DIRECT FIELD ACOUSTIC TESTING IN A SEMI-REVERBERANT ENCLOSURE

• US 20150253292A1
• Filed: 10/15/2013
• Published: 09/10/2015
• Est. Priority Date: 10/15/2012
• Status: Active Grant

• Current Assignee: MSI Dfat LLC
• Original Assignee: MSI Dfat LLC
• Inventors: Larkin, Paul, Polk, Matthew, Hayes, Dann
• Granted Patent: US 10,317,373 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01M 7/00 Vibration-testing of structures; Shock-testing of structures G01M9/00 takes precedence
• CPC Class Codes: G01N 2291/023 Solids
• CPC Class Codes: G01N 2291/0289 Internal structure, e.g. defects, grain size, texture
• CPC Class Codes: G01N 2291/105 two or more emitters, two or more receivers
• CPC Class Codes: G01N 2291/2698 Other discrete objects, e.g. bricks
• CPC Class Codes: G01N 29/04 Analysing solids using acoustic emission techniques G01N29/14
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/223 Supports, positioning or alignment in fixed situation mounting transducers per se G10K11/004
• CPC Class Codes: G01N 29/226 Handheld or portable devices
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04R 5/02 Spatial or constructional arrangements of loudspeakers

Abstract

An acoustic testing system includes at least four control microphones, at least four acoustic transducers, an acoustic enclosure with pre-determined reverberant characteristics which contains the at least four control microphones and the at least four acoustic transducers, a control system configured to produce a predetermined acoustic field as measured by the at least one control microphone. A unit under test is also disposed within the acoustic enclosure. Using an acoustic enclosure with pre-determined reverberant characteristics results of the increased proportion of reflected sounds in the area proximate to the unit under test such that less power is required to achieve a given acoustic test level than in a purely direct field acoustic test.

Claims

1. An acoustic testing system comprising:

at least four control microphones;

at least four acoustic transducers or groups of transducers;

an acoustic enclosure with pre-determined reverberant characteristics which contains said at least four control microphones and said at least four acoustic transducers or groups of transducers; and

a control system configured to produce a predetermined acoustic field as measured by said at least four control microphones,

wherein the at least four acoustic transducers or groups of transducers are operatively coupled to the control system such that the output of each transducer is separately controllable by the control system such that a separate output signal is received by each transducer from the control system.

2. The acoustic testing system of claim 1, wherein said control system is operatively coupled to said at least four control microphones such that said control system receives at least one input signal from said at least four control microphones.

3. The acoustic testing system of claim 2, wherein said input signal is an averaged signal from said plurality of control microphones.

4. The acoustic testing system of claim 2, wherein said input signal comprises a separate input signal from each of said at least four control microphones.

5. The acoustic testing system of claim 1, wherein said acoustic enclosure includes an acoustic treatment on walls of said acoustic enclosure.

6. The acoustic testing system of claim 1, wherein said control system accounts for reflected sounds from said acoustic enclosure such that said predetermined acoustic field measured by said at least four control microphones is achieved with less power than said predetermine acoustic field without said enclosure.

7. The acoustic testing system of claim 1, wherein said control system is configured to compare an output signal of each of said at least four control microphones with respect to each acoustical transducer or transducer group to a reference spectrum to create a matrix of error functions;

and

wherein said separate output signals received by each acoustic transducer are corrected drive signals computed from the matrix of error functions.

8. The acoustic testing system of claim 7, wherein the reference spectrum is expressed as a fixed band-width narrow-band power spectral density.

9. The acoustic testing system 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 acoustic testing system of claim 1, further comprising a combiner configured to combine each of said separate output signals to form at least four secondary output signals each composed of combinations of one or more of said at least four separately controllable controller output signals, wherein said at least four acoustic transducers or groups of transducers is operatively coupled to at least one of said at least four secondary output signals such that the output of the at least one transducer or transducer group varies in response to changes in at least two of the at least four separately controllable controller output signals.

11. The acoustic testing system of claim 10, wherein the combiner combines said at least four separately controllable output signals by attenuating, amplifying, filtering, delaying, adding, subtracting, correlating or any other manipulation of said at least four separately controllable output signals.

12. The acoustic testing system of claim 1, wherein the acoustic enclosure is selected from the group consisting of a 20 foot shipping container, a 40 foot shipping container, a 45 foot high cube shipping container, a 53 foot high cube shipping container, and a 7 foot by 5 foot by 5 foot container.

13. The acoustic testing system of claim 1, wherein the acoustic enclosure has an internal volume of less than 4000 cubic feet.

14. The acoustic testing system of claim 11, wherein the acoustic enclosure has an internal volume of less than 3000 cubic feet.

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

positioning at least four acoustic transducers and at least four control microphones around the unit under test;

positioning the unit under test, the at least four acoustic transducers, and the at least four control microphones within an acoustic enclosure with pre-determined reverberant characteristics;

applying a setup signal to each of the acoustic transducers;

separately monitoring the acoustic output of each of the acoustic transducers using the at least four control microphones;

comparing an output signal of each control microphone with respect to each acoustic transducer to a reference spectrum to create a matrix of error functions;

computing a corrected drive signal for each acoustic transducer; and

applying each corrected drive signal to the respective acoustic transducer .

16. The method of claim 15, further comprising the steps of:

after applying the corrected drive signals to the acoustic transducers, monitoring the acoustic output of each of the acoustic transducers using the at least four control microphones;

comparing a second output of the at least four control microphones with respect to all of the acoustic transducers to the reference spectrum to create an updated matrix of error functions;

computing an updated corrected drive signal for each acoustic transducer; and

applying each updated corrected drive signal to the respective acoustic transducer.

17. The method of claim 15, wherein the output signal of the at least one control microphone is converted to 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 15, wherein the acoustic enclosure wherein the acoustic enclosure is selected from the group consisting of a 20 foot shipping container, a 40 foot shipping container, a 45 foot high cube shipping container, a 53 foot high cube shipping container, and a 7 foot by 5 foot by 5 foot container.

20. The method of claim 15, wherein the acoustic enclosure has an internal volume of less than 4000 cubic feet.

21. The method of claim 20, wherein the acoustic enclosure has an internal volume of less than 3000 cubic feet.