Direct Field Acoustic Test (DFAT)

Transcription

1 Paul Larkin May 2010 Maryland Sound International 4900 Wetheredsville Road Baltimore, MD

2 Background Original motivation to develop a relatively low cost, accessible acoustic test system Use commercially available equipment Acoustic speakers, audio amplifiers and supporting equipment Evolved into more specialized, custom equipment Provide Portability, Ease of use, Simplicity, Safety Entire system is moved to the test article location Diagnostic tool, Model correlation, Development & Qualification testing Summary of the method Setup speaker circle (diameter+8 x height+2 ) to surround test article Connect generator, power distribution, amplifiers, control systems Bare system checkout: -12dB, -8dB, -4dB, 0dB Normal procedure is to test a simulator first Open circle, place simulator, close circle, mic placement, test to full level Actual test Open circle, remove simulator, place article, close circle, test to full level Entire process takes 4 days, Flight article required for 1 day 2

3 Background History First test was performed at Ball Aerospace in 1998 NASA/JPL QuickSCAT at 135dB Stock audio equipment using manual control 2001 Introduced analog closed-loop control (Norsonic RTA & Shaper) Introduced digital closed-loop control (M+P) Speaker upgrades & configuration changes 2007 Introduced narrow-band closed-loop control (Spectral Dynamics) 2009 Introduced more powerful amplifiers (10,000 w/channel) Optimized coupling of speakers and amplifiers Focused on minimizing distortion while providing required transient peaks Consistent practice, detailed procedures and attention to safety 2010 Introduced cleanroom compatibility and MIMO control Experience Test articles up to 12 diameter x 22 tall Levels up to = 148.3dB Clients include: NASA/JPL, NASA/GSFC, USAF, OSC, Ball, ITT, Goodrich, DARPA, + 12 Geo clients (Intelsat, SES, Thales-Alenia, PanAmSat, BSS, Optus) Launched with: Ariane, Atlas, Delta, Pegasus, Proton, Sea/Land Launch, Soyuz, Taurus 3

4 Current Equipment Amplifiers ( units) Custom MSI amplifiers manufactured by Powersoft Up to 11,000 w/channel Custom optimized software to provide control and monitoring Gain, crossover settings, filter types, roll-off, compression, output limits Speakers (current typical systems) 36 3-way + 24 Subs=60 cabinets to way+60 Subs=252 cabinets) Commercial drivers w/msi proprietary assembly to optimize performance 4 frequency ranges: sub, low, mid, high 2 cabinet types: Sub + 3-way Power & Distribution (generator + 4 cabinets) KVA power supply required Instrumentation Microphones high SPL, pressure type (8-16 control, 8-16 monitor) Data-logging sound level meters and dosimeters 4

5 Current Equipment 5

6 Current Equipment 6

7 Layout 7

8 Configuration 54 MSI VT-499, 36 MSI VT-4215, 12 ft tall 8

9 Configuration 192 MSI VT-499, 60 MSI VT-4215, 24 ft tall 9

10 Control Spectral Dynamics Jaguar hardware 1 to 256 independent output (drive) channels 8 to 588 simultaneous input channels 90dB of dynamic range DC to 20kHz frequency range NIST traceable calibration (calibration constants stored on board for each channel) Random-Acoustic Control software Input provided as nth octave SPL or narrow-band PSD 3200 spectral line PSD computed from 4 frames of 8192 points each loop Control is always performed in the narrow-band Output can be displayed as nth octave or narrow-band SPL or PSD All normal random control features are available (notching/limiting) Safety parameters Hardware manual abort switch, Two software abort buttons Composite control alarm and abort on tolerances on +/-db at N nth-octave bands, or N spectral lines, or N% lines over the entire bandwidth Individual or control channel abort on overall rms or peak response Any channel can limit 10

11 Recent Testing Test Levels Actual completed tests Future Frequency (Hz) Commercial Ariane & Soyuz Ariane & Landlaunch Proton DOD Envelop All Margined Overall SPEC = Envelope of Ariane 5, Soyuz, HIIA, Sea Launch, Land Launch, Proton Future Goal is 155dB with low coherence DFAT Recommended Practice in committee (IEST) 11

12 Recent Testing Uniformity of Field Small S/C, 145dB, 60 sec. Data in Column:!C!F!G!H!I!J!K!L!M!N Specification Tolerance Control Microphone SPL, scaled to 0dB (db, ref = 2e-5 Pa), dataset: SPL_time22 Data in Row Band Center Freq (Hz) SPL Spec (db) Tolerance (db) Lower Upper Bound (db) Bound (db) Average Control Mic 1 (Channel 1) Mic 2 (Channel 2) Mic 3 (Channel 3) Mic 4 (Channel 4) Mic 5 (Channel 5) Mic 6 (Channel 6) Mic 7 (Channel 7) Mic 8 (Channel 8) Mic 9 (Channel 9) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± / / / / / / OASPL (db) /

13 Recent Testing Uniformity of Field Small S/C, 145dB, 60 sec. 150 Control Microphones SPL (db, ref = 2e-5 Pa) Mic 1 (Channel 1) Mic 2 (Channel 2) Mic 3 (Channel 3) Mic 4 (Channel 4) Mic 5 (Channel 5) Mic 6 (Channel 6) Mic 7 (Channel 7) Mic 8 (Channel 8) Mic 9 (Channel 9) Test Spec Avg Control Tolerance (high) Tolerance (low) 100 Frequency (Hz) 13

14 Recent Testing Uniformity of Field - Small S/C, 145dB, 60 sec Composite Control SPL (cumulative) versus Time SPL_time1 SPL_time2 SPL_time3 SPL_time4 SPL_time5 SPL_time6 SPL_time7 SPL_time8 SPL_time9 SPL_time10 SPL_time11 SPL_time12 SPL (db, ref = 2e-5 Pa) SPL_time13 SPL_time14 SPL_time15 SPL_time16 SPL_time17 SPL_time18 SPL_time19 SPL_time20 SPL_time21 SPL_time22 SPL_time23 SPL_time24 SPL_time25 SPL_time26 SPL_time27 SPL_time28 SPL_time30 SPL_time31 SPL_time32 SPL_time33 SPL_time34 Test Spec Tolerance (high) Tolerance (low) Frequency (Hz) 14

15 Recent Testing Induced Acceleration 15

16 Recent Testing Response Limiting Acoustic Panel Test with Response Limiting Limit #3 - September 8, 2005 at 13:48am Results File = Larkin_ psd9 Results File = Larkin_ psd24 Channel Response Limit Channel = 1.15 Grms Channel Response Limit Channel = Grms Response (No Limit) Response (Limit #3) Limit 10-3 PSD (g 2 /Hz) Frequency (Hz) 16

17 Conclusions Advantages of DFAT Test can be performed on location Lower risk than transporting Cost is usually less than packing and shipping Multiple control system safety features Schedule can be reduced Test article needed for one day DFAT setup done in parallel Characteristics of DFAT 145dB for 60 sec. Acceptable to major launch vehicle contractors Proven history over 10 years Similar structural response to reverberant testing Narrow-band control Can employ random vibration control and limiting techniques DFAT is not the same as reverberant testing Wave interference occurs at specific frequencies and spacial locations Similar to structure-chamber interaction in reverberant testing Diffuse option will be available by November 2010 Multiple independent sources with MIMO control 17

18 MIMO Control Multiple Input Multiple Output Control for Acoustics Spectral Dynamics Jaguar Control System 4 MIMO Boards 4 x 3 = 12 drive outputs 4 x 4 = 16 inputs Square control scheme with 12 drives and 12 control mics Specify magnitude, phase and coherence at each control mic 4 roving monitor mics to assess the rest of the sound field Speaker Setup Small speaker circle (12 diameter x 6 high) to surround test article Simulated test article (blanketed shipping boxes approx. 4 x 4 x 8 high) 9 stacks of 3-way boxes, 3 stacks of Subs, one drive to each stack One control mic in front of each stack Same configuration tested with MISO and MIMO control MISO uses one drive to all speakers MIMO uses 12 independent, uncorrelated drives to each speaker stack 18

19 MIMO Control 140 Single Drive - 8 Control Microphones Mic 1 (Channel 1) Mic 2 (Channel 2) Mic 3 (Channel 3) SPL (db, ref = 2e-5 Pa) Mic 4 (Channel 4) Mic 5 (Channel 5) Mic 6 (Channel 6) Mic 7 (Channel 7) Mic 8 (Channel 8) Test Spec Avg Control Tolerance (high) Tolerance (low) Frequency (Hz)

20 SPL (db, ref = 2e-5 Pa) MIMO Control Drives - 12 Control Microphones Mic 1 (Channel 1) Mic 2 (Channel 2) Mic 3 (Channel 3) Mic 4 (Channel 4) Mic 5 (Channel 5) Mic 6 (Channel 6) Mic 7 (Channel 7) Mic 8 (Channel 8) Mic 9 (Channel 9) Mic 10 (Channel 10) Mic 11 (Channel 11) Mic 12 (Channel 12) Test Spec Avg Control Tolerance (high) Tolerance (low) Frequency (Hz)

21 MIMO Control Single Drive Overall Worst 1/3- Octave Band All Channels Control Monitor Range Std Dev Range Std Dev Drives and 4 monitors were used for MIMO testing Data below represents worst case monitor locations within 12 of test article, response was ~ +3dB Typical 1/3-octave max variation of ~ ±3dB over all locations 12 Drives Overall Worst 1/3- Octave Band All Channels Control Monitor Range Std Dev Range Std Dev

22 MIMO Control DFAT Coherence for Single Source

23 MIMO Control DFAT Coherence with 12 Sources

24 MIMO Control - Conclusions MIMO provides a significant improvement over MISO control More uniform field Lower coherence More closely represents the flight measurements and reverberant results Only one simple control strategy was investigated Magnitude (Pa 2 /Hz), phase = 0, ±180, coherence = 0.8 at 20Hz to 0.2 at 2000Hz Some increase in drive voltage is required Overall drive voltage (rms) has increased Increase has been spread over the bandwidth Mostly applied to valleys in the drive spectrum Required to maintain low coherence by adjusting phase Response still limited by amplifier output capability 24