Transfer function of open ear importance in assessment of hearing protection devices noise reduction

Introduction. Objective assessment of the noise redaction (NR) of individual hearing protection devices (HDP) in industrial conditions is actual problem despite numerous studies in this direction in many countries.

This study aimed to implement the F-MIRE method for measuring the NR of HDPs, considering the transfer function of the outer ear.

Materials and methods. HDP performance indicators measured by the real ear attenuation threshold (REAT) method in the free field, do not fully reflect the protective properties of HDP in specific production conditions and for a specific employee, according to many researchers.

The measurement method using two microphones, called Field-MIRE (F-MIRE), allows you to determine NR as the difference in sound pressure, external noise and noise inside the external auditory meatus (EAM). But since these microphones are located in different acoustic conditions, it becomes necessary use at least two blocks of correction coefficients to get real results. One block — considering the properties of the acoustic probe, the second — should consider the transfer function of open ear.

The measurements of the TFOE in 18 volunteers and the evaluation of the NR of the SOMZ-1 "Jaguar" earmuff in industrial conditions were carried out.

Results. This study has shown the effectiveness of the implementation of the F-MIRE method for an adequate assessment of the NR of earmuff in industrial conditions. The special headband uses for measuring the TFOE allows you to standardize the location of measuring microphones relative to the volunteer's head and reduce the uncertainty of measurements. Unlike the REAT method with binaural listening in a free field, the F-MIRE method allows you to determine the TFOE for each ear of an employee. Our research has shown that TFOE differences between the right and left ears one-man can be significant.

Conclusion. The NR determination by the difference of sound pressures measured by an external microphone and a MIRE microphone, without considering the acoustic properties of the outer ear underestimates both spectral and single-digit NR indicators.

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