SELF-INSERTION LOSS LIMITS OF ACOUSTICAL TEST FIXTURES FOR HEARING PROTECTOR MEASUREMENTS

摘要

When measuring the insertion loss of a hearing protection device (HPD) with an acoustical test fixture (ATF), the measured insertion loss can be limited by the self-insertion loss (SIL) of the ATF. The SIL is impacted by any pathways that allow acoustic energy to reach the ATF ear simulator microphones via a route other than through the HPD being measured. Standards that specify the use of an ATF for HPD measurements (such as ANSI/ASA S12.42 or ISO 4869-3) include minimum requirements for the SIL of the ATF, as one component in ensuring the validity of insertion loss measurements made on HPD samples. Traditionally, SIL has been measured with any artificial flesh simulations removed from the ATF and with the ear simulator microphones blocked by metal plugs or isolation caps. Such measurements may not be representative of the SIL obtainable when the ATF is configured for HPD measurements. We propose a method for measuring the ATF SIL with all flesh simulations in place and as configured for HPD measurements and present data measured on several commercially available ATFs. We also propose insertion loss limits to be met by ATFs when measured with this method, in the hopes that such limits will be useful to future revisions to HPD measurement standards using ATFs.