Kurmann Soundpost pickup, which is popular among Irish fiddlers.
An unusual idea, which placed the pickup in the soundpost of your bowed instrument.
(The soundpost is the small piece of wood hold in place inside the violin, viola, cello or doublebass between the bottom and the top plate.)
Now there is another soundpost pickup on the market sold thorugh the Violorama website.
Where the Kurmann Soundpost had a special cable running from the instrument to a bespoke preamp with internal EQ filters. The Violorama soundpost has a more common RCA plug and a RCA cable to XLR plug with a built in FET buffer preamp with no EQ.