A baffle is a shielding structure used to increase the effective length of the external path between two points in an acoustic system. For instance, in a recording studio, a movable baffle, also known as a flat or a gobo, may be used to separate performers, and in an auditorium, baffles may be used to achieve better sound diffusion and reflection.
The most common use of the term is to refer to the material surrounding a loudspeaker. In the simplest case, this is a piece of wood on which the speaker is mounted to prevent sound waves from escaping around the edges. The aim is to avoid cancellation between the sound waves produced at the front and rear of the speaker which have a phase difference of 180 degrees due to the back and forth motion of the speaker diaphragm.
When the distance between front and rear is less than a quarter wavelength, the frequency response falls off because of cancellation. More complex baffles, such as the bass reflex baffle, can be designed to surround the speaker and improve low frequency response.