Circular piece inserted into a speaker diaphragm or speaker cone near the bottom, small part of the cone (the apex) covering the voice coil. The dust cap prevents air and airborne particles from penetrating down to the voice coil and other components of the speaker driver. Most dust caps are bowed outward from the speaker driver like a small portion of a sphere (convex), however, some dust caps are flat, bowed in (concave), or even bullet-shaped. Co-axial speakers replace the dust cap with a tweeter mounted inside the midrange/midbass driver itself.