Patent ID: 11956612
Assignee: PURIFI APS
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H | IPC H

Claim 12:
13. An electrodynamic loudspeaker comprising a motor, the motor including a magnetic circuit assembly arranged about a motor axis, the magnetic circuit assembly comprising:
an outer magnet, a magnetically permeable top plate, a magnetically permeable bottom plate,
a center pole piece and an air gap for receipt of a voice coil;
wherein the air gap is formed by an inner axially extending wall of the magnetically permeable top plate facing an axially extending peripheral wall section of the center pole piece to define a width, a bottom, a top and height of the air gap;
an outwardly projecting magnetically permeable member arranged above the top of the air gap;
said center pole piece comprising a magnetic member extending axially from at least the bottom of the air gap to a magnetically permeable bottom member or to the magnetically permeable bottom plate;
wherein said magnetic member exhibits a relative alternating current (AC) magnetic permeability smaller than 10, or smaller than 5 or smaller than 2;, the loudspeaker further comprising:
a frame,
a displaceable diaphragm attached to the voice coil, said voice coil being arranged in the air gap of the motor,
wherein the magnetic circuit assembly is configured such that a variation of inductance of the voice coil over a predetermined displacement range of the voice coil defined by an outwards displacement limit and an inwards displacement limit is less than 10% or less than 7.5% or less than 5%, measured at 31 Hz; wherein said displacement range corresponds to 0.5 times a difference of the height of the voice coil and the height of the air gap.