The use of personal hearing protection devices (HPDs) is often recommended to protect workers' hearing from noise-induced damage when no other means of reducing noise levels at the source is effective. The effects of HPDs on speech communication cannot be neglected in spite of their benefit in reducing the risk of hearing loss. While much research has been directed at speech perception, much less is known on how HPDs affect speech production. The tendency of talkers to raise their vocal effort in noise, known as the Lombard effect, is often disrupted by HPDs due to their occlusion effect and the lower noise at the ears as well as the attenuated feedback from one’s own voice. Three main knowledge gaps are addressed in this thesis. The first gap is to characterize speech produced by talkers with or without HPDs under realistic acoustic conditions while immersed in an external noise field. The second gap is to evaluate more comprehensively speech production under protected and unprotected talker and listener ear conditions in different types of fluctuating and continous noises. The third gap is to assess the alterations in the characteristics of speech produced by talkers wearing level-dependent HPDs set at different transmission gain settings and in comparison with passive HPDs. This thesis extends methods used to recover Lombard speech elicited in an external noise field. For this purpose, two noise suppression methods, direct waveform subtraction (DWS) and adaptive noise cancellation (ANC), were found to adequately remove noise from speech recorded for SNRs as low as −10 dB. Moreover, this work contributes new knowledge on the effects of conventional passive HPDs on speech production. When talker wears HPD in noise then speech level were found to decrease by up to 9 dB in continuous noises and by 7 dB in fluctuating noises compared to open ears, while speech levels were found to increase by about 5 dB in all noises when the listener wears HPD. Furthermore, changes in pitch and spectral levels were consistent with changes in speech levels. The effects of level-dependent HPD on speech production, depending on the chosen transmission gain setting, revealed that it led to smaller decrease in talkers’ speech levels in noise compared to conventional passive HPD. These findings indicate that the level-dependent HPDs may impede communication less than conventional passive HPDs, while providing protection against high levels of noise.

Despite the enactment of hearing protection laws and recommended standards over the last four decades, the prevalence of hearing loss among workers has remained unchanged. Limiting the amount of time spend in high noise areas, as well as wearing hearing protection devices, can reduce the effects of noise on hearing loss. Though research has examined the consistency of use of hearing protection devices (HPD) among workers, the importance of fit, and a real-world comparison to the marketed attenuation needed further examination. The goal of this project is to evaluate the effectiveness of HPDs used by agricultural and industrial workers enrolled in a hearing conservation program by comparing personal attenuation rating (PAR) to the manufacturer’s reported noise reduction rating (NRR). The two study groups were selected since workplaces are required to train workers enrolled in an OSHA Hearing Conservation Program on proper insertion techniques, but farmers do not typically receive any training on using hearing protection unless they are employed elsewhere. The effectiveness of the inserted HPDs were quantified via the 3M E-A-RfitTM Dual Ear Validation System, and the results were compared to the NRR provided by the manufacturer. The fit of hearing protection was evaluated for 60 farmers (247 plug pairs) and 76 workers (275 plug pairs), using four models of earplugs (two formable and two non-formable). The results show that although formable ear plugs have higher reported NRRs, a higher percentage of participants achieved PARs greater than or equal to the A-weighted adjusted NRR-7 for the non-formable plugs.

The research described herein was undertaken to determine how masked thresholds changed when individuals wore an active noise reduction (ANR) hearing protection device (HPD), a passive HPD, or no HPD. An ANR earmuff, a passive earmuff, and a user-molded foam earplug were tested in two types of noises (pink and red) at two different noise levels (85 dBA and 100 dBA). The signal used was an industry-standard backup alarm. The experimental design was completely within-subjects. An ascending method of limits was used to obtain 15-20 correct positive responses, which were then averaged to obtain the masked thresholds for each treatment condition. A visual probability monitoring task was incorporated in the experimental design to provide a loading task for the participants. In addition to masked thresholds, comfort and mental workload were assessed. Finally, participants were asked to rank each of the three HPDs with respect to their perceived ability to facilitate hearing the signal in noise. Results indicated that in 85 dBA noise, masked thresholds were lower when hearing protection devices were worn, compared to the unoccluded condition. Additionally, the results indicated that the ANR device provided a significant advantage (lower masked thresholds) over the passive earmuff in the low-frequency biased red noise (across both noise levels) and the 100 dBA noise level (across both noise spectra). However, the ANR earmuff exhibited no significant advantage over the user-molded foam earplug in any of the conditions. Rather, the user-molded foam earplug produced significantly lower masked thresholds at 100 dBA. The results also indicated that there was no difference between the three devices in their perceived ability to facilitate detection of the signal. There was also not a significant difference in comfort ratings between the three HPDs, although there were several complaints about the comfort of the ANR earmuff during the experiment. / Master of Science

Orientador: João Candido Fernandes / Banca: Edson Antonio Capello Sousa / Banca: Andrea Cintra Lopes / Resumo: O objetivo desta pesquisa foi determinar os níveis de atenuação de Dispositivos de Proteção Auditivos (DPAs), usando um teste chamado Resposta Auditiva de Estado Estável (RAEE). O teste RAEE é um exame eletrofisiológico que usa elétrodos para captar a atividade elétrica do tronco encefálico, sem depender da resposta do indivíduo, eliminando a subjetividade, assim como aspectos ligados à atenção, tempo de resposta, níveis de audição, etc. Neste método foram avaliados dez indivíduos, por meio da RAEE, estimulando-se o sistema de audição, primeiro sem protetor e, subsequentemente, com dois tipos de protetores auditivos, a saber um de inserção intra-auricular outro circunauricular de uso comum no mercado. Os resultados evidenciaram valores inferiores àqueles expressos no Certificado de Aprovação: para o plug, uma diferença de 10,3 dB, e para a concha, 4,3 dB. Na repetição dos testes, encontrou-se uma boa repetitividade, com diferença entre zero e 5 dB para 75% das frequências testadas. / Abstract: The purpose of this research was to determine the levels of attenuation of Hearing Protection Devices (HPDs) using a test called Auditory Steady-State Response (ASSR). The ASSR test is an electrophysiological examination that uses electrodes to capture the electrical activity of the auditory nerve and the brainstem without depending on the individual's response, thus eliminating the subjectivity of personal factors such as attention, response time, hearing ability, etc. This paper presents the results of a ten test which evaluated the hearing threshold of individuals, by first stimulating the hearing system without a protector and subsequently with a hearing protector. The results of this study were lower than those expressed in the Certificate of Approval: to plug a gap of 10.3 dB and dB the ear mufflers. The repetition of tests found a good repeatability with a difference between zero and 5 dB for 75% of the frequencies tested. / Mestre

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-18Bitstream added on 2014-06-13T18:34:56Z : No. of bitstreams: 1 queiroz_jl_me_bauru.pdf: 1056571 bytes, checksum: 740ab85f7a95dbf39493eb3d2218a8b5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo desta pesquisa foi determinar os níveis de atenuação de Dispositivos de Proteção Auditivos (DPAs), usando um teste chamado Resposta Auditiva de Estado Estável (RAEE). O teste RAEE é um exame eletrofisiológico que usa elétrodos para captar a atividade elétrica do tronco encefálico, sem depender da resposta do indivíduo, eliminando a subjetividade, assim como aspectos ligados à atenção, tempo de resposta, níveis de audição, etc. Neste método foram avaliados dez indivíduos, por meio da RAEE, estimulando-se o sistema de audição, primeiro sem protetor e, subsequentemente, com dois tipos de protetores auditivos, a saber um de inserção intra-auricular outro circunauricular de uso comum no mercado. Os resultados evidenciaram valores inferiores àqueles expressos no Certificado de Aprovação: para o plug, uma diferença de 10,3 dB, e para a concha, 4,3 dB. Na repetição dos testes, encontrou-se uma boa repetitividade, com diferença entre zero e 5 dB para 75% das frequências testadas. / The purpose of this research was to determine the levels of attenuation of Hearing Protection Devices (HPDs) using a test called Auditory Steady-State Response (ASSR). The ASSR test is an electrophysiological examination that uses electrodes to capture the electrical activity of the auditory nerve and the brainstem without depending on the individual's response, thus eliminating the subjectivity of personal factors such as attention, response time, hearing ability, etc. This paper presents the results of a ten test which evaluated the hearing threshold of individuals, by first stimulating the hearing system without a protector and subsequently with a hearing protector. The results of this study were lower than those expressed in the Certificate of Approval: to plug a gap of 10.3 dB and dB the ear mufflers. The repetition of tests found a good repeatability with a difference between zero and 5 dB for 75% of the frequencies tested.

Noise pollution is widespread in today’s society, from traffic to industrial sources, and many people are confined to unhealthy acoustic environments through their employment. When noise cannot be eliminated at the sound source, the protective measure is usually to equip the employee with hearing protection devices (HPDs), e.g. earmuffs, that attenuates the noise. Applying excessive attenuation can render the wearer disconnected from her acoustic environment and present risks and social isolation. HPDs using level-dependent function (LDF) uses ambient microphones together with a signal processing unit and internal loudspeakers to achieve attenuation flexibility – if ambient noise is low, the loudspeakers can amplify the sound to combat an excessive passive attenuation of the HPD, and if ambient noise is high this amplification is decreased to maintain healthy sound levels. Appropriate levels of attenuation allows the user to detect ambient sounds which contributes to the their situational awareness. Besides attenuating the sounds however, HPDs does change the spectral content of the sound which may complicate the ability to identify them. This thesis has focused on exploring the human ability to identify sounds, design a method for measuring this ability, implement it and evaluate its result and the method itself. The thesis has been conducted in collaboration with 3MTM PeltorTM and was intended to evaluate the effect of earmuffs with LDF on the ability to identify sounds in a process industry soundscape. The progression of the thesis was structured within the Double Diamond process, where literature reviews, benchmarking and workshops informed the research and resulted in a method design that was analyzed using a repeated measures ANOVA based on empirical data from 16 participants. Surprisingly, the results showed no statistically significant advantage from wearing a HPD using LDF, as opposed to no LDF, in the user accuracy or certainty in sound identification. The reasons for this are discussed with a focus on evaluating the usefulness of the designed method in future efforts to develop HPDs that afford reliable sound identification. / Bullerföroreningar är ett utbrett problem i dagens samhälle, från trafik till industriella källor, och många människor är låsta till en ohälsosam akustisk miljö via sin anställning. När buller inte kan elimineras vid ljudkällan är skyddsåtgärden vanligtvis att förse arbetstagaren med hörselskydd, exempelvis hörselkåpor, som dämpar bullret. Att använda en överdriven dämpning kan dock göra att användaren avskiljs helt från sin akustiska miljö och innebära risker samt social isolering. Hörselskydd utrustade med nivåberoende funktion (LDF) använder mikrofoner tillsammans med en signalbehandlingsenhet och interna högtalare för att uppnå flexibilitet i dämpningen – om omgivande buller är lågt kan högtalarna förstärka ljudet för att motverka en överdriven passiv dämpning erbjuden av hörselskyddet, om omgivande buller däremot är högt kan denna förstärkning minskas för att vidhålla sunda ljudnivåer. Lämpliga dämpningsnivåer gör att användaren kan upptäcka omgivande ljud som bidrar till deras situationsmedvetenhet. Förutom att dämpa ljuden så ändrar dock hörselskydd också det spektrala innehållet i ljudet vilket kan komplicera förmågan att identifiera ljuden. Denna masteruppsats har fokuserat på att utforska människans förmåga att identifiera ljud, utforma en metod för att mäta denna förmåga, implementera metoden och utvärdera dess resultat samt metoden i sig. Uppsatsen har genomförts i samarbete med 3MTM PeltorTM och var avsedd att utvärdera effekten av hörselkåpor, utrustade med LDF, på förmågan att identifiera ljud i ett ljudlandskap likt det i en processindustri. Projektet var strukturerad enligt Double Diamondprocessen, där litteraturstudier, benchmarking och workshops har informerat och väglett arbetet och resulterat i en metod som analyserats med hjälp av variansanalys baserat på empiriska data från 16 deltagare. Överraskande nog så visade resultaten ingen statistiskt signifikant fördel med att bära ett hörselskydd som är utrustat med LDF till skillnad från ett hörselskydd som saknar denna funktion, vad gäller användarens förmåga att korrekt identifiera ljud samt rapporterad säkerhet i svaren. Orsaker till detta diskuteras med fokus på att utvärdera användbarheten av den utformade metoden i framtida ansträngningar för att utveckla hörselskydd som erbjuder tillförlitlig ljudidentifiering.