The invention relates to an acoustic panel assembly. There is a need for a simple and inexpensive acoustic panel assembly. An acoustic panel assembly includes a parent panel and an insert panel. The parent panel has a higher density body and a sound reflecting skin. The insert panel is mounted to the parent panel, and includes a sound absorbing body, a lower density rim and a sound transmitting skin. The parent panel includes a border portion which surrounds an opening which engages an outer edge of the insert panel. The border portion and the edge engage each other and form an interlocking joint. The border portion defines an annular groove which receives the outer edge of the insert panel. The body of the parent panel comprises a higher density expanded polypropylene material, and rim body of the insert panel comprises a lower density expanded polypropylene material.