Abstract: An improved variable volume air controller for use in conjunction with a conditioned air distribution system is disclosed which comprises an insulated lined housing having an inlet, an outlet, and a control assembly operative to vary the volume of air flowing therethrough. An air flow diffuser is also provided being positioned in overlying relationship to the inlet opening which operates to substantially improve air flow distribution over the cross sectional area of the housing whereby the control assembly may operate to provide improved relatively noise-free modulation of air flow. Additionally, a stop assembly is provided which cooperates with a portion of the control assembly to limit movement thereof beyond a true full open position as well as to inhibit air flow induced vibration thereof when the control assembly is in a full open position.