Abstract
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 fulfil 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.
Original language | English |
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Journal | Acustica |
Volume | 85 |
Pages (from-to) | 825-831 |
ISSN | 0001-7884 |
Publication status | Published - 1999 |