Abstract: A core having a coil wound thereon is fixed to a base at the bottom. The base is fixed to a case made of synthetic resin by insert molding. A diaphragm is fixed to the case in circumference, and also a magnetic flux guide member is fixed to the case in circumference. Since the diaphragm and the magnetic flux guide member is commonly fixed to the case, no variation in the distance between the diaphragm and the magnetic flux guide member would occur for every product. Further, a gap L is formed between the magnet and the magnetic flux guide member, and an air hole is formed in the magnetic flux guide member. This improves the passage of air and reduces air dumper effect without modifying the magnet in shape.

Abstract: A core having a coil wound thereon is fixed to a base at the bottom. The base is fixed to a case made of synthetic resin by insert molding. A diaphragm is fixed to the case in circumference, and also a magnetic flux guide member is fixed to the case in circumference. Since the diaphragm and the magnetic flux guide member is commonly fixed to the case, no variation in the distance between the diaphragm and the magnetic flux guide member would occur for every product. Further, a gap L is formed between the magnet and the magnetic flux guide member, and an air hole is formed in the magnetic flux guide member. This improves the passage of air and reduces air dumper effect without modifying the magnet in shape.

Abstract: A base is integrally formed with a synthetic resin case by insert molding. A fixing portion of a core is engaged with a fixing hole of the base. An assembly jig is used to press the fixing portion to caulk the core to the base. The distance between a free end of the core and a diaphragm supporting portion of the case is guraranteed at a desired value.