Real Ear Attenuation At Threshold Research Articles

Earplug fit-testing system applying pure-tone audiometer

As for the sound attenuation measurement method of hearing protectors, such as earplugs and earmuffs, the real-ear attenuation at threshold (REAT) method is established by some standards such as ISO, ANSI, AS, etc. As known, however, sound attenuation differences between workers wearing protectors in real occupational noise fields are not small due to personal size-fitness or wearing conditions of hearing protectors. Although personal hearing protector fit-testing systems have been developed and standardized in Western countries, the systems have not yet been standardized in Japan, so they are not applicable easily. The authors tried to apply the pure-tone audiometric system equipped with circumaural earphones used for a medical check-up to the fitting system for earplugs on this occasion, where the Japanese guidelines for preventing noise-induced impairments were revised for the first time in about 30 years. This paper describes the overview of the earplug fit-test system applying the audiometer and trial test results of sound attenuation ratings by the proposed system.

A new method for measurement of impulsive peak level attenuation of hearing protectors

ASA/ANSI S12.42-2010 contains the first standardized test method for measuring the performance of hearing protection devices (HPDs) with high-level impulsive noise. This standard defines the impulsive peak insertion loss (IPIL) as a time-domain metric that quantifies the reduction in peak sound pressure level provided by an HPD for impulsive noises. However, IPIL as defined in S12.42-2010 is dependent on the spectrum of the impulsive noise source used for measurements of HPDs. Recent studies of HPDs with impulsive noise have led to the investigation of frequency-domain metrics and calculation methods. Using frequency-domain calculations allows the impulsive peak level attenuation to be computed for a wide range of impulsive noises, not only those used for the measurement. Consequently, significant revisions to S12.42 are under consideration and a new standard, ISO 4869-7, is being developed in parallel with the ANSI revision. This presentation highlights key proposals and substantive changes including: measurement and calculation of the frequency-dependent impulsive insertion loss (IIL), incorporation of frequency-domain aspects such as real-ear attenuation at threshold (REAT) limits to attenuation, and a new impulsive peak level attenuation metric (IPLA) to be calculated from the REAT-bounded IIL.

A Tester to Evaluate the Correct Placement of Earplugs.

The use of hearing protection devices is one possible way of reducing the negative impact of noise on hearing. However, it is important to keep in mind that only properly used hearing protection devices provide adequate hearing protection. The aim of this article is to describe a newly developed tester to verify the correct placement of earplugs in the ear canal. This tester was developed using easily accessible and low-cost components. It implements the real-ear attenuation at threshold (REAT) method by which the sound attenuation of hearing protection devices is determined. The headphones with a greater low-frequency attenuation value were selected for use in the tester. The results of the sound attenuation measurement performed with the use of the tester did not differ by more than 5 dB compared to the measurements performed with the use of the Norsonic NOR838 system dedicated to this purpose. The developed tester is considered to be a device that will obtain reliable sound attenuation values. Thus, it can also be used as a device with which the correct placement of earplugs in the ear canal can be assessed.

Verification of Attenuation for Premolded Hearing Protection Devices Designed for Music.

High-fidelity premolded earplugs (HiFi HPDs) are designed to provide relatively uniform attenuation across frequencies. The primary goal of this study was to verify the amount and flatness of individual user attenuation. HiFi HPD attenuation was measured using real-ear attenuation at threshold (REAT) measurements under circumaural earphones. Participants were 16 adults tested using commercial HiFi HPDs marketed for use at recreational music events and/or for use by musicians. There was significant individual variation in attenuation both within and across HiFi HPD brands. In addition to significant differences in achieved attenuation, there were significant differences in the uniformity of the attenuation. These data suggest verification of attenuation is important in musicians who are at risk for music-induced hearing disorders even when using "over-the-counter" uniform-fit HPDs.

A comparison of methods to measure the sound attenuation of active noise reduction hearing protectors

Hearing protectors equipped with active noise reduction (ANR) functions have become popular and widespread in recent years. It is important to assess the sound attenuation performance of the ANR hearing protectors properly, which remains a problem. This work studies several typical measurement methods, including the real-ear attenuation at threshold (REAT), microphone in real-ear (MIRE), and the acoustic test fixture (ATF). In order to reduce the masking effect from the noise generated from the ANR electronic system when ANR is turned on during the REAT test, a modified tone sound instead of one-third octave band noise is used as the test signal. The results obtained from the different measurement methods on several ANR headphones and earphones are compared and the differences are discussed. It is found that the measurement differences among those methods are huge. The values of active insertion loss measured by the REAT method are much lower than those assessed by the MIRE procedure. This work contributes to the development of the test methods to assess the sound attenuation of the ANR hearing protectors.

Detection thresholds with active hearing protection devices in quiet and noise

The Real-Ear Attenuation at Threshold (REAT) method is a standardized (ANSI/ASA S12.6) method of assessing the passive attenuation of hearing protection devices (HPD), including electronic HPDs with the electronics turned off. Characterizing HPDs with electronics turned on is performed with the Microphone in Real Ear (MIRE) method, or with an acoustic test fixture, as described in ANSI/ASA S12.42. It has been proposed that the REAT method may be useful for characterizing the effect of HPDs on detection of ambient sounds for HPDs with hear-through microphones, including the effects of electronics noise from the HPD. In this study, detection thresholds were measured with three electronic earmuff-type HPDs using a method similar to the REAT method. Detection thresholds were obtained for warble tones presented from a loudspeaker placed in front of the subject in a sound treated room. Thresholds were measured with unoccluded ears and with three HPDs with hear-through capability in quiet and in noise. In addition, thresholds were measured with one of the HPDs with foam earplugs inserted into both ears to simulate a conductive hearing loss. The results point to the interaction between device noise, ambient noise, and human absolute thresholds as limitations on the detectability of ambient sounds.

High fidelity hearing protection devices: Attenuation in human ears and manikin devices

Flatness of attenuation was measured for high-fidelity hearing protection devices (HPDs) using microphone-in-real-ear (MIRE) and behavioral real-ear-attenuation-at-threshold (REAT) protocols. In addition, participants completed the words-in-noise (WIN) test with and without HPDs, and provided subjective ratings of perceived sound quality via surveys administered after listening to music with and without HPDs. Attenuation was also measured using a manikin device, with both the manikin-based microphone and the MIRE probe tube used to make measurements inside the artificial ear coupler. Among human participants, statistically significant correlations revealed decreased WIN performance and poorer music quality ratings as achieved HPD attenuation increased. There was also a statistically significant correlation in which shallower slope (flatter attenuation) was correlated with higher perceived music quality ratings. Achieved attenuation decreased in the coupler when the probe tube was inserted into the manikin, suggesting HPD seals were compromised by the probe tube. Consistent with the manikin data, attenuation in human ears was greater when measured using REAT, suggesting similar compromise of the HPD seal during MIRE tests. To assure high fidelity HPDs are well fit, REAT testing is recommended to verify both overall attenuation and flatness of attenuation in individual listeners.

Observations on the correlation of subjective and objective attenuation measurements on earplugs.

Real-ear attenuation at threshold (REAT) has been recognized as the gold-standard method to evaluate the attenuation of hearing protection devices (HPDs). The question is often posed as to whether or not REAT measurements could be replaced with objective, insertion loss (IL) measurements conducted on acoustical test fixtures for assessing the performance and consistency of HPDs. To understand how IL data correspond to REAT data for earplugs, both methods were used to assess three earplugs. The resulting data were compared, and the HPD attenuation ranked at each frequency. In most cases, after correction for bone conduction limits, occlusion effect, and physiological noise, IL data show good agreement with REAT values. Discrepancies at some frequencies were found and varied by HPD. The IL data did not identify the high standard deviation of the REAT results on one earplug. The IL data did not correspond well to the REAT values, resulting in differences as large as 12 dB at some frequencies. In conclusion, IL and REAT procedures are used for different purposes when assessing attenuation characteristics of HPDs. While close agreement was found at most frequencies, IL data may not reflect the REAT performance of HPDs equivalently in all aspects.

Validation of clinical techniques for verification of uniform attenuation earplugs

Objective: Uniform attenuation earplugs (UAE) theoretically provide near even attenuation across frequencies when built to a manufacturer’s specifications. Unfortunately, there is no current research available confirming if custom-molded uniform attenuation earplugs (UAE) are made to specifications nor is there guidance available on clinical methods of measuring attenuation of uniform attenuation earplug (UAE) devices. The goal of this study was to evaluate different procedures for UAE verification and to determine the most accurate clinically accessible verification protocol. Design: Attenuation was measured using probe microphone techniques, as well as real-ear attenuation at threshold (REAT) measurements under circumaural earphones, soundfield speakers and supra-aural earphones. Comparisons were made to a reference system created in the laboratory. Study sample: Seventeen adult participants, totaling 30 ears. Results: The results of this study demonstrate that the REAT measured in the soundfield using a narrowband noise stimulus with masking in the contralateral ear is currently the most accurate and widely available method of verifying UAEs. Conclusions: Factoring in clinical efficiency, the authors of this study recommend verifying attenuation levels using a soundfield REAT procedure as best clinical practice. In addition, the data suggests that REAT measurements under circumaural earphones are an acceptable second choice method.

Attenuation of ultrasonic noise in the 10-16 kHz frequency range by earplugs

The aim of the study was to determine attenuation of earplugs for ultrasonic noise in the frequency range of 10-16 kHz. The attenuation of earplugs in 1/3-octave-bands with the centre frequencies of 10 kHz, 12.5 kHz, and 16 kHz using the REAT (real-ear attenuation at threshold) method based on the measurements of hearing threshold of subjects. The study was carried out for 29 models of earplugs commonly used in the industry designed by various manufacturers, including 13 models of foam earplugs, 10 models of flanged earplugs, 5 models of headband earplugs and one model of no-roll earplugs. The values of the measured attenuation of earplugs are in the range 12.9-33.2 dB for the 10 kHz frequency band, 22.8-35.2 dB for the 12.5 kHz frequency band and 29.5-37.2 dB for the 16 kHz frequency band. The attenuation of earplugs in the frequency range 10-16 kHz has higher values (statistically significant changes) for foam earplugs than flanged earplugs (p = 0.0003 vs. p = 0.0006) or headband earplugs (p = 0.0002 vs. p = 0.04). The tests indicated that there is no uniform relation between the sound attenuation in the frequencies range of 10-16 kH and the catalogue H parameter (high-frequency attenuation value) of earplugs. Therefore, it is not possible to easily predict the attenuation of ultrasonic noise in the frequency range of 10-16 kHz using the sound attenuation data for the normally considered frequency range (up to 8 kHz). Med Pr 2018;69(4):395-402.

Observation on the variability of fitting by two experimenters at REAT and the agreement with objective measurement on three premolded earplugs

Real ear attenuation at threshold (REAT) has been recognized as the gold standard method to evaluate the attenuation of hearing protection devices (HPDs). It has been standardized in ANSI, ISO/EN and AS/NZS documents. The fitting of HPDs is one of the key factors of REAT measurement. The experimenter fit protocol of ANSI S3.19 is considered one precise approach to obtain the “best fit” of HPDs. A study of the attenuation obtained between the three fits for two experimenters on the same ten subjects on three premolded three-flange earplugs was conducted at 3M E-A-RCAL laboratory, including two models of Chinese brands earplugs and 3MTM E-A-RTM UltraFit earplug. Good agreement was shown between the REAT results that were obtained by the two experimenters. The REAT result of one Chinese brand earplug shows much higher variability within subjects. Comparing with the insertion loss (IL) measured by G.R.A.S 45CB, which has been corrected for bone conduction, occlusion effects and physiological noise, produced IL for two of the tested earplugs that did not showed good agreement with REAT results at most, but not frequencies. The discrepancies will be discussed.

Fit-testing systems for hearing protectors: ANSI standards to the rescue

To standardize the performance of fit-testing systems for hearing protection devices (HPDs), an ANSI/ASA standard has been in development since 2008. As of this writing, BSR/ASA S12.71 “Performance criteria for systems that estimate the attenuation of passive hearing protectors for individual users” has been submitted for public comment and ballot. This standard refers to fit-testing systems as field attenuation estimation systems (FAESs). In this talk, we introduce important FAES concepts, as handled in the draft S12.71. There are two types of FAESs: physical systems that take an objective measurement and psychophysical systems that rely on subjective responses from the user being tested. FAESs may produce a quantitative output as a personal attenuation rating (PAR) or simply indicate pass/fail for a given HPD fit. For all types of systems, S12.71 specifies methods to assess the quality of the attenuation estimates, by comparing the FAES results to a laboratory real-ear attenuation at threshold (REAT) measurement. Other important considerations covered in S12.71 include the maximum levels of ambient noise in which FAESs may be operated, the incorporation of uncertainties due to HPD fitting and spectral variability in users’ noise exposures, calibration intervals, and information that must be provided to users.

Attenuation of earmuffs used simultaneously with respiratory protective devices

In the work environment, apart from the noise, employees may be exposed to other harmful factors. Therefore, they wear hearing protectors and other personal protective equipment. The aim of the study was to determine whether simultaneous use of earmuffs and respiratory protective devices affects the attenuation of earmuffs. The study was conducted in laboratory conditions using the subjective REAT (Real Ear Attenuation at Threshold) and objective MIRE (Microphone in Real Ear) methods. The REAT method was used to measure sound attenuation of earmuffs, while MIRE was used to determine changes in attenuation of earmuffs due to the use of other personal protective equipment. The study showed reduction in attenuation of earmuffs due to the use of a full face mask up to 20 dB. Using a full face mask causes that attenuation of earmuffs in the low frequency range is close to zero. Reduction in attenuation due to the use of half masks for complete with particle filters (half masks) is 3-15 dB. Simultaneous use of earmuffs and filtering half masks makes small changes in attenuation not exceeding 3 dB. The study showed that full face masks give the greatest reduction in attenuation of earmuffs. On the other hand, the least reduction is observed in the case of filtering half masks. There is a significant difference between the reduction in attenuation of earmuffs worn with half masks for complete with particle filters because they may be equipped with different kind of the head strap. Med Pr 2017;68(3):349-361.

Inter-laboratory comparison of three earplug fit-test systems

ABSTRACTThe National Institute for Occupational Safety and Health (NIOSH) sponsored tests of three earplug fit-test systems (NIOSH HPD Well-Fit, Michael & Associates FitCheck, and Honeywell Safety Products VeriPRO). Each system was compared to laboratory-based real-ear attenuation at threshold (REAT) measurements in a sound field according to ANSI/ASA S12.6-2008 at the NIOSH, Honeywell Safety Products, and Michael & Associates testing laboratories. An identical study was conducted independently at the U.S. Army Aeromedical Research Laboratory (USAARL), which provided their data for inclusion in this article. The Howard Leight Airsoft premolded earplug was tested with twenty subjects at each of the four participating laboratories. The occluded fit of the earplug was maintained during testing with a soundfield-based laboratory REAT system as well as all three headphone-based fit-test systems. The Michael & Associates lab had the highest average A-weighted attenuations and smallest standard deviations. The NIOSH lab had the lowest average attenuations and the largest standard deviations. Differences in octave-band attenuations between each fit-test system and the American National Standards Institute (ANSI) sound field method were calculated (Attenfit-test - AttenANSI). A-weighted attenuations measured with FitCheck and HPD Well-Fit systems demonstrated approximately ±2 dB agreement with the ANSI sound field method, but A-weighted attenuations measured with the VeriPRO system underestimated the ANSI laboratory attenuations. For each of the fit-test systems, the average A-weighted attenuation across the four laboratories was not significantly greater than the average of the ANSI sound field method. Standard deviations for residual attenuation differences were about ±2 dB for FitCheck and HPD Well-Fit compared to ±4 dB for VeriPRO. Individual labs exhibited a range of agreement from less than a dB to as much as 9.4 dB difference with ANSI and REAT estimates. Factors such as the experience of study participants and test administrators, and the fit-test psychometric tasks are suggested as possible contributors to the observed results.

Using Auditory Steady-State Responses for Measuring Hearing Protector Attenuation.

Introduction:Present methods of measuring the attenuation of hearing protection devices (HPDs) have limitations. Objective measurements such as field microphone in real-ear do not assess bone-conducted sound. Psychophysical measurements such as real-ear attenuation at threshold (REAT) are biased due to the low frequency masking effects from test subjects’ physiological noise and the variability of measurements based on subjective responses. An auditory steady-state responses (ASSRs) procedure is explored as a technique which might overcome these limitations.Subjects and Methods:Pure tone stimuli (500 and 1000 Hz), amplitude modulated at 40 Hz, are presented to 10 normal-hearing adults through headphones at three levels in 10 dB steps. Two conditions were assessed: unoccluded ear canal and occluded ear canal. ASSR amplitude data as a function of the stimulation level are linearized using least-square regressions. The “physiological attenuation” is then calculated as the average difference between the two measurements. The technical feasibility of measuring earplug attenuation is demonstrated for the group average attenuation across subjects.Results:No significant statistical difference is found between the average REAT attenuation and the average ASSR-based attenuation.Conclusion:Feasibility is not yet demonstrated for individual subjects since differences between the estimates occurred for some subjects.

Spectral analysis of hearing protector impulsive insertion loss

Objective: To characterise the performance of hearing protection devices (HPDs) in impulsive-noise conditions and to compare various protection metrics between impulsive and steady-state noise sources with different characteristics. Design: HPDs were measured per the impulsive test methods of ANSI/ASA S12.42-2010. Protectors were measured with impulses generated by both an acoustic shock tube and an AR-15 rifle. The measured data were analysed for impulse peak insertion loss (IPIL) and impulsive spectral insertion loss (ISIL). These impulsive measurements were compared to insertion loss measured with steady-state noise and with real-ear attenuation at threshold (REAT). Study sample: Tested HPDs included a foam earplug, a level-dependent earplug and an electronic sound-restoration earmuff. Results: IPIL for a given protector varied between measurements with the two impulse noise sources, but ISIL agreed between the two sources. The level-dependent earplug demonstrated level-dependent effects both in IPIL and ISIL. Steady-state insertion loss and REAT measurements tended to provide a conservative estimate of the impulsively-measured attenuation. Conclusions: Measurements of IPIL depend strongly on the source used to measure them, especially for HPDs with less attenuation at low frequencies. ISIL provides an alternative measurement of impulse protection and appears to be a more complete description of an HPD’s performance.

Noise reduction ratings of active noise cancellation headsets

The recent promulgation of the MIL-STD 1474 E, “Design Criteria Standard Noise Limits,” combines data from the Real Ear Attenuation at Threshold (REAT) and the Microphone in Real Ear (MIRE) measurements to estimate the noise reduction rating of active noise cancellation (ANC) hearing protection devices. This paper will examine the American National Standards Institute standards, S12.6, S12.42, and S12.68 to assess the performance of four aviation headsets measured with REAT and MIRE methods. We will compare the protection estimates for different noises with the Noise Reduction Statistic for A-weighting (NRSA), Noise Reduction Statistic for Graphical (NRSG), and Octave Band rating methods. The NRSG method provides an efficient and accurate alternative to the Octave Band rating method. In the International Standards Organization, the ISO 4869 standard part 6 is under development to measure the attenuation of ANC protectors. Comparison with the proposed ISO 4869-6 standard will be conducted.

Review of the 2016 Edition of ANSI S12.6 and its place in the panoply of standards on the measurement of real-ear attenuation at threshold since 1957

The American standard specifying the procedure for the measurement of real-ear attenuation at threshold (REAT), often termed the gold standard in measuring hearing protector attenuation, was recently approved as an updated version, ANSI 12.6-2016. REAT was first standardized worldwide in the late 1950s in an American standard ANSI Z24.22-1957 and the method has evolved with time. Changes have affected the electroacoustic requirements for the sound field, instrumentation, audiometric method, and permissible background noise, but more importantly have also improved the specification of how the experimenter works with and fits the test subjects. So too, estimates of uncertainty are now included, and in the 2016 version they have been clarified and brought into harmony with ISO 4869-1. The author, who has been the chair since 1985 of the ANSI working group responsible for S12.6, will compare and contrast the various methods and present representative data as well as a discussion of the expanded uncertainties that are specified. Those values, for the 1/3-octave band test bands from 125 Hz to 8000 Hz, vary from approximately 1.5-2 dB for earmuffs and 2-3 dB for earplugs for within-laboratory testing, to 4-6 dB for earmuffs and 6.5-8 dB for earplugs for between laboratory measurements.

Attenuation of hearing protectors: A systematic comparison of subjective and objective measurement methods

A key component when selecting a hearing protector is the noise attenuation offered by the device. The subjective Real-Ear Attenuation at Threshold (REAT) test method is the most commonly used procedure to measure attenuation. On the other hand, with the increase popularity of individual fit testing and miniaturization of electronic components, the Microphone-In-Real-Ear approach (MIRE), and its field counterpart F-MIRE, are becoming more appealing and well suited for estimating attenuation in laboratory or in “real world” occupational conditions. In this approach, two miniature microphones are used to measure sound pressure levels in the ear canal under the protector and outside of the protector. This study presents a systematic evaluation of the various factors relating the subjective and objective attenuation values. Experiments on human subjects were carried out where the subjects were instrumented on both ears with microphones outside and underneath their protector. They were then asked to go through...

Soft tissue conduction as a possible contributor to the limited attenuation provided by hearing protection devices.

Context:Damage to the auditory system by loud sounds can be avoided by hearing protection devices (HPDs) such as earmuffs, earplugs, or both for maximum attenuation. However, the attenuation can be limited by air conduction (AC) leakage around the earplugs and earmuffs by the occlusion effect (OE) and by skull vibrations initiating bone conduction (BC).Aims:To assess maximum attenuation by HPDs and possible flanking pathways to the inner ear.Subjects and Methods:AC attenuation and resulting thresholds were assessed using the real ear attenuation at threshold (REAT) procedure on 15 normal-hearing participants in four free-field conditions: (a) unprotected ears, (b) ears covered with earmuffs, (c) ears blocked with deeply inserted customized earplugs, and (d) ears blocked with both earplugs and earmuffs. BC thresholds were assessed with and without earplugs to assess the OE.Results:Addition of earmuffs to earplugs did not cause significantly greater attenuation than earplugs alone, confirming minimal AC leakage through the external meatus and the absence of the OE. Maximum REATs ranged between 40 and 46 dB, leading to thresholds of 46–54 dB HL. Furthermore, calculation of the acoustic impedance mismatch between air and bone predicted at least 60 dB attenuation of BC.Conclusion:Results do not support the notion that skull vibrations (BC) contributed to the limited attenuation provided by traditional HPDs. An alternative explanation, supported by experimental evidence, suggests transmission of sound to inner ear via non-osseous pathways such as skin, soft tissues, and fluid. Because the acoustic impedance mismatch between air and soft tissues is smaller than that between air and bone, air-borne sounds would be transmitted to soft tissues more effectively than to bone, and therefore less attenuation is expected through soft tissue sound conduction. This can contribute to the limited attenuation provided by traditional HPDs. The present study has practical implications for hearing conservation protocols.