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On the Sound Field Requirements in the Hearing Protector Standard ISO 4869-1

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The sound field requirements in the ISO 4869-1 standard for hearing protector attenuation measurements comprise two parts: 1) a sound level difference requirement for positions around the head of the listener (ie at positions 15 cm from a reference point; up-down, front-back and left-right) and 2) a directivity requirement for the sound incidence at the reference point, measured with a directional microphone, to ensure an approximate diffuse sound field. The level difference requirement (1) is not difficult to fulfill but the directivity requirement (2) may lead to contradicting results if the measurement procedure in the standard is used with different types of microphones. In this paper the directivity requirement is discussed on a theoretical basis. The requirement is evaluated in relation to the widely used anechoic tetrahedron setup (four loudspeakers in the corners of a tetrahedron) and an anechoic square setup (four loudspeakers in the corners of a rectangle). It is shown that the formulation in the standard is misleading and that a better test method is needed for the diffuseness requirement.

Document Type: Research Article

Publication date: November 1, 1999

More about this publication?
  • Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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