The purpose of this study was to facilitate the comparison of typical industrial and military impulse noise to that reproducible in a laboratory by means of categorization of the different types of impulse noise. This categorization enables us to define laboratory impulse noise sources which can then be used to study the non-linear attenuation characteristics of hearing protectors in a laboratory environment. A literature survey on the characteristics of impulse noise has shown that they can be grouped within four categories. These categories are briefly described below. Type 1 sources are long B-duration impulses which have most of their acoustic energy distributed in lower frequency ranges (i.e. below 2 kHz). Type 2 sources have short B-durations with most of the acoustic energy distributed in the higher frequency ranges (i.e. above 2 kHz). Type 3 sources are Friedlander type waves with long A-durations between 2 and 6 ms, with the majority of the acoustic energy concentrated in the lower frequencies. Type 4 sources are Friedlander type waves with short A-durations between 0.2 and 2 ms, with the majority of the acoustic energy in the high frequency part of the spectrum. Type 1 and 2 sources are commonly found in industry whereas type 3 and 4 sources are most commonly encountered in a military, mining and quarry environments. A literature survey on methods of producing impulse noise in laboratory environments has been carried out to model impulse noises found in the workplace to facilitate the measurement of hearing protector attenuation against impulse noise. Methods of modelling three of the four types of impulse noise have been found, however methods of modelling type 4 impulses which are produced by large calibre weapons have not been found. The peak levels and the extent of the low frequency energy produced by such weapon is extremely difficult to produce on a laboratory environment. However some success using a membrane device for medium calibre weapons is reported. For testing lower level impulses, loudspeaker systems can be utilized.
On the performance of hearing protectors in impulse noise
Applied Acoustics ; 54 , 2 ; 165-181
1998
17 Seiten, 5 Bilder, 2 Tabellen, 39 Quellen
Aufsatz (Zeitschrift)
Englisch