An air spring assembly includes a primary airbag mounted to a piston air bag such that the piston airbag provides a rolling surface for the primary airbag. The receiver circuit also comprises an adjustment circuit for adjusting the demodulated signal from the first receiver. Each of second and third preferred embodiments is a thin, freestanding microporous polyolefin web that has an inorganic surface layer containing no organic hydrogen bonding component for the inorganic particles. The constructive solution has no moving solid parts, and the incoming wind is an inherent moving component of the engine.