damper airstream 7 onto swirl vanes 8 to increase or decrease simultaneously bringing about strong changes to the throw of discharged swirl airstream 9 into the occupancy space as throw is a function of airflow rate multiplied by discharge velocity such changes in the throw of swirl airstream 9 compromise comfort as over throw increases the threat of draughts and under throw that of stagnation moreover due to the extremely low momentum of discharged swirl airstream 9 at low airflow rates the minimum airflow rate is typically limited to approximately 30 and 40 of the maximum airflow rate so as to prevent the cold and dense supply air from dumping into the occupancy space when supply airstream airflow rate 3 is turned down in order to reduce the throw sensitivity of discharged swirl airstream 9 to changes in supply airstream airflow rate 3 in order to reduce the threat of swirl airstream 9 from dumping at low airflow rates and as a means of incorporating independent variable air volume vav adjustability into individual diffusers diffusers of the prior art may adjust supply airstream airflow rate 3 via electrically pneumatically or thermally powered actuator 10 to open 6 a and close 6 b a diffuser damper mechanism in the diffuser that varies the airflow rate at a largely constant velocity of damper airstream 7 onto largely radial swirl blades 8 thereby discharging swirl airstream 9 of varying volume flow rate at largely constant discharge velocity over a large portion of the turndown range however the high velocity of damper airstream 7 onto the active.