Wearable audio device with nulling magnet
A wearable audio device with an electro-acoustic transducer that is configured to create audio output. The transducer has a transducer magnet that produces a transducer magnetic field having a magnetic field strength, and a magnetic structure such as a cup that guides the transducer magnetic field. The transducer magnet is on the inside of the magnetic structure. There is a magnetic field sensor outside of the magnetic structure; the magnetic field sensor is constructed and arranged to sense the Earth's magnetic field. A nulling magnet is coupled to or proximate the outside of the magnetic structure and is constructed and arranged to produce a nulling magnetic field that reduces the strength of the transducer magnetic field at the magnetic field sensor.
1. A wearable audio device, comprising:
an electro-acoustic transducer for creating audio output, the electro-acoustic transducer comprising a transducer magnet that produces a transducer magnetic field having a magnetic field strength, and a magnetic structure that guides the transducer magnetic field, wherein the transducer magnet is on an inside of the magnetic structure, and the magnetic structure has an outside;
a magnetic field sensor outside of the magnetic structure and constructed and arranged to sense the Earth's magnetic field; and
a nulling magnet coupled to the outside of the magnetic structure and constructed and arranged to produce a nulling magnetic field that reduces the strength of the transducer magnetic field at the magnetic field sensor.
2. The wearable audio device of claim 1 , wherein the magnetic field sensor comprises a three-axis magnetometer.
3. The wearable audio device of claim 1 , wherein the nulling magnet comprises a permanent magnet.
4. The wearable audio device of claim 1 , wherein the nulling magnet comprises an electromagnet.
5. The wearable audio device of claim 1 , comprising an earbud comprising an earbud body, and wherein the electro-acoustic transducer, the magnetic field sensor, and the nulling magnet are all located within the earbud body.
6. The wearable audio device of claim 5 , wherein the earbud body is constructed and arranged to be positioned so as to direct the audio output toward the ear of the wearer.
7. The wearable audio device of claim 1 , wherein the transducer magnet, the magnetic structure, and the nulling magnet are aligned along a longitudinal axis.
8. The wearable audio device of claim 7 , wherein the magnetic field sensor is also aligned along the longitudinal axis.
9. The wearable audio device of claim 7 , wherein the transducer magnet, the magnetic structure, and the nulling magnet are symmetric with respect to the longitudinal axis.
10. The wearable audio device of claim 1 , wherein the nulling magnet is cylindrical.
11. The wearable audio device of claim 1 , wherein the nulling magnet is annular.
12. The wearable audio device of claim 11 , wherein the nulling magnet comprises a central opening, and wherein the wearable audio device further comprises an acoustically-resistive mesh over the central opening of the nulling magnet.
13. The wearable audio device of claim 1 , further comprising a magnetic field shield located between the nulling magnet and the magnetic field sensor.
14. The wearable audio device of claim 13 , wherein the magnetic field shield comprises a cup comprising magnetic material.
15. The wearable audio device of claim 1 , wherein the transducer magnetic field at the magnetic field sensor has a direction along a magnetic field axis, and wherein the nulling magnetic field at the magnetic field sensor has an opposite direction along the magnetic field axis.
16. The wearable audio device of claim 1 , wherein the magnetic field sensor has a sensed magnetic field range where it operates linearly, and wherein the nulling magnetic field reduces the strength of the transducer magnetic field at the magnetic field sensor such that the sensed magnetic field strength is in the sensed magnetic field range where the magnetic field sensor operates linearly.
17. A wearable audio device, comprising:
an electro-acoustic transducer for creating audio output, the electro-acoustic transducer comprising a transducer magnet that produces a transducer magnetic field having a magnetic field strength, and a rear plate comprising magnetic material, wherein the rear plate is configured to guide the transducer magnetic field, wherein the transducer magnet is on an inside of the rear plate, and the rear plate has an outside;
a body constructed and arranged to be positioned at an ear of a wearer so as to direct the audio output at the ear of the ear;
a three-axis magnetometer positioned in the body outside of the rear plate and constructed and arranged to sense the Earth's magnetic field in three orthogonal axes; and
a nulling magnet positioned in the body proximate the outside of the rear plate, the nulling magnet constructed and arranged to produce a nulling magnetic field that reduces the strength of the transducer magnetic field at the three-axis magnetometer;
wherein the transducer magnet, the rear plate, and the nulling magnet are symmetric with respect to a longitudinal axis.
18. The wearable audio device of claim 17 , wherein the nulling magnet is cylindrical.
19. The wearable audio device of claim 17 , further comprising a shield can comprising magnetic material and located outside of the rear plate and the nulling magnet.
20. The wearable audio device of claim 17 , wherein the electro-acoustic transducer further comprises a voice coil gap outside of the transducer magnet, and a cup comprising magnetic material and located outside of the rear plate.