1. Free-field sound source location

In a free field, i.e. in the absence of any reflection, each listener is able to locate the origin of a sound or noise with greater or lesser acuity, depending on whether the source is in front of, behind or above him or her. It is therefore necessary, first and foremost, to precisely define the coordinates giving the geometric location of the sound source.

To determine the position, real or apparent, of a source, we use a spherical coordinate system (r, q, j) defined as follows:

• r is the source-listener distance;

• q is the azimuth angle ;

• j is the site angle, also known as the elevation (figure 1 ).