In addition to clauses 7.2.1 and 7.2.2 of EN ISO 3744:1995 a set of 12 microphones on the hemispherical measurement surface may be used. The location of 12 microphone positions distributed on the surface of a hemisphere of radius r are listed in the form of Cartesian coordinates in the following table. The radius r of the hemisphere shall be equal to or greater than twice the largest dimension of the reference parallelepiped. The reference parallelepiped is defined as the smallest possible rectangular parallelepiped just enclosing the equipment (without attachments) and terminating on the reflecting plane. The radius of the hemisphere shall be rounded to the nearest higher of the following values: 4, 10, 16 m.
The number (12) of microphones may be reduced to six, but the microphone positions 2, 4, 6, 8, 10 and 12 following the requirements of clause 7.4.2 of EN ISO 3744:1995 have to be used in any case.
Generally the arrangement with six microphone positions on a hemispherical measurement surface has to be used. If there are other specifications laid down in a noise test code in this Directive for a specific equipment, these specifications shall be used.
Coordinates of the 12 microphone positions
| Number of microphone | x/r | y/r | z |
|---|---|---|---|
| 1 | 1 | 0 | 1,5 m |
| 2 | 0,7 | 0,7 | 1,5 m |
| 3 | 0 | 1 | 1,5 m |
| 4 | - 0,7 | 0,7 | 1,5 m |
| 5 | - 1 | 0 | 1,5 m |
| 6 | - 0,7 | - 0,7 | 1,5 m |
| 7 | 0 | - 1 | 1,5 m |
| 8 | 0,7 | - 0,7 | 1,5 m |
| 9 | 0,65 | 0,27 | 0,71 r |
| 10 | - 0,27 | 0,65 | 0,71 r |
| 11 | - 0,65 | - 0,27 | 0,71 r |
| 12 | 0,27 | - 0,65 | 0,71 r |