Abstract: A low-frequency sound generator for generating intense sound, which generator includes an open resonator tube. Pressurized gas is supplied to the resonator tube as pulses through a feeder system which includes a valve slide member which controls the pressure of the supplied gas. The gas pulses develop standing sound waves in the resonator tube which provides a varying gas pressure. Means in the resonator tube is operable in response to changes in the gas pressure to provide positive feedback of the sound pressure in the resonator tube to the feeder system at a resonant frequency of the resonator tube.

Abstract: A method of producing pressed rocket propellant with good flash suppression and a high burning velocity, i.e. containing optimal quantities of flash reducing agent and catalysts. The meethod is characterized by the entire quantity of flash reducing agent required in order to achieve the result desired being mixed into a separate quantity of propellant while the entire quantity of catalysts required in order to achieve the result desired is mixed into the remaining quantity of propellant, after which these propellants containing either flash reducing agent or catalysts are converted into an appropriate form and mixed in layers or in its entirety and thereafter pressed into the form desired. In the body of propellant obtained, the flash reducing agent and catalysts will be separated, and will not interfere with each other's function.

Abstract: A low-frequency sound generator for generating intense sound, which generator includes an open resonator tube. Pressurized gas is supplied to the resonator tube as pulses through a feeder system which includes a valve slide member which controls the pressure of the supplied gas. The gas pulses develop standing sound waves in the resonator tube which provides a varying gas pressure. Means in the resonator tube is operable in response to changes in the gas pressure to provide positive feedback of the sound pressure in the resonator tube to the feeder system at a resonant frequency of the generator.

Abstract: A device for cleaning a fabric filter from adhering dust comprises a loud speaker element forming a dividing wall or a part of such a wall between a chamber receiving the filter, and an open resonator which communicates with the chamber.