Experimental study of acoustical test fixture for sound attenuation of in-ear hearing protectors

The three present methods of sound attenuation measurement for hearing protectors are: real-ear attenuation at threshold, microphone in real ear and acoustical test fixture (ATF). The international organization for standardization has developed a standard of ATF for sound attenuation of over-the-ear hearing protectors. However, there is no harmonized standard of ATF for in-ear hearing protectors. In this paper, the acoustical test fixture for sound attenuation of in-ear hearing protectors is studied. The sound attenuation performance of several major types of in-ear hearing protectors has been tested with different test equipment and a variety of test signals. Through the analysis and comparison of test results, the following conclusions can be reached: (1) The error caused by wearing operation is mainly related to the material and structure of the test article, and the error can be reduced by calcutating the average after eliminating the idiosyncratic data for several times; (2) There are significant differences between the test results with different test equipment, therefore, the test equipment should be determined according to the test requirements and clearly indicated; (3) The sound attenuation of memory-foam hearing protectors increases with the sound pressure level of the test signal. The results can be referred for the standardization research of ATF for sound attenuation of in-ear hearing protectors.