in the quench liquid that are most intense in the plane centered between the radiating transducer faces which is congruent with the path of the ribbon of filaments the pressure fluctuations produce several beneficial effects that improve the uniformity and speed of filament quenching or coagulation on a macroscopic scale the quench liquid is driven into and out of the filament ribbon to improve the uniformity of the liquid contact with all of the filaments particularly those not in the surface layer of the ribbon on a microscopic scale localized high velocity liquid eddies and currents penetrate the filament boundary layers to continually carry fresh quench liquid to the filament surfaces also cavitation bubbles form and collapse as the sound pressure field alternates below and above the ambient pressure creating extremely localized shock waves these microscopic phenomena combine to increase thermal diffusion and mass transfer rates thereby increasing the speed of the quench coagulation process the treated fiber bundle and entrained liquid exits the chamber through port 7 the quenched coagulated mpd i filaments are normally subjected to a wash draw where the filaments are washed and drawn and then collected before or after drying the following example of the invention is not intended as limiting the fibers or filaments of these examples were prepared from aromatic polymers such as are disclosed in u s pat no 3 063 966 to kwolek morgan and sorenson 3.