A method of producing a spread multi-filament bundle and an apparatus is used in which an arbitrary number of multi-filament bundles of higher strength are simultaneously spread with high speed and a high-quality. The time interval is divided into a plurality of subintervals. The present invention can produce a high fine particle fraction and modest throat deposition in conjunction with reduced aerosol plume velocity and impact force. The diaphragms also minimize loss of normally-free-flowing fluid from a fluid-bearing.