Abstract: A plurality of openings are provided on the surface of a body casing which comprises a noise reduction chamber, and plate members (a reflecting plate and a sound waves introduction plate) are provided extending from an edge of each opening to the noise reduction chamber. The opening edges at which these plate members are attached have acute corners or rounded corners.

Abstract: A main body casing of a ventilator is formed with an outer airflow opening and an inner airflow opening and a ventilating path for connecting these airflow openings is formed in the main body casing. The ventilator ventilates a room and prevents entry of noise from outside into the room through the ventilating path. The ventilating path is bifurcated and these two ventilating paths have different lengths from each other so that a noise sound wave entering through one of the ventilating paths and a noise sound wave entering through the other ventilating path are out of phase with each other to cancel out each other's sound wave energy when the sound waves meet.

Abstract: A sound-deadening louver is attached to vents that are formed in a wall structure. The louver is composed of a plurality of blades that are inclined at an angle to the surface of the wall structure. Each blade has a sound-deadening chamber therein, and an opening is formed on that side which faces each vent in the wall structure. First reflecting plates and second reflecting plates are mounted in the blade so as to extend from an edge portion of the opening into the sound-deadening chamber. The first reflecting plates have a curved shape, while the second reflecting plates have a flat shape.