Using Probe Microphone Systems to Verify Open Fittings

Question

Answer

The following procedure can be used, and only takes about 30 seconds. What you are essentially doing in this case is comparing the patient's individual ear canal resonance with and without the hearing aid in place.

Follow these steps:
Inspect the ear canal with your otoscope. Ensure it is clear, and take note of the geography in order to place the probe tube in the proper position.

1. Present 5 seconds of pink noise and measure the patient's ear canal resonance.
2. Place hearing instrument in the ear. Turn it OFF or on MUTE.
3. Present 5 seconds of pink noise, and measure the Occluded Response.
4. Compare the two curves to determine if and how the ear canal resonance has been affected by the placement of the hearing instrument dome or receiver in the ear canal (Figure 1).

Figure 1. Open fitting. Figure reprinted with permission from Hearing Review. Click Here for Larger View (PDF)

If the fitting is truly open, the two curves should overlay one another, indicating the responses are virtually the same. In this case, placement of the dome or the receiver in the ear canal does not create occlusion. If the fitting is partially occluded (Figure 2) or closed (Figure 3), the occluded response curve will fall below the initial (unaided) curve. The effect can range from slight to significant.



Figure 2. Partially occluded fitting. Figure reprinted with permission from Hearing Review. Click Here for Larger View (PDF)



Figure 3. Fully occluded or closed fitting. Figure reprinted with permission from Hearing Review. Click Here for Larger View (PDF)

If the fitting is partially occluded or fully occluded and your goal is an open fitting, try using a smaller dome or eartip, a more vented dome or eartip, or using a tube fitting (no dome) if the product allows.

All the measurements shown here were made using the Otometrics AURICAL Modular Fitting System. I hope this information is helpful to you! Thanks for your question.

For more information on verification of open fittings, please refer to the Hearing Review article Three Probe Microphone Measurement Techniques to Enhance Open Fittings that covers this topic in more detail.

Wendy Switalski, AuD, is president of Audiometric Consultants Inc, in Waterford, Michigan, an audiometric equipment distributorship serving Michigan and Northern Ohio. She is also the owner of Alliance Hearing Care, an audiology clinic in the metro-Detroit area, and a consultant for Otometrics, specializing in the development and implementation of fitting systems.

For more information about Otometrics, visit www.otometrics.com, or the GN Otometrics web channel on AudiologyOnline for more information