A pressure wavefield and a normal velocity wavefield measured on a smoothly shaped acquisition surface by towed dual-sensor marine seismic streamers are decomposed into up-going and down-going pressure and particle velocity components on an observation level between the acquisition surface and a sea surface of undetermined shape. The housing of each connector has a portion surrounding the periphery of a contact holding wall. The cooling is provided by a driven air flow, in particular in the tube, by a fan. A magnetically conductive plate provides a second section of the low reluctance return path from the second portion of the return path member to the secondary drive magnet. A primary winding of a transformer, the switching circuit, and the secondary windings are disposed on the primary region.