use 25 mm foam. Jecklin is shown in his book with a disk of the same diameter but covered with lamb’s fleece. The NHK (Japanese national broadcasting) version of the disk extends this covering to include the circumference of the disk as well.
The following text is reproduced from Jürg Jecklin’s 1980's paper Microfon Aufnahme Systeme. Note that Mr. Jecklin's suggestions and dimensions have changed a bit over the years. As of 2009 he was teaching at the Universität für Musik und Darstellende Kunst Wien (the Vienna University of Music and Performing Arts) and has published an excellent paper on microphones that contains updated details on the "OSS-Scheibe" aka "Jecklin Disk." A: The OSS technique (OSS = optimum stereo signal)
The idea of a new microphone arrangement is the result of the dissatisfaction about the sound of usual music recordings, which has made itself felt during the course of approximately 4000 recording sessions. Almost any sound engineer knows how it feels when the recording does not sound like he imagines it should, despite the use of a lot of microphones. In such a case, i.e., if the technical expenditure cannot be increased meaningfully, one should start again and look for a new recording concept. The present recording technique of electronic music has grown out of the basic arrangement of two microphones (stereophonics). Since the recordings with only two microphones normally are not satisfactory, additional supporting microphones often a large number of them are used. Therefore, the solution of the problems has to start with the two insufficient main microphones. On the one hand, the stereo main microphone arrangement must guarantee an optimum sound; and, on the other hand, it must provide the correct stereo signal for reproduction via two loudspeakers in the room. The procedure for the conception of the OSS technique was therefore as follows: I. Selection of suitable microphones