a transducer head assembly supported above a surface has the spacing of its transducer head from the surface maintained at a predetermined value by a pressure - sensitive regulator which responds to changes in fluid flow pressure resulting from spacing changes to correct variations from the predetermined spacing . the assembly includes a pair of expandable chambers which are coupled to each other through a fluid restrictor and which carry the transducer head , the expandable chambers being sensitive to pressure changes and causing the transducer head to move toward and away from the surface in response to such changes to correct the fluid flow pressure .