Acoustic detection of in-ear headphone fit

1. A method performed by an in-ear headphone, the method comprising:

obtaining an audio signal from an audio source device paired with the in-ear headphone;

driving, using the audio signal, a speaker of the in-ear headphone to output a sound into an ear canal of a user, wherein a first ear tip is coupled to the in-ear headphone and is inserted into the ear canal of the user;

obtaining a microphone signal that is responsive to the sound;

determining a parameter associated with the microphone signal; and

causing a display screen to display a message indicating that the first ear tip does not properly fit within the ear canal and to replace the first ear tip with a second ear tip based on the parameter being below a threshold.

2. The method of claim 1 , wherein the parameter is based on a difference between a frequency response of the microphone signal and a target frequency response for at least one frequency band.

3. The method of claim 2 , wherrein the at least one frequency band is a low-frequency band that is less than 1000 Hz.

4. The method of claim 3 , wherein the parameter is further based on a difference between the frequency response and the target frequency response for a high-frequency band that is equal to or greater than 1000 Hz.

5. The method of claim 4 , wherein the parameter is a first parameter, wherein the threshold is a second parameter that is based on another difference between a previously measured frequency response while a second ear tip was coupled to the in-ear headphone and the target frequency response at the frequency band.

6. The method of claim 5 , wherein the first parameter and the second parameter are based on differences between respective measured frequency responses and the target frequency response at the low-frequency band and the high-frequency band.

7. A method performed by an in-ear headphone, the method comprising:

obtaining a first audio signal from an audio source device paired with the in-ear headphone;

driving, using the first audio signal, a speaker of the in-ear headphone to output a sound into an ear canal of a user, wherein a first ear tip is coupled to the in-ear headphone and is inserted into the ear canal of the user;

obtaining a microphone signal that is responsive to the sound; and

notifying the user to replace the first ear tip with a second ear tip in response to a parameter associated with the microphone signal being less than a threshold by at least one of

driving the speaker with a second audio signal containing speech instructions for the user to replace the first ear tip with the second ear tip, and

causing a display screen of the audio source device to display text instructions for the user to replace the first ear tip with the second ear tip.

8. An audio source device comprising

a processor; and

a memory having stored therein instructions which when executed by the processor causes the audio source device to

cause an in-car headphone to perform an ear tip fitting measurement for each of a plurality of ear tips, while the ear tip is coupled to the in-ear headphone and is inserted into an ear canal of a user;

obtain, for each ear tip of the plurality of ear tips, a fit parameter that is determined by the ear tip fitting measurement and is indicative of how well a corresponding ear tip fits within the ear canal of the user; and

determine which of the plurality of ear tips is to be used based on a comparison of fit parameters for the plurality of ear tips.

9. The audio source device of claim 8 , wherein the instructions to determine which of the plurality of ear tips is to be used comprises instructions to select one of the plurality of ear tips that has a higher fit parameter than each of the other of the plurality of ear tips.

10. The audio source device of claim 9 , wherein each fit parameter is based on differences between a frequency response that is measured while a corresponding ear tip is coupled to the in-ear headphone and a target frequency response at two or more frequency bands.

11. The audio source device of claim 10 , wherein each fit parameter is based a difference at a low-frequency band and another difference at a high-frequency band.

12. The audio source device of claim 11 , wherein the low-frequency band is below 1000 Hz and the high-frequency band is at or above 1000 Hz.

13. The audio source device of claim 10 , wherein the ear tip that has the higher fit parameter has lower differences at the two or more frequency bands than the other of the plurality of ear tips.

14. The audio source device of claim 10 , wherein the memory further comprises instructions to notify the user which of the plurality of ear tips is to be used by at least one of 1) displaying text instructions on a display screen indicating which of the plurality of ear tips to use and 2) driving a speaker with an audio signal containing speech instructions indicating which of the plurality of ear tips to use.

15. An in-ear headphone comprising:

a speaker;

an internal microphone that is configured to capture sound inside an ear canal of a user;

at least one sensor;

a processor; and

memory having instructions which when executed by the processor causes the in-ear headphone to

obtain sensor data produced by the at least one sensor;

determine, based on the sensor data, that the in-ear headphone has been inserted into the ear canal of the user;

after determining that the in-ear headphone has been inserted, drive, using an audio signal, the speaker to output a sound into the ear canal of the user;

responsive to the sound, measure a frequency response of a microphone signal captured at the internal microphone; and

transmit, over a wireless communication link, a parameter associated with the frequency response of the microphone signal to an audio source device.

16. The in-ear headphone of claim 15 , wherein the parameter is based on differences between the measured frequency response and a target frequency response at a low-frequency band and a high-frequency band.

17. The in-ear headphone of claim 16 , wherein the low-frequency band is below 1000 Hz and the high-frequency band is at or above 1000 Hz.

18. The in-ear headphone of claim 15 , wherein the memory has further instructions to process the audio signal to determine whether an energy level of spectral content of the audio signal at a frequency band is above a threshold, wherein the instructions to measure the frequency response is in response to the energy level being above the threshold.

19. The in-ear headphone of claim 18 , wherein, in response to the energy level being below the threshold, the memory has instructions to

continue to drive the speaker with the audio signal; and

wait to measure the frequency response until a future portion of the audio signal is obtained that contains spectral content at the frequency band having an energy level that exceeds the threshold.

20. The in-ear headphone of claim 15 , wherein the audio signal is used to drive the speaker after waiting for a period of time from when it is determined that the in-ear headphone has been inserted into the ear canal of the user.