Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2007. / Includes author's previously published papers. "Dissertation submitted for the award of the degree of Master of Engineering Science on the 25th of September, 2006. Qualified on the 28th November, 2006" Includes bibliography (p. 191-199) Also available in print form.

Federal regulations specify that an employee working for eight hours cannot legally be exposed to noise which has a time-weighted average greater than 90 decibels on the A scale. The industrial workforce is comprised of not only people with normal hearing acuity, but of individuals who suffer from hearing loss. While current noise regulation standards are deemed appropriate for those with normal hearing, it is difficult to apply these standards to persons wearing hearing aids on the job. The ambient, or unamplified, noise levels that fall below the maximum permitted by OSHA standards may very well be amplified to levels greater than 90 dBA, by the hearing aid. If this were the case, the company employing the hearing aid user would technically be in violation of the OSHA regulations. This study addressed the question of what noise exposure might be expected for hearing aid users on the job in different situations, as well as in non-vocational settings. The research involved two methods, conducted to determine the noise levels created by hearing aids with different amounts of gain and to determine whether the amplified noise levels exceed those requiring intervention under current regulations. For both methods, ambient and amplified noise levels for each condition were gathered in specified increments, and were compared with regard to current regulatory standards. The resultant data revealed that when ambient noise levels average between 80 and 84 dBA, amplification provided by even a mild gain hearing aid caused the eight hour time-weighted averages (TWA's) to increase to levels above the 90 dBA maximum permissible levels as delineated by OSHA. Moderate and high gain aids further increased these levels. The results of this study suggest that the hearing aid users in industrial and perhaps non-industrial settings may very well be exposed to intensity levels which exceed OSHA maximums, even when ambient levels do not. The extent to which these arc exceeded are based on the gain and output of the hearing aid in use.

In order to help reduce hearing loss, the Occupational Safety and Health Administration regulates noise levels in work environments. However, hearing aids are the primary rehabilitative service provided for individuals with an occupational hearing loss. Very little is being done to monitor hearing aid use in the work environment. Noise which may be safe to an unaided ear can amplified to levels that are damaging to the ear when a hearing aid is being worn. However, it is necessary for some individuals to wear amplification in these noisy environments for safety reasons. As a consequence it is important that these individuals be able to understand speech in the presence of industrial noise while wearing amplification. The purpose of this study was to determine if there is a significant difference in speech intelligibility between linear hearing aids and different types of non-linear hearing aids when they are used in the presence of industrial noise. Twenty-four normal hearing subjects were selected for this study. Each subject was ask to identify words in four CID W-22 lists which had been recorded through a linear hearing aid and two different non-linear hearing aids. Test results showed significantly better word· recognition for the linear in quiet condition over all other conditions. Significantly higher scores were obtained for the TILL condition than were obtained for the Linear in noise and the BILL condition. These preliminary results suggest that an individual wearing amplification in a noisy work environment would benefit with a TILL circuit. The TILL circuit would provide better speech intelligibility in this type of environment. Therefore, providing a safer work environment for the hearing aid user.

Thesis (M. Sc.)--University of Hong Kong, 1995. / Includes bibliographical references (leaves 72-75).

This thesis is focused on the industrial environment. This study aims to understand the difficulties wireless communications have when performing in these types of environment with a specific standard (and protocol) Zigbee. These difficulties are due mainly to the physical effects and interferences as well the electromagnetic waves from these wireless transmission signals can suffer. The background of this project is to analyze how industries can implement wireless sensor networks (using Zigbee standard) for their factories in order for them to be beneficial i.e. reliable or if it is possible. Industries normally tend to keep in the path of the old fashioned way i.e. wired systems which are more robust and can cope with the hard system requirements. Some study on these environment effects (interference as well) is performed. The results show how this (Zigbee) sensor network could be or should be implemented in order to have the best performance (disposition of devices, type of environment considering only industrial environments, etc.). Specifically, these results show that Zigbe wireless sensor networks are limited to some conditions in order to obtain the desired reliability. These conditions are that these networks must be performed in absorbing environments, LoS disposition of devices, not too long diatance between devices and not other networks in the same area using the same frequency band. The limitation of absorbing environments is because the dispersion effects in the (highly) reflective environments are critically damageful for the link. The limitation of the other devices operating in the same frequency band in a close area is due to the fact that Zigbee has no frequency diversity. Last but not least, the limitations to LoS and not too long maximum range (approximately 50 meters) are related since the range would be (much) lower than 50 meters if the communication was in NLoS disposition of devices. The noise in this environment is also studied and modeled. The results show that as the impulsive index (which is ameasure of the number of impulses that reach the receiver in a certain unit of time) takes larger values, the distribution approximates that of a Gaussian and as A takes lower values the reults show an impulsive characteristic. The Probability of error is computed for values of A less than 1, where the impulsive characterstic is shown, and as A takes larger values the error is greater.

Hearing protection devices (HPDs), a widely used countermeasure against noise-induced hearing loss, are laboratory-tested for their attenuation (noise reduction) capabilities. Unfortunately, laboratory tests overestimate the in-workplace performance of the devices, potentially leading to inadequate protection for the user. Many factors affect in-field effectiveness, including the physical design and "wearability" of the protector. Wearability, a highly subjective aspect which encompasses such characteristics as user comfort, ease of use, and acceptability, directly affects performance by influencing the regularity of use and the manner in which a protector is worn. This research investigated the influence of the user's work-related activities over a prolonged wearing period, and of variations in headband compression force and cushion material (liquid- or foam-filled) on achieved noise attenuation and wearability (comfort and acceptability) of earmuff hearing protectors. REAT (real-ear attenuation at threshold) testing procedures were used to collect attenuation data on 24 subjects, both prior-to and following completion of a simulated work task. Bipolar rating scales were utilized to collect pre- and post-task wearabi1ity data. Statistical analyses demonstrated that the work-related movement and wearing time significantly reduced achieved attenuation and, for higher compression earmuffs, also degraded perceived comfort and acceptability. A high headband compression force was 1inked to increased attenuation and to poorer user comfort and acceptance. The data revealed no significant difference in achieved attenuation or wearability between cushion types. The results illustrate the powerful influence of physical activity on HPD effectiveness and the criticality of certain earmuff design parameters to both attenuation and wearability. Furthermore, the existing tradeoff in earmuff design between comfort and attenuation was clearly demonstrated. / Master of Science

Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

This study aimed to investigate the effectiveness of the Quiet earplug noise protectors worn by a group of South African industrial workers exposed to excessive noise in the workplace. This was achieved by investigating the prevalence and amplitudes of distortion product otoacoustic emissions (DPOAEs), as they have been found to be sensitive to the effects of noise on the cochlea (Vinck, Van Cauwenberge, Leroy,&Corthals, 1999, p. 52). DPOAEs were recorded before and after noise exposure and were compared in order to determine whether the earplugs are providing sufficient protection against cochlear damage. DPOAEs were recorded using a test protocol where the primaries are fixed at L1 = 60dB SPL and L2 = 35dB SPL (L1 - L2 = 25dB) with an f2/f1 ratio of 1.18. The f2 frequencies were selected to correspond closely to the audiometric test frequencies of 2000Hz, 3000Hz, 4000Hz, 6000Hz and 8000Hz. The study found the prevalence of DPOAEs to be statistically stable and repeatable. This was true for DPOAEs measured successively during the same test sitting, as well as comparing prevalence determined before and after exposure to eight hours of noise. DPOAE prevalence alone was therefore not found to be a good indication of the temporary threshold shift (TTS) associated with the effects of noise on the cochlea. However, a significant finding of the study was that normal DPOAEs were recorded in only six right ears (24%) and seven left ears (28%) before noise exposure, even though all the subjects presented with hearing thresholds better than 25dB SPL. This may mean that cochlear pathology is already evident in some of the subjects tested. Further results of the study showed DPOAE amplitudes to be sensitive to the negative effects of excessive noise, as there was a significant difference between DPOAE amplitudes measured before and after the noise exposure. DPOAE amplitudes, specifically in the frequencies that are known to be affected by noise such as 4000Hz and 6000Hz, measured after the work-shift were significantly smaller than those measured before exposure to noise. Although correct usage of the earplugs could not be controlled for the duration of the noise exposure, each subject was instructed on the correct usage of the hearing protection before entering the noise zone. Bearing this limitation of the study in mind, because DPOAE amplitudes were reduced the implication is that the Quiet earplugs are not providing sufficient protection against the harmful effects of noise. / Dissertation (M (Communication Pathology))--University of Pretoria, 2005. / Speech-Language Pathology and Audiology / Unrestricted

A study was conducted to determine the dependency of sound attenuation capabilities of earmuffs and earcaps on various application instruction techniques including: (1) no instruction, (2) no instruction with 70 dBA auditory feedback, (3) manufacturers' package instruction, (4) detailed instruction, and (5) modeled instruction. The hearing protection devices (HPDs) studied were: two earcaps (Willson #20 Sound-Ban, Flents #055 Peace & Quiet Headband), and four earmuffs (E-A-R model 1000, Siebe Norton Industrial model 4540, Peltor H6A/v, and Willson 365A Sound Barrier). HPD comfort and wearer preferences were also assessed. Furthermore, typical excessive industrial machinery noises were sampled and analyzed across the 1/3 octave frequencies. Finally, an example is provided as to how these machinery noise spectra can be matched with HPD attenuation spectra to ascertain the protector which would afford optimal protection for a given noise situation. Fifty subjects (twenty-five males and twenty-five females) participated in the experiment. Attenuation characteristics of the HPDs were evaluated utilizing the real-ear attenuation at threshold (REAT) method. A three-way mixed factorial design was used for data collection and analysis of attenuation results. Bipolar scales were used to assess individual HPD comfort, and the HPDs examined were ranked to obtain user preferences. In the analysis of attenuation results, analysis of variance CANOVA) and pairwise comparisons were utilized to detect statistical significance. The comfort scales and ranking scores were evaluated using the Friedman one-way block design. Attenuation results for the earmuffs and earcaps tested showed that they were much less susceptible than earplugs (from a previous study by Epps, 1984) to changes in user insertion/donning instruction technique and also not as dependent on user gender. The main effect of gender was not significant, and in general, any instruction was better than no instruction at all but the effects of those instructions did not differ significantly among each other. As expected, there were main effect differences among the HPDs as to their attenuation capabilities, rated discomfort, and user preference. Because the main objective was on assessing donning instruction effects on HPD attenuation, the comfort/preference assessment was based on only a short (25 minutes) wearing time during the attenuation tests. Therefore, the comfort/preference ratings could likely vary given longer wearing periods and different work environments. All results found are discussed on the basis of the sample data obtained and conclusions drawn from these results should be limited to these experimental conditions and subsequent analyses, as actual attenuation achieved in practice may differ. The example of HPD-machinery noise matching illustrates that the attenuation/spectral matching procedure may indeed be a feasible way of selecting optimal protection for workers. / Master of Science