George Dodd

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.

Speech Intelligibility in Classrooms: Specific Acoustical Needs for Primary School Children

Classrooms for primary school children should be built to criteria based on childrens speech intelligibility needs which in some respects – e.g. reverberation time – differ markedly from the traditional criteria for adults. To further identify why the needs of children and adults for speech perception are so different we have measured the ‘integration time’ of speech for adults and children using a novel technique to obviate the complicating effects of differing language. The results for children are significantly different than for adults (35 ms c.f. 50 ms) and recommendations for classroom design based on the childrens requirements have been made. When groups of children engage in ‘co-operative learning’ activities in the classroom, the “cafe effect” produces a rising activity noise level. We suggest the Lombard Effect is responsible for this. Measurements show children are more susceptible to the effect and we have developed a prediction model for activity noise in a classroom.

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.

Lightweight floor/ceiling systems with improved impact sound insulation

Contrary to common belief, a relatively simple and practical lightweight timber based floor/ceiling can have impact sound insulation superior to that of concrete slab based systems. This paper presents examples of such systems that include vibration isolation/damping features, such as rubber ceiling batten clips, glass fibre wool, and a sand-sawdust mixture layer. We give enough details to reproduce our experiments and build the proposed lightweight systems.

Development of Locally Resonant Structures for Sonic Barriers

The application of metamaterials or structured material principles to sound insulation has produced a new isolation concept known as locally resonant structures (LRS). LRS combine interacting components specifically arranged to generate localised resonances within the structure. LRS have exceptional sound transmission loss (TL) performance in defined frequency bands, which can be tailored for any desired region of the spectrum. Low frequency noise (below 1 kHz) is where irritating acoustic intrusion frequently occurs but is both challenging and expensive to prevent with conventional solutions, and where the LRS is a potentially compact and relatively lightweight solution. Numerical models based on networks of single-degree of freedom oscillators were used to understand how the components of the LRS can be manipulated to generate a designated TL performance spectrum. Designs with the desired TL characteristics were then modelled using FEA software, and samples were fabricated for testing. This paper will focus on results obtained by testing the LRS samples in an impedance tube adapted for TL experimentation. These results showed that the highest performing network arrangements combined layers of multiple resonators with incremental resonant frequencies to increase system bandwidth. Experimental data for various LRS arrangements shows good correspondence to modelling predictions. Samples yielded systems with attenuation peaks of 80dB over band widths approaching 350 Hz at frequencies well below 1 KHz These results provide insight into the benefits and limitations of complex LRS, and how to use this technology for practical applications.

Development of locally resonant structures for sonic barriers

The intrusion of unwanted sound is a matter of increasing concern worldwide as growing sound pollution impacts human health, productivity and wellbeing. Lower frequency noise is particularly important, as this is where the human ear is most sensitive. Irritating acoustic intrusion increasingly occurs in buildings, yet sound insulation at low frequencies is challenging and expensive. Meta-materials o er a relatively new approach to achieving sound and vibration isolation. This approach is being used to develop panels with internal resonant structures that are only a few centimetres thick yet strongly interact with acoustic waves. These structures can yield signi cantly greater transmission loss than conventional insulation systems. Numerical models based on networks of single-degree of freedom oscillators were used to understand how the components of the locally resonant structure (LRS) can be manipulated to generate sound transmission loss (STL) performance spectrums. Designs with the desired STL characteristics were then examined in detail and samples were fabricated using industry-standard materials and processes. This paper focuses on the acoustic testing of these LRS samples at low frequencies. Comparisons were made between, numerical predictions and experimental results (small scale (plane wave) to large scale (di use eld) conditions). The highest performing network arrangements combined layers of resonators with multiple resonances to increase system bandwidth. At frequencies below 1 kHz the samples yielded large attenuation gains with peaks of 80dB under normal incidence, and good correspondence to modelling predictions. In di use eld conditions the samples still showed signi cant STL improvements above that of a conventional panel over bandwidths in the order of 300 Hz. The resulting systems have the potential to provide signi cantly higher transmission loss at low frequencies than conventional wall systems of similar size and weight.

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. Implications for Rehabilitation Secondary mobility devices can be used by individuals with visual impairment to avoid obstacles above waist height. Audification allows for skill-based response enabling intuitive obstacle avoidance and localization of point sound sources. Localization of peripheral sounds was shown in this study to be better with audified ultrasound than audition.