Test Report on the. Authors: April 17, 2014

Transcription

1 Test Report on the Performance of 3M TM E-A-Rfit TM Validation System Authors: Jérémie Voix, P.Eng., Ph.D. Jan Pienkowski, B.Sc. Aidin Delnavaz, P.Eng., Ph.D. April 17, 2014 Abstract This report details the findings of a side-by-side comparison between the attenuation measurements made using a real-ear attenuation at the threshold (REAT) method, following ANSI S12.6 guidance, versus the measurements performed with 3M TM E-A-Rfit TM Validation System for three earplug models on groups of up to 20 test subjects at the ÉTS Laboratoire d acoustique industrielle (Université du Québec) research labs. The observed average prediction errors of PAR for 3M TM 1100 Uncorded Foam Earplug, 3M TM E-A-R TM Classic TM Uncorded Earplug foam, and 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded samples are respectively 2.1 db, 0.3 db and 1.0 db (all are under-predictions), while measurement uncertainties are respectively 4.3 db, 3.3 db and 3.1 db. These data suggest that the 3M TM E-A-Rfit TM Validation System is suitable for estimation of the real-ear attenuation of these hearing protection devices as, on average, it tends to slightly underestimate the attenuation and shows a limited overall measuring uncertainty and therefore provides, on average, a conservative estimate of the field attenuation.

2 Contents 1 Introduction 3 2 Mandate Details Mandate timeline HPD Testing Facilities Audiometric sound booth Instrumentation Test Procedure Experimental Steps Data Analysis Test Results Measurement on probed earplug Measurement on regular (unmodified) earplug Conclusions 12 7 Appendices 14 A 3M TM 1100 Uncorded Foam Earplug 15 B 3M TM E-A-R TM Classic TM Uncorded Earplug foam 21 C 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded 27 List of Figures 1 Audiometric booth Background noise level in the audiometric booth Print screen of REAT Master (V3) M TM E-A-Rfit TM Validation System Different types and variations of tested earplug samples A.1 Mean and standard deviation of the 3M TM 1100 Uncorded Foam Earplug group attenuation A.2 Scattergram of predicted (F-MIRE on x-axis) vs. reported (REAT on y-axis) ( noise reduction for ) 3M TM 1100 Uncorded Foam Earplug (N=40). Right ear: - :Left ear

3 A.3 Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM 1100 Uncorded Foam Earplug (N=40) A.4 Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM 1100 Uncorded Foam Earplug (N=40) A.5 Histogram with superimposed fitted normal density of surrogate error.. 20 B.1 Mean and standard deviation of the 3M TM E-A-R TM Classic TM Uncorded Earplug foam group attenuation B.2 Scattergram of predicted (F-MIRE on x-axis) vs. reported (REAT on y- axis) noise ( reduction for 3M TM E-A-R ) TM Classic TM Uncorded Earplug foam (N=40). Right ear: - :Left ear B.3 Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM E-A-R TM Classic TM Uncorded Earplug foam (N=40) B.4 Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM E-A-R TM Classic TM Uncorded Earplug foam (N=40) B.5 Histogram with superimposed fitted normal density of surrogate error.. 26 C.1 Mean and standard deviation of the 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded group attenuation (N=33 for REAT - Regular and N=39 for others) C.2 Scattergram of predicted (F-MIRE on x-axis) vs. reported (REAT on y-axis) noise reduction ( for 3M TM E-A-R TM UltraFit ) TM Uncorded Earplug premolded (N=39). Right ear: - :Left ear C.3 Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded (N=39) C.4 Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded (N=33) C.5 Histogram with superimposed fitted normal density of surrogate error.. 32 List of Tables 1 Test details The average error of prediction (ε A ) and measuring uncertainty (µ meas ) in db The average surrogate error (δ A ) and standard deviation (σ surr ) in db

4 1 Introduction 3M s Personal Safety Division Hearing Solutions Business Unit contracted in 2011 with the ÉTS industrial laboratories to conduct a laboratory study of the 3MTM E-A-Rfit TM Validation System. This study consisted of a side-by-side comparison measurements on three different 3M brand earplugs, between the earplug attenuation values measured by the real-ear attenuation at the threshold (REAT) method specified in ANSI S and the earplug attenuation values estimated using the field-microphone in real-ear (F- MIRE) method implemented in the E-A-Rfit system. REAT is a subjective test based on the use of threshold audiometry, that is finding the quietest sounds one can hear (hearing sensitivity). In this method, the test subjects are instructed to track their hearing thresholds both with and without earplugs. The difference in the two thresholds indicates the attenuation of the earplug [1]. Unlike REAT, MIRE is an objective measurement based on the signals captured by microphones. This test, when applied in occupational settings, becomes field MIRE and is designated by F-MIRE. In this method, the sound pressure levels are simultaneously recorded in the earcanal under the hearing protector as well as those outside the earplug. The difference when appropriately corrected is an estimation of the earplug attenuation [2]. The purpose of the current study was to assess the suitability of E-A-Rfit system developed by 3M to predict the noise reduction of earplugs reported by the standard REAT test. The instrumentation and measurements for REAT were all in compliance according to ANSI S12.6 [3] requirements and all F-MIRE measurements were obtained using the E-A-Rfit system [4]. The organization of this report is as follows. The details of the study requirements are presented in Section 2. The hearing protection device (HPD) testing facilities and the procedure are elaborated in Sections 3 and 4 respectively. The results of the tests are discussed in Section 5 followed by conclusion in Section 6. Also, all graphs and plots are presented in Appendices A, B, C for 3M TM 1100 Uncorded Foam Earplugs, 3M TM E-A-R TM Classic TM Uncorded Earplugs foam and 3M TM E-A-R TM UltraFit TM Uncorded Earplugs premolded respectively. 2 Mandate Details 3M s Personal Safety Division Hearing Solutions Business Unit introduced the E-A-Rfit system in 2007 and has continued to evolve and improve the hardware and software that comprises the system. One of the co-authors of this study (Dr. Voix) was involved in the initial development of the system and has continued to collaborate with 3M since that time. The objectives of the study were for an independent laboratory to evaluate the current version of the system to validate that they obtained similar results as in the 3M E- A-RCAL laboratories in Indianapolis. This evaluation focuses on three of the popular products that are included in the E-A-Rfit system, namely, the 3M TM 1100 Uncorded 3

5 Foam Earplug, the 3M TM E-A-R TM Classic TM Uncorded Earplug foam, and the 3M TM E- A-R TM UltraFit TM Uncorded Earplug premolded. 2.1 Mandate timeline STAGE 1: The mandate includes the request to the Comité d éthique de la recherche (CÉR) de l ÉTS (Internal Review Board for ÉTS) to deliver an approval certificate; Preparation of the validation study, following the recommended guidelines provided by Mr. Berger. This preparation includes the creation of spreadsheet templates, electronic forms and any document required by the envisioned experiment (such as the subject identification form required for the anonymization of the data). STAGE 2: Recruit, schedule, select (per ANSI S12.6 clause 5) and train a sufficient number of test subjects, so that the 3 models of hearing protectors could be tested on 20 test subjects. Input of all test subjects hearing threshold within the 3M TM E-A-Rfit TM Validation System. The mandate includes conducting a predefined test sequence (detailed in section 4.1 for every of the 20 test subjects on each of the 2 hearing protector model, in order to compare the measured F-MIRE attenuation values to the REAT attenuation values. STAGE 3: Process the data and transfer the measured values to the attenuation spreadsheet template provided by 3M. This spreadsheet will provide for REAT - Probed, REAT - Regular and F-MIRE tables, with the respective 2 lines per subject per protector. Utilize Matlab scripts to compute the compensation calculations. The mandate includes the use of the equipment available at the Laboratoire d acoustique industrielle of ÉTS and specifically includes: Eckel double-wall audiometric sound booth, AC40 clinical audiometer from InterAcoustics and REATmaster testing software from VIAcoustics. 3M provided ÉTS with the following equipment and consumables in order to complete the study: 1 E-A-Rfit Validation System software V or more recent. 4

6 2 One extra E-A-Rfit microphone. 3 At least 80 3MTM E-A-RTM ClassicTM Probed Earplugs foam (20 subjects x 2 ears x 2 trials) as well as 80 3MTM E-A-RTM ClassicTM Uncorded Earplugs foam. 4 At least 80 3MTM 1100 Uncorded Foam Earplugs Probed (20 subjects x 2 ears x 2 trials), as well as 80 unmodified (regular) 3MTM 1100 Uncorded Foam Earplugs. 5 At least 40 3MTM E-A-RTM UltraFitTM Probed Earplugs premolded (20 subjects x 2 ears x 2 trials), as well as 40 unmodified (regular) 3MTM E-ARTM UltraFitTM Uncorded Earplugs premolded. 3 HPD Testing Facilities The industrial acoustics laboratories at E TS are dedicated to research and training in the field of industrial noise control and hearing protection. The laboratories are used for many research activities, sponsored or granted, and host typically over a dozen graduate students for their master or doctorate projects. 3.1 Audiometric sound booth All tests of this report were conducted in a 27 m3 double wall Eckel audiometric sound booth as shown in Fig. 1. (a) Top-view (b) Entrance Figure 1: Audiometric booth The facility meets the background noise requirements specified by standards for HPD testing (ANSI/ASA S , ISO :1990, ANSI S ), or audiometric measurements (ANSI S ) as shown in Fig. 2. 5

7 Figure 2: Background noise level in the audiometric booth 3.2 Instrumentation On top of the typical clinical audiometer and sound reproduction system (already detailed in 2) expected in such an HPD testing facility, the validation study made use of an original piece of software, REATmaster to track and record the open and occluded hearing thresholds of the test subjects.this software (see screen-capture in Fig. 3) was initially developed by Nelson Acoustics for the NASA Glen Research Center in conjunction with technical input from NIOSH and is specially designed for the testing of hearing protection attenuation using REAT. The system features various automatic audiometric tracking programs with sophisticated stimulus generation for free field hearing threshold determination for both occluded and unoccluded conditions. The E-A-Rfit system is shown in Fig. 4 and is used for conducting the F-MIRE measurements. 6

8 Figure 3: Print screen of REAT Master (V3) Figure 4: 3M TM E-A-Rfit TM Validation System 7

9 4 Test Procedure 4.1 Experimental Steps Test subjects were contacted and invited for the tests in compliance with the standard of ANSI S12.6 clause 5 and according to the protocol guidelines approved by the Comité d éthique de la recherche de l ÉTS, the Internal Review Board of the institution in order to form groups of 20 test subjects. The duration of the test for each participant was about three hours which was held in one session with a break in the middle. The tests were held during the period of April 2012 to September 2012 and participants received compensation for their participation and time according to the internal review board policies. Three types of earplug samples were tested: 1) 3M TM 1100 Uncorded Foam Earplug, 2) 3M TM E-A-R TM Classic TM Uncorded Earplug and 3) 3M TM E-A-R TM UltraFit TM Uncorded Earplug. The required earplugs were supplied by 3M according to the mandate mentioned in section 2. For each type, there were two variations: I) regular and II) probed (i.e. test) earplugs. The latter is normally used for F-MIRE test purposes. All types and variations of the tested earplugs are shown in Fig. 5. Figure 5: Different types and variations of tested earplug samples Each test subject went through reading the test conditions, signing the required consent forms, passing visual inspection and audiometric tests described in ANSI S12.6 in the subject selection criterion section. All test subjects hearing thresholds were entered into the 3M TM E-A-Rfit TM Validation System. The main part of the test consisted in conducting the following test sequence for every one of the twenty test subjects and on each of the three hearing protector models. For each fitting, a new unused test probe and/or earplug was utilized. 8

10 1 REAT: Open, followed by protected hearing thresholds on probed protector; [O1,P1] 2 F-MIRE on the same fit of probed protector; [F-MIRE1] 3 REAT: Protected threshold on unmodified (regular) protector followed by Open threshold; [P2,O2] 4 REAT: Protected threshold on unmodified (regular) protector followed by Protected on probed protector; [P3,P4] 5 F-MIRE on the same fit of probed protector; [F-MIRE2] For the F-MIRE tests, the trained laboratory technician first checked that the microphone tip was tightly screwed on the EARfit system microphone doublet, then inserted the probe microphone inside the probed earplug and finally fitted the instrumented earplug inside the earcanal of the test subject. Immediately after the F-MIRE measurement, a REAT evaluation was conducted without changing the fit of the earplug. The technician was also responsible for inserting the regular earplugs for the second REAT evaluations with the intent that the fit of the earplug for the REAT evaluation would be the same as the insertion for the F-MIRE evaluation previously conducted. 4.2 Data Analysis Table 1: Test details REAT - Probed REAT - Regular F-MIRE P1-O1 P2-O2 F-MIRE1 P4-O2 P3-O2 F-MIRE2 Both F-MIRE data and REAT data were extracted as octave-band attenuation values. The F-MIRE data is available for the left and right ears separately, while the REAT is a binaural measurement. To compare the F-MIRE and REAT attenuation, left and right F-MIRE data had to be combined into a binaural equivalent value [2] which calculation, detailed in the separate Matlab scripts, requires the use of the left and right hearing thresholds values for the subject under test. Finally, each of the F-MIRE and REAT attenuation values are combined into a single number value, later referred to as overall attenuation value, to ease the interpretation of the results obtained. This overall attenuation value represents the difference between the A-weighted overall protected level and the C-weighted overall exposure level of a arbitrary defined pink noise. Such calculation is traditionally used in hearing protection assessment (the Noise Reduction Rating relies on such similar computation) and can be easily performed using a standard electronic spreadsheet. It is interesting to note that the E-A-Rfit software already natively reports a single number value, dubbed Personal Attenuation Rating (PAR), that could have been used directly for the analysis. This 9

11 PAR value however is computed in a much more sophisticated way, similar to the Noise Reduction Statistic (NRS A ) defined in the recent ANSI S12.68 standard [5], that relies on a rather intensive calculation of the average difference between an overall A-weighted protected level and the A-weighted overall exposure level on a large dataset of industrial noise spectra. Although the computation of such PAR value from the REAT octaveband is possible using the ad-hoc Matlab scripts embedded into the E-A-Rfit system, it was considered simpler to reproduce them with an electronic spreadsheet to compare the F-MIRE and REAT results. 5 Test Results The results of the tests are categorized based on the type of earplugs and are presented in appendices A, B and C for 3M 1100, Classic, and UltraFit earplug types respectively. The graphs of the mean and standard deviation of the octave-band attenuation values obtained on the group of test-subject are presented in Figures A.1, B.1 and C.1 for the 3M 1100, Classic, and UltraFit earplug types respectively. Since 20 test subjects were to be tested two times each, each graph should contain N=40 trials. Due to software data recording problems 6 of 40 REAT measurements on the regular earplug and 1 of 40 REAT measurements on the test probe were lost for the UltraFit and it was logistically not possible to schedule retests. Thus N=33 or 39, as shown on the respective charts in Appendix C. It can be seen in all 3 graphs that the F-MIRE and REAT attenuation values on the probed earplug are within a few db on average for the group. It can also be seen from the points on the extreme right of the graphs, that the overall attenuation values, whether measured using F-MIRE or REAT on a probed earplug or using REAT on a surrogate earplug are very close together. This supports the fact that the E-A-Rfit system is, on a group of subjects, both accurate (F-MIRE values are very close to the REAT values considered as the true value, statistically speaking) and precise (since the dispersion of the overall F-MIRE attenuation - represented by the standard deviation, on top of the graphs - has the same magnitude than the REAT attenuation). Nevertheless, the E-A-Rfit system has been designed to test individual test subjects, rather than group of subjects, it is important to assess how precise and accurate such F-MIRE system is on an individual basis. The sub-sections 5.1 and 5.2 below will therefore detail the results obtained when comparing on an individual basis, the F- MIRE attenuation to the REAT attenuation, both on the probed earplug (retaining the original fit) and the standard earplug (fitted separately by the laboratory technician inside the test subject s earcanal). 5.1 Measurement on probed earplug The left and right F-MIRE attenuation values are compared to the binaural REAT values in Figures A.2, B.2 and C.2. As explained in section 4.2, in these figures and in the following ones, the overall attenuation value represent the difference between 10

12 the overall C-weighted unprotected sound pressure level and the overall A-weighted protected sound pressure level. It can be seen that taken separately, each individual left and right ear F-MIRE attenuation value can be significantly different than the binaural REAT attenuation value. The computation of an equivalent binaural attenuation is required for the F-MIRE procedure in order to be able to compare to REAT, which by nature is a binaural measurement. The binaural attenuation for F-MIRE versus REAT tests are illustrated in Figures A.3, B.3 and C.3, illustrating how F-MIRE predicts REAT for each tested earplug type, on an individual basis. As explained in section 4.2, these binaural values are computed from the left and right F-MIRE attenuation (presented in Figures A.2, B.2 and C.2) and take into account the test-subject hearing thresholds from left and right ears, so that a combination of the best ear and worse earplug attenuation is used for every octave-band. It appears that the attenuation values measured by E-A-Rfit system at 8 khz are intentionally limited through the bone-conduction limit of the software set to about 50 db as seen in Figures A.3 and A.2 for 3M 1100 and in Figures B.3 and B.2 for Classic type of earplugs. Therefore, an adjustment to the bone conduction limit may be worth re-examining at 8 khz for 3M 1100 and Classic earplugs. The average of the prediction error (ε A ) is listed in Table 2 along with the corresponding measuring uncertainty (µ meas ). Table 2: The average error of prediction (ε A ) and measuring uncertainty (µ meas ) in db Earplug Type ε A µ meas 3M Classic UltraFit These values in Table 2 are perhaps the ones of greatest interest. Note especially the comparison of the REAT probed and the F-MIRE since they are measurements on the exact same fit of the earplug, and they compare quite well, especially for the overall attenuation values. The agreements are generally within 3 db and the overall F-MIRE attenuation slightly underestimates the REAT attenuation, hence representing a conservative error. 5.2 Measurement on regular (unmodified) earplug Figures A.4, B.4 and C.4 illustrate the difference between the REAT attenuation values on the probed earplug and on the regular earplug of the same model. This difference between the probed earplug (surrogate) in comparison to a regular earplug of the same type is called the surrogate error. This surrogate error represents the possible difference in the attenuation of the probed earplug compared to the standard earplug: if, on average, the surrogate error is a positive value, the probed earplug is less attenuating then the standard earplug, conversely, if the average surrogate error is a negative value, 11

13 the probed earplug provides more attenuation than the standard earplug. The dispersion of surrogate error values, represented by the standard deviation of such value for a group of subjects, is primarily an indication of the ability of the laboratory technician to achieve the exact fit of both probed and regular earplugs. Fitting an earplug consistently the same way inside a test subject s earcanal requires great dexterity and practice. Given that many random and/or unrelated factors can affect such fit-refit capability, it is expected that the statistical distribution of the surrogate error tends to follow a normal distribution. While different statistical tests of composite normality could be proposed, the Figures A.5, B.5 and C.5 simply overlay the obtained histograms of the observed surrogate error with the continuous fitted normal density function, for illustration purposes. It can be seen that the average surrogate error is very close to zero, hence that the probed earplug is a good surrogate for the standard earplug, and that the histograms are more or less symmetrical across zero, meaning that the technician did not introduce any consistent bias in the fitting and refitting of the earplugs. The average surrogate error (δ A ) and its corresponding standard deviation (σ surr ) is presented in Table 3. The relatively large value for the σ surr in the current test is most probably due to the relative inexperience of the lab technician with the fitting of non-custom earplugs. Table 3: The average surrogate error (δ A ) and standard deviation (σ surr ) in db Earplug Type δ A σ surr 3M Classic UltraFit Conclusions The results for the attenuation measurements obtained via the REAT method, based on ANSI S standard, and those estimated via use of the E-A-Rfit software were presented and discussed in this report. The side-by-side comparison between the attenuation measurements were also demonstrated. The observed average prediction errors of PAR for 3M 1100, Classic and UltraFit earplug samples are respectively 2.1 db, 0.3 db and 1.0 db (all are under-prediction), while measurement uncertainties are respectively 4.3 db, 3.3 db and 3.1 db. Both series of values prove that the adopted E-A-Rfit Validation System is suitable for field attenuation measurement of such hearing protection devices as, on average, it tends to slightly underestimate the attenuation and shows a limited overall measuring uncertainty and therefore provides, on average, a conservative estimate of the field attenuation. 12

14 References [1] Berger, E. H. (2000). Hearing Protection Devices, The Noise Manual, 5th Edition, edited by E. H. Berger, L. H. Royster, J. D. Royster, D. P. Driscoll, and M. Layne, Am. Ind. Hyg. Assoc., Fairfax, VA, [2] Voix, J., & Laville, F. (2009). The objective measurement of individual earplug field performance. The Journal of the Acoustical Society of America, 125(6), [3] ANSI (1984), Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn S , New-York, NY. [4] 3M Occupational Health and Environmental Safety Division (2010), 3M TM E-A- Rfit TM Validation System, E-A-Rfit Validation Brochure, St. Paul, USA. [5] ANSI (2012), Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn, S (R2012), New-York, NY. 13

15 7 Appendices 14

16 A 3M TM 1100 UNCORDED FOAM EARPLUG A 3M TM 1100 Uncorded Foam Earplug 15

17 A 3M TM 1100 UNCORDED FOAM EARPLUG Figure A.1: Mean and standard deviation of the 3M TM 1100 Uncorded Foam Earplug group attenuation 16

18 A 3M TM 1100 UNCORDED FOAM EARPLUG Figure A.2: Scattergram of predicted (F-MIRE on x-axis) vs. reported ((REAT on y- axis) noise reduction for 3M TM 1100 Uncorded Foam Earplug (N=40). Right ear: - ) :Left ear 17

19 A 3M TM 1100 UNCORDED FOAM EARPLUG Figure A.3: Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM 1100 Uncorded Foam Earplug (N=40). 18

20 A 3M TM 1100 UNCORDED FOAM EARPLUG Figure A.4: Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM 1100 Uncorded Foam Earplug (N=40). 19

21 A 3M TM 1100 UNCORDED FOAM EARPLUG Figure A.5: Histogram with superimposed fitted normal density of surrogate error 20

22 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM B 3M TM E-A-R TM Classic TM Uncorded Earplug foam 21

23 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM Figure B.1: Mean and standard deviation of the 3M TM E-A-R TM Classic TM Uncorded Earplug foam group attenuation 22

24 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM Figure B.2: Scattergram of predicted (F-MIRE on x-axis) vs. reported (REAT on ( y-axis) noise reduction for 3M TM E-A-R TM Classic TM Uncorded Earplug foam (N=40). Right ) ear: - :Left ear 23

25 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM Figure B.3: Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM E-A-R TM Classic TM Uncorded Earplug foam (N=40). 24

26 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM Figure B.4: Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM E-A-R TM Classic TM Uncorded Earplug foam (N=40). 25

27 B 3M TM E-A-R TM CLASSIC TM UNCORDED EARPLUG FOAM Figure B.5: Histogram with superimposed fitted normal density of surrogate error 26

28 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED C 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded 27

29 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED Figure C.1: Mean and standard deviation of the 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded group attenuation (N=33 for REAT - Regular and N=39 for others) 28

30 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED Figure C.2: Scattergram of predicted (F-MIRE on x-axis) vs. reported (REAT on y-axis) ( noise reduction for 3M TM ) E-A-R TM UltraFit TM Uncorded Earplug premolded (N=39). Right ear: - :Left ear 29

31 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED Figure C.3: Scattergram of binaural predicted (F-MIRE on x-axis) vs. binaural reported (REAT on y-axis) noise reduction for 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded (N=39). 30

32 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED Figure C.4: Scattergram of REAT on regular earplug (on x-axis) vs. REAT on probed earplug (on y-axis) for 3M TM E-A-R TM UltraFit TM Uncorded Earplug premolded (N=33). 31

33 C 3M TM E-A-R TM ULTRAFIT TM UNCORDED EARPLUG PREMOLDED Figure C.5: Histogram with superimposed fitted normal density of surrogate error 32