Abstract: The device includes a pressure-reducing chamber arranged immediately upstream of an air conditioning diffuser. It includes a shutter which pivots about an axis and which tends to reduce the useful area of the diffuser in question, under the action of a counterweight.The air introduced into the chamber, by means of a normally open motorized damper, exerts on one of the faces of the shutter, a pressure which tends to oppose the effect of the counterweight and tends to increase the useful area of the diffuser.A sensor which serves as a stop during the opening of the shutter, reacts on the motorized damper to tend towards a balance of the forces applied on the shutter, for a particular area of diffusion defined by the position of the sensor.The displacement of the sensor, operated by an ambient thermostat for example, enables the variation of the airflow by changing the free area of circulation.The speed of circulation is practically constant and depends on the counterweight acting on the shutter.