Acoustic transducer
This invention relates to acoustic drivers with stationary and moving coils. Time varying signals are applied to the moving and stationary coils to control the movement of a diaphragm, which produces audible sound. The time varying signals correspond to an input audio signal such that the sound corresponds to the input audio signal. Some of the described embodiments include multiple moving coils, multiple stationary coils or both. Some embodiments include feedback for adjusting one or more of the signals based on a characteristic of the acoustic driver. Various compensation and other features of the invention are also described in relation to various embodiments.
1. A method of operating an acoustic transducer, the method comprising:
receiving an input audio signal;
generating a time-varying stationary coil signal in a stationary coil, wherein the stationary coil signal corresponds to the input audio signal and wherein the stationary coil induces magnetic flux in a magnetic flux path;
generating a time-varying moving coil signal in a moving coil, wherein:
the moving coil is disposed within the magnetic flux path;
the moving coil signal corresponds to both the stationary coil signal and the input audio signal; and
the moving coils are coupled to a moving diaphragm which moves in response to the moving coil signal and the stationary coil signal.
2. The method of claim 1 wherein the stationary coil signal corresponds to the square root of the audio input signal.
3. The method of claim 2 wherein the moving coil signal corresponds to the square root of the audio input signal.
4. The method of claim 1 wherein generating the stationary coil signal includes generating a stationary coil control signal corresponding to the input audio signal and generating the stationary coil signal corresponding to the stationary coil control signal.
5. The method of claim 1 wherein generating the stationary coil signal includes generating a stationary coil control signal corresponding to the input audio signal and generating the stationary coil signal corresponding to the square root of the stationary coil control signal.
6. The method of claim 2 wherein generating the moving coil signal includes dividing a version of the input signal by a version of the stationary coil control signal.
7. The method of claim 1 wherein the stationary coil signal is unidirectional and the moving coil signal is bidirectional.
8. The method of claim 1 wherein the stationary coil signal is bidirectional and the moving coil signal is unidirectional.
9. The method of claim 7 wherein the at least one of the stationary coil signals is maintained above a minimum signal level.
10. The method of claim 7 wherein the unidirectional signals are maintained above a minimum signal level, unless the magnitude of the moving coil signal exceeds a threshold.
11. The method of claim 1 including rectifying the input audio signal to produce a rectified input audio signal and wherein the stationary coil signal corresponds to the rectified input audio signal.
12. The method of claim 1 including providing a bucking coil in series with the moving coil and wound with a polarity opposing the polarity of the selected moving coil.
13. The method of claim 12 including mounting the bucking coil to a stationary component of the acoustic transducer.
14. The method of claim 1 wherein the stationary coil signal is generated at one a plurality of selected signal levels.
15. The method of claim 1 wherein magnetic flux path flows in a magnetic material and including compensating the stationary coil signal based on a characteristic of the magnetic material.
16. The method of claim 15 wherein the characteristic is a saturation characteristic of the magnetic material.
17. The method of claim 15 wherein the characteristic is the remanent magnetization of the magnetic material.
18. The method of claim 15 wherein the moving coil signal is adjusted based on the characteristic of the magnetic material.
19. The method of claim 1 wherein the acoustic transducer includes a driver and further including sensing a characteristic of the driver and adjusting the moving coil signal in response to the sensed characteristic.
20. The method of claim 19 wherein the sensed characteristic is the acceleration of a moving component of the driver.
21. The method of claim 8 wherein the at least one of the stationary coil signals is maintained above a minimum signal level.
22. The method of claim 8 wherein the unidirectional signals are maintained above a minimum signal level, unless the magnitude of the moving coil signal exceeds a threshold.