Evaluation of the Acoustic Test Field Generated by Two Direct Field Acoustic Test Methodologies Compared to a Reverberant Chamber

Demonstration tests were conducted with two different direct field acoustic test methodologies in current practice as well as with a reverberant chamber. The same acoustic specification and small-scale test article were used for all three test approaches, and the same high bay test space was used for both direct field test methodologies. The direct field acoustic tests were conducted by their respective vendors, each providing their own sound production and control equipment and using their current preferred practice for control methodology. Acoustic field measurements were made by the Jet Propulsion Laboratory using a microphone array arranged in a 5 x 5 grid with 8-inch spacing placed in various locations and orientations around the acoustic field. For each test approach, the generated acoustic field was evaluated using metrics including comparison to specified test levels, spatial variability and coherence. Test article acceleration responses were also measured for comparison. This paper provides a summary description of the tests, salient results from each of the tests with respect to the various evaluation metrics, with a particular emphasis on comparison of the direct field test approaches to the reverberant chamber test as a baseline approach.