The thesis deals with computational modelling of heavy duty off-road vehicle driveline components. The thesis is divided to two main parts. The first part deals about modal analysis of selected driveline components. MBS computational study was performed based on modal analysis results. The second part of thesis deals with experimental verification of computational model. Pass-by noise and vibration measurement was performed. Measured signals were processed in frequency domain to find noise and vibration sources.

Dynamic finite element modeling and analysis of a refrigeration compressor was investigated as part of a noise emission study. Natural frequencies and normal mode shapes were calculated for the major structural components of the compressor. The components were later combined to form a model of the compressor assembly which was subsequently solved for its dynamic properties. Model development included coordination with test data for verification and revision to improve model prediction accuracy. Considerable efforts were made to accurately represent the hermetic shell which presents several inherent modeling difficulties due to its geometry and other characteristics which result from a deep drawn manufacturing process. The importance of physical simplifications such as geometry representation, thickness variation, attachments, the welded seam, and residual stresses were established. In addition, theoretical limitations of the finite element method were addressed as a cause for analysis-test discrepancies. Housing models developed were found to agree within 12% of experimental natural frequencies up to 1100 Hz. Compatibility of analytical normal modes with resonant dwell experimental deflection shapes was considered. Analytical forced vibration response showed situations when the deflected shapes can be a superposition of modes rather than the pure mode shape. Analytical simulation of the test setup improved the agreement of analysis and test data. Additional components modeled include the internal compressor mechanism and its supports. Analysis showed that interactions with the internal components, particularly resonances within the suspension springs, are important for a valid representation of the compressor assembly. Resonances within the internal suspension components more than double or nearly triple the number of resonance frequencies in the compressor assembly. / Master of Science

Thesis (M. Tech.) - Central University of Technology, Free State, 2006 / Occupational noise affects industries in many countries around the world, and there is strong evidence from previous research linking it to noise-induced hearing loss (NIHL). More than 30 million workers in the United States of America alone were exposed to hazardous noise at the workplace before 1998. In South Africa, workers are not supposed to be exposed to a noise rating limit at or above 85dB(A). Abattoir employees are subjected to high noise levels when compared to the occupational noise rating limit of 85dB(A). Noise is generated from various mechanised and manual processes and activities in the abattoir during the slaughter of different animal species. Noise sources include conveyers, circular saws, air conditioners and pumps, pneumatic and other mechanical equipment. The aim of this study was to characterise noise exposure in different grades of abattoirs during the slaughter of cattle and sheep. The grading of abattoirs was previously done according to Grade A-E. Grade A-C is now referred to as high throughput abattoirs while Grade D and E are referred to as low throughput abattoirs. Personal and environmental noise exposure levels of workers in Grade A, C and D abattoirs in the Free State were therefore investigated. Noise measurements were done in accordance with the methods stipulated in the South African National Standards (SANS) Code of Practice 10083. Environmental and personal sampling were conducted with a calibrated Type 1 Quest integrated sound level meter (ISLM) and a Quest noise dosimeter respectively. Calibration was checked before and after taking measurements to ensure reliability and validity of results. The average noise exposure level in the high throughput abattoirs was above the recommended standard of 85dB(A). In the low throughput abattoirs the noise exposure levels were below this level. There were no statistically significant differences between the noise exposure levels during the slaughter of different species (P>0.05), or between Grade A and Grade C (P>0.05). There was a statistically significant difference (P<0.05) however between Grade A and Grade D noise exposure levels. The results indicate that workers in Grade A and C abattoirs are exposed to unacceptable noise levels. Further research is recommended to include all categories of abattoirs and to determine the impact of noise exposure on the worker’s hearing in order to develop strategies to protect employees from the effects of excessive exposure to noise.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis addresses the complications that are encountered when characterising the performance of differential microwave LNAs. The predominant sources of noise in electronic circuits are introduced and equivalent two-port noise models for active devices are derived. Correlation between noise generators are defined by means of the noise correlation matrix and existing network theory is adapted to include noise analysis of twoport and multi-port networks. Mixed-mode scattering parameters are introduced in order to define the signal performance of differential and common-mode propagation in multi-port networks and, by applying the same theory, the mixed-mode correlation matrix for a three-port dLNA is derived. Furthermore, an expression is derived for de-embedding the differential noise figure of a three-port dLNA using two single ended measurements. Two dLNA designs, both incorporating wideband 180°-Hybrid ring couplers, are discussed and the differential signal and noise performance of the dLNAs are compared to that of their constituent single ended LNAs. / AFRIKAANSE OPSOMMING: Hierdie tesis behandel die komplikasies wat ontwerpers in die gesig staar tydens die karakterisering van mikrogolf differensiële laeruis versterkers. Die hoof ruisbronne in stroombane word bespreek en ekwivalente tweepoortnetwerkmodelle vir aktiewe toestelle word afgelei. Korrelasie tussen ruisbronne word gedefnieer deur middel van ruiskorrelasiematrikse en bestaande tweepoort- en multipoort-netwerkteorie word aangepas om ruismodelle in te sluit. Weens die feit dat differensiële- en gemene-wyse voortplanting van seine voorkom in multipoortnetwerke word gemengde-modus S-parameters behandel. Dieselfde teorie maak dit vervolgens moontlik om die gemengde-modus ruiskorrelasiematriks van ’n drie-poort differensiële laeruis versterker af te lei. Verder word daar ’n wyse voorgestel waarmee die differensiëleruissyfer van ’n drie-poort differensiële laeruis versterker vanuit twee enkel ruissyfermetings bereken kan word. Twee differensiële laeruis versterker ontwerpe, waarvan beide wyeband 180 -differensiaalkoppelaars implementeer, word bespreek en die differensiëlesein- asook die differensiëleruis-werking word vergelyk met die werking van die omsluite ongebalanseerde laeruis versterkers.

Följande studie har utförts på begäran av energiföretaget Norrenergi AB, där det finns en önskan att tillförlitlighetssäkra den nuvarande driften av stofttransportsystemet tillhörande två av värmeverkets hetvattenpannor. Studien har undersökt huruvida det finns möjlighet att framförallt minska underhållskostnaderna. Studien har framförallt inriktats mot två stofttransportfläktar som vardera tillhör ett stofttransportsystem, eftersom mycket underhållsarbete lagts på de fläktarna. En jämförelse med andra liknande verk har även utförts då det visats att Norrenergi AB:s lösning av stofttransporten är ytterst ovanlig. Vidare har en analys av fläktarna utförts, vilken visade att de är underdimensionerade för systemet. Det har konstaterats utifrån genomförda SPM-, temperatur- och bullermätningar. Olika typer av lösningar på problemet har undersökts och då på en förändring av hela systemet, alternativt enbart av fläktarna eller lagren till stofttransportfläktarna. Rapporten har utmynnat i flera förslag vilka innefattar en ny systemutformning, installation av nya fläktar samt en uppgradering av det nuvarande systemet, där installation av nya fläktar rekommenderas. / This study has been carried out at the request by the energy company Norrenergi AB. It consists of an analysis on how they can reduce the maintenance regarding two dust transporting fans installed in the flue gas cleaning compartment of their thermal power plant. The study also compares what solutions other plants have regarding the dust-transport. The solution installed at Norrenergi AB was found to be rather unusual. Measurements and calculations have been performed to investigate further what have caused the high maintenance on the fans. The study looks into what upgrades are available to the entire dust transporting system. The result of the study turned into different suggestions, which includes a new configuration of the dust transporting system, and installation of new fans and also an upgrade of the existing dust transporting system. Among the suggestions the final recommendation is the alternative of installing new fans.

O ruído é um fator que contribui negativamente para a habilidade de compreensão da fala, o que pode prejudicar o desenvolvimento da criança com deficiência auditiva. Nas salas de aula, a fala raramente é transmitida a criança sem que haja interferência do ruído de fundo. Ao mesmo tempo, a efetiva transmissão da informação auditiva é imprescindível para um melhor desempenho acadêmico. Na maioria dos ambientes de aprendizagem, o que mais interfere para que haja uma boa percepção da fala é a relação sinal/ruído (S/R). O Sistema de Frequência Modulada (FM) funciona como o meio mais efetivo para melhorar a captação do sinal da fala e eliminar os efeitos da distância, ruído e reverberação em ambiente educacional. Objetivo: Avaliar a relação S/R a que crianças com deficiência auditiva estão expostas em ambiente escolar e comparar com o limiar de recepção da fala no ruído. Métodos: O trabalho foi realizado com crianças com deficiência auditiva e com linguagem oral estabelecida, usuárias de aparelho de amplificação sonora individual (AASI) e/ou implante coclear (IC) acoplados ao Sistema FM. A mensuração da relação sinal ruído foi realizada através da utilização de um gravador digital portátil e um programa de processamento de áudio para computador. Para avaliação da percepção da fala no ruído, foi aplicada a versão brasileira do teste Hearing in Noise Test (HINT), em campo livre em dois momentos: primeiramente com a criança utilizando apenas seus AASIs e/ou IC e em um segundo momento com o Sistema FM acoplado ao dispositivo individual. Resultados: Todas as crianças apresentaram melhor percepção da fala no ruído com o uso do Sistema FM. Apenas em uma sala de aula a relação sinal/ruído está adequada. Observou-se que a posição do aluno na sala de aula realmente influencia na qualidade da relação S/R a qual o mesmo está exposto. Também foi comprovado que, quanto maior o número de alunos, mais baixa é a relação S/R da sala de aula. Conclusão: A relação S/R da sala de aula em situação real de ensino mostrou-se com um valor mais próximo à relação S/R em que o paciente consegue compreender o discurso com o uso do Sistema FM, demonstrando que o uso do dispositivo é essencial para melhor compreensão da fala nesse ambiente. / Noise is a factor that contributes negatively to the ability to understand speech, which can harm the development of children with hearing impairment. In classrooms, speech is rarely transmitted to children without interference from background noise. At the same time, the effective transmission of auditory information is essential for better academic performance. In most learning environments, which further interferes so there is a good speech perception is the signal/noise ratio (S/N). The Personal Frequency Modulation (FM) Systems serves as the most effective way to improve the uptake of speech signal and eliminate the effects of distance, noise and reverberation in the educational environment. Objective: To evaluate the S/N ratio that hearing impaired children are exposed in a school environment and compare with the speech reception threshold in noise. Methods: The study was conducted with children with hearing impaired and spoken language established, users of a hearing aids and/or cochlear implant (CI) coupled to FM system. The measurement of signal to noise ratio was achieved by the use of a portable digital recorder and an audio processing program for computer. To assess speech perception in noise was applied the Brazilian version of the Hearing in Noise Test (HINT), in two stages: first with the child using only their hearing aid\'s and/or CI and a second time with FM system coupled to individual device. Results: All children had better speech perception in noise using the FM system. Only in a one classroom the S/N ratio is adequate. It was observed that the position of the student in the classroom really affect the quality of the S/N ratio to which it is exposed. It was also proven that the higher the number of students, the lower the S/N ratio of the classroom. The S/N ratio of the classroom in a real school showed up with a value closer to the S/N ratio in which the patient can understand speech using the FM system, demonstrating that the use of this device is essential to better understand speech in these environments.

O ruído é um fator que contribui negativamente para a habilidade de compreensão da fala, o que pode prejudicar o desenvolvimento da criança com deficiência auditiva. Nas salas de aula, a fala raramente é transmitida a criança sem que haja interferência do ruído de fundo. Ao mesmo tempo, a efetiva transmissão da informação auditiva é imprescindível para um melhor desempenho acadêmico. Na maioria dos ambientes de aprendizagem, o que mais interfere para que haja uma boa percepção da fala é a relação sinal/ruído (S/R). O Sistema de Frequência Modulada (FM) funciona como o meio mais efetivo para melhorar a captação do sinal da fala e eliminar os efeitos da distância, ruído e reverberação em ambiente educacional. Objetivo: Avaliar a relação S/R a que crianças com deficiência auditiva estão expostas em ambiente escolar e comparar com o limiar de recepção da fala no ruído. Métodos: O trabalho foi realizado com crianças com deficiência auditiva e com linguagem oral estabelecida, usuárias de aparelho de amplificação sonora individual (AASI) e/ou implante coclear (IC) acoplados ao Sistema FM. A mensuração da relação sinal ruído foi realizada através da utilização de um gravador digital portátil e um programa de processamento de áudio para computador. Para avaliação da percepção da fala no ruído, foi aplicada a versão brasileira do teste Hearing in Noise Test (HINT), em campo livre em dois momentos: primeiramente com a criança utilizando apenas seus AASIs e/ou IC e em um segundo momento com o Sistema FM acoplado ao dispositivo individual. Resultados: Todas as crianças apresentaram melhor percepção da fala no ruído com o uso do Sistema FM. Apenas em uma sala de aula a relação sinal/ruído está adequada. Observou-se que a posição do aluno na sala de aula realmente influencia na qualidade da relação S/R a qual o mesmo está exposto. Também foi comprovado que, quanto maior o número de alunos, mais baixa é a relação S/R da sala de aula. Conclusão: A relação S/R da sala de aula em situação real de ensino mostrou-se com um valor mais próximo à relação S/R em que o paciente consegue compreender o discurso com o uso do Sistema FM, demonstrando que o uso do dispositivo é essencial para melhor compreensão da fala nesse ambiente. / Noise is a factor that contributes negatively to the ability to understand speech, which can harm the development of children with hearing impairment. In classrooms, speech is rarely transmitted to children without interference from background noise. At the same time, the effective transmission of auditory information is essential for better academic performance. In most learning environments, which further interferes so there is a good speech perception is the signal/noise ratio (S/N). The Personal Frequency Modulation (FM) Systems serves as the most effective way to improve the uptake of speech signal and eliminate the effects of distance, noise and reverberation in the educational environment. Objective: To evaluate the S/N ratio that hearing impaired children are exposed in a school environment and compare with the speech reception threshold in noise. Methods: The study was conducted with children with hearing impaired and spoken language established, users of a hearing aids and/or cochlear implant (CI) coupled to FM system. The measurement of signal to noise ratio was achieved by the use of a portable digital recorder and an audio processing program for computer. To assess speech perception in noise was applied the Brazilian version of the Hearing in Noise Test (HINT), in two stages: first with the child using only their hearing aid\'s and/or CI and a second time with FM system coupled to individual device. Results: All children had better speech perception in noise using the FM system. Only in a one classroom the S/N ratio is adequate. It was observed that the position of the student in the classroom really affect the quality of the S/N ratio to which it is exposed. It was also proven that the higher the number of students, the lower the S/N ratio of the classroom. The S/N ratio of the classroom in a real school showed up with a value closer to the S/N ratio in which the patient can understand speech using the FM system, demonstrating that the use of this device is essential to better understand speech in these environments.

Trafikbuller är den miljöstörning som påverkar flest människor i Sverige. Studier visar att buller kan påverka människors hälsa genom att orsaka hörselskador, stress, sömnsvårigheter och i förlängningen hjärt- och kärlsjukdomar. Idag byggs städerna i Sverige allt tätare, vilket gör att antalet bullerstörda personer fortsätter att öka. För att dämpa buller används ofta höga och breda bullerskärmar, vilket inte är att föredra i urban miljö. Ny forskning undersöker därför andra alternativ, bland annat hur växter och gröna områden kan verka bullerreducerande. Forskare menar att växter med hjälp av sina stammar, bladverk och substratet de står i kan reducera ljud genom reflektion, absorption och spridning av ljudenergin. Detta examensarbete syftade till att utvärdera olika växtelement ur bullerreducerande synpunkt. Växters bullerreducerande förmåga är något varken akustiker eller landskapsarkitekter generellt sett tar hänsyn till och därför ansågs en kunskapssammanställning ligga i tiden. För att göra detta har en litteraturstudie, två intervjuer samt mätningar på två växtelement utförts. Mätningarna gjordes på häckar längs Luthagsesplanaden i Uppsala och på en fasad med klätterväxter på Norr Mälarstrand i Stockholm. Litteratur- och intervjustudien visade att växtbeklädda bullerbarriärer hade högst potential att reducera buller längs vägar, gröna tak högst potential att reducera buller in på innergårdar och gröna fasader högst potential att dämpa buller på torg. Växter har också möjlighet att osynliggöra ljudkällor, vilket gör att vi upplever ljudet som lägre. Mätningarna visade att häcken på Luthagsesplanaden hade möjlighet att dämpa ljudet precis bakom häcken med upp till 3 decibel (dBA). Minskningen höll sig inte ända in till fasaden vilket tros bero på att det reflekterade ljudet dominerar i gaturummet samt att den avskärmande effekten minskar med ökat avstånd. Höga frekvenser dämpades bäst av häcken med den högsta dämpningen på 18 dBA för frekvensbandet 16000 Hz. Dämpningen av de höga frekvenserna syns även in vid fasaden med en dämpning kring 4-5 dBA. Häcken efterliknades i modelleringsprogrammet CadnaA med den nordiska beräkningsmodellen för vägtrafikbuller, men inget objekt tycktes kunna representera häcken på ett reproducerbart sätt. På Norr Mälarstrand visades ingen signifikant skillnad i varken ljudtrycksnivå eller frekvensfördelning från fasaden med klätterväxter. En dämpning på upp till 4 dBA för frekvenser över 800 Hz kan dock antydas in vid fasaden. Vid modellering av fasaden visades att varken en reflekterande eller en absorberande fasad kunde representera klätterväxterna. / Traffic noise is the environmental problem that affects most people in Sweden. Studies show that noise can affect human health by causing hearing damage, stress, insomnia and cardiovascular disease. Swedish cities today are built increasingly close, increasing the number of people that are affected by noise. Today, the most common way to reduce noise is to use barriers. In towns, this is not preferable and new research brings up other suggestions that can fit into an urban environment. Some studies are investigating how plants can reduce noise. Research has shown that plants by their trunks, foliage and substrate can reduce sound by reflection, absorption and diffusion. This thesis aimed to identify and evaluate various plant elements through a noise abatement perspective. This perspective is something neither acoustician nor landscape architects in general takes into account and was therefore considered useful. To do this, a literature study, two interviews and measurements were made. The measurements were made on hedges along Luthagsesplanaden in Uppsala and on a facade with climbing plants on Norr Mälarstrand in Stockholm. The literature and the interviews showed that vegetated noise barriers had the highest potential to reduce noise along roads, green roofs had the maximum potential to reduce noise in courtyards and green facades had the maximum potential to reduce noise in squares. Plants are also able to hide sound sources, enabling us to perceive the sound as lower. The measurements showed that the hedge were able to lower the sound pressure level up to 3 decibels (dBA). This reduction did not last to the facade, which is believed to be due to reflected sound dominating the street canyon and that the shielding ability decreases with increasing distance. The hedge was able to lower the higher frequencies the most with the maximum attenuation of 18 dBA for the frequency 16000 Hz. The attenuation of high frequencies is also visible close by the facade with attenuation around 4-5 dBA. The hedge were imitated by different elements in the sound modeling program CadnaA with the help of the Nordic calculation model for road traffic noise, but no element seemed to be able to represent the hedge. The measurement at Norr Mälarstrand showed no significant difference in either sound pressure level or frequency distribution by the facade with climbing plants. However, a damping of up to 4 dBA for frequencies above 800 Hz could be hinted from the measurement by the facade. When modeling the same it was shown that neither an absorbing facade nor a reflecting facade could represent the facade with climbing plants.

The study investigated the feasibility of including DPOAEs in the annual medical surveillance test battery for the identification of NIHL in a group of employees in a manufacturing industry in KwaZulu-Natal. Feasibility was investigated by exploring the sensitivity, specificity and predictive efficiency of DPOAEs, the ability of DPOAEs to detect subtle noise-induced cochlea changes, the test-retest reliability of DPOAEs and lastly, the duration of time taken to conduct the DPOAE test bilaterally. A cross-sectional and repeated measures within-in participant design was utilized in the study. A purposive convenience sampling technique was used, as well as a stratified sampling approach in order to realize objective two of the study. The study consisted of 60 participants, which were further stratified into four test groups, i.e. Group A: 0-3 years, Group B: 3.1-6 years and Group C: 6.1-9 years and Group D: 9.1-13 years of working within the beverage manufacturing industry. A high sensitivity and negative predictive value was reported in the current study, suggesting that DPOAEs may be able to identify those who present with subtle cochlea changes as a result of exposure to occupational noise. The sensitivity of DPOAEs was 100% at 1, 2, 4, 6 and 8kHz in the right ear and at 4 and 6kHz in the left ear. The specificity of DPOAEs in the current study ranged between 55%-97% across the frequency range in the right ear and 49%-88% in the left ear. A negative predictive value of 100% was obtained bilaterally across the frequency range, except at 8kHz in the left ear. Visual inspection of the DPgram in the current study revealed a bilateral reduction in DPOAE amplitudes for all test groups in the high frequency region of the DP-Gram, namely, 5477Hz and 7303Hz, in the absence of a statistically significant difference (p>0.05). A greater frequency range appears to be affected in this group of workers, indicating that the type of noise, namely, impulse noise, may result in cochlea changes. Corresponding changes on the pure tone audiogram were not observed, however, noise notch configurations were observed for the groups with a longer history of noise exposure. This was not seen bilaterally as is typically expected with NIHL. Good test-retest reliability across the frequency range obtained in the current study further indicates the feasibility of including DPOAEs in the annual medical surveillance test battery. Additionally, the current study calculated an average of 86 seconds (1 minute 26 seconds) to conduct the DPOAE test bilaterally, confirming that DPOAEs are a quick test to administer. The findings of this study suggest that DPOAEs may be used to monitor early subtle noise-induced cochlea changes for workers exposed to noise in the beverage manufacturing industry as part of the annual medical surveillance test battery. / Thesis (M.Comm.Path.)-University of KwaZulu-Natal, Westville, 2013.

Made available in DSpace on 2015-05-14T12:47:12Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2059659 bytes, checksum: f3d773c696e3797e353a21eae5946320 (MD5) Previous issue date: 2012-03-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / INTRODUCTION: NIHL (Noise Induced Hearing Loss) is a condition that results from the accumulation of prolonged exposure to noise, causing a slow and progressive hearing impairment, sensorneural, not very deep, but irreversible. The dentist, individuals exposed to noise in their workplace, is susceptible to NIHL. OBJECTIVE: To analyze the auditory and possible risk factors that interfere with the hearing of the dentists from USFs (Unidades de Saúde da Família / Familiar Health Unities) in Joao Pessoa / PB. METHODOLOGY: There were interviews, audiological evaluations, instrumental and environmental noises within 65 dentists from Family Health Units in Joao Pessoa / PB to identify auditory characteristics and risk factors for hearing-surgeons dentists by using proportion measures calculation for categorical variables, and having the Statistical Logistic Regression Method. RESULTS: It was observed that 43.07% of the dentists who were evaluated had lower hearing in, at least, some of the characteristic frequencies of NIHL. It was found that the main ear symptoms cited by these professionals were to have the sensation of hearing loss (55%), and buzzer (50%), and also that the instruments which showed values above the allowed limits were turbine high rotation (61%) and the compressor (55%). The variables considered as risk factors for hearing loss based on logistic regression were: age over 45 years old, working time more than 10 years, a feeling of hearing loss, tinnitus and noise level of the compressor greater than 85 dB. CONCLUSION: The ear symptoms (tinnitus and hearing loss) are presented in a large number of dentists, and the noise emitted by the instruments used by these professionals is often high, presenting some risk factors for Noise Induced Hearing Loss and some of them may be prevented or controlled through specific strategies. / INTRODUÇÃO: A Perda Auditiva Induzida por Ruído (PAIR) é uma patologia decorrente do acúmulo de exposições a ruído prolongadas, gerando uma deterioração auditiva progressiva e lenta, sensorioneural, geralmente não muito profunda mas irreversível. Sabe-se que o cirurgião-dentista, indivíduo exposto ao ruído no ambiente de trabalho, é susceptível à PAIR. OBJETIVO: Analisar o perfil auditivo e possíveis fatores de risco que interferem na audição dos cirurgiões-dentistas das USFs (Unidades de Saúde da Família) de João Pessoa/PB. METODOLOGIA: Realizaram-se entrevistas, avaliações audiológicas e dos ruídos instrumental e ambiental com 65 cirurgiões-dentistas das Unidades de Saúde da Família de João Pessoa /PB, a fim de identificar características do perfil auditivo e de fatores de risco para a audição dos cirurgiões-dentistas, utilizando o cálculo de medidas de proporção para as variáveis categóricas, e tendo como método estatístico a Regressão Logística. RESULTADOS: Observou-se que 43,07% dos cirurgiões-dentistas avaliados apresentaram rebaixamento auditivo em pelo menos alguma das frequências características da PAIR. Verificou-se ainda que os principais sintomas otológicos citados por estes profissionais foram a sensação de déficit auditivo (55%), e o zumbido (50%). Os instrumentos que mais se apresentaram com valores de intensidade acima dos limites permitidos foram a turbina de alta rotação (61%) e o compressor (55%). As variáveis consideradas como fatores de risco para a perda auditiva com base na Regressão Logística foram: idade acima de 45 anos, tempo de trabalho maior que 10 anos e nível de ruído do compressor maior que 85 dB, além da presença dos sintomas de sensação de déficit auditivo e zumbido. CONCLUSÃO: A sintomatologia otológica (zumbido e diminuição auditiva) está presente em grande número dos cirurgiões-dentistas e o ruído emitido pelos instrumentos utilizados por estes profissionais é muitas vezes elevado. Constataram-se alguns fatores de risco para a Perda Auditiva Induzida por Ruído, podendo alguns destes ser prevenidos ou controlados por meio de estratégias específicas.