Noise cancellation earphone
An active noise cancellation earphone ( 1 ) has an acoustic path including a cavity ( 36 ) and a pipe ( 20 ) leading to the auditory canal ( 40 ) which are arranged to form an oscillator in use which has the effect of recovering the open loop system phase characteristics at a selected frequency or frequency range. The earphone ( 1 ) also has two parts ( 5,18 ) which can be adjusted relative to each other to allow the earphone ( 1 ) to be comfortably and correctly positioned in use.
1. An earphone for a feedback active noise cancellation system, the earphone comprising a housing having an acoustic outlet adapted to be received in the auditory canal of the ear, a speaker and a microphone provided in the housing anteriorly of the speaker, the speaker and microphone being adapted to be connected to a feedback controller to provide a close-loop active noise cancellation system, the earphone having an acoustic path from the speaker through a pipe to the acoustic outlet such that a Helmholtz resonance occurs between the pipe and the auditory canal at a predetermined frequency over a predetermined frequency range to thereby improve the stability of the closed-loop system.
2. The earphone of claim 1 wherein the resonance provides a phase recovery.
3. The earphone of claim 1 wherein the pipe comprises a tubular acoustic path.
4. The earphone of claim 1 wherein the predetermined frequency is substantially within the range 500 Hz to 1 kHz.
5. The earphone of claim 1 wherein the housing includes a sealing means to substantially acoustically seal the acoustic outlet at the entrance to the auditory canal.
6. The earphone of claim 1 wherein a cavity is provided in the acoustic path between the speaker and the pipe.
7. The earphone of claim 6 wherein the cavity provides an acoustic impedance between the speaker and the pipe.
8. The earphone of claim 1 wherein the housing comprises an auricle portion adapted to be received in the auricle of a human ear, and a canal portion adapted to be received in the auditory canal, the auricle portion holding the speaker and microphone, the canal portion being rotatably mounted relative to the auricle portion such that the canal portion can be angularly adjusted relative to the auricle portion dependent on the ear geometry of a user to allow the canal portion to be received in the auditory canal and the auricle portion to be supported in the auricle.
9. The earphone of claim 8 wherein the housing includes a sealing means to substantially acoustically seal the acoustic outlet at the entrance to the auditory canal, and wherein the canal portion includes a sealing means to make an effective acoustic seal between the canal portion and the auditory canal of a user.
10. The earphone of claim 8 wherein a cavity is provided in the acoustic path between the speaker and the pipe and wherein the cavity is provided between the auricle portion and the canal portion.
11. The earphone of claim 10 wherein the housing has a stem dependent therefrom, the stem being adapted for location externally to the ear.
12. The earphone of claim 8 including a locking means, activation of the locking means preventing adjustment of the canal portion relative to the auricle portion.
13. The earphone of claim 12 wherein deactivation of the locking means allows adjustment of the canal portion relative to the auricle portion.
14. The earphone of claim 8 wherein the canal portion is received in the entrance of the auditory canal.
15. The earphone of claim 8 wherein the canal portion is mounted eccentrically relative to the auricle portion.
16. The earphone of claim 8 wherein the canal portion has a central axis disposed at an angle to a central axis of the auricle portion.
17. The earphone of claim 1 including a carrier for carrying the speaker and the microphone, the carrier being adapted to be retained within the housing.
18. The earphone of claim 1 , including feedback noise cancellation circuitry adapted to receive a feedback signal from the microphone and provide an appropriate signal to the speaker to provide active noise cancellation.