Ear Seal Integrity Test

HearingTech

Correct functioning of custom made hearing protectors is dependent upon the acoustical sealing of the ear mould in the ear. 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 & 15), the measured attenuation has the intermediate value (12,5 dB). 

Seal Integrity Meter
   
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. 		Occlusion Effect
   
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).  

 		Probe Tube
   
“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.  

"EE"-tone Generator

 

Measurement procedure

1.       Explain to the person being tested the purpose and the procedure.

2.       Take the hearing protectors and carefully remove the filters with the filter lifter.

3.       Select the appropriate probe tube, provided with the transparent adapter corresponding to the filter geometry.  Insert the adapter carefully and completely into the filter compartment of the ear mould. Allow the person being tested to insert the ear moulds and check the fitting of both the ear mould and the adapter – re-adjust when needed. It is not a problem to press against the adapter or tubing.

4.       Place the transducer ear hook over the pinna so, that the microphone is facing away from the ear.

5.       Insert firmly with a little rotation the red adapter of the probe tube, into the transducer housing until a ‘snap’ is felt.

6.       Switch on the meter by pressing the button with the “Seal Integrity” text. Instruct the test subject not to make any vocal sound.

7.       Position the “EE”-tone Generator at approximately 30cm distance from the ear mould being tested and activate by pressing the green button. Take care not to cover the speaker outlet at the housing backside with your fingers.

8.       While generating the “EE”-tone test sound, read off the ear mould attenuation value from the SI-meter display. When the reading shows lower than expected, the fitting of the probe tube adapters and ear mould should be checked. Readjust the mould by applying a little force while moving the pinna a little up and down. Measure again.

9.       The quality of the ear mould is ok when an attenuation of 17.5 dB or higher is measured.
If less is measured, the attenuation of the mould can be considered as too low and improvement of the ear mould should be investigated.

10.   Repeat the procedure for the other ear mould. When needed, re-activated the SI-meter by pressing the Seal Integrity button - the meter switches off automatically after 3 minutes or after re-pressing the same button again.

Important

The attenuation measured with the SI-meter is average:  5 dB below the result from the method as used with the Type Approval (Real Ear Attenuation at Threshold) and from which the specifications of the used filter are calculated.

This difference is caused by the difference in measurement method (SI: monaural and objective versus REAT: binaural and subjective), where the main part is caused by the masking effect due to the physiological noise from the test subject.

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