turning now to the fig1 there is shown in cross - section a cylindrically symmetrical transducer head assembly 10 and a fluid ( such as air ) source 12 , in this embodiment a positive pressure pump . the assembly 10 is fixedly mounted by plate 14 relative to a flexible disc 16 which may rotate with a back plate turntable 18 . while it is preferred that the pump pressure be kept constant , it is not necessary to maintain the pump pressure at any precise level and such pressure may vary , with the system automatically responding to compensate for such variation . the assembly 10 includes a first chamber 20 coupled to the pump 12 and a second chamber 22 coupled to said chamber 20 through a variable restrictor 24 , by means of apertures 25 , which controls the flow of fluid between the two chambers . a transducer head 26 is carried by the assembly 10 by means of movable diaphragms d 3 , d 2 and d 1 and is capable of upwards and downwards motion . the transducer head 26 , in this embodiment , acts as a focusing lens for a low powered laser beam 27 which reflects off a mirror 29 and then off of the surface of the disc 16 . the information contained in the surface irregularities of the disc causes changes in the angle or intensity of the beam representative of such information . attached to transducer head 26 and diaphragm d 1 , which has one or more apertures therein ( not shown ) to allow the passage of fluid therethrough , is a plate 28 having a small aperture 30 therein opposite the disc 16 . for the purposes of explanation , it will be assumed that the outside ambient pressure is considered to be p 1 , the pressure within chamber 22 to be p 2 and the pressure within chamber 20 created by pump 12 to be p 3 , with p 3 & gt ; p 2 & gt ; p 1 . in addition , the area of diaphragms d 3 , d 2 and d 1 can be represented by areas a 3 , a 2 and a 1 , respectively , with a 2 & gt ; a 3 & gt ; a 1 . as such , the total forces acting on the diaphragms d 3 , d 2 and d 1 is : f . sub . t = ( p . sub . 3 -- p . sub . 1 ) a . sub . 3 --( p . sub . 3 -- p . sub . 2 ) a . sub . 2 --( p . sub . 2 -- p . sub . 1 ) a . sub . 1 equation ( 1 ) if the resistance of restrictor 24 is r 1 and is adjusted to have a similar flow resistance characteristic as the transducer head 26 , the flow q through the restrictor 24 can be expressed by : ## equ1 ## it then follows that : if the head height is to be kept constant , the sum of the forces on the transducer head 26 must be able to be kept equal to zero . in this condition : ## equ2 ## where h is the distance of the plate 28 from the disc 16 , k is a constant and μ is the viscosity of fluid ( air ), it is evident that the head height can be maintained constant under the present assembly construction by keeping q / p 2 - p . sub . 1 a constant , i . e . by regulating the flow rate through the aperture 30 in plate 28 . from equation ( 5 ), it is seen that the flow resistance characteristics of the transducer head 26 is determined essentially by the spacing h the viscosity μ and the constant k which is dependent on the configuration of the aperture 30 . since the flow q varies as the third power of the height h small changes in head to disc spacing are accompanied by substantial changes in pressure p 2 and flow q . these changes are corrected , however , in the present invention by the motion of the transducer head 26 . that is , if the pressure p 2 increases because h has decreased , a corresponding increase is caused in pressure p 3 through the restrictor 24 causing a net upward motion of the diaphragms and an upward motion of the transducer head 26 . this upwards motion would increase the flow of fluid through the aperture 30 causing the head spacing h to increase and the pressure p 2 to decrease until an equilibrium value is reached . similarly , if the pressure p 2 decreases because h has increased , a corresponding decrease is caused in pressure p 3 through the restrictor 24 causing a net downward motion of the diaphragms and a downward motion of the transducer head 26 . this downward motion would decrease the flow of fluid through the aperture 30 causing the head spacing to decrease and the pressure p 2 to increase until an equilibrium value is reached . in fig2 a second embodiment of the invention is shown in which the pump 12 &# 39 ; is now a negative - pressure ( vacuum ) pump and p 1 & gt ; p 2 & gt ; p 3 . in such an embodiment , in order for the head spacing h to be kept constant the areas of the diaphragms d 3 , d 2 &# 39 ; and d 1 &# 39 ; have to be changed , as shown , so that a 1 &# 39 ;& gt ; a 3 & gt ; a 2 &# 39 ;, in order to satisfy the conditions of equation ( 4 ). in fig3 a modification of the invention shown in fig1 is illustrated in which the diaphragm d 1 is eliminated and the plate 14 is extended to form a leakproof slip seal with the plate 28 . the plate 14 is shown as having a lip 32 and an &# 34 ; o &# 34 ; ring 34 so that the head 26 can have full travel and still maintain such a fluid tight slip seal . alternatively , lip 32 could comprise a magnetic ring with a ferrofluid being contained between lip 32 and plate 28 to form a fluid tight slip seal . in this embodiment , the apertures ( not shown ) formerly in diaphragm d 1 are now replaced by a tube 36 connecting chamber 22 and the region between head 26 and plate 28 . as is shown in fig4 the chambers 20 and 22 do not have to have a common diaphragm d 2 , but may have separated diaphragms such as diaphragm d 2 for chamber 22 and diaphragm d 3 &# 39 ; for chamber 20 . if the fluid between diaphragms d 2 and d 3 is deemed incompressible then the forces acting on each such diaphragm will promptly be transmitted to the other one . in the event the fluid is not incompressible and very large or rapid forces are expected , it may be advisable to further strengthen the diaphragms d 2 and d 3 &# 39 ; to reduce flexing or to further mechanically couple diaphragms d 2 and d 3 &# 39 ;, such as by connecting rings , in order to prevent a degradation of the response time of the system . as is apparent from the above modifications and variations , numerous other variations and modifications will , of course , occur to those skilled in the art without departing from the principles of the present invention . the transducer head 26 , for example , may be of the conventional variety and carry an electromagnetic transponder thereon to sense magnetic changes in the disc 16 . accordingly , the scope of the invention should be limited only by the claims appended hereto .