Test system for evaluating feedback performance of a listening device

1. A test system for evaluating acoustic feedback characteristics of a listening device by changing the transfer function of the signal path from an acoustic output to an acoustic input of the listening device, the test system comprising:

a variable filter comprising

an acoustic input,

an acoustic output,

a control unit for changing a transfer function of the filter,

an acoustic input transducer for converting an input sound to an electric input signal,

a variable electric filter for filtering the electric input signal and providing a filtered output signal, and

an acoustic output transducer for converting the filtered output signal to a filtered output sound;

a first acoustic propagation element and/or a second acoustic propagation element for propagating acoustic sound, the first acoustic propagation element acoustically connecting the acoustic output of the listening device with the acoustic input of the variable filter, the second acoustic propagation element acoustically connecting the acoustic output of the variable filter with the acoustic input of the listening device,

wherein the system is configured to allow a determination of acoustic feedback or a level of acoustic feedback of the listening device at different frequencies.

2. A test system according to claim 1 wherein the variable filter is designed to compensate for unintended filtering of the first and/or second acoustic propagation elements.

3. A test system according to claim 1 comprising a memory for storing estimates of current feedback values.

4. A test system according to claim 3 comprising an analyzing unit for accessing and analyzing the feedback data collected by the test system and stored in the memory.

5. A test system according to claim 4 wherein the analyzing unit comprises a feedback estimation unit for estimating current feedback in the listening device.

6. A test system according to claim 4 wherein the analyzing unit comprises a communication interface to the variable filter and/or to the listening device.

7. A test system according to claim 4 wherein the analyzing unit is adapted for running a fitting software of the listening device allowing the control of data and processing parameters of the listening device and the reading of data from the listening device.

8. A test system according to claim 1 comprising a structural element for emulating an operational condition of the listening device, when the listening device is mounted in the test system at or on said structural element.

9. A test system according to claim 1 comprising a chamber for enclosing one or more of the listening device, the variable filter and the propagation elements.

10. A test system according to claim 1 comprising a variable delay unit, allowing a time delay of the acoustic feedback path to be varied.

11. Use of a test system according to claim 1 , wherein the listening device is a hearing instrument or a headset.

12. A test system according to claim 1 , further comprising:

the listening device to be tested.

13. The test system according to claim 12 , wherein

the listening device comprises a feedback estimation unit for estimating current feedback in the listening device.

14. The test system according to claim 13 , wherein

the listening device comprises a memory for storing estimates of current feedback values.

15. The test system according to claim 14 , wherein

the memory of the listening device form part of a data logger for logging various operational parameters, including the occurrence of acoustic feedback, of the listening device, over time.

16. A test system according to claim 1 , further comprising:

a test microphone for picking up a feedback signal from the second acoustic propagation element, the test microphone being located in the vicinity of the listening device when the listening device is mounted in the test system.

17. A test system for evaluating acoustic feedback characteristics of a listening device by changing the transfer function of the signal path from an acoustic output to an acoustic input of the listening device, the test system comprising:

a variable filter, including

an acoustic input,

an acoustic output,

a control unit for changing a transfer function of the filter; and

a first acoustic propagation element and/or a second acoustic propagation element for propagating acoustic sound, the first acoustic propagation element acoustically connecting the acoustic output of the listening device with the acoustic input of the variable filter, the second acoustic propagation element acoustically connecting the acoustic output of the variable filter with the acoustic input of the listening device; and

a test microphone for picking up a feedback signal from the second acoustic propagation element, the test microphone being located in the vicinity of the listening device when the listening device is mounted in the test system, wherein

the system is configured to allow a determination of acoustic feedback or a level of acoustic feedback of the listening device at different frequencies.

18. A test system for evaluating acoustic feedback characteristics of a listening device by changing the transfer function of the signal path from an acoustic output to an acoustic input of the listening device, the test system comprising:

a variable filter, including

an acoustic input,

an acoustic output,

a control unit for changing a transfer function of the filter, and

an enclosure comprising a cavity with a variable volume allowing an acoustic resonance frequency of the system to be varied; and

a first acoustic propagation element and/or a second acoustic propagation element for propagating acoustic sound, the first acoustic propagation element acoustically connecting the acoustic output of the listening device with the acoustic input of the variable filter, the second acoustic propagation element acoustically connecting the acoustic output of the variable filter with the acoustic input of the listening device, wherein

the system is configured to allow a determination of acoustic feedback or a level of acoustic feedback of the listening device at different frequencies, and

the system is adapted to provide that the listening device can be located in the cavity of the variable filter during test.

19. A test system according to claim 18 , further comprising:

a test microphone for picking up a feedback signal from the second acoustic propagation element, the test microphone being located in the vicinity of the listening device when the listening device is mounted in the test system.

20. A method of characterizing acoustic feedback at different frequencies from an acoustic output to an acoustic input of a listening device, the method comprising:

providing a variable filter for selecting a part of a frequency range of operation of the listening device, the variable filter including

an acoustic input,

an acoustic output,

a control unit for changing a transfer function of the filter,

an acoustic input transducer for converting an input sound to an electric input signal,

a variable electric filter for filtering the electric input signal and providing a filtered output signal, and

an acoustic output transducer for converting the filtered output signal to a filtered output sound;

acoustically connecting the acoustic output of the listening device to the acoustic input of the variable filter with a first acoustic propagation element;

acoustically connecting the acoustic output of the variable filter to the acoustic input of the listening device with a second acoustic propagation element; and

determining acoustic feedback or a level of acoustic feedback of the listening device in different parts of the frequency range.