Sound transmission loss of periodic Mindlin plates with non-uniformly spaced mass attachmentsa).

The sound transmission loss (STL) of wall partitions, especially in the coincidence region, is investigated. A Mindlin plate with periodically attached masses in a periodic "supercell" pattern is analyzed theoretically and experimentally for sound attenuation. Modeling the masses as points, analytical expressions for predicting the dispersion relation and frequency bandgaps of the plate are developed. The results show that varying the distances between the masses or the masses themselves can lead to the emergence of additional lower-frequency bandgaps and slightly decrease the bandwidth of the primary complete bandgap. Additionally, a triangular periodic pattern of point masses can provide a larger complete bandgap than the conventional rectangular pattern. The results are validated by numerical analyses using the wave and finite element method. Experimental testing is conducted on large-scale plates (2.4 m × 1 m) with periodically attached masses under diffuse field conditions, demonstrating the benefits of utilizing multiple scattering to increase the STL in the coincidence region of the bare plate. The proposed approach is seen to significantly increase the STL of wall partitions in the coincidence region and provides insights into the fundamental principles of sound and vibration attenuation in complex structures based on multiple scattering.

The learning effect of an active-learning room-acoustics coursework.

This paper investigates the learning effect of a developed coursework for an engineering acoustics course offered to fourth year and postgraduate engineering students at the University of Auckland, New Zealand. The coursework incorporated practical active-learning activities and was developed to help students gain understanding of complex concepts related to the room-acoustics measurement and analysis and also introduce students to some of the practical tasks that are typical of a practising acoustical engineer in New Zealand. The learning effect of the coursework was measured by comparing students' performance in two quizzes that were run before and after students worked on the coursework. Students' performance on the final examination was also analyzed. An analysis of the common mistakes made by students in the assignment report was also conducted. Overall, the analysis suggests that the coursework generally improved the students' understanding of the material that it covered.

Framing sound: Using expectations to reduce environmental noise annoyance.

BACKGROUND: Annoyance reactions to environmental noise, such as wind turbine sound, have public health implications given associations between annoyance and symptoms related to psychological distress. In the case of wind farms, factors contributing to noise annoyance have been theorised to include wind turbine sound characteristics, the noise sensitivity of residents, and contextual aspects, such as receiving information creating negative expectations about sound exposure. OBJECTIVE: The experimental aim was to assess whether receiving positive or negative expectations about wind farm sound would differentially influence annoyance reactions during exposure to wind farm sound, and also influence associations between perceived noise sensitivity and noise annoyance. METHOD: Sixty volunteers were randomly assigned to receive either negative or positive expectations about wind farm sound. Participants in the negative expectation group viewed a presentation which incorporated internet material indicating that exposure to wind turbine sound, particularly infrasound, might present a health risk. Positive expectation participants viewed a DVD which framed wind farm sound positively and included internet information about the health benefits of infrasound exposure. Participants were then simultaneously exposed to sub-audible infrasound and audible wind farm sound during two 7 min exposure sessions, during which they assessed their experience of annoyance. RESULTS: Positive expectation participants were significantly less annoyed than negative expectation participants, while noise sensitivity only predicted annoyance in the negative group. CONCLUSION: Findings suggest accessing negative information about sound is likely to trigger annoyance, particularly in noise sensitive people and, importantly, portraying sound positively may reduce annoyance reactions, even in noise sensitive individuals.

Quantification of the Psychoacoustic Effect of Noise from Small Unmanned Aerial Vehicles.

This paper presents the results of a study evaluating the human perception of the noise produced by four different small quadcopter unmanned aerial vehicles (UAVs). This study utilised measurements and recordings of the noise produced by the quadcopter UAVs in hover and in constant-speed flight at a fixed altitude. Measurements made using a ½â€³ microphone were used to calculate a range of different noise metrics for each noise event. Noise recordings were also made using a spherical microphone array (an Eigenmike system). The recordings were reproduced using a 3D sound reproduction system installed in a large anechoic chamber located at The University of Auckland. Thirty-seven participants were subjected to the recordings and asked to rate their levels of annoyance in response to the noise, and asked to perform a simple cognitive task in order to assess the level of distraction caused by the noise. This study discusses the noise levels measured during the test and how the various noise metrics relate to the annoyance ratings. It was found that annoyance strongly correlates with the sound pressure level and loudness metrics, and that there is a very strong correlation between the annoyance caused by a UAV in hover and in flyby at the same height. While some significant differences between the distraction caused by the UAV noise for different cases were observed in the cognitive distraction test, the results were inconclusive. This was likely due to a ceiling effect observed in the participants' test scores.

Can expectations produce symptoms from infrasound associated with wind turbines?

OBJECTIVE: The development of new wind farms in many parts of the world has been thwarted by public concern that subaudible sound (infrasound) generated by wind turbines causes adverse health effects. Although the scientific evidence does not support a direct pathophysiological link between infrasound and health complaints, there is a body of lay information suggesting a link between infrasound exposure and health effects. This study tested the potential for such information to create symptom expectations, thereby providing a possible pathway for symptom reporting. METHOD: A sham-controlled double-blind provocation study, in which participants were exposed to 10 min of infrasound and 10 min of sham infrasound, was conducted. Fifty-four participants were randomized to high- or low-expectancy groups and presented audiovisual information, integrating material from the Internet, designed to invoke either high or low expectations that exposure to infrasound causes specified symptoms. RESULTS: High-expectancy participants reported significant increases, from preexposure assessment, in the number and intensity of symptoms experienced during exposure to both infrasound and sham infrasound. There were no symptomatic changes in the low-expectancy group. CONCLUSIONS: Healthy volunteers, when given information about the expected physiological effect of infrasound, reported symptoms that aligned with that information, during exposure to both infrasound and sham infrasound. Symptom expectations were created by viewing information readily available on the Internet, indicating the potential for symptom expectations to be created outside of the laboratory, in real world settings. Results suggest psychological expectations could explain the link between wind turbine exposure and health complaints.

The power of positive and negative expectations to influence reported symptoms and mood during exposure to wind farm sound.

OBJECTIVE: Wind farm developments have been hampered by claims that sound from wind turbines causes symptoms and negative health reports in nearby residents. As scientific reviews have failed to identify a plausible link between wind turbine sound and health effects, psychological expectations have been proposed as an explanation for health complaints. Building on recent work showing negative expectations can create symptoms from wind turbines, we investigated whether positive expectations can produce the opposite effect, in terms of a reduction in symptoms and improvements in reported health. METHOD: 60 participants were randomized to either positive or negative expectation groups and subsequently exposed to audible wind farm sound and infrasound. Prior to exposure, negative expectation participants watched a DVD incorporating TV footage about health effects said to be caused by infrasound produced by wind turbines. In contrast, positive expectation participants viewed a DVD that outlined the possible therapeutic effects of infrasound exposure. RESULTS: During exposure to audible windfarm sound and infrasound, symptoms and mood were strongly influenced by the type of expectations. Negative expectation participants experienced a significant increase in symptoms and a significant deterioration in mood, while positive expectation participants reported a significant decrease in symptoms and a significant improvement in mood. CONCLUSION: The study demonstrates that expectations can influence symptom and mood reports in both positive and negative directions. The results suggest that if expectations about infrasound are framed in more neutral or benign ways, then it is likely reports of symptoms or negative effects could be nullified.

Where did that sound come from? Comparing the ability to localise using audification and audition.

PURPOSE: A prototype device was developed to allow individuals to hear ultrasound reflections off environmental obstacles. Previous studies have shown that this device allows for better distance judgement than audition and allows for effective passage through the centreline of apertures. The purpose of this research was to evaluate audification as a method to localise direct sound sources as compared to audition. METHOD: In an anechoic environment, participants localised point-sound sources for three conditions: auditory, audified ultrasound with receivers facing laterally, and audified ultrasound with receivers facing forward. RESULTS: Azimuth localisation was similar within a range of -35° to 35° in front of the participant among all conditions. At the periphery, -70° and 70°, audified ultrasound was more accurate than audition for novice participants. No difference was evident in user elevation accuracy for these signals among the different conditions. CONCLUSION: Audification of ultrasound can be effective for localising point-source sounds in the azimuth direction, but more evidence is required to evaluate accuracy in the vertical direction. [Box: see text].

Epidemiology of noise-induced hearing loss in New Zealand.

INTRODUCTION: Hearing loss is a major cause of disability in the world. Occupational noise exposure is likely to contribute to a very high proportion of the cases of hearing loss in adults. Concern has been raised by the Accident Compensation Corporation (ACC) in New Zealand about the fact that the number of new cases of noise-induced hearing loss (NIHL) is not declining, despite the health and safety legislation and establishment of hearing conservation programmes in industry. To inform strategies for prevention, a review of the burden of NIHL in New Zealand was undertaken, particularly focusing on the trends in compensation claims and costs, and the associated sociodemographic patterns. METHODS: A review of the peer-reviewed published literature was conducted to identify national and international estimates of NIHL prevalence. The ACC claims dataset (July 1995 to June 2006) was analysed to describe annual trends in new NIHL claims, cost to ACC, and claimants' age, gender and occupational group. RESULTS: There is currently no reliable information regarding the overall incidence and prevalence of NIHL in New Zealand. ACC data reveals a substantial increase in the number of new NIHL claims annually, rising from 2823 in July 1995-June 1996, to 5580 in July 2005-June 2006. Together with ongoing claims the overall costs of NIHL claims increased by an average of 20% each year (a six-fold increase over the decade) resulting in a total cost to ACC of $193.82M over the review period. Collectively, agriculture and fisheries workers, trades workers, machine operators, and assemblers accounted for 53% of new claims. Most claims were lodged in middle age or later, with the vast majority of claimants (95%) being men. The relationship of age with the probability of making a claim changed significantly over the study period with rates in older age groups increasing faster than in younger. CONCLUSIONS: The substantial and increasing societal costs despite decades of NIHL control legislation suggests that current strategies addressing this problem are not effective, inadequately implemented, or both.