Test system for evaluating feedback performance of a listening device

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.

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.

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.