dif·fus·er 
(dĭ-fyzər)
(dĭ-fyzər)n.
1. One that diffuses, as:
a. A light fixture, such as a frosted globe, that spreads light evenly.
b. A medium that scatters light, used in photography to soften shadows.
c. A device, such as a cone or baffle, placed in front of a loudspeaker diaphragm to diffuse the sound waves.
2. A flow passage in a wind tunnel that decelerates a stream of gas or liquid from a high to a low velocity.