This work undertook the examination of the perceived barriers that exist to the management of occupational noise exposure in the workplace. Exposure to excessive levels of noise results in cumulative damage to the hearing mechanism of the ear and a subsequent hearing loss. This hearing loss is permanent and does not recover over time. Initially the conventional method of addressing or controlling noise exposure was through Hearing Conservation Programs and more recently through Occupational Noise Management Programs that take more of a risk management approach. However, the numbers of new hearing loss claims submitted through the various ???workcover??? and ???worksafe??? authorities in Australia continue to remain very high. Hearing loss claims rank within the top two in number of new claims each year. The research conducted shows that there are four main barriers perceived by individuals that work against the institution of effective preventive action. These four main barriers in order of priority are hearing protectors, information, culture and management, and are themselves each composed of several lesser factors. Each of the barriers was examined more closely in an attempt to better understand how they operate and the potential to discover how they may be overcome. To briefly summarise the main barriers: 1) Hearing protectors are uncomfortable, impede communication and are unpleasant to wear; 2) Individuals would like more information on noise reduction and for this information to be supplied by management; 3) workplace and management culture needs to be supportive of occupational health and safety in general and with the implementation of supportive preventive measures in particular; and 3) management needs to be seen to place importance on occupational health and safety in the workplace in general and the reduction of excessive noise in particular. By being aware of the barriers and operation the design of future more effective intervention or better noise management programs should be possible.

Tonal noise propagating in ducts and radiating from their outlets is a common problem in situations where a fan or a blower is used to drive exhaust gases through the exhaust duct out to the environment. It is also a problem in the exhausts of large diesel engines such as those used to power large marine vessels. One way of attenuating tonal noise propagating in ducts is to use one or more side branch resonators, each of which is specifically designed for optimal performance at a particular frequency. One of the major problems associated with the use of side branch resonators is that any slight change in excitation frequency decreases the effectiveness of the resonators. The change in excitation frequency can be caused by a change in the speed of the engine, fan or blower, or change in temperature in the duct, which changes the speed of sound, and hence the wavelength of the noise. Resonators incorporating a provision for altering their geometry in real - time in order to adapt to environmental or operating condition changes is one approach that has been used by previous researchers. In particular, adaptive Helmholtz resonators have received considerable attention in the literature. Previous work has involved the use of one or more pressure sensors located in the duct downstream of the resonator to provide a cost function to be minimised by an electronic control system which alters the geometry of the resonator. However, in many cases, especially where the duct serves as a passage for exhaust gases to be driven out to the environment, it is not desirable to mount microphones in the duct. Also, microphones located remote from the resonator introduce wiring problems as well as the need to mount the microphones at the correct location in the duct, which will change as the wavelength of the tonal noise in the duct changes as a result of changes in operating or environmental conditions. It is highly desirable to have a completely self - contained Helmholtz resonator ( HR ) which can be attached to the duct and for which the only external wiring needed is the power supply. The work described in this thesis is concerned with the development of a self - contained adaptive HR which can be optimally tuned by using signals from two microphones located in the cavity and neck of the resonator, respectively. The primary focus of the work is the development of a novel cost function, which can be used by an electronic controller to optimally tune the HR. The scope of the analysis has been restricted here to the ' no mean flow ' condition. The theoretical and numerical analysis of the duct - HR system is first conducted using the well known transfer matrix method and finite element analysis ( FEA ) software package ANSYS, respectively. The net acoustic power transmission in the duct downstream of the HR is estimated by using the two - microphone method. Analysing the duct - HR system with the transfer matrix method mandates the incorporation of three end - correction factors which are related to the unflanged open end of the duct, neck - cavity interface and neck - duct interface. However, because of the complexity in estimating the end - correction factor of the neck at the neck - duct interface due to the generation of a complex sound field in the vicinity of the neck opening, the transfer matrix method only approximates the in - duct net acoustic power transmission. This implies that changing the value of the neck - duct interface end - correction factor changes the calculated frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs. On the other hand, ANSYS does not require the inclusion of any kind of end - correction factors apart from the actual physical dimensions of the system, and is thus much more accurate than the transfer matrix method. To minimise the in - duct net acoustic power transmission downstream of the HR, a number of different cost functions that were related to the net acoustic power transmission were investigated theoretically, numerically and experimentally. These all involved either the acoustic pressure at the top of the closed end of the cavity of the HR or at the neck wall of the HR close to the neck - duct interface or the amplitude of the pressure transfer function between two microphones located in the resonator. The two potential cost functions which were initially considered to be maximised for indicating the minimisation of the in - duct net acoustic power transmission downstream of the resonator were : ( a ) the pressure at the top of the closed end of the cavity, and ( b ) the amplitude of the pressure transfer function between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. It was found that the location of the microphone in the neck was extremely important, with the best location being at the centre of the duct adjacent to the neck opening. However, this location was not considered practical because a microphone in the duct can obstruct the mean flow of gas in the duct. The best location for mounting the microphone in the neck was found to be at the neck wall as close as possible to the neck - duct interface. The results are shown in two different ways : ( 1 ) broadband analysis, whereby the in - duct net acoustic power transmission downstream of the HR, the pressure at the top of the closed end of the cavity and the pressure transfer function between the pressure at the top of the closed end of the cavity and at the neck wall close to the neckduct interface are plotted as a function of frequency, and ( 2 ) single frequency analysis, whereby all the aforementioned results are plotted as a function of the cylindrical cavity length ( for a fixed cavity diameter ) for a single, tonal frequency. For broadband analysis, the numerical ( ANSYS ) results showed that the frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs differs from the frequencies which correspond to the maximum responses of cost functions ( a ) and ( b ) described above. For single frequency analysis, when trying to optimise the performance of a duct - mounted HR at a particular frequency by altering its volume, the optimal dimensions of the HR required to attain the maximum reduction of in - duct net acoustic power transmission at that frequency differ from the dimensions of the HR which correspond to the maximised responses of the cost functions ( a ) and ( b ). These results were validated experimentally using a 3 m long circular duct of 0.1555 m diameter with an attached cylindrical HR. During the experimental work, only plane waves were propagating down the duct and there was no mean flow in the duct. Instead of only focusing on the amplitude of the pressure transfer function between the pressures at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface, the phase difference between the same locations in the HR was also considered. It was found that the phase difference depends on the quality factor ( or damping ) of the entire acoustic system. Experiments were conducted with varying dimensions of the HR and two novel cost functions were empirically derived. Both cost functions, which does not include any kind of measurement remote from the HR, are based on the damping ( or the quality factor ) of the duct - HR system and the phase difference between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. The effectiveness and performance of both cost functions were found to be excellent for minimising the in - duct net acoustic power transmission downstream of the HR. However, the second cost function is preferred because the procedure involved for measuring the system damping is more convenient from the practical point of view than the procedure for the first one. The quality factor of the duct - mounted HR, at the frequency at which noise needs to be attenuated, was determined by tuning the length of the cavity of the HR so as to maximise the amplitude of the pressure transfer function of the HR. This estimated quality factor was found to be directly related to the transfer function phase which corresponds to the minimum in - duct net acoustic power transmission at the tonal frequency. Once this optimum transfer function phase is known, an active control system can be used to drive a motor to adjust the cavity length of the HR to achieve the optimum phase. / Thesis (M.Eng.Sc.)--School of Mechanical Engineering, 2006.

The harmful effects of aircraft noise, with respect to both comfort and occupational health, have long since been recognised, with many examples of sound control now implemented in commercial aircraft. However, the single engine light aircraft cabin is still an extremely noisy environment, which apparently has been side-lined by both cost and weight constraints, especially with respect to low frequency sound reduction. Consequently, pilots and passengers of these aircraft are still exposed to potentially damaging noise levels and hearing damage can only be avoided by the proper use of ear defenders. Minimisation of the noise around the occupants of the aircraft reduces the dependency of personal ear defenders and is conducive to a more comfortable, hygienic and less stressful environment. This thesis describes the basis of a theoretical and experimental project, directed at the design and evaluation of a practical active noise control (ANC) system suitable for a single engine light aircraft. Results from initial experiments conducted in a single engine aircraft demonstrated the viability of ANC for this application. However, the extreme noise, the highly damped cabin, the multiple tone excitation, the severe weight limitations and the requirement of air worthiness certification severely complicated the problem of achieving noise reduction throughout the entire aircraft cabin. Compromising the objective to only achieving local control around the occupants still presented difficulties because the region of attenuated noise around the error sensors was so small that a nearby observer experienced no sound level reduction whatsoever. The objective was therefore to move the control zone away from the error sensor and place a broad envelope of noise reduction immediately around the occupant's head, through the use of virtual sensors , thus creating the perception of global noise control. While virtual sensors are not new (Garcia-Bonito et al. (1996)), they are currently limited to acoustic pressure estimation (virtual microphones) via the initial measurement of an observer / sensor transfer function. In this research, new virtual sensor algorithms have been developed to: 1. minimise the sound level at the observer location, 2. broaden the control region, 3. adapt to any physical system changes and 4. produce a control zone that may ultimately follow an observer's head The performance of the virtual sensors were evaluated both analytically and experimentally in progressively more complex environments to identify their capabilities and limitations. It was found that the use of virtual sensors would, in general, attenuate the noise at the observer location more effectively than when using conventional remotely placed error sensors. Such a control strategy was considered to be ideal for a light single engine aircraft, because it would only require small light speakers (possibly fitted into a head-rest) to achieve a broad control zone that envelopes the region around the occupants heads. / Thesis (Ph.D.) -- University of Adelaide, Dept. of Mechanical Engineering), 2000.

Thesis (M.S.)--State University of New York at Binghamton, Department of Electrical and Computer Engineering, 2006. / Includes bibliographical references.

<p>I dagens samhälle är runt två miljoner svenskar störda av trafikbuller, samtidigt som bilismen och vägtransporterna ökar. För att få en säkrare trafikmiljö med ett jämnare körsätt är det populärt att bygga om vanliga korsningar till cirkulationsplatser.</p><p>Denna rapport fokuserar på vad som händer med bullernivåerna då trafiken passerar en cirkulationsplats. Undersökningarna har genomförts genom att beräknade bullernivåer jämförts med uppmätta värden från olika cirkulationsplatser. Arbetet inleds med en litteraturstudie om ljud- och bullerfrågor.</p><p>Bullermätningar utfördes vid totalt åtta olika cirkulationsplatser, där både ekvivalentnivåer och maxvärden samlades in. Därefter beräknades medelvärden av dessa. Ekvivalentnivåer korrigerade för variationer i trafikmängden beräknades också. Dessa olika värden jämfördes sedan med modellerade värden, beräknade med både 1996 års beräkningsmodell och med en ny modell kallad Nord2000.</p><p>Resultaten från mätningarna tyder på att ekvivalentnivåerna, vid ett bestämt avstånd från vägen, generellt minskar desto närmare cirkulationsplatsen man kommer. Även tidigare forskning i frågan tyder på att trafikbullernivåerna tenderar att minska i anslutning till en cirkulationsplats. Detta fenomen kan troligtvis förklaras med den minskade hastigheten hos fordonen runt cirkulationsplatsen.</p><p>Maxnivåerna uppvisar en större spridning mellan mätpunkterna än vad ekvivalentnivåerna gör, vilket troligen beror på att maxnivåerna är väldigt känsliga för enskilda fordonspassager. Dock visar resultat från nio av elva mätningar att även maxnivåerna ökar med avståndet till cirkulationsplatsen.</p><p>Vid jämförelse av de modellerade och uppmätta värdena visar det sig att 1996 års modell i genomsnitt visar 1,1 dBA lägre och Nord2000 visar 1,4 dBA lägre än de uppmätta värdena. Att Nord2000 i medel ger en större avvikelse än 1996 års modell kan bero på det finns betydligt fler parametrar i Nord2000 att ställa in. Därmed kan modellen bli känsligare för till exempel en felaktigt skattad fordonshastighet, acceleration eller vindstyrka.</p>

In order to examine the potential impact of military jet overflights and other disturbances on productivity of peregrine falcons (Falco peregrinus), we observed behavioral reactions of peregrines to disturbances at nests along the Tanana River, Alaska during the 1995-1997 breeding seasons. Military jets conducted low-altitude flights over a sample of nests under observation in each year (experimental nests), while other nests were not intentionally overflown (reference nests). Other disturbances occurred at random. Animal noise monitors (ANMs), which collect and store data on noise disturbance levels, were deployed at each observed nest. A total of 878 above-threshold (��� 85 dB) overflights were recorded by the ANMs during the course of the study. A total of 401 close (defined as ��� 1000 m slant distance from the nest) overflights by subsonic F-16, F-15, A-10, Harrier, Jaguar, or Tornado jet aircraft were recorded during observations. Close overflights by military jets accounted for 63% of all observed potential disturbances at experimental nests; they accounted for 2.6% of all observed potential disturbances at reference nests. Other potential disturbances at reference nests included civilian fixed-wing aircraft (41%), boats (33%), avian predators (17%), helicopters (5%), and mammalian predators (1%). Peregrine falcons responded differently to animate and inanimate sources of disturbance, and responded most intensely and most frequently to other raptors, particularly conspecifics. Flight reactions were common, but not in response to inanimate sources. Among inanimate potential disturbances, falcons responded most intensely to boats (6% of reactions involved flight), and least intensely to helicopters (3%) and fixed-wing aircraft (2%). Intensity of reactions to military jets was indistinguishable from that to either boats or other aircraft. Intense behavioral responses (including flight reactions) to military jet overflights were rarely observed in this study, even at slant distances <500 m, and no intense behavioral responses were observed at slant distances >550 m. Peregrine falcon productivity (number of fledglings produced per nesting attempt) in the study area was within the normal range for Interior Alaska and the Tanana River. Dose of jet aircraft disturbance was not correlated with productivity. Productivity was, however, negatively correlated with reactivity of both individual falcons and mated pairs. Those falcons that responded more intensely to overflights tended to have lower productivity. The sensitivity of breeding peregrine falcons to low-altitude jet overflights is a better indicator of subsequent productivity than actual dose of overflights. This is likely a reflection of lower parental quality/investment among breeding pairs with high reactivity (i.e., younger, less experienced parents are less likely to be productive). / Graduation date: 1999

Although the adverse auditory effects of noise have been the focus of occupational health research for decades, little is known about the nonauditory health effects that result from noise exposure. The focus of this research was the nonauditory health effects of exposure to commercial aircraft noise (CAN) overflights. It was theorized that CAN exposure resulted in an ongoing stress-response that had the potential to be harmful to human health over time. Two aspects of CAN were considered; the sound level intensity (dBA), and the frequency of overflights. Data were collected by a stratified random sampling design in the CAN exposed neighborhoods of Eagan, St. Paul, Minneapolis, and Bloomington, and in control communities of Shoreview and Mounds View, all located in Minnesota (n=4000). A written questionnaire was used to measure; (1) health (MOS-36 Scale), (2) behavioral and emotional coping strategies, (3) noise sensitivity, (4) annoyance levels, and (5) demographic data. Aircraft noise levels and overflight data were obtained in cooperation with the Metropolitan Airport Sound Abatement Commission. Results showed significantly higher stress levels and lower health measures by CAN exposure type. These findings occurred primarily in communities exposed to high frequencies of aircraft overflights. Multivariate analysis revealed significant reductions for the three main health measures of General Health (GH), Sense of Vitality (Vitality), and Mental Health (MH), based on CAN exposure type. Post-hoc contrast analysis indicated that GH, Vitality, and MH scores were worst with high frequency of overflights. Behavioral copers had significantly fewer stress symptoms and used fewer stress medications than non-behavioral copers. Non-normalized emotional copers had significant negative associations with Gil, Vitality, and MH; however, these correlations were weak. Noise sensitivity levels were not significantly different among the CAN exposed communities; however noise annoyance levels were significantly higher than controls, and were the highest with high frequency of overflights. Finally, multivariate analysis of covariance indicated significant reduction for health measures based on CAN exposure types after adjusting for all effect modifiers (covariates) in the study. Vitality was the most consistently impacted by CAN exposure, and this was particularly the case for subjects exposed to high frequency of aircraft overflights. / Graduation date: 1996

Graduation date: 1996

I dagens samhälle är runt två miljoner svenskar störda av trafikbuller, samtidigt som bilismen och vägtransporterna ökar. För att få en säkrare trafikmiljö med ett jämnare körsätt är det populärt att bygga om vanliga korsningar till cirkulationsplatser. Denna rapport fokuserar på vad som händer med bullernivåerna då trafiken passerar en cirkulationsplats. Undersökningarna har genomförts genom att beräknade bullernivåer jämförts med uppmätta värden från olika cirkulationsplatser. Arbetet inleds med en litteraturstudie om ljud- och bullerfrågor. Bullermätningar utfördes vid totalt åtta olika cirkulationsplatser, där både ekvivalentnivåer och maxvärden samlades in. Därefter beräknades medelvärden av dessa. Ekvivalentnivåer korrigerade för variationer i trafikmängden beräknades också. Dessa olika värden jämfördes sedan med modellerade värden, beräknade med både 1996 års beräkningsmodell och med en ny modell kallad Nord2000. Resultaten från mätningarna tyder på att ekvivalentnivåerna, vid ett bestämt avstånd från vägen, generellt minskar desto närmare cirkulationsplatsen man kommer. Även tidigare forskning i frågan tyder på att trafikbullernivåerna tenderar att minska i anslutning till en cirkulationsplats. Detta fenomen kan troligtvis förklaras med den minskade hastigheten hos fordonen runt cirkulationsplatsen. Maxnivåerna uppvisar en större spridning mellan mätpunkterna än vad ekvivalentnivåerna gör, vilket troligen beror på att maxnivåerna är väldigt känsliga för enskilda fordonspassager. Dock visar resultat från nio av elva mätningar att även maxnivåerna ökar med avståndet till cirkulationsplatsen. Vid jämförelse av de modellerade och uppmätta värdena visar det sig att 1996 års modell i genomsnitt visar 1,1 dBA lägre och Nord2000 visar 1,4 dBA lägre än de uppmätta värdena. Att Nord2000 i medel ger en större avvikelse än 1996 års modell kan bero på det finns betydligt fler parametrar i Nord2000 att ställa in. Därmed kan modellen bli känsligare för till exempel en felaktigt skattad fordonshastighet, acceleration eller vindstyrka.

Design metrics such as area, timing and power are generally considered as the primary criteria in the design of modern day circuits, however, the minimization of power supply noise, among other noise sources, is appreciably more important since not only can it cause a degradation in these parameters but can cause entire chips to fail. Ensuring the integrity of the power supply voltage in the power distribution network of a chip is therefore crucial to both building reliable circuits as well as preventing circuit performance degradation. Power supply noise concerns, predicted over two decades ago, continue to draw significant attention, and with present CMOS technology projected to keep on scaling, it is shown in this work that these issues are not expected to diminish. This research also considers the management and on-chip detection of power supply noise. There are various methods of managing power supply noise, with the use of decoupling capacitors being the most common technique for suppressing the noise. An in-depth analysis of decap structures including scaling effects is presented in this work with corroborating silicon results. The applicability of various decaps for given design constraints is provided. It is shown that MOS-metal hybrid structures can provide a significant increase in capacitance per unit area compared to traditional structures and will continue to be an important structure as technology continues to scale. Noise suppression by means of current shifting within the clock period of an ALU block is further shown to be an additional method of reducing the minimum voltage observed on its associated supply. A simple, and area and power efficient technique for on-chip supply noise detection is also proposed.