Speaker magnetic circuit

Abstract

A yoke includes a disk-like base end portion and a columnar center pole protruding from a center portion of the base end portion. An annular magnet is arranged on the base end portion. An annular top plate is arranged on the magnet so that an inner circumferential surface thereof is opposite to an outer circumferential surface of the center pole. A non-magnetic ring member is arranged on an inner circumferential surface side of the magnet, the non-magnetic ring member having a same inner circumferential diameter as an inner circumferential diameter of the top plate.

What is claimed is:  
     
       1. A speaker magnetic circuit comprising:
 a yoke including a disk-like base end portion and a columnar center pole protruding from a center portion of the base end portion; 
 an annular magnet arranged on the base end portion; 
 an annular top plate arranged on the magnet so that an inner circumferential surface thereof is opposite to an outer circumferential surface of the center pole, the annular top plate having a smaller inner circumferential diameter than an inner circumferential diameter of the annular magnet; and 
 a non-magnetic ring member arranged on an inner circumferential surface of the magnet, the non-magnetic ring member having a same inner circumferential diameter as an inner circumferential diameter of the top plate, an upper end of the non-magnetic ring member, which is located on the annular top plate side, contacting a lower surface of the annular top plate, and a lower end of the non-magnetic ring member, which is located on the base end portion side, not contacting the base end portion. 
 
     
     
       2. The speaker magnetic circuit according to  claim 1 , further comprising:
 a voice coil arranged in a magnetic gap formed between the outer circumferential surface of the center pole and the inner circumferential surface of the top plate, 
 wherein the lower end of the non-magnetic ring member is located more on the base end side than an end portion of the voice coil, the end portion being located on the base end portion side, when an audio signal is inputted to the voice coil and the voice coil is located most on the base end portion side. 
 
     
     
       3. The speaker magnetic circuit according to  claim 2 , wherein, between the lower end of the non-magnetic ring member and the base end portion, a gap larger than the magnetic gap is formed, the gap being formed between the outer circumferential surface of the center pole and an inner circumferential surface of the magnet. 
     
     
       4. The speaker magnetic circuit according to  claim 1 , wherein the non-magnetic member is formed of metal containing aluminum. 
     
     
       5. The speaker magnetic circuit according to  claim 1 , wherein an inner circumferential surface of the non-magnetic ring member is a smooth surface free from irregularities. 
     
     
       6. The speaker magnetic circuit according to  claim 1 , wherein a plurality of longitudinal grooves arrayed in a circumferential direction is formed on an inner circumferential surface of the non-magnetic ring member. 
     
     
       7. The speaker magnetic circuit according to  claim 1 , wherein a plurality of dot-like recessed portions is formed on an inner circumferential surface of the non-magnetic ring member.