Advancements and Current Status of Direct Field Acoustic (DFA) Testing Since Inception

For several decades, large reverberant field acoustic (RFA) testing - and more recently, direct field acoustic (DFA) testing - have been employed in the aerospace industry to qualify spacecraft, payloads, and larger, low-surface-density structures such as solar arrays and reflectors. These tests are used to assess design integrity and detect potential faults in design and fabrication. In general, the sound pressure levels in RFA testing are well understood; most chambers generate a diffuse field above the Schrödinger cut-off frequencies, although standing waves pose challenges by causing excessive structural excitations due to coupling. In contrast, DFA testing initially faced challenges related to non-homogeneity, standing waves, and other field inconsistencies. Over the past several years, significant progress has been made in control systems and speaker technology to mitigate some of these issues. This paper reviews the development of DFA testing since its inception (QuickSat), highlighting technical issues addressed and remaining challenges. Topics discussed include standing waves, field diffusivity, sound pressure levels (SPLs) measured by control and response microphone, placement of control microphones, and structural interactions that may alter the sound field.