US 12,425,775 B2
Magnetic circuit for acoustic transducer, and speaker unit
Takahiro Terada, Hamamatsu (JP); Yukio Wakui, Iwata (JP); Tsunenori Sano, Hamamatsu (JP); and Masao Noro, Hamamatsu (JP)
Assigned to YAMAHA CORPORATION, Hamamatsu (JP)
Filed by YAMAHA CORPORATION, Hamamatsu (JP)
Filed on Sep. 8, 2023, as Appl. No. 18/463,366.
Application 18/463,366 is a continuation of application No. PCT/JP2022/009245, filed on Mar. 3, 2022.
Claims priority of application No. 2021-037777 (JP), filed on Mar. 9, 2021.
Prior Publication US 2023/0421962 A1, Dec. 28, 2023
Int. Cl. H04R 9/02 (2006.01); H01F 7/08 (2006.01)
CPC H04R 9/025 (2013.01) [H01F 7/081 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A magnetic circuit for an acoustic transducer, the magnetic circuit comprising:
a yoke;
a magnet; and
a top plate,
wherein the yoke includes a bottom surface portion and a pole piece provided perpendicular to the bottom surface portion,
the magnet and the top plate are provided in that order on the bottom surface portion,
a magnetic gap in which a voice coil is disposed is formed between the pole piece and the top plate,
at least one of the pole piece and the top plate includes: a composite material part in a position facing the magnetic gap; and a protective layer covering at least a surface of the composite material part,
the composite material part is formed from a soft magnetic composite material, and
a material of the protective layer differs from the soft magnetic composite material.