PURPOSE:To obtain excellent frequency characteristics free of the coloring of a reproduced sound, by covering at least one side of a honeycomb core, used for the diaplragm of a speaker, etc., with a skin material made of a composite material of independent foamed resin and specified reinforcing fiber. CONSTITUTION:A speaker 1 consists of a magnetic circuit assembly composed of a pole pipece 2, a magnetic 3, and a top yoke 4, a vibration system assembly composed of a diaphragm 6, a voice coil bobbin 7, a voice coil 8, etc., and a frame 5. The diaphragm 6 has skin materials 14 adhered to front and rear surfaces of a honeycomb core 13 made of Al foil. The the rear side of the diaphragm 6, the voice coil bobbin 7 is bonded and the bobbin 7 inserted into a magnetic gap 12 is wounded with the voice coil 8. To obtain the skin material 14, foamed resin, such as epoxy resin, is formed and foamed by using reinforcing fiber 16 of one among carbon fiber, glass fiber, graphite fiber, silicon carbide fiber, boron fiber, and organic high-elasticity fiber, thus forming independent foamed resin 15 having uncontinuous air bubbles independent of one another.