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 Affinity2.0/Equinox2.0 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 Affinity2.0/Equinox2.0 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 measurementoverlaps 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. [online] Audiology Online. Available at: http://www.audiologyonline.com/articles/practical-guide-to-cros-bicros-977 [Accessed 24 Mar. 2017].

Pumford, J. (2005). Benefits of probe-mic measures with CROS/BiCROS fittings. The Hearing Journal, [online]58(10), p.34. Available at: http://www.blog-audioprothesiste.fr/wp-content/uploads/2013/02/Pumford-2005-Benefits-of-probe-mic-measures-with-CROS-BiCROS-fittings.pdf [Accessed 24 Mar. 2017].