It is known that musicians are exposed to potentially harmful sound levels during the course of regular practice, rehearsal, and performance. As a result, these individuals may have an increased risk of noise-induced hearing loss (NIHL). Previous research has shown that in typical daily practice, musicians can exceed daily recommended exposure limits (O'Brien et al., 2013). This research suggests that classical musicians are at high risk for NIHL according to t he National Institute for Occupational Safety and Health ( US Department of Health and Human Services, 1998) and the Occupational Safety and Health Administration (OSHA) guidelines . In addition, distortion-product otoacoustic emission (DPOAE) amplitude shifts have been found to be a sensitive measure for impact of high noise levels on inner-ear function (Lonsbury-Martin et al., 1990). The very livelihoods of musicians could depend on the development of NIHL awareness and prevention strategies. This study reports the sound-level exposures that University of Arizona music students experience in two hours of solitary practice and whether any correlative change in DPOAE amplitude occurred. Utilizing noise dosimetry, measurements of average sound levels and equivalent exposure for an eight-hour period were taken and compared to NIOSH and OSHA guidelines. Changes in inner-ear function were measured by DPOAE amplitudes taken immediately before and after each practice session. The goal of this research is to present data regarding sound-level exposure and address any significance in the correlative relationship between practice-session exposure levels and any shift in outer hair-cell function as determined by pre- and post-practice DPOAE evaluation.

Low-frequency noise is a health concern for workers in industrial workshops; rooms of highly varying size and dimensions, usually containing obstacles (the ‘fittings’). Low-frequency noise can be generated from sources such as reciprocating or rotating machinery, or ventilation systems. As the exposure time to the noise lengthens, workers are increasingly at risk to harmful effects such as hearing loss, communication difficulty, personal discomfort, and even nausea from induced body vibrations. Passive methods of noise control, such as absorption or barriers, generally perform better at high frequencies, but are inadequate at low frequencies. A proposed solution is active noise control, which relies on destructive interference of sound waves to reduce noise levels. However, this depends on phase, and how it is affected when sound waves encounter diffracting obstacles. In addition, the geometrical configuration of the active-control system must be optimized, which can be done using a prediction model. Sound-prediction models can also estimate the decibel level of sound within a given room configuration created by a source and the attenuation provided by the control system. Therefore, it is of interest to develop a model that predicts sound propagation in fitted rooms with phase. In this thesis, sound-pressure fields were investigated in rooms containing parallelepiped obstacles at low frequencies for which the wavelength is comparable to the obstacle dimensions. The geometric theory of diffraction (GTD) was used to model edge diffraction from an obstacle and, thus, the pressure field in shadow regions. A ray-tracing prediction model was improved to consider both the amplitude and phase of sound fields, and also the effects of edge diffraction. To validate the prediction model, experiments were performed in an anechoic chamber where a source and diffracting objects were located. In collaboration with Dr Valeau at the Université de Poitiers in France, a second model based on the finite element method (FEM) was used to compare prediction results. It was found that the phase depends mostly on the direct unblocked source-to-receiver distance. The FEM and experimental results showed that occluding objects cause phase shifts. The implementation of first-order diffraction into the ray-tracing program was successful in predicting shadow zones, thus producing a better prediction of realistic sound fields in rooms with obstacles. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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The work reported here is an experimental and theoretical investigation of high-frequency electrical noise generated in extrinsic single-crystal n-type germanium at high electric fields. The electric field was pulsed so that the lattice temperature remained near 77°K. During the pulse, the electrons quickly reach a non-equilibrium steady-state due to their gaining energy from the electric field and brought to a steady-state by means of collisions with the lattice vibrations. Previous work has been concerned with noise measurements made at right angles to the electric field direction, where anisotropic behaviour was observed. The present measurements, made in the direction of the electric field, also show a high degree of anisotropy. The electrical noise generated is described by the noise temperature, Tn, obtained by adapting the Nyquist formula to the non-equilibrium case. Measurements of Tn, performed at frequencies of 70Mc/s and 30Mc/s, indicated a uniform noise spectrum in this frequency range for all the samples used. The anisotropy of Tn suggested that Tn was explainable on the basis of the many-valley model of the conduction band of germanium, established by previous experimental investigations of the high-field mobility anisotropy. A feature of the many-valley model is that electrons in different valleys of the conduction band, will in general, exhibit different transport behaviour and as a result, transitions between these valleys will result in a noise phenomenon described as "intervalley noise". However, for measurements of Tn in the <100> direction, the "intervalley noise" will vanish, allowing a direct measure of the electron "heating" due to the electric field, the “hot electron noise”. In the <111> an <110> directions, both intervalley and hot electron noise are expected. Both contributions to Tn are evaluated by means of Barrie's extension to the case of many-valley germanium of Stratton's high-field transport theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The aim of the investigation is to identify and interrelate particular parameters that influence the magnitude of noise levels to which rock drillers are subjected. The percussive rock drill is known to be an excessively noisy machine. Currently, exhaust mufflers and other silencing devices are being developed but as yet acceptable noise levels have not been established. The definition of acceptable sound power levels for drills must recognize that the sound levels to which the drill operator is exposed are modified by the acoustic properties of the working environment. For the initial phase of the investigation a representative rock drill was selected as a noise source. Comparative sound levels generated by this machine were measured in a free field environment and in typical underground working places. Increases in the sound pressure levels in each octave band from 63 to 16,000 hertz were observed when the drill was operated in both stopes and drifts. For the subsequent phase of the investigation, studies were conducted on an assortment of commercially available rock drills. The changes in measured sound levels have been related to: the acoustic properties of the working place, the drill position relative to the walls, the length of drill steel exposed from the hole, and the drill air supply pressure. Based on the measurements taken throughout the investigation, sound pressure level correction factors are proposed. By applying these factors to sound levels generated under free field conditions, predictions of rock drill sound pressure levels present in underground working places can be made. In addition, when studies of rock drill noise levels in various operating configurations are being conducted, use of the factors permits reduction of observed sound level measurements to a common datum. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

In the past, spectral analysis of Arctic Sea ambient noise has been carried out by octave band pass filtering and linear rectification, followed by analogue Integration. To relate this integral to the power spectral density of the noise, the amplitude distribution of the noise has been assumed to be Gaussian, giving rise to certain errors. A system is proposed which consists of a stage of variable gain followed by a polarity coincidence statistical wattmeter and measures the power spectral density of ambient noise after band pass filtering. The wattmeter will handle an input signal dynamic range of at least 20 dB and does so regardless of the statistical nature of the noise. This dynamic range is extended dynamically by controlling the gain of the driving stage. The gain level is automatically adjusted during a one minute "adaptive" time interval so that the noise delivered to the wattmeter is over the region of optimal system operation. Measurement of the power spectral density of the ambient noise is then made in the subsequent four minute interval. A prototype wattmeter has been constructed and tested. The gain level is determined by requiring that the noise not exceed fixed levels more than a certain percentage of the time. This automatic adjustment is carried out during a one minute adaptive time interval, and a relatively accurate measure of the mean square value of the noise is determined during the four minutes that follow. For purposes of testing the prototype, d.c. inputs and sinusoidal inputs of wide frequency and amplitude ranges were used. The actual root mean square value of the inputs was measured with a thermal milliammeter and a precision voltage divider. The results of these tests show the region of operation where the input-output relationship of the wattmeter is linear. From these results, suggestions are made.as to how the proposed system could be modified to replace the analogue system used for Arctic Sea ambient noise spectral analysis. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The effects of cortical arousal on state complexity and evaluative importance were examined. Arousal was manipulated using two levels of white noise. In Study 1, a three-dimensional social domain was created using behavioral descriptions of eight fictitious people. In Study 2, subjects memorized these descriptions, and later, from memory, made similarity judgments among these eight targets while being exposed to either loud or soft white noise. The first hypothesis was that loud noise would effect an increase in the relative importance of the evaluation dimension. The second hypothesis was that this increased use of evaluation would be a result of a reduction in state complexity-evidenced by the other dimensions becoming less important. The results fully supported the first hypothesis and partially supported the second. There was also some support for the hypothesis that trait complex compared to trait simple individuals would be more affected by loud noise. However, the prediction that sensitizers would be more affected by the loud noise than repressors was not supported. The limitations of the second stud-y and new directions for research are discussed. / Arts, Faculty of / Psychology, Department of / Graduate

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No description available.