Standardized acoustic test fixtures for testing ear protection devices and noise cancelling headsets
Regular paper
G.R.A.S. Sound & Vibration A/S
Wednesday 3 june, 2015, 11:40 - 12:00
0.4 Brussels (189)
Abstract:
This paper is a study supported by practical tests on different methods and
standards for measuring ear protection and the differences between these
methods. Several acoustic test fixtures can be used for measuring the
Insertion Loss of Hearing Protectors Devices (HPD) and Active Noise
Cancelation (ANC) Devices. First, it is very important to have an Acoustic
Test Fixture (ATF) with a very high self-insertion loss to insure that the
measured insertion loss on the Device Under Test (DUT) is not influenced by
false signals introduced in the ATF itself. Secondly, it is important to
decide whether a more humanlike shape with a corresponding Head Related
Transfer Function is needed, or a more simplified ATF can be used. In the
first case, the ANSI standard s12.42 describes a proper method, while ISO
4869-3 describes the second method. The ANSI s12.42 ATF is designed with a
special ear canal extension, which is longer than the standard extension,
known from other ATFs like KEMAR, and is fitted with fleshlike material to
better adapt In the Ear (ITE) devices. Thirdly, a large circum-aural pinna is
included to ensure a perfect seal for all kinds of Over The Ear hearing
protection devices. Furthermore, the total system consisting of ear simulator,
ear canal extension and pinna are heated to body temperature. The ISO 4869-3
defines a more simple solution for circum-aural HPD’s, but can as well as the
ANSI standardized ATF bee combined with pinnas, ear canal extensions and ear
simulators for testing ITE devices. The two types of ATF are especially good
when testing the new high quality ANC hearing protectors and headsets, which
is why this presentation also looks at the challenges when measuring on ANC
devices.