velocity equalling sonic velocity at the prevailing pressure in the chamber 7 the gas jets which stream out through the discharge openings 13 form a more or less integrated continuous shroud which surrounds the central core jet streaming out at supersonic velocity from the laval nozzle 11 with sonic velocity and thereby muffles the emanated sound for sufficient effect regarding the capacity for suppressing turbulence in the core jet and therewith suppressing also undesired slowing down of the core jet as sound generation within a critical region it is believed to be suitable that the total discharge area of the peripheral discharge openings 13 is larger than the opening area in the central system whether it be the central system including a single laval opening 11 or several all considered in the most narrow section of the openings the discharge area of the outer system should be preferably 1 4 times suitably 1 5 to 3 times or approximately double the opening area in the central system at the same time the peripheral discharge openings 13 themselves generate a gas flow with relatively low noise level where it is significant that the peripheral gas air jets have the possibility of co ejecting air from the surroundings the slit formed openings 13 in the nozzle 1 lie therefore near the outer edges in the front of the nozzle 1 at the same time as the nozzle body 5 protrudes from the casing 2 for co ejection of.