Hearing aids fitting True-ear coupling difference test

Hearing aids fitting True-ear coupling difference test
It is generally recommended to test this data when hearing aids are selected for children younger than 5 years of age, or when the volume of the external auditory canal has changed significantly. Because some optional formulas do not take into account the natural amplification characteristics of the ear canal, the data needs to be corrected. At the same time, if the child is not very cooperative in the optional, we can directly adjust the hearing aid in the 2CC coupling cavity after obtaining the true ear coupling difference data. Reach the matching goal. The following uses the Aurical device as an example to explain the steps on the true ear coupling difference test.
①Before testing, the hearing aid test microphone and the real ear reference microphone must first be calibrated. Because the hearing aid test microphone in Aurical is used to test the coupling part, and the real ear reference microphone is used to test the real ear part. Without calibration, the measurement of the true ear coupling difference will be wrong.

② Enter the real ear test mode, select the item for calibrating the hearing aid test microphone in the settings, and place the hearing aid test microphone and the real ear reference microphone together, facing the speakers in the test box. The speaker is in a half-off state as shown in Figure 7-2. Select the start test item to perform the command operation to complete the calibration. Then calibrate the real-ear reference microphone and the real-ear test microphone as usual. Also close to the two microphones, about 30cm away from the speaker. Select the probe calibration item to perform and complete the calibration.
Figure 7-2 Hearing aid test microphone and speaker position during real ear test
③ If necessary, you can modify the HA-2 coupling cavity, and drill an Imm hole in its body (see Figure 7-3), so that the probe tube of the real ear test microphone can enter the cavity of the coupling cavity and probe the tube at the same time. Enter as little as possible, and seal leaky connections with items such as plasticine. This method is not commonly used in practice.
Figure 7-3 Modified HA-2 coupling cavity
④ Select the test mode and the coupling test mode in the settings, both select the cymbal, select the true ear coupling difference test in the mode, and then you can test.
⑤ The response obtained in the second step is to test the response of the microphone to the snoring sound. The previous test simulates the real ear coupling test. This test simulates the real ear test. The difference between the two is theoretically the true ear coupling difference test. Very accurately, the value of the true ear coupling difference is zero, and the interface shows a flat line.
⑥ Save the conclusion and enter the real test.
⑦ Put the probe tube in the proper position in the ear canal, wear ear molds or plug-in ear plugs, connect the sound generating end of the external earphone to the end of the sound tube of the ear mold or plug-in ear plugs, and select the true ear coupling difference test Mode test, you can measure the real ear test microphone response.
After connecting the sound generating end of the external earphone to the 2CC coupling cavity inlet tube for testing, the microphone in the test box can test the response in the 2CC coupling.
Comparison the above two test results. The difference between them is the true ear coupling test difference.
⑩The above method is to use the microphone in the test box to test the response in the 2CC coupling, and use the test microphone to test the response in the real ear. A test microphone can also be used to test the response in the 2CC coupling cavity and the real ear, which means that a microphone can be used for testing, so the requirements for calibration will be reduced. However, the insertion gain mode needs to be selected in the test, because the device treats the test in the real ear as the real ear unhearing gain, and the test in the coupling cavity as the real ear hearing gain. The real ear coupling difference is inserted in the real ear. The form of gain.

5. The relationship between real-ear hearing gain, real-ear intervention gain, coupling gain, and ear simulator gain
Some articles list the difference between the real ear hearing gain and the coupling gain or ear simulator gain when introducing the formula.
Generally speaking, for complete ear canal, ear canal, and in-ear hearing aids, for a certain signal strength, the value of real-ear hearing aid is greater than the coupling gain or ear simulator gain (see 6.1.2 for ear molds). Because in the test case, the diffraction generated by the sound wave after reaching the surface of the head is eliminated by the reference microphone. The reference microphone is connected to the feedback loop. The purpose is to make the intensity of the speaker’s sound reaching the external ear canal mouth consistent with the target intensity. In the test case, the diffraction effect produced by the hearing aid microphone is greater than the diffraction effect on the surface of the head. The more empty the ear cavity, the greater the local effect of the microphone, especially for high-frequency sounds. In addition, measured in the real ear
The residual ear canal volume was smaller than that in the coupler. This is the main reason for the difference from a true-ear coupler. Other influencing factors such as air vents, because this is the case in the coupling test, and this is the case in the real ear. Comprehensively speaking, we can see that the true ear gain is greater than the coupling gain.
The difference between the real-ear hearing aid gain and the real-ear intervention gain value is related to the real-ear non-hearing gain. The real-ear intervention gain can be calculated from the ear-hearing gain and the coupling gain or the ear simulator gain relationship.
6. Hearing Aid Threshold Test and Functional Gain
In the sound field, the difference between the threshold values ​​for hearing aids and non-hearing conditions is called functional gain. Except in certain circumstances, functional gain is the same as intervention gain, but both have their advantages. The intervention gain is more accurate, the test time is less, and the frequency of reflection is more comprehensive. Compared with functional gain, interventional gain is mostly used clinically. However, the hearing aid threshold has no feedback vibration during the test and can reflect the minimum signal strength heard at each frequency. This test is particularly valuable for patients with severe hearing loss in the clinic. Because sometimes the output gain of the OSPL90 has a limit on it, despite the large insertion gain, there is actually nothing.
effect. In addition, for children who cannot cooperate with real ear analysis, the hearing aid threshold can be determined by playing audiometry in a free sound field.
Of course, in the process of testing a complete in-canal hearing aid, headphones can also be selected as the test sound source.