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Published Articles


The Volume 15, No 4, December 2010




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A Comparison Study of Foam versus Custom Silicone Earplugs Used as Part of an Intelligent Electronic Hearing Protector System

Olav Kvaloy, Tone Berg and Viggo Henriksen


https://doi.org/10.20855/ijav.2010.15.4267


During the development of an intelligent hearing protection and communication system the attenuation of two different earplugs were measured. Both earplugs were measured separately and in combination with earmuffs. Foam earplugs and custom-moulded silicone earplugs were both used. The hearing protection system in question is able to measure the ear canal with respect to leaks. If a leak is detected, the system will warn the user. The measurements show that the foam plug gives higher attenuation than the silicone plug at all frequencies, but particularly at frequencies below 2 kHz. It has a steadily increasing attenuation from 30 dB - 43 dB over the frequency range 125 Hz- 8 kHz. The silicone plug attenuates around 26 dB, from 125 Hz - 1 kHz. Above this range, the attenuation increases to approximately 40 dB. With extra earmuffs added, the attenuation is 40 dB or better at all frequencies except 125 Hz, and the two plugs offer nearly identical protection. The results show that the mean and standard deviation of the attenuation for the foam earplug is as good as for an optimally fitted earplug. In the case of the silicone earplug, the mean attenuation is comparable to a typical custom earplug, but the standard deviation is better than comparable earplug. This finding is a result of the leakage control acting as a "supervisor" in the fitting of the earplugs.


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Modelling Speech Intelligibility in the Noisy Work- place for Normal-hearing and Hearing-impaired Listeners Using Hearing Protectors

Christian Giguere, Chantal Laroche and Veronique Vaillancourt, Sigfrid D. Soli


https://doi.org/10.20855/ijav.2010.15.4268


A speech intelligibility model was developed and validated for use in workplace environments with hazardous noise levels that require the use of hearing protection devices (HPDs). Two speech perception studies were carried out in laboratory simulations of eight workplace noise environments. The first experiment (n = 32 normal-hearing individuals) was used to develop a general model for speech intelligibility that can be tuned to the specific charac- teristics of the noise. The second experiment (n=35) was used to validate the general model for use with listeners covering a wide range of hearing profiles (up to severe hearing loss) and wearing HPDs (earplugs or earmuffs). The model took into account the characteristics of the noise, the signal-to-noise ratio (SNR), the attenuation of the hearing protector, and the hearing status of the listener. Good prediction of speech intelligibility scores in noise with HPDs required the use of correction factors to deal with both audibility (threshold) and distortion (supra threshold) effects arising from hearing loss. Correction factors due to audibility effects were computed from the Speech Intelligibility Index and the pure-tone audiogram. Correction factors due to distortion effects were based on the Hearing-in-Noise Test.


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Powered Electronic Augmentations in Hearing Protection Technology Circa 2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission, and Tactical Communications Devices: Review of Design, Testing, and Research

John G. Casali


https://doi.org/10.20855/ijav.2010.15.4269


Augmented or enhanced hearing protection devices (HPDs), as contrasted with conventional HPDs, which attenuate noise strictly through static, passive means, have proliferated in the past decade. These advancements in HPDs are generally delineated into passive (non-powered) and active (powered electronic) designs. While passive augmentations are reviewed in a parallel paper elsewhere in this issue,1 active augmentations include various analog and digital circuits for achieving electronic phase cancellation of noise; electronic modulated sound transmission circuits, which amplify a passband of ambient sound and transmit it through the HPD (ceasing to amplify at a predetermined noise level); and tactical communications and protection systems (TCAPS), which may include any of the aforementioned electronic elements plus microphone/receiver communications elements. The intended benefits of electronic augmented HPDs, some of which are realized in practice and others not, include more natural hearing for the user, improved speech communications and signal detection, reduced noise-induced annoyance, improved military tactics, stealth and gunfire protection, and provision of protection that is somewhat tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of active augmented HPDs that were available or have been prototyped circa early-2010. In some cases, no empirical research on the augmentations and their performance was available in the research literature; in these cases, this review relied on patents, corporate literature, and/or the author's experience. For other technologies, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law pertaining to specific augmentation technologies are mentioned herein,2 along with that proposed law's cited ANSI standards, as well as ISO standards that address hearing protector attenuation testing.


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Passive Augmentations in Hearing Protection Technology Circa 2010 including Flat-Attenuation, Passive Level-Dependent, Passive Wave Resonance, Passive Adjustable Attenuation, and Adjustable-Fit Devices: Review of Design, Testing, and Research

John G. Casali


https://doi.org/10.20855/ijav.2010.15.4270


Augmentations or enhancements to conventional HPDs, that is, those which attenuate noise strictly through static, passive means, are generally delineated into passive (non-electronic) and active (powered electronic) designs. While powered electronic augmentations are reviewed in Casali1 (a parallel paper elsewhere in this issue), passive augmentations are represented by mechanical networks to achieve flat-by-frequency attenuation; level-dependent leakage pathways that house acoustically-variable occluders to yield minimal attenuation during quiet periods but sharply increasing attenuation upon intense noise bursts (such as gunfire); quarter-wave resonance ducts to bolster attenuation of specific frequencies; selectable cartridges or valves that enable passive attenuation to be adjusted for specific exposure needs; and dynamically adjustable-fit devices that provide adjustment features to enable personalized fit to the user as well as some degree of attenuation control. Intended benefits of passive augmented HPDs (akin to those of active devices as well) include (1) more natural hearing for the user, (2) improved speech communications and signal detection, (3) reduced noise-induced annoyance, (4) improved military tactics, stealth maintenance and gunfire protection, and (5) provision of protection that is tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of passive augmented HPDs that were available or have been prototyped circa early-2010. In cases where no empirical research results on the passive augmentations and their performance were available in the research literature, this review relied on patents, corporate literature, and/or the author's experience. For certain augmentations, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law that pertain only to specific passive augmentation technologies are mentioned herein,2 along with references to relevant standards on hearing protector attenuation testing.


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Intra-Subject Fit Variability for Field Microphone- In-Real-Ear Attenuation Measurement for Custom Molded Earplugs

Jeremie Voix and Cecile Le Cocq


https://doi.org/10.20855/ijav.2010.15.4271


Over the last few years, several field attenuation measurement systems (FAMS) have been introduced to the in- dustrial marketplace to measure the individual end-user attenuation for some hearing protection devices (HPDs). Although individual measurement is necessary to determine whether a given user is properly protected in his or her real-life noise environment (assuming that the exposure level is known), one unknown remains with a FAMS measurement: how reliable are the predictions made from the instantaneous measurement (over a few minutes), for determining the attenuation that will be achieved later in the field (over months or years) by the end-user who may fit them slightly differently every time? This paper will address that question for one FAMS, the field microphone- in-real-ear (F-MIRE) measurement technique, and we will study, in the laboratory, how consistently subjects can fit and refit HPDs without assistance. A new metric, the intra-subject fit variability, will be introduced and will be quantified for custom-molded earplugs as fitted by inexperienced test subjects. This paper will present the experi- mental process used and statistical calculations performed to quantify the intra-subject fit variability. The number of successive refits required for a given prediction accuracy will also be presented, as well as the uncertainty component associated with the intra-subject fit variability when using an F-MIRE field attenuation measurement system.


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