The attenuation of the ear mould must always be higher than the filter attenuation in order for the applied filter to determine the required attenuation.
One method used to test the ear mould seal, is the so called "air leakage" measurement. However, this method of measurement is not considered to be satisfactory. Leakage of the applied air pressure means certainly that the fitting of the ear mould is not correct.
But 'no leakage' does not indicate anything about the real attenuation of the ear mould, which is the figure that has to be determined.
To perform proper acoustical measurements a Seal Integrity Test has to be performed. The test equipment for carrying out the measurement is packed in a special carrying case containing:
- a Seal Integrity Meter;
- a "EE"-tone Generator;
- a set of Probe Tubes and
- a filter lifter.
Seal Integrity Meter
The Seal Integrity Meter contains two specially designed sound level meters, which measure sound only within the frequency range between 200 and 400 Hz. The sound is measured by two, acoustically separated microphones which are housed inside the transducer (1). One microphone (2) measures the ambient sound level while the other microphone (3) simultaneously measures the sound level inside the ear canal - behind the ear mould, via the probe tube (4) and the ear mould (5). A digital signal processor calculates the difference in the measured sound levels and presents the result (the attenuation) on the Seal Integrity Meter display. A light indicating the value closest to the value measured will illuminate. When two lights are lit simultaneously (e.g. 10 and 15), the measured attenuation has the intermediate value (12,5 dB).
Occlusion Effect
With the Seal Integrity Meter the occlusion effect can also be measured. The occlusion effect is the measure wherein a person's own voice is heard when the ear is occluded. To perform this measurement, the 'occlusion effect' button has to be activated and the person being tested has to generate the test sound by his own voice. This measurement is mainly of interest for the adjustment of hearing aid ear moulds.
Probe Tube
The Probe Tube is to connect the transducer acoustically to the ear mould. At one end the Probe Tube is provided with a red adapter (6), for connection to the transducer microphone and at the other end with a transparent adapter for the ELACIN Compact filter (7) or the ER filter (8).
"EE"-tone Generator
For the measurement of the Seal Integrity a test sound ("EE"-tone) has to be generated. For this purpose the "EE"-tone Generator is designed. By pressing the green button (9) the desired test sound is generated at the backside of the generator housing (10). As long as the test sound of the Generator dominates, ambient noise will not affect the measurement.
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