Sound production using speaker enclosure with reduced internal pressure
Techniques are provided for generating sound using a speaker mounted to an enclosure (e.g., speaker cabinet) wherein a gas pressure level (e.g., air pressure level) inside the enclosure is lower than an ambient air pressure level outside the enclosure. The reduced gas pressure level within the enclosure provides an environment with a reduced pressure level at a back side of a speaker cone of the speaker, which enhances a low frequency response for a given speaker size, while also minimizing resonant frequencies and phase cancellation issues which could otherwise occur with conventional speaker systems in which acoustic sound waves are generated at the back side of the speaker cone. A pressure compensation system is utilized counteract a force applied to the front side of the speaker cone as a result of the gas pressure level inside the enclosure being lower than the ambient air pressure level outside the enclosure.
1. An earphone device comprising:
an earphone comprising a speaker cone and a voice coil assembly coupled to the speaker cone;
a sealed enclosure, wherein a front side of the speaker cone is disposed outside the sealed enclosure and a back side of the speaker cone is disposed inside the sealed enclosure, wherein sealed enclosure is configured to maintain a gas pressure level inside the sealed enclosure which is lower than an ambient air pressure level outside the sealed enclosure; and
a control system configured to generate a position control signal and apply the position control signal to a voice coil of the voice coil assembly;
wherein the position control signal is configured to generate an electromagnetic force that is sufficient to move the voice coil to a target null position, while allowing the voice coil to move back and forth about the null position in response to an audio signal applied to the voice coil during operation of the earphone.
2. The earphone device of claim 1 , wherein the earphone is configured to be one of inserted partially and inserted wholly within an ear canal of an individual.
3. The earphone device of claim 1 , wherein the earphone is configured to be one of inserted partially and inserted wholly within an ear pinna of an individual.
4. The earphone device of claim 1 , is configured to be one of partially external and wholly external to an ear pinna of an individual.
5. The earphone device of claim 1 , wherein the earphone is configured to one of partially surround or wholly surround an ear pinna of an individual.
6. The earphone device of claim 1 , wherein the gas pressure level inside the sealed enclosure is in a range of 10% to 95% lower than the ambient air pressure level outside the sealed enclosure.
7. The earphone device of claim 1 , wherein the control system comprises a summing amplifier, wherein the summing amplifier comprises a first input to receive the position control signal, and a second input to receive the audio signal.
8. The earphone device of claim 7 , wherein summing amplifier is configured to (i) combine the position control signal and the audio signal to thereby generate a voice coil control signal and (ii) apply the voice coil control signal to a primary voice coil winding of the voice coil.
9. The earphone device of claim 1 , wherein the control system is configured to (i) apply the position control signal to a secondary voice coil winding of the voice coil, and (ii) apply the audio signal to a primary voice coil winding of the voice coil.
10. The earphone device of claim 1 , wherein the control system comprises:
control signal generator circuitry which is configured to generate the position control signal that is applied to the voice coil; and
a force sensor fixedly positioned on an inner surface of a rest stop element of the voice coil assembly;
wherein the force sensor is configured to detect an amount of force that the voice coil asserts against the rest stop element when the voice coil is in a rest position when the earphone is initially powered up and differential pressure is applied to the front and back side of the speaker cone; and
wherein the force sensor is configured to generate a force control signal which is indicative of the detected amount of force that the voice coil asserts against the rest stop element with the voice coil in the rest position.
11. The earphone device of claim 10 , wherein:
the force control signal is applied to the control signal generator circuitry;
the control signal generator circuitry is configured to utilize the force control signal to generate an initial position control signal upon power up of the earphone; and
the control system is configured to utilize the initial position control signal to cause a coarse position adjustment of the voice coil to the target null position upon the power up of the earphone.
12. The earphone device of claim 1 , wherein a gas within the sealed enclosure comprises air.
13. The earphone device of claim 1 , wherein a gas within the sealed enclosure comprises an inert gas such as dry nitrogen.
14. The earphone device of claim 1 , wherein the control system comprises a position sensor which is configured to determine a position of the voice coil, and generate a position feedback control signal which is utilized by the control system to generate the position control signal.
15. The earphone device of claim 14 , wherein:
the position sensor comprises:
a sensor device fixedly coupled to the voice coil assembly; and
a position encoder scale element which is disposed on a movable element of the voice coil assembly, and which is aligned to the sensor device; and
the sensor device is configured to read the position encoder scale element to detect a position of the movable element of the voice coil assembly and generate the position feedback control signal in response to the detected position of the movable element.
16. The earphone device of claim 15 , wherein the movable element comprises a voice coil former of the voice coil assembly.
17. The earphone device of claim 15 , wherein the movable element comprises a primary voice coil winding of the voice coil assembly.
18. The earphone device of claim 15 , wherein the position sensor comprises at least one of an absolute linear encoding system and an incremental linear encoding system.