Measuring Gunshots with Commercial Sound Level Meters

Transcription

1 Measuring Gunshots with Commercial Sound Level Meters Deanna K. Meinke, Ph.D. Gregory A. Flamme, Ph.D. William J. Murphy, Ph.D. Donald S. Finan, Ph.D. Michael Stewart, Ph.D. Stephen M. Tasko, Ph.D. James E. Lankford, Ph.D.

2 Disclaimers The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy. The sound level meters utilized in this study were a convenience sample of instruments commercially available at the time of the study, and were either owned by the researchers or provided on loan by the manufacturer.

3 Introduction Gunshot sound levels are frequently measured using commercial sound level meters primarily for the identification of peak sound pressure levels for regulatory or policy compliance and ultimately to determine risk of auditory damage. Commercially available sound level meters are marketed specifically for the purposes of impulse noise measurements. The measurement data from these sound level meters can be obtained from more than one source; the LED display reading and from the AC output data file.

4 Research Questions How does the accuracy of the impulse noise measurements made with a commercial sound level meter compare to the gold standard laboratory system measurements? Are there differences between the sound level meter LED display output values and the AC output values?

5 Sound Level Meter Basic Block Diagram Digital Signal Acquisition & Processing Fast, Slow = Log db AC Output DC Output

6 Methods: Environment Rudyard, Michigan Field Site

7 Methods: Sound Level Meters (n=5) Make Model PreAmp Mic Weighting Larson Davis 831 LXT PRMLXT1 PCB 377C10 Z 824 PRM902 B&K 4136 Z 824 PRM902 B&K 4136 Z 831 PRM831 PCB 377C10 Z 3M Sound Pro Integral Quest QE 4110 Z

8 Methods: Experimental Set-up Colt AR-15 Rifle shooting Federal American Eagle.223 Remington 55 grain FMJ

9 Methods: Experimental Set-up Each meter tested at 5 different peak SPLs: 130, 140, 150, 160 and 170 db

10 Methods: Experimental Set-up Each meter tested at 5 different peak SPLs: 130, 140, 150, 160 and 170 db

11 Methods: Experimental Set-up All Mics: Grazing incidence, separated by 1 inch, 1.5 meter height; Calibrated pre and post measurement for each test position

12 Methods: Experimental Set-up Laboratory System:

13 Methods: Experimental Set-up 1 Researcher per Station to read and report LED display after shot fired

14 Methods: Data Analysis Excel for recording SLM display quantities MATLAB for gold standard system and SLM AC output Peak, LAeq8, AHAAH AHU (warned), AHAAH AHU (unwarned) Stata for inferential statistics Mixed regression model, with observations nested within shots

15 Results AC output versus display value Peak LAeq8

16 Results Accuracy of SLM AC peak SPLs

17 Results Accuracy of SLM AC peak SPLs

18 Results Accuracy of SLM AC LAeq8

19 Results Accuracy of SLM Warned AHU

20 Results Accuracy of SLM Unwarned AHU

21 Results Accuracy of MPE estimates MPE error ratio (SLM / Field) LD LXT LD 831 LD LD M SoundPro LD LXT LD 831 LD LD M SoundPro LD LXT LD 831 LD LD M SoundPro LD LXT LD 831 LD LD M SoundPro LD LXT LD 831 LD LD M SoundPro LIAeq100ms AHU Warned LAeq8 AHU Unwarned

22 Results Mixed-model ANOVA Dependent variables assessed Peak, LAeq8, A-duration, Warned AHU, Unwarned AHU Model DV = peak + meter + peak*meter Observations nested within shots Bonferroni adjustment

23 Results Mixed-model ANOVA A-duration model was not significant, all others were. 95 % CI for marginal means does not include zero in most cases. Especially for Peak and LAeq8 Between-meter significant differences begin at 140 peak db SPL. At 140: At 170: Peak, LAeq8 Warned AHU, Unwarned AHU

24 Conclusions Sound level meters are not a replacement for a field research system Rigorous testing of any system is necessary Adequate microphone specifications are necessary, but not sufficient for accuracy Preamp, AC output, and recording apparatus must be able to handle the impulse signal Display dynamic range AC output dynamic range Accuracy declines with increasing level

25 Implications Use of a commercial sound level meter utilized for impulse noise measurements may underestimate auditory hazard for impulse sound levels at or above approximately 150 db peak SPL. Purchasing a new 1/8 inch microphone may not necessarily extend the range of your measurements. Sound level meter instrument specifications may need to specify the accuracy and range for specific outputs and impulse levels.

26 Raise your hand if you have questions