Direct field acoustic testing system, controls, and method

1. A method of direct field acoustic testing of a unit under test comprising the steps of:

positioning at least four acoustic transducer groups and at least one control microphone around the unit under test;

applying a setup signal to each of the acoustical transducers;

separately monitoring the acoustic output of each of the acoustical transducer groups using the at least one control microphone to create a matrix of transfer functions representing an output signal of each control microphone with respect to each acoustical transducer group;

computing corrected drive signals corresponding to the acoustical transducer groups by comparing the matrix of transfer functions to a reference spectrum, wherein the reference spectrum is expressed as a matrix containing only reference power spectral density functions for each control input corresponding to the acoustic field at the location of each control microphone such that reference cross spectral density functions for each combination of control inputs are set to zero; and

applying each corrected drive signal to the respective acoustical transducer group.

2. The method of claim 1 wherein the reference spectrum is expressed as a fixed band-width narrow band spectral density.

3. The method of claim 2 , wherein the band-width of the fixed band-width narrow band spectral density is less than or equal to 12.5 Hz.

4. The method of claim 1 , further comprising the steps of:

after applying the corrected drive signals to the acoustical transducer groups, monitoring the acoustic output of the acoustical transducer groups using the at least one control microphone;

comparing an updated output of the at least one control microphone in response to the corrected drive signals with respect to all of the acoustical transducer groups to the reference spectrum to create an updated matrix of error functions;

computing an updated corrected drive signal for each acoustical transducer group; and

applying each updated corrected drive signal to the respective acoustical transducer group.

5. The method of claim 4 wherein the drive signals are updated in real time.

6. The method of claim 4 wherein the reference power spectral density functions for all of the control inputs are the same.

7. A method of direct field acoustic testing of a unit under test comprising the steps of:

positioning at least four acoustic transducer groups and a plurality of control microphones around the unit under test;

applying a setup signal to each of the acoustical transducers;

separately monitoring the acoustic output of each of the acoustical transducer groups using the control microphones to create a matrix of transfer functions representing an output signal of each control microphone with respect to each acoustical transducer group;

computing corrected drive signals corresponding to the acoustical transducer groups by comparing the matrix of transfer functions to a reference spectrum;

applying each corrected drive signal to the respective acoustical transducer group;

after applying the corrected drive signals to the acoustical transducer groups, monitoring the acoustic output of each of the acoustical transducer groups using the control microphones;

comparing only a magnitude response of an updated output of each control microphone in response to the corrected drive signals with respect to all of the acoustical transducer groups to the reference spectrum to create an updated matrix of error functions, wherein the control of phase and coherence relationships between acoustical fields at the control microphone locations is suppressed;

computing an updated corrected drive signal for each acoustical transducer group; and

applying each updated corrected drive signal to the respective acoustical transducer group.

8. The method of claim 7 wherein the reference spectrum is expressed as a fixed band-width narrow band spectral density.

9. The method of claim 8 , wherein the band-width of the fixed band-width narrow band spectral density is less than or equal to 12.5 Hz.

10. The method of claim 7 , wherein the drive signals are updated in real time.

11. A method of direct field acoustic testing of a unit under test comprising the steps of:

positioning at least four separately controllable acoustic transducer groups and at least four control microphones around the unit under test, wherein the number of separately controllable acoustic transducer groups and the number of separate control inputs from the control microphones is equal;

applying a setup signal to each of the acoustical transducers;

separately monitoring the acoustic output of each of the acoustical transducer groups using the control microphones to create a square matrix of transfer functions representing an output signal of each control microphone with respect to each acoustical transducer group;

computing corrected drive signals corresponding to the acoustical transducer groups by comparing the matrix of transfer functions to a reference spectrum; and

applying each corrected drive signal to the respective acoustical transducer group.

12. The method of claim 11 wherein the reference spectrum is expressed as a fixed band-width narrow band spectral density.

13. The method of claim 12 , wherein the band-width of the fixed band-width narrow band spectral density is less than or equal to 12.5 Hz.

14. The method of claim 11 , further comprising the steps of:

after applying the corrected drive signals to the acoustical transducer groups, monitoring the acoustic output of the acoustical transducer groups using the control microphones;

comparing an updated output of each control microphone in response to the corrected drive signals with respect to all of the acoustical transducer groups to the reference spectrum to create an updated matrix of error functions;

computing an updated corrected drive signal for each acoustical transducer group; and

applying each updated corrected drive signal to the respective acoustical transducer group.

15. The method of claim 14 , wherein the drive signals are updated in real time.

16. A method of direct field acoustic testing of a unit under test comprising the steps of:

positioning at least four acoustic transducer groups and a plurality of control microphones around the unit under test;

applying a setup signal to each of the acoustical transducers;

separately monitoring the acoustic output of all of the acoustical transducer groups using the plurality of control microphones to create a vector of transfer functions equal to the number of control microphones;

computing a corrected drive signal by comparing the matrix of transfer functions to a reference spectrum;

splitting the corrected drive signal into separate drive signals corresponding to the number of acoustic transducer groups;

independently randomizing the spectrum of each separate drive signal;

applying the independently randomized separate drive signal to the corresponding acoustical transducer group.

17. The method of claim 16 wherein the reference spectrum is expressed as a fixed band-width narrow band spectral density.

18. The method of claim 17 , wherein the band-width of the fixed band-width narrow band spectral density is less than or equal to 12.5 Hz.

19. The method of claim 16 , further comprising the steps of:

after applying the independently randomized separate drive signals to the acoustical transducer groups, monitoring the acoustic output of each of the acoustical transducer groups using the at least one control microphone;

comparing an updated output of the at least one control microphone with respect to all of the acoustical transducer groups to the reference spectrum to create an updated average error function;

computing an updated corrected drive signal for each acoustical transducer group; and

applying each updated corrected drive signal to the respective acoustical transducer group.

20. The method of claim 19 , wherein the drive signals are updated in real time.