The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part I: Review of previous work and the design of an improved test fixture

This paper gives a comprehensive progress report on the development of objective methods for measuring the attenuation of hearing protection devices (HPD’s), and focuses on the use of acoustic test fixtures (ATF’s), i.e., artificial heads. While there are many publications on ATF’s for the evaluation of circumaural HPD’s (earmuffs), only one serious attempt to construct an ATF for the evaluation of intra-aural HPD’s (earplugs) could be found. Consequently, no ATF for testing earplugs has been standardized so far, while two standardized ATF’s currently exist for testing earmuffs [see ANSI S3.19-1974 (1975) and ISO/DIS 6290 (1983)]. Both ATF’s are suited, however, only for production testing and are not designed for HPD-type testing. It is believed that both ATF’s do not provide sufficiently high accuracy for HPD-type testing. A new ATF with appropriate circumaural and intra-aural flesh simulations was constructed, including a suitable ear simulator and a cast of an average pinna. Objectives for design and construction of the new ATF are discussed. The effect of using artificial flesh on the insertion loss of earmuffs (max. 5 dB at 125 and/or 250 Hz) and the effect of using a pinna (max. 12 dB lower insertion loss at 2 kHz) were evaluated.