An acoustic device includes a first member; a second member; a cavity formed by joining the first member and the second member together; and a port to communicate the cavity with an outside. The port is disposed at a joint portion between the first member and the second member. The first member includes a bottom plate disposed opposite the second member with the cavity in between and a side wall extending from the bottom plate toward the second member, and an edge face of the side wall, opposite the bottom plate, contacts the second member, to form different cavities. The acoustic device further includes a hole that penetrates the side wall and a material of the second member has a density greater than that of the first member.