The Josephson Engineering SPB40A is intended for use only with the Josephson C617SET microphone equipped with the Microtech Gefell MK221 capsule. Using the baffle results in an on-axis boost from 1.5 to 8 kHz, with a maximum of about 2.5 dB at 3.5 kHz, and a smooth variation in a high-frequency roll-off for sounds arriving off-axis. There is some attenuation of higher frequencies due to the scattering of incident sound, which becomes more pronounced off-axis.
The spacing between the microphone and the surface of the sphere is critical and is determined by the use of a military-specification o-ring. If it needs to be replaced it can be obtained from Josephson or other sources, it is a type AS3578-211 in Buna-N rubber.
When installing the sphere on the microphone, gently twist the sphere clockwise as you press it onto the microphone. It will come to a firm stop with the edge of the sphere just below the second row of holes in the capsule grille. When removing the sphere, use the same clockwise motion while pulling the sphere off the microphone. This will prevent unscrewing the capsule grille from the capsule.