Direct Field Acoustic Test (DFAT) Recommended Practice Paul Larkin June 8, 2009 The Aerospace Corporation 2009 The Aerospace Corporation 2009
Introduction to DFAT Original motivation to develop low cost acoustic test system DFAT is better than no test Use commercial, off-the-shelf (COTS) equipment Acoustic speakers, stereo amplifiers & open-loop control Provide Portability, Ease of use, Simplicity Diagnostic tool, Model correlation, Development testing Later developed closed-loop control system Available systems were costly Should be based on standard vibration test equipment The standard had experience with narrow-band acoustic control Currently developing a 148 db system Matching of controller/amplifiers, more powerful amplifiers, more compact devices Current Testing Uniformity of field, Induced Accelerations, DFAT vs. Chamber Testing 2
Contents of the RP 1. Introduction 1. The acoustic environment 2. Acoustic simulation 3. Current practice 4. DFAT method 2. Terms and Definitions 3. Background 1. History 2. Development/Characterization testing 3. Verification testing 4. Effectiveness 4. Facility 1. Space requirements 2. Power requirements 3. Facility evaluation, SPL mapping and Pre-test 4. Logistics 5. Handling 3
Contents of the RP 5. Sound Equipment 1. Speakers 2. Amplifiers 3. Other??? (X-over) 6. Instrumentation 1. Microphones 2. PSD s & SPL s 7. Sound Field Control 1. Instrumentation 2. Analog vs Digital 3. Nth Octave vs Narrow-band 4. Spec conversion 5. Closed-loop vs Open-loop 6. Recommendations Uniformity Repeatability Mixing/Phasing 4
Contents of the RP 8. Testing 1. Configuration 2. Low level runs (checkout) 3. Test duration 9. Comments on Direct vs. Reverberant 1. Induced accelerations 2. Uncertainty 3. Uniform (reverberant) field vs. Direct (shaped) field 10. References 5
Configuration MSI/VA-4, MSI/M4 horns, EAW/SB-1000 6
Configuration MSI/VA-4, EAW/SB-1000 7
Configuration 8
Configuration 9
Configuration 192 JBL/VT-4889, 60 EM/Quake, 24 ft tall 10
Recent Testing TEST LEVELS: Actual completed tests SPEC Ariane & Recent Frequency (Hz) (+3/-1dB) Ariane & Soyuz Landlaunch Proton Requirement Envelop All 31.5 132.9 130.2 132.1 132.8 136.1 136.1 63 137.0 134.2 136.3 137.7 139.9 139.9 125 139.9 138.2 138.0 140.7 142.3 142.3 250 139.9 138.8 138.0 139.3 141.0 141.0 500 137.0 136.4 135.8 134.2 133.7 137.0 1000 128.5 127.8 127.3 127.1 127.3 128.5 2000 125.8 124.2 123.4 121.0 124.4 125.8 4000 123.3 115.9 118.6 123.3 8000 119.1 112.3 115.5 119.1 Overall 145.2 143.7 143.6 145.0 146.7 147.0 SPEC = Envelope of Ariane 5, Soyuz, HIIA, Sea Launch, Land Launch, Proton 11
Typical Chamber (nth-octave control) Narrow-band Spectrum DFAT Recommended Practice Recent Testing Structure Chamber Interaction Structure Response to nth Octave chamber control (Notice lower frequency response is driven by chamber modes). PSD Plot 1000 100 10 1 Acoustic Full Level Test FEM 0.5% Damping Analysis/Test verified structural modes are at 172, 173, 218, 239,246,260 & 264 Hz. Amplitude SD 0.1 0.01 0.001 0.0001 0.00001 10 0.000001 100 1000 0.0000001 Frequency (Hz) OE1' Full Level Acoustic Test GRMS 21.4 FEM with 0.5% Damping 35.9 12
Recent Testing Induced Acceleration 100 10 SA_PY_TMX_Y-1 SA_PY_TMX_Y-2 1 0.1 ASD, g^2/hz 0.01 0.001 0.0001 0.00001 0.000001 0.0000001 10 100 1000 10000 Frequency, Hz 13
Recent Testing Uniformity of Field 145 140 135 130 Triangular Acoustic Test setup - 10/15/08 Company-X Program-Y test data Results File = Company-X\Program-Y\_00db\_v5f.002.psd9 TEST CONTROL SUMMARY Reference +/-3dB Reference +/-6dB Reference +/-9dB 8 Controls SPL (db) 125 120 115 110 105 100 95 10 1 10 2 10 3 10 4 Frequency (Hz) 14
Recent Testing Uniformity of Field 145 140 135 130 Triangular Acoustic Test setup - 10/15/08 Company-X Program-Y test data Results File = Company-X\Program-Y\_00db\_v5f.002.psd9 TEST CONTROL SUMMARY Reference +/-3dB Reference +/-6dB Reference +/-9dB 8 Monitors SPL (db) 125 120 115 110 105 100 95 10 1 10 2 10 3 10 4 Frequency (Hz) 15
Recent Testing RESPONSE LIMITING: 10-1 10-2 Acoustic Panel Test with Response Limiting Limit #3 - September 8, 2005 at 13:48am Results File = Larkin_090808.001.psd9 Results File = Larkin_090808.009.psd24 Channel 6 --- Response Limit Channel = 1.15 Grms Channel 6 --- Response Limit Channel = 0.775 Grms Response (No Limit) Response (Limit #3) Limit 10 3 10 2 Acoustic Panel Test with Response Limiting Limit #3 - September 8, 2005 at 13:48am Results File = Larkin_090808.001.psd9 Results File = Larkin_090808.009.psd24 Drive (no limit) = 269 mv (rms) Drive (limit #3) = 254 mv (rms) No Limit Limit #3 10-3 10 1 PSD (g 2 /Hz) 10-4 10-5 Voltage (mv 2 /Hz) 10 0 10-6 10-1 10-7 10-2 10-8 10 1 10 2 10 3 10 4 Frequency (Hz) 10-3 10 1 10 2 10 3 10 4 Frequency (Hz) 16
Recent Testing Normal (Gaussian) Distribution: 1 0.9 DFAT Chamber Pressure DFAT Chamber Accel. DFAT Testing 1 0.9 Probability Density Function Acoustic Chamber 2 Multiple Microphones 0.8 DFAT High Bay Accel. DFAT High Bay Pressure 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0-8 -6-4 -2 0 2 4 6 0-4 -3-2 -1 0 1 2 3 4 17
Recent Testing Normal (Gaussian) Distribution??? 1 Probability Density Function Acoustic Chamber 1 Multiple Accelerations 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0-4 -3-2 -1 0 1 2 3 4 18
Future Work Increase capability to 148dB Demo July 6-10 Increase run time to 30 sec minimum First part launch, second part margin Publish results on uniformity of field Larkin, Van Dyke, Maahs, +++ Publish results on induced accelerations Larkin, Van Dyke, Maahs, +++ Publish results on Direct vs. Reverberant testing Does uniformity of field affect the structure (direct) Do chamber modes affect the structure (reverberant) Study the real environment Spacial variation How normal is normal??? (according to Gauss) 19
Conclusions A first attempt has been made to quantify the important parameters for DFAT Much new work has been completed by multiple people Need to collect and coordinate the data sets Final Edit and Draft by October 2009 Incorporate latest testing results Obtain sponsoring organization for release and control (planned annual update) AIAA IEST More community involvement Sign-up to edit a section 20