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CROS and BiCROS fitting

This Quick Guide is intended to give a brief explanation on how to fit CROS and BiCROS type hearing aids. The instructions in this guide have been adapted from the methods stated by Hayes (2006) and Pumford (2005), links to these articles are provided at the bottom of this document.

The following points of instruction apply to the whole of this document and will aid understanding as to what is being measured in the different conditions:

  • The probe microphone is always placed in the aidable or normal hearing ear, never in the unaidable ear.
  • The patient will move position so that the loudspeaker is within the range of -900 through 00 to +900 relative to the front of the client at different stages in the procedure. Images have been used below to aid your understanding of this.
  • The reference microphone is always located on the same side of the head as the loudspeaker.

CROS Hearing Aids

The objective of this measurement is to make signals from the unaidable side of the head sound the same as signals from the side of the better or normal hearing ear.

Dedicated protocols have been created for optimum application of this test, please speak to your local distributor to get and import these for use.

  1. Calibrate and insert both probe microphones.

  2. Measurement One: Measure the REUR/REUG of the best ear with the patient at 450 or 900 to the speaker.
    Note: The CROS system is not added to the ear at this point.

    Run the ‘Better Ear REUR/REUG’ Measurement. This should lead to a curve similar to below.

    Note: Make sure that if you run your first condition at 450 then the second condition should be at -450. This is also required for measurements run at 900. If this isn’t done then the measurement curves are not comparable.

  3. Measurement Two: Move the patient so that the loudspeaker and reference microphone are to the side of the unaidable ear (-450 or -900 relative to the poorer ear). Add the CROS system to your patients ear and turn it on. You must also enable the CROS setting in your Affinity/Equinox or Callisto Suite (shown in the image below).

    Note
    : You do not need to swap earside in order to perform this measurement, all measurements are performed to the same earside from the first measurement.
    Run the ‘CROS Response’ measurement.

    The CROS Setting is available in the following location of your Suite.

    This measurement should lead to a curve similar to the below.
  4. You now need to adjust your CROS system until the REAR/REIG from the second measurement overlaps the REUR/REUG from the first measurement. Imagine the first measurement to be your target in this scenario.

    Note:
    Probe microphone measurements cannot be applied to transcranial/bone-anchored CROS fittings.

BiCROS Hearing Aids

The objective of this test is similar to what has been shown above, however there is a hearing aid on the better ear for which we need to take consideration for.
The same dedicated protocol as used in the CROS instructions above is used for optimum application of this test, please speak to your local distributor to get and import these for use.

  1. Ensure you have already Fitted the hearing aid without the CROS features enabled to a suitable algorithm based on the patients scenario (i.e. NAL-NL1, NAL-NL2 or DSL).

  2. Calibrate and insert both probe microphones.

  3. Measurement One: Measure the REUR/REUG of the best ear with the patient at 450 or 900 to the speaker. Remember to ensure the hearing aid is inserted and enabled in this scenario.

    Run the ‘Better Ear REUR/REUG’ Measurement. This should lead to a curve similar to below.

    Note: Make sure that if you run your first condition at 450 then the second condition should also be at 450. This is also required for measurements run at 900. If this isn’t done then the measurement curves are not comparable.

  4. Measurement Two: Move the patient so that the loudspeaker and reference microphone are to the side of the unaidable ear (-450 or -900 relative to the poorer ear). Enable the CROS system and the CROS setting in your Affinity/Equinox or Callisto Suite.

    Note: You do not need to swap earside in order to perform this measurement, all measurements are performed to the same earside from the first measurement.
    Run the ‘CROS Response’ Measurement.

    The CROS Setting is available in the following location of your Suite.

    This measurement should lead to a curve similar to the below.
  5. You now need to adjust your CROS system until the REAR/REIG from the second measurement overlaps the REUR/REUG from the first measurement. Imagine the first measurement to be your target in this scenario.

    Note: Probe microphone measurements cannot be applied to transcranial/bone-anchored CROS fittings.

Further Reading
For more information on this topic then please see the following articles:

Hayes, D. (2006). A Practical Guide to CROS/BiCROS Fittings.
Pumford, J. (2005). Benefits of probe-mic measures with CROS/BiCROS fittings. 

May 2017
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