NK/RD and NK/RDM are air duct diffusers with adjustable round nozzles designed for low- and medium-pressure installations directly in round ventilation ducts. Nozzles of diameter sizes 57 (RD) and 35 (RDM) are ended with sinusoidal outlets that allows for high air diffusion. Nozzles position an be adjusted to any direction so that shape of the air stream can be regulated. They can be used with constant and variable airflow. The air can be supplied at the temperature lower or higher than the temperature in the ventilated room.