Abstract: A method and a device for reducing the noise caused by throttling a gas flow in a flow channel (1), where after the throttling part (2) there is a wider part (3). The wider part (3) following the throttling part (2) of the flow channel (1) has at least one deviation of the cross-section (D) formed by a wall protrusion (5) in a short part (1) of the channel. The cross-section of the channel wall protrusion (5) taken length-wise of the channel tapers towards the central part of the channel. In a trans- or supersonic flow the protrusion causes a straight shock wave, a so-called Mach disk, in the flow, and this disk is made to occur and to remain within a wide pressure drop ratio range.