Loudspeaker

1. A loudspeaker, comprising:

a diaphragm;

a voice coil for driving the diaphragm; and

a magnetic circuit including a yoke, a magnet provided on the yoke, and an upper plate provided on the magnet, for producing a magnet field that is perpendicular to the voice coil,

wherein the surface of the upper plate circumscribed by the voice coil includes surface irregularities without substantial depth and which do not conform to the shape of the diaphragm such that when reflecting sound waves created by the diaphragm, the upper plate diffuses the sound waves, and

the surface of the upper plate circumscribed by the voice coil does not include a through hole.

2. A loudspeaker according to claim 1 , wherein a depression is formed in a central portion of the upper plate.

3. A loudspeaker according to claim 2 , wherein a thermosetting resin or a photocurable resin is provided in at least a portion of the depression.

4. A loudspeaker according to claim 3 , wherein the thermosetting resin is one selected from the group consisting of an epoxy resin, a polyurethane resin, a phenol resin, a urea resin, a melamine resin, and an alkyd resin.

5. A loudspeaker according to claim 3 , wherein the photocurable resin is one selected from the group consisting of an acrylic resin and an epoxy resin.

6. A loudspeaker according to claim 2 , wherein a groove is formed in a vicinity of a periphery of the upper plate.

7. A loudspeaker according to claim 1 , wherein a groove is formed in a vicinity of a periphery of the upper plate.

8. A loudspeaker according to claim 1 , wherein the surface irregularities comprise one or more depressions.