Recent developments in high-level acoustics testing apply to Direct Field Acoustic Testing (DFAT) and traditional Reverberant Chamber Acoustic Testing (RCAT). Both testing methodologies benefit from the introduction of narrowband and Multiple Input/Multiple Output (MIMO) adaptive digital control. Paper discusses advantages of using modern MIMO control technology in DFAT and RCAT. MIMO DFAT control uses multiple independent drive signals to control the acoustic field's response Nth fractional octave spectra. Multiple drives are sent to multiple acoustic exciters or loudspeaker stack subsystems via their respective amplifiers and associated signal conditioning. Multiple control microphones are placed at points within the resulting acoustic field. Control is performed in the frequency domain by determining the control-response Spectral Density Matrix (SDM) from the vector of microphone responses using FFT processing. Iterations of this adaptive optimal control process update the vector of drive signals to cause the respective microphone's PSD, sound pressure level (SPL) spectra, and the relative coherence and phase between them, to match the corresponding elements of the test specified control-reference SDM. The control-reference SDM represents the desired acoustic field with their specified PSD magnitudes for each microphone location as well as the relative phase and coherence between each pair of control microphone responses. Effectively, adaptive optimal method controls the acoustic-field response levels at each control microphone location, as well as the relative coherence and phase between each pair of microphones, to meet its individual requirement based on the acoustic-excitation it receives from all the speakers or acoustic modulators as a result of the vector of independent drive signals, as their drive SDM is updated. Control updates to the drive SDM account for the initial control errors and unavoidable nonlinearities. Result can be a nearly incoherent acoustic field at the higher frequencies, with minimum variation between control microphones.
