Electronic Hearing Protectors Research Articles

Measuring the effect of electronic hearing protection devices on behavioral detection thresholds

Electronic hearing protection devices can provide amplification for quiet ambient sounds, while still providing protection against loud sounds. These can be important in environments with sporadic and unpredictable hazardous noise, but also with a need for maintaining awareness of ambient sounds, or for conducting face-to-face communication. This study’s aim was to understand what impact electronic hearing protection devices have on auditory detection thresholds. Human subjects were used to measure thresholds for narrowband noise bursts without hearing protection, with electronic hearing protectors powered off, and with electronic hearing protectors powered on with several gain settings. In addition, electroacoustic measurements were made of the input/output functions and electronic noise floors of the hearing protectors at the same gain settings. The data showed that thresholds in quiet with electronic hearing protectors were higher than without, regardless of the device amplification. This could be attributed to the hearing protector electronic noise limiting performance. Thresholds measured with ambient masking noise were similar across open ear and device conditions, reflecting that the signal-to-noise ratio for ambient sounds does not change with amplification. Listeners with a simulated conductive hearing loss had lower thresholds with an electronic hearing protector than without, suggesting a benefit of the device amplification.

Learning to localize a broadband tonal complex signal with advanced hearing protectors and TCAPS: the effectiveness of training on open-ear vs. device-occluded performance

(1) determine if untrained, normal-hearing listeners could learn, with regimented practice trials, to localise a dissonant tonal complex while wearing electronic hearing protectors and achieve equivalent performance to the unoccluded ear, (2) determine if different protector designs affect the localisation learning curve, and (3) determine if a sequential training regimen could be used to determine whether a device is not amenable to training effects. All subjects completed paired training and testing trials, in 12 Learning Units (LU), first with the open ear., then half with device A, a US Army TCAPS (INVISIO® X50), and the other half with device B (a prototype). Both groups then finished with the opposite device. Ten subjects participated, with thresholds below 25 dBHL, bilateral symmetry below 15 dBHL, and naivety with electronic protectors and localisation testing. Subjects eventually approached their open ear capability with device A, but never reached equivalent open ear nor asymptotic performance with device B. Depending upon a protector’s sound transduction, frequency response, and other characteristics, different amounts of training are required to adapt. The training protocol has value in determining device acceptability based on the training burden required, especially when mission-related localisation performance is important.

Stop gambling with your hearing

In 2014, the National Hearing Conservation Association took its chances and held its 39th annual conference, titled Stop Gambling with your Hearing, in Las Vegas. The authors who contributed to this issue of the International Journal of Audiology demonstrated that they could be relied upon to deliver a royal flush when it comes to advancing research and knowledge for worker hearing loss prevention. The papers that we were privileged to shepherd through the review process share common themes: epidemiologic and workplace assessments of hearing and new methods to better assess hearing and the effects of wearing hearing protection upon the speech intelligibility and localization. Hearing loss prevention starts with education and testing. The study by Flamme et al. has expanded the work from last year’s supplement, considering how audiometric testing may be changed. Will pure-tone audiometry become passe? The potential to integrate hearing testing with hearing protector fit-testing seems natural, and combining testing with training in the use of personal protection technology makes sense. Without question, occupational hearing conservation programs must begin with engineering noise controls to reduce exposures for at risk workers. Cantley et al. explored the relationship between hearing loss and tinnitus and workplace injury. They found an increased risk of acute injury among workers with tinnitus and high-frequency hearing loss. Although their research does not draw strong correlations between tinnitus and increased incidence of workplace injury, the communication needs of hearing impaired workers cannot be overlooked. Helleman et al. considered the effects of interrupted exposures to loud music at night clubs - often cited as a potential cause of hearing loss. Their research suggests that quiet zones within clubs little effect on the hearing of the subjects they evaluated. However, providing club patrons a place to get out of the noise was still thought to be important because high noise levels present a risk in and of themselves. Hong et al. investigated the relationships between occupational exposures and hearing among elderly Latino Americans. They concluded that a reduction of occupational exposure to noise and chemicals will have a positive impact on better hearing later in life. Worker adoption of hearing protection use is challenged by the effect of attenuation on communication. When passive hearing protection is worn properly, it further degrades the ability of a hearing impaired worker to communicate. Giguere et al. investigated the effect of hearing protection on communication for persons with various degrees of hearing impairment. Sound restoration hearing protection had positive benefits for both impaired and normal hearing persons. Whereas Giguere used the Hearing in Noise Test (HINT) to estimate Speech Reception Threshold, Hiselius et al. utilized the Call-sign Acquisition Test (CAT) to determine the effect of different amounts of hearing protection on communication ability. Hiselius’ approach proved to be an efficient means of assessing several products. Both methods are useful for determining worker communication needs and abilities with a system that could be implemented in conjunction with hearing protection fit testing. In addition to affecting speech intelligibility, hearing protection use can critically impact localization ability. Casali and Robinette investigated the performance of different electronic hearing protectors on localization for groups who received varying amounts of training. They demonstrate that localization ability improved after listeners acclimated to hearing the world through a new set of filters. Finally, we consider the effect of diet and dietary supplements on hearing. Rosenhall provides evidence that high quality diet is associated with better hearing and high frequency hearing. Although establishing such correlations is complex and not conclusive, good dietary habits appear to be important to maintaining hearing health. We invite you to read this special supplement and consider how you may implement new techniques within your practice of hearing loss prevention. We wish to highlight and thank our sponsors who contributed to the supplement: National Hearing Conservation Association, National Institute for Occupational Safety and Health, and Safe-in-Sound Excellence in Hearing Loss Prevention Award™ along with Roger Angelelli, Council for Accreditation in Occupational Hearing Conservation (CAOHC), Honeywell Inc., and HTI Inc..

Flexible piezoelectric energy harvesting from jaw movements

Piezoelectric fiber composites (PFC) represent an interesting subset of smart materials that can function as sensor, actuator and energy converter. Despite their excellent potential for energy harvesting, very few PFC mechanisms have been developed to capture the human body power and convert it into an electric current to power wearable electronic devices. This paper provides a proof of concept for a head-mounted device with a PFC chin strap capable of harvesting energy from jaw movements. An electromechanical model based on the bond graph method is developed to predict the power output of the energy harvesting system. The optimum resistance value of the load and the best stretch ratio in the strap are also determined. A prototype was developed and tested and its performances were compared to the analytical model predictions. The proposed piezoelectric strap mechanism can be added to all types of head-mounted devices to power small-scale electronic devices such as hearing aids, electronic hearing protectors and communication earpieces.

The challenge of localizing vehicle backup alarms: Effects of passive and electronic hearing protectors, ambient noise level, and backup alarm spectral content

A human factors experiment employed a hemi-anechoic sound field in which listeners were required to localize a vehicular backup alarm warning signal (both a standard and a frequency-augmented alarm) in 360-degrees azimuth in pink noise of 60 dBA and 90 dBA. Measures of localization performance included: (1) percentage correct localization, (2) percentage of right--left localization errors, (3) percentage of front-rear localization errors, and (4) localization absolute deviation in degrees from the alarm's actual location. In summary, the data demonstrated that, with some exceptions, normal hearing listeners' ability to localize the backup alarm in 360-degrees azimuth did not improve when wearing augmented hearing protectors (including dichotic sound transmission earmuffs, flat attenuation earplugs, and level-dependent earplugs) as compared to when wearing conventional passive earmuffs or earplugs of the foam or flanged types. Exceptions were that in the 90 dBA pink noise, the flat attenuation earplug yielded significantly better accuracy than the polyurethane foam earplug and both the dichotic and the custom-made diotic electronic sound transmission earmuffs. However, the flat attenuation earplug showed no benefit over the standard pre-molded earplug, the arc earplug, and the passive earmuff. Confusions of front-rear alarm directions were most significant in the 90 dBA noise condition, wherein two types of triple-flanged earplugs exhibited significantly fewer front-rear confusions than either of the electronic muffs. On all measures, the diotic sound transmission earmuff resulted in the poorest localization of any of the protectors due to the fact that its single-microphone design did not enable interaural cues to be heard. Localization was consistently more degraded in the 90 dBA pink noise as compared with the relatively quiet condition of the 60 dBA pink noise. A frequency-augmented backup alarm, which incorporated 400 Hz and 4000 Hz components to exploit the benefits of interaural phase and intensity cues respectively, slightly but significantly improved localization compared with the standard, more narrow-bandwidth backup alarm, and these results have implications for the updating of backup alarm standards.

A qualitative assessment of the performance of electronic, level-dependent earmuffs when used on firing ranges

A qualitative workplace trial was undertaken to examine the performance of sound restoration, level-dependent electronic hearing protectors (HPs) in a high impulsive noise environment using participants who were very experienced in the regular use of passive HPs. The results indicate that this type of HP is well accepted by experienced users, particularly so, by those who appreciate reliable communication while wearing the devices.

Vehicle Backup Alarm Localization (or Not): Effects of Passive and Electronic Hearing Protectors, Ambient Noise Level, and Backup Alarm Spectral Content

A parametric human factors experiment employed a hemi-anechoic sound field in which listeners were required to localize a vehicular backup alarm warning signal in 360-degrees azimuth. Measures of localization performance included: 1) percentage correct localization, 2) percentage left/right localization errors, 3) percentage front/rear localization errors, and 4) the absolute deviation in degrees from the alarm's location. In summary, the data demonstrated that normal hearing listeners did not improve in their ability to localize the backup alarm warning signal in 360-degrees azimuth when wearing augmented hearing protectors (including dichotic sound transmission earmuffs, flat attenuation earplugs, and level-dependent earplugs), as compared to when wearing conventional passive earmuffs or earplugs of the foam or flanged types. Furthermore, a diotic sound transmission earmuff resulted in the poorest localization. Localization was also degraded in 90 dBA pink noise, as compared to the relatively quiet condition of 60 dBA pink noise. An augmented backup alarm which incorporated 400 Hz and 4000 Hz components to exploit the benefits of interaural phase and intensity cues slightly improved localization compared to the standard, more narrow-bandwidth backup alarm, and these results have implications for the updating of backup alarm standards.

Vehicle Backup Alarm Localization (or Not): Effects of Passive and Electronic Hearing Protectors, Ambient Noise Level, and Backup Alarm Spectral Content

A parametric human factors experiment employed a hemi-anechoic sound field in which listeners were required to localize a vehicular backup alarm warning signal in 360-degrees azimuth. Measures of localization performance included: 1) percentage correct localization, 2) percentage left/right localization errors, 3) percentage front/rear localization errors, and 4) the absolute deviation in degrees from the alarm's location. In summary, the data demonstrated that normal hearing listeners did not improve in their ability to localize the backup alarm warning signal in 360-degrees azimuth when wearing augmented hearing protectors (including dichotic sound transmission earmuffs, flat attenuation earplugs, and level-dependent earplugs), as compared to when wearing conventional passive earmuffs or earplugs of the foam or flanged types. Furthermore, a diotic sound transmission earmuff resulted in the poorest localization. Localization was also degraded in 90 dBA pink noise, as compared to the relatively quiet condition of 60 dBA pink noise. An augmented backup alarm which incorporated 400 Hz and 4000 Hz components to exploit the benefits of interaural phase and intensity cues slightly improved localization compared to the standard, more narrow-bandwidth backup alarm, and these results have implications for the updating of backup alarm standards.

Effects of binaural electronic hearing protectors on localization and response time to sounds in the horizontal plane

The effects of electronic hearing protector devices (HPDs) on localization and response time (RT) to stimuli were assessed at six locations in the horizontal plane. The stimuli included a firearm loading, telephone ringing and .5-kHz and 4-kHz tonebursts presented during continuous traffic noise. Eight normally hearing adult listeners were evaluated under two conditions: (a) ears unoccluded; (b) ears occluded with one of three amplitude-sensitive sound transmission HPDs. All HPDs were found to affect localization, and performance was dependent on stimuli and location. Response time (RT) was less in the unoccluded condition than for any of the HPD conditions for the broadband stimuli. In the HPD conditions, RT to incorrect responses was significantly less than RT to correct responses for 120 degrees and 240 degrees , the two locations with the greatest number of errors. The RTs to incorrect responses were significantly greater than to correct responses for 60 degrees and 300 degrees , the two locations with the least number of errors. The HPDs assessed in this study did not preserve localization ability under most stimulus conditions.

Effect of electronic hearing protectors on speech intelligibility : Durkin, J. Bureau of Mines, Pittsburgh, Pennsylvania, USA. Report of Investigation 8358, 1979, 19 pp; abstr in CIS Abstracts (CIS 79-1891)

Effect of electronic hearing protectors on speech intelligibility : Durkin, J. Bureau of Mines, Pittsburgh, Pennsylvania, USA. Report of Investigation 8358, 1979, 19 pp; abstr in CIS Abstracts (CIS 79-1891)