Insight into the sound field during a Direct Field Acoustic Test (DFAT)

Over the past 2 decades acoustic testing for the space industry has evolved from the ubiquitous reverberant chambers to using loudspeakers in what has been defined as Direct Field Acoustic Testing (DFAT). The initial need was to create a versatile system to provide a portable test facility to qualify space hardware on site as opposed to go to a dedicated test facility. Since that initial test carried out by MSI in the late '90s equipment and control strategies have improved and today it is possible to recreate an acoustic field which is very similar to that of a reverberant chamber. Using Multi-Input-Multi-Output (MIMO) control strategy has solved many of the initial issues. And it allows for control of the field's diffusivity. However, unlike a test in a reverberant chambers, the acoustic fields produced in a DFA test is dependent on the parameters used by the controller, its specific technology, and the whole sound generation system. This paper attempts to provide a qualitative overview and insight in the acoustic field generated by a set of loudspeakers set around a test item. Particular focus is placed on the diffusivity of the field as this is a characteristic that is linked to the structural response of the device under test.