Verifying Ear Level FM Systems

The purpose of this quick guide is to describe how to do real-ear verification of Ear Level FM systems with the Interacoustics Affinity Hearing Aid Analyzer, using FM-specific targets. The verification method is based on the AAA Clinical Practice Guidelines for Remote Microphone Hearing Assistance Technologies for Children and Youth Birth to 21 Years. For more information, please refer to the AAA Guidelines.

What are Ear Level FM systems?

Ear Level FM systems are intended to be used by patients who have normal or near-normal hearing and help increase the signal to noise ratio. They can be used, for example, in classroom settings for a child having learning difficulties or auditory processing disorders (APD). Typical use will include an ear-level FM receiver, coupled to a thin tube, in an open ear configuration. The steps below guide clinicians on how to perform straightforward realear verification of the ear level FM system, in order to verify the maximum output and the recommended volume setting for the FM receiver.

Verification steps

1. Prepare the patient for normal real ear:
   • Position patient in front of the Affinity loudspeaker
   • Place the probe tube in the ear
   • Position the ear level FM receiver on the ear
     
2. From Noah or from the Affinity Suite AUD screen, enter the audiogram. The audiogram will be within the range of normal/near normal.
3. Click on the REM tab.
   
4. Once in the REM screen, select the "Ear Level, FM only" protocol from the drop down list.
   
5. Place the FM transmitter microphone inside the test chamber, facing the reference microphone
   
   NOTE: The test box reference microphone is the active microphone
   
   
6. Close the lid of the test chamber.
7. Measure the MPO:
   • Click on MPO to access the MPO test
   • Set the FM transmitter volume control to MAX
   • Click Start to measure the Real-Ear Saturation Response
   • If the MPO measurement is too high, adjust the FM output
     
8. Measure the REAR and match target between 1kHz and 4kHz.
   • Select the appropriate FM-specific target:
     • FM Boom or
     • FM Chest
     • the choice should reflect what is used with the FM system being tested
   • Measure the REAR by clicking the Start button
   • Adjust volume control on the FM receiver to match the targets between 1kHz and 4kHz
     
9. Re-measure the RESR/MPO at user setting

References

American Academy of Audiology (April 2011). Clinical Practice Guidelines: Remote Microphone Hearing Assistance Technologies for Children and Youth Birth to 21 Years (includes supplement A).

Angelo, Kamilla & Fuglholt, Merethe L. (2013). Amigo Star. A New Ear-Level FM-Only Receiver. Pediatric Knowlegdge Brief.

Eiten, Leisha R. FM for Children, Chapter 7. Assessing Open Ear Edulink Fittings.

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