Directivity of a source close to a wall
Considering a monopolar source (enclosure of small dimensions compating to the wavelength) placed close to a perfectly reflective infinite surface.
Effect of the wall can be seen as an existence of an image source producing a volume velocity identical to the actual one.
The pressure response of such a system is written in the far field and at low frequencies (kd << 1) as:
(avec
).
Directivity diagrams of such system are presented below for three values of kd.
The main effect of the wall is to double the pressure (which corresponds to redused solid radiation angle), but the finite distance between the sources also induces a slight directivity, which becomes important only for
.
