Measuring earplug noise attenuation: A comparison of laboratory and field methods.

Hearing protection device (HPD) fit-testing is a recommended best practice for hearing conservation programs as it yields a metric of the amount of attenuation an individual achieves with an HPD. This metric, the personal attenuation rating (PAR), provides hearing health care, safety, and occupational health personnel the data needed to select the optimal hearing protection for the occupational environment in which the HPD will be worn. Although commercial-off-the-shelf equipment allows the professional to complete HPD fit tests in the field, a standard test methodology does not exist across HPD fit-test systems. The purpose of this study was to compare the amount of attenuation obtained using the "gold standard" laboratory test (i.e., real-ear attenuation at threshold [REAT]) and three commercially available HPD fit-test systems (i.e., Benson Computer Controlled Fit Test System [CCF-200] with narrowband noise stimuli, Benson CCF-200 with pure tone stimuli, and Michael and Associates FitCheck Solo). A total of 57 adults, aged 18 to 63, were enrolled in the study and tested up to seven earplugs each across all fit-test systems. Once fitted by a trained member of the research team, earplugs remained in the ear throughout testing across test systems. Results revealed a statistically significant difference in measured group noise attenuation between the laboratory and field HPD fit-test systems (p < .0001). The mean attenuation was statistically significantly different (Benson CCF-200 narrowband noise was +3.1 dB, Benson CCF-200 pure tone was +2.1 dB, and Michael and Associates FitCheck Solo was +2.5 dB) from the control laboratory method. However, the mean attenuation values across the three experimental HPD fit-test systems did not reach statistical significance and were within 1.0 dB of one another. These findings imply consistency across the evaluated HPD fit-test systems and agree with the control REAT test method. Therefore, the use of each is acceptable for obtaining individual PARs outside of a laboratory environment.

Personal attenuation ratings versus derated noise reduction ratings for hearing protection devices.

National and international regulatory and consensus standards setting bodies have previously proposed derating hearing protector ratings to provide a better match between ratings determined in a laboratory and the real-world measurements of attenuation for workers. The National Institute for Occupational Safety and Health has proposed a derating scheme that depends upon the type of protector. This paper examines four real-world studies where personal attenuation ratings (PARs) were measured at least twice, before and after an intervention in earplug fitting techniques. Results from these studies indicate that individualized earplug fitting training dramatically improves a worker's achieved PAR value. Additionally, derating schemes fail to accurately predict the majority of achieved PARs. Because hearing protector fit testing systems are now readily available for use in the workplace, personal attenuation ratings provide a better estimate of worker noise exposures and are able to identify those persons who need additional instruction in fitting hearing protection devices.

The Effect of Using an Active Earmuff on High Frequency Hearing in United States Marine Corps Weapons Instructors.

OBJECTIVES: To investigate the change in hearing and perceived comfort over 1 year related to using an active hearing protection device (HPD) among United States Marine Corps (USMC) personnel routinely exposed to hazardous noise. METHODS: USMC Weapons Instructors (n = 127) were issued an active earmuff that met military standards and was compatible with other protective equipment. These participants completed pre- and post-hearing tests and comfort surveys. A control cohort (n = 94) was also included to compare individual changes in high-frequency pure tone average (HF-PTA) over 1 year. RESULTS: The control group's HF-PTA was 3 dB worse than the intervention group after only 1 year. Survey responses revealed perceived improvements in the ability to hear and understand, situational awareness, and safety. CONCLUSIONS: Active HPDs can reduce hearing loss and improve hearing-related occupational tasks.

How hearing conservation training format impacts personal attenuation ratings in U.S. Marine Corps Training Recruits.

OBJECTIVE: The purpose of this fit-testing study in the field was to systematically compare three Hearing Protection Device (HPD) fit-training methods and determine whether they differ in the acquisition of HPD fitting skill and resulting amount of earplug attenuation. DESIGN: Subjects were randomly assigned to receive HPD fit-training using one of three training methods: current, experiential HPD (eHPD), and integrated. Personal Attenuation Ratings (PARs) were acquired via HPD fit-testing and used to verify attenuations pre- and post-training. STUDY SAMPLE: US Marine training recruits (n = 341) identified via HPD fit-testing for remedial HPD fit-training and assigned to three cohorts. RESULTS: The post-training HPD fit-test passing rate differed by training method, with pass rates ranging from 50% (current) to nearly 92% (eHPD). The difference between group delta PAR values were significantly higher (>9 dB) in both the eHPD and integrated methods compared to the current method. CONCLUSION: The HPD fit-training methods that teach "what right feels like" (eHPD and integrated) provided a greater number of trainees with the skill to achieve noise attenuation values required for impulse noise exposures encountered during basic training. The attenuation achieved by those methods was significantly greater than the current training method.

The viability of hearing protection device fit-testing at navy and marine corps accession points.

INTRODUCTION: The viability of hearing protection device (HPD) verification (i.e., fit-testing) on a large scale was investigated to address this gap in a military accession environment. MATERIALS AND METHODS: Personal Attenuation Ratings (PARs) following self-fitted (SELF-Fit) HPDs were acquired from 320 US Marine Corps training recruits (87.5% male, 12.5% female) across four test protocols (1-, 3-, 5-, and 7- frequency). SELF-Fit failures received follow-up to assess potential causes. Follow-up PARs were acquired (Experimenter fit [EXP-Fit], followed by Subject re-fit [SUB Re-Fit]). EXP-Fit was intended to provide a perception (dubbed "ear canal muscle memory") of what a correctly fitted HPD should feel like. SUB Re-Fit was completed following EXP-Fit to determine whether a training recruit could duplicate EXP-Fit on her/his own without assistance. RESULTS: A one-way analysis of variance (ANOVA) (N = 320) showed that SELF-Fit means differed significantly between protocols (P < 0.001). Post-hoc analyses showed that the 1-freq SELF-Fit mean was significantly lower than all other protocols (P < 0.03) by 5.6 dB or more. No difference was found between the multi-frequency protocols. For recruits who were followed up with EXP-Fit (n = 79), across all protocols, a significant (P < 0.001) mean improvement of 25.68 dB (10.99) was found, but PARs did not differ (P = 0.99) between EXP-Fit protocols. For recruits in the 3-freq and 5-freq protocol groups who experienced all three PAR test methods (n = 33), PAR methods differed (P < 0.001) but no method by protocol interaction was found (P = 0.46). Post hoc tests showed that both EXP-Fit and SUB Re-Fit had significantly better attenuation than SELF-Fit (P < 0.001), but no difference was found between EXPFit and SUB Re-Fit (P = 0.59). For SELF-Fit, the 1-freq protocol resulted in a 35% pass rate, whereas the 3-, 5-, and 7-freq protocols resulted in >60% pass rates. Results showed that once recruits experienced how HPDs should feel when inserted correctly, they were able to properly replicate the procedure with similar results to the expert fit suggesting "ear canal muscle memory" may be a viable training strategy concomitant with HPD verification. Fit-test duration was also measured to examine the tradeoff between results accuracy and time required to complete each protocol. DISCUSSION: Results from this study showed the critical importance of initial selection and fitting of HPDs followed by verification (i.e., fit-testing) at Navy and Marine Corps accession points. Achieving adequate protection from an HPD is fundamentally dependent on obtaining proper fit of the issued HPD as well as the quality of training recruits receive regarding HPD use.

Preferred and minimum acceptable listening levels for musicians while using floor and in-ear monitors.

PURPOSE: This study examined the impact that changing on-stage music and crowd noise levels during musical performance had on preferred listening levels (PLLs) and minimum acceptable listening levels (MALLs) across both floor and in-ear monitors. METHOD: Participants for this study were 23- to 48-year-old musicians, with and without hearing loss, who had 10 years of musical training or comparable professional experience. For this study, PLLs and MALLs were established for the musician's own voice, whereas the levels of other onstage musical signals were systematically varied. PLLs for in-ear monitors were found at significantly lower levels than for floor monitors (approximately 0.6 dB). RESULTS: PLLs for in-ear monitors were found at significantly lower levels than for floor monitors (approximately 0.6 dB). However, despite large spectral differences, PLLs across the 2 monitor types were small enough that the same recommended exposure time would be advocated based on National Institute for Occupational Safety and Health and Occupational Safety and Health Administration recommendations. MALL data also indicated significantly lower levels (approximately 6.0 dB) when musicians were using in-ear monitors in comparison to floor monitors. CONCLUSION: The much larger difference suggests that musicians' risk of noise exposure may be reduced by the use of in-ear monitors. However, given the similar PLL results and known monitor output levels, proper counseling would likely be required before this potential advantage would be realized.

Individual differences within and across feedback suppression hearing aids.

BACKGROUND: New and improved methods of feedback suppression are routinely introduced in hearing aids; however, comparisons of additional gain before feedback (AGBF) values across instruments are complicated by potential variability across subjects and measurement methods. PURPOSE: To examine the variability in AGBF values across individual listeners and an acoustic manikin. RESEARCH DESIGN: A descriptive study of the reliability and variability of the AGBF measured within six commercially available feedback suppression (FS) algorithms using probe microphone techniques. STUDY SAMPLE: Sixteen participants and an acoustic manikin. RESULTS: The range of AGBF across the six FS algorithms was 0 to 15 dB, consistent with other recent studies. However, measures made in the participants ears and on the acoustic manikin within the same instrument suggest that across instrument comparisons of AGBF measured using acoustic manikin techniques may be misleading, especially when differences between hearing aids are small (i.e., less than 6 dB). Individual subject results also revealed considerable variability within the same FS algorithms. The range of AGBF values was as small as 7 dB and as large as 16 dB depending on the specific FS algorithm, suggesting that some models are much more robust than others. CONCLUSIONS: These results suggest caution when selecting FS algorithms clinically since different models can demonstrate similar AGBF when averaging across ears, but result in quite different AGBF values in a single individual ear.