Of these there are really four. The current player is Bobby Jacobs. The longest serving was Bert Ruiter. The first was Martijn Dresden. On Moving Waves the credit goes to the man best known as Cyriel Havermans, although Jan Akkerman apparently did most of it. One also ought to mention Tato Gomez on the first four tracks of the 1985 Van Leer Akkerman album and Ruud Jacobs and his double bass on Beethoven's Revenge from that album.