A magnetic assembly and a loudspeaker a magnetic assembly. The magnetic assembly has a pole piece that is designed to form an outer air gap and an inner air gap for coaxial voice coils of the loudspeaker. The same magnet is used for the magnetic circuits of the two voice coils. The pole piece is shaped to split the magnetic circuits into a low frequency magnetic circuit and a high frequency magnetic circuit. A convex dome is attached to the high frequency voice coil.
1. A magnetic assembly for a loudspeaker comprising:
a magnet for producing a magnetic field;
a top plate provided adjacent a top surface of the magnet;
a rear plate provided adjacent a rear surface of the magnet;
a pole piece positioned adjacent the top plate and the rear plate, the pole piece having a through bore defining an inside surface of the pole piece, the inside surface of the pole piece facing the through bore;
a first projection that projects into the through bore from said inside surface of the pole piece;
a second projection that projects into the through bore of the pole piece from a surface of the rear plate;
wherein the pole piece and the top plate are positioned adjacent each other to define a first air gap for a first voice coil;
wherein the first projection and the second projection are arranged adjacent each other to define a second air gap within said through bore for a second voice coil.
2. A magnetic assembly according to claim 1 , wherein the pole piece and the rear plate are positioned adjacent each other to define a third gap.
3. A magnetic assembly according to claim 2 , wherein the third gap is defined by one or more non-magnetic spacers.
4. A magnetic assembly according to claim 3 , wherein the one or more non-magnetic spacers locate and fix the pole piece relative to the rear plate.
5. A magnetic assembly according to claim 3 , wherein the spacer is configured so that the third gap is between 1 mm and 2 mm.
6. A magnetic assembly according to claim 1 , wherein the magnet is a ring magnet, made out of a ferrite material.
7. A magnetic assembly according to claim 1 , wherein the top plate and the rear plate have an annular shape.
8. A magnetic assembly according to claim 7 , wherein the pole piece is positioned within an inner edge of the annular top plate.
9. A magnetic assembly according to claim 8 , wherein the pole piece is cylindrical.
10. A magnetic assembly according to claim 1 , wherein the first projection has an annular shape.
11. A magnetic assembly according to claim 10 , wherein the first projection is positioned closer to a base of the pole piece than to a top of the pole piece.
12. A magnetic assembly according to claim 1 , wherein the first projection is integrally formed with the pole piece.
13. A magnetic assembly according to claim 1 , wherein the pole piece, the first and second projections, the top plate and the rear plate are arranged so that the first air gap and the second air gap are annular having a common central axis.
14. A loudspeaker comprising:
a magnetic assembly comprising:
a magnet producing a magnetic field;
a top plate adjacent a top surface of the magnet;
a rear plate adjacent a rear surface of the magnet;
a pole piece positioned adjacent the top plate and the rear plate, the pole piece having a through bore defining an inside surface of the pole piece, the inside surface facing the through bore;
a first projection projecting into the through bore from said inside surface of the pole piece;
a second projection projecting into the through bore of the pole piece from a surface of the rear plate;
wherein the pole piece and the top plate are positioned adjacent each other to define a first air gap;
wherein the first projection and the second projection are arranged adjacent each other to define a second air gap within said through bore;
a frame coupled to the magnetic assembly;
a first voice coil mounted within the first air gap;
a cone attached between the frame and the first voice coil;
a second voice coil mounted within the second air gap; and
a dome attached to the second voice coil.
15. A loudspeaker according to claim 14 , wherein the dome is convex in shape relative to a propagation direction of a sound wave produced by the loudspeaker.
16. A loudspeaker according to claim 14 , wherein the first and second voice coils are coaxial and wherein the dome and the cone are positioned so that sound waves produced by the dome are guided by the cone.
17. A loudspeaker according to claim 16 , further comprising a phase corrector positioned in front of the dome for correcting a phase of the sound wave produced by the dome.
18. A loudspeaker according to claim 16 , wherein the second voice coil has a smaller diameter than the diameter of the first voice coil.
19. A coaxial loudspeaker comprising:
a frame coupled to a magnetic assembly;
a first voice coil mounted within a first air gap of the magnetic assembly;
a cone attached between the frame and the first voice coil;
a second voice coil mounted within a second air gap of the magnetic assembly;
a dome attached to the second voice coil; and
a phase corrector positioned between the dome and the cone for correcting a phase of sound waves produced by the dome;
wherein an apex of the dome is fixed to the phase corrector.
20. A coaxial loudspeaker according to claim 19 , wherein the magnetic assembly comprises:
a magnet for producing a magnetic field;
a top plate provided adjacent a top surface of the magnet;
a rear plate provided adjacent a rear surface of the magnet;
a pole piece positioned adjacent the top plate and the rear plate;
a first projection that projects from an inside surface of the pole piece;
a second projection that projects from a surface of the rear plate;
wherein the pole piece and the top plate are positioned adjacent each other to define a first air gap for a first voice coil;
wherein the first projection and the second projection are arranged adjacent each other to define a second air gap for a second voice coil.
21. A magnetic assembly according to claim 1 , wherein the pole piece is tubular.