Dual axial magnetic flux induction speaker.

CORRESPONDING APPLICATION

[0001] The present application claims the priority of the prior Swiss national application No CH 00425/20 filed on the 8th April 2020 in the name of Michel OLTRAMARE, the content of this prior application being incorporated by reference in its entirety into the present application. TECHNICAL FIELD

[0002] The present invention relates to induction motor devices comprising at least one fixed coil, one mobile armature and magnets. Such a device may for example form an induction loudspeaker.

[0003] More precisely, the present invention relates to the means for driving the movement of the diaphragm of an induction loudspeaker. PRIOR ART

[0004] The diaphragms of loudspeakers working in the low and medium frequencies are generally caused to move by an actuator or motor. There are mainly two types of actuators for loudspeakers: the actuators the most often used, with a mobile coil connected to the diaphragm, referred to as “voicecoil”, and induction actuators, with fixed coil and magnets, and a mobile armature fixed to the diaphragm.

[0005] Numerous patents relate to the composition of induction motors with a fixed coil: U.S. Pat. No. 2,621,261A, 4,965,839A, 5,062,140A, 5,742,696A, 6,359,996B1, 6,542,617B1 and also 8,009,857B2. These patents all mention radial magnetic flux actuators, with magnets placed all around a central core.

[0006] Other patents mention audio systems comprising two magnets and creating an axial magnetic flux: CN105491491A, CN109195077A, KR20140091365A, KR20180085393A, US2010054501A1, US2015271605A1, US2018206040A1, WO2013013502A1, WO2017028034A1. However, none of these inventions has adapted this system of axial magnetic flux to an induction system.

[0007] On conventional induction loudspeakers, as described in the patent U.S. Pat. No. 8,009,857B2, the magnets are placed radially inside or outside of a magnetic air space where the armature is moving. Thus configured, the magnets create a single magnetic field present over the whole circumference of the actuator. Since the magnetic field is generated by the magnets, a good quality of magnet is preferable. However, the higher the strength of the magnet, the lower is its Curie temperature, in other words the temperature at which it is demagnetized. However, the temperature in the core of a loudspeaker tends to rise rapidly. Although some patents provide solutions for cooling loudspeakers: GB1348535A, JPH03239099A, JPS5586288A, JPS56161798A, JPS59216394A or else the application PCT/IB2020/050963 filed on the 6 Feb. 2020 in the name of M. Michel OLTRAMARE, it is necessary to reach a compromise on the power of the magnet depending on the maximum temperature of its environment.