An approximate of the Green's function can be obtained by taking the cross-correlation of ambient noise that has been simultaneously recorded on separate sensors. This method is applied for two experiments, which illustrate the advantages and challenges of this technique. The first experiment is in the ultrasonic regime [5-30] MHz and uses capacitive micromachined ultrasonic transducer arrays to image the near field and compares the passive imaging to the conventional pulse-echo imaging. Both the array and target are immersed in a fluid with the sensors recording the fluid's random thermal-mechanical motion as the ambient noise. The second experiment is a passive ocean monitoring experiment, which uses spatiotemporal filtering to rapidly extract coherent arrivals between two vertical line arrays. In this case the ambient noise in the frequency band [250 1500] Hz is dominated by non-stationary shipping noise. For imaging purposes, the cross-correlation needs to extract the Green's function so that the imaging can be done correctly. While for monitoring purposes, the important feature is the change in arrivals, which corresponds to the environment changing. Results of both experiments are presented along with the advantages of this passive method over the more accepted active methods.

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Skiriūtė D. Transporto triukšmo tyrimai Tauragėje: Aplinkos inžinerijos bakalauro darbas/mokslinis vadovas lekt. R. Klimas; Šiaulių universitetas, Technologijos fakultetas, Statybos inžinerijos katedra. – Šiauliai, 2011. Didžiąją miesto triukšmo dalį (apie 80%) sukelia transportas. Transporto priemonės yra toks specifinis triukšmo šaltinis, kad jis įsiskverbia į bet kurią miesto teritoriją – gyvenamuosius ir pramonės rajonus, ligoninių ir sanatorijų zonas, miestų centrus, poilsio zonas. Transporto triukšmas sukelia diskomfortą ne tik gyventojams, bet ir įvairių įstaigų darbuotojams, vaikams, moksleiviams, gyvūnams. Tokio triukšmo padariniai žmonėms yra įvairios sveikatos problemos. Atliekant transporto triukšmo tyrimus Tauragės mieste pasirinkta 15 vietų: mokyklų, darželių–lopšelių, viešųjų tyliųjų miesto zonų, parkų, ligoninės, gyvenamųjų namų teritorijose. Gauti rezultatai lyginami su higienos norma, ir tai suteikia galimybę parašyti išvadas ir pateikti pasiūlymus triukšmo mažinimui. Mažinant transporto triukšmo sklaidą Tauragės mieste būtina taikyti triukšmo mažinimo priemones: mažinti automobilių eismą miesto centrinėje dalyje, įrengiant aplinkelį; riboti eismą gatvėse; įrengti dviračių ir pėsčiųjų takus; organizuoti viešojo transporto maršrutus ir dažniau juo naudotis; skatinti biotransporto naudojimą; plėsti dviračių takų tinklą. / Transport makes the major part (60-80%) of the city noise. The vehicle is the specific source of noise that it penetrates into any area – in residential and industrial areas, in hospitals and sanatoriums areas, in urban centers, and recreation areas. Traffic noise causes discomfort, not only residents but also the employees of the different companies, children, school children and animals. A range of health problems is effects of such noises to people. Performing the research of the traffic noise in Tauragė town 15 places were selected following: in the areas of schools, kindergartens, nurseries, public silent areas of the city, hospitals, and residential areas. The obtained results are compared with standards of hygiene, and this provides an opportunity to write conclusions and to make proposals for the prevention of noise. Reducing traffic noise in the dissemination in Tauragė town the noise reducing measures must be applied: to reduce automobile traffic in the central part of the town installing a bypass; to limit traffic on the streets; to install the bicycle and pedestrian paths; to organize public transport routes, and to use it more frequently; to construct the noise protection barriers.

This thesis aims at preparing a user-friendly software tool for the prediction and analysis of the noise generated in Heating, Ventilating and Air Conditioning (HVAC) Systems elaborating the standardized prediction formulae and data coming from the research studies. For the analysis portion of the software, different types of indoor noise criteria are introduced and implemented in the software to ease the investigation of the level and the quality of the sound perceived by the occupant in a room through such criteria. General software structure and implementation of HVAC elements are explained by different userinterface samples in the thesis. Several case studies are presented to demonstrate the capabilities of the tool prepared in VISUAL BASIC programming language within the scope of the study.

Includes bibliographical references (leaves 287-305) / 310 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1991

[Truncated abstract] The subject of fan noise generating mechanisms and its control has been studied intensively over the past few decades as a result of the ever-increasing demand for more powerful fans. A unique feature of fan noise is that it consists of high-level discrete frequency noise related to the blade passing frequency, and low-level broadband noise due mostly to turbulent airflow around the fan. Of the two types of fan noise, the discrete frequency noise is the more psychologically annoying component. Past research into fan noise has shown that the discrete frequency fan noise are dipole in nature and are caused predominantly by the fluctuating lift acting on the surfaces of the fan blades. Based on this, several theoretical models have been established to correlate these fluctuating lift forces to the far-field sound pressure. However, one general assumption in these models is that the fan blades are assumed rigid, and the consequence of such an assumption is that it is unclear if the far-field sound pressure is caused solely by the aerodynamic lift force, or whether the blade vibration also plays a substantial role in the generation of the far-field fan noise. One of the goal of this thesis was thus to experimentally quantify the contribution of blade vibration to far-field fan noise and it was found that blade vibration, whilst coherent with the far-field fan noise, did not contribute significantly. Aside of this, several experiments aimed at filling knowledge gaps in the understanding of fan noise characteristics were also be conducted, in particular, to understand the relationship between far-field sound pressure level to blade lengths as well as the number of blades on the fan. The experiments showed that for fans with many blades, the dependency of the far-field sound pressure on blade length is stronger than fans with less blades. Furthermore, dipole measurements showed that the dipole characteristics of fan noise does not occur only at the discrete frequencies, but also within a range of broadband frequencies, implying that the source for both discrete and broadband is the same. The second section of this thesis deals with the study of vortex shedding and its active control. When a circular cylinder (or any object) is placed in a flow within a specified Reynolds number range, flow separation and periodical wake motion is formed behind the cylinder, which is known as vortex shedding. It has been found in previous research that this wake motion is affected by acoustic field imposed on it via loudspeakers. This suggests that there is a strong acoustic-vortex relationship. However, little of this relationship is understood as conventional methods of studying vortex centre around the use of hot-wire anemometry, which effectively measures the velocity fluctuation in the flow. This thesis is the first in using a microphone to study the acoustic characteristic of the vortex wake, and experimental results shows that the two parallel shear layers of the wake carry the strongest pressure signals at the vortex shedding frequency, whilst the entrapped region between the layers carries the strongest pressure signals at the first harmonic.

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.

This study dealt with the effect of low-level noise and high-level noise, of white noise and varied noise, and of high manifest anxiety and low manifest anxiety on college students' performance on a coding task. The conclusions of the study, based upon the hypotheses, were as follows: 1. Level of anxiety does not affect performance on a coding task. 2. The level of white and level of varied noise does not affect performance on a coding task. 3. Varied noise has a positive effect on performance on a coding task.

Common practice in acoustic design does not consider air gaps. Thereare different opinions about air gaps and their affect on noise reduction.The report analyzes the credibility of the requirements used in a theoretical calculation model that addresses noise reduction in acoustic screens. Several measurement results from empirical attempts in a realistic environment for different screen models are compared.The result shows that a horizontal 50-millimeter gap has no noticeable impact on noise reduction. The result for horizontal air gaps against ground is of particular interest as it allows a simplified foundation to be used.Vertical air gaps have a greater negative influence on noise reduction but the results presented in the report can be used when lower demands are set on screens.An economic analysis shows that the result from the experiment when using a simplified foundation results in a cost reduction ofapproximately 300 SEK per meter acoustic screen.

O ruído de baixa frequência é um limitador de desempenho em circuitos analógicos, digitais e de radiofrequência, introduzindo ruído de fase em osciladores e reduzindo a estabilidade de células SRAM, por exemplo. Transistores de efeito de campo de metalóxido- semicondutor (MOSFETs) são conhecidos pelos elevados níveis de ruído 1= f e telegráfico, cuja potência pode ser ordens de magnitude maior do que a observada para ruído térmico para frequências de até dezenas de kHz. Além disso, com o avanço da tecnologia, a frequência de corner —isto é, a frequência na qual as contribuições dos ruídos térmico e shot superam a contribuição do ruído 1= f — aumenta, tornando os ruídos 1= f e telegráfico os mecanismos dominantes de ruído na tecnologia CMOS para frequências de até centenas de MHz. Mais ainda, o ruído de baixa frequência em transistores nanométricos pode variar significativamente de dispositivo para dispositivo, o que torna a variabilidade de ruído um aspecto importante para tecnologias MOS modernas. Para assegurar o projeto adequado de circuitos do ponto de vista de ruído, é necessário, portanto, identificar os mecanismos fundamentais responsáveis pelo ruído de baixa frequência em MOSFETs e desenvolver modelos capazes de considerar as dependências do ruído com geometria, polarização e temperatura. Neste trabalho é proposta uma técnica para análise de ruído de baixa frequência baseada na autocorrelação dos espectros de ruído em função de parâmetros como frequência, polarização e temperatura. A metodologia apresentada revela informações importantes sobre os mecanismos responsáveis pelo ruído 1= f que são difíceis de obter de outras formas. As análises de correlação realizadas em três tecnologias CMOS comerciais (140 nm, 65 nm e 45 nm) fornecem evidências contundentes de que o ruído de baixa frequência em transistores MOS tipo-n e tipo-p é composto por um somatório de sinais telegráficos termicamente ativados. / Low-frequency noise (LFN) is a performance limiter for analog, digital and RF circuits, introducing phase noise in oscillators and reducing the stability of SRAM cells, for example. Metal-oxide-semiconductor field-effect-transistors (MOSFETs) are known for their particularly high 1= f and random telegraph noise levels, whose power may be orders of magnitude larger than thermal noise for frequencies up to dozens of kHz. With the technology scaling, the corner frequency — i.e. the frequency at which the contributions of thermal and shot noises to noise power overshadow that of the 1= f noise — is increased, making 1= f and random telegraph signal (RTS) the dominant noise mechanism in CMOS technologies for frequencies up to several MHz. Additionally, the LFN levels from device-to-device can vary several orders of magnitude in deeply-scaled devices, making LFN variability a major concern in advanced MOS technologies. Therefore, to assure proper circuit design in this scenario, it is necessary to identify the fundamental mechanisms responsible for MOSFET LFN, in order to provide accurate LFN models that account not only for the average noise power, but also for its variability and dependences on geometry, bias and temperature. In this work, a new variability-based LFN analysis technique is introduced, employing the autocorrelation of multiple LFN spectra in terms of parameters such as frequency, bias and temperature. This technique reveals information about the mechanisms responsible for the 1= f noise that is difficult to obtain otherwise. The correlation analyses performed on three different commercial mixed-signal CMOS technologies (140-nm, 65-nm and 40-nm) provide strong evidence that the LFN of both n- and p-type MOS transistors is primarily composed of the superposition of thermally activated random telegraph signals (RTS).