Dissertation made openly available per email from author, 7/22/2016.

Noise sensitivity is a condition characterised by an excessive reaction to harmless levels of sound that would not normally affect typically functioning people. Previous research have found that reactions such as the reduction of attention and concentration as well as the presence of medically unexplained common symptoms such as headaches and fatigue appear in sufferers. The aim of the present study was to investigate whether such a class of sound sensitive individuals are affected by exposure to a potentially unpleasant sound source more than a relatively low sound sensitive group of individuals. Forty adults between 18-54 years of age were exposed to a white noise sound stimulus within a soundproof exposure chamber for 45 minutes. The sound pressure level of the sound varied over the course of the exposure session. The dependent variables of the study were perceived intensity, unpleasantness and effect on concentration, symptoms and cognitive strain. After the exposure session, participants were asked to fill in an online survey that included a 21 item Noise Sensitivity Scale. This was used to group the participants accordingly to a low or high NSS group. The high NSS group compared to the low NSS group had higher ratings for unpleasantness and negative effects on concentration after time point four, at which point the noise stimulus had been introduced. No differences were observed in ratings of Intensity of the noise stimulus between groups. The high NSS group also demonstrated higher ratings for symptoms after the noise stimulus had been introduced. In addition they also demonstrated a lower level of improvement for the cognitive task in comparison to the low NSS group. The findings from this study imply that individuals suffering from hyperacusis can be negatively affected by the presence of annoying sound stimuli. Hyperacusis can mean that sounds can become unpleasant to sufferers as well as potentially affecting their ability to concentrate. / Ljudkänslighet är ett tillstånd som karaktäriseras av en överreaktion på ofarliga ljudnivåer, som normalt inte skulle påverka majoriteten av befolkningen. Tidigare forskning har funnit symptom så som minskad uppmärksamhet och koncentration, samt medicinskt oförklarade symptom som huvudvärk och utmattning förekommer hos drabbade. Syftet med den nuvarande studien var att undersöka hur vida ljudkänsliga personer påverkas mer av en potentiellt obehaglig ljudkälla än en grupp av icke-ljudkänsliga. Fyrtio vuxna mellan 18-54 år exponerades för vitt brus under experimentet. Beroende variabler var upplevd intensitet, obehag, effekt på koncentration, symptom, och kognitiv belastning. Efter experimentet fyllde deltagarna i en online-enkät som inkluderade 21 item Noise Sensitivity Scale. Denna skala användes för att gruppera deltagarna i en hög och en låg NSS-grupp. Jämfört med den låga NSS-gruppen, hade den höga NSS-gruppen högre skattningar av obehag och negativa effekter på koncentrationen efter tidpunkt fyra, då ljud stimulit introducerades. Inga skillnader i intensitets-skattningar hittades mellan grupper. Den höga NSS-gruppen visade högre skattningar av symptom efter att ljud stimulit introducerats. De visade även lägre grad av förbättring på den kognitiva uppgiften jämfört med den låga NSS-gruppen. Denna studies resultat antyder att individer som lider av hyperakusis kan påverkas negativt av störande ljud. Drabbade kan uppfatta ljud som obehagliga, samt potentiellt påverka koncentrationsförmåga negativt.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

High levels of machine noise result in health issues for those people exposed to the machine for extended periods. Machine noise is becoming a more significant design consideration, often because of legislative requirements. Decanting centrifuges are machines with a rotating bowl. They have a number of noise sources, the most significant being structural noise, vortex/turbulence noise and siren noise. Due to the size, mass and speed of the rotating bowl, the bowl is the main source of structural noise. The structural noise is produced by all surfaces that are directly coupled to the bowl’s bearings. Due to the speed of rotation of the bowl, the turbulence from the various trailing edges generates broad spectrum vortex noise. Siren noise due to air flow through the bowl also generates significant noise especially at the lower harmonics of the bowl rotation frequency. Strategies to reduce decanter machine noise include: • Decoupling the surfaces of the from the main bearings of the rotating bowl and hence reduce the amount of structurally transmitted noise. • Smoothing the surface of the bowl to minimise the edges that produce vortices that are shed and produce vortex/turbulence noise. • As siren noise is produced due to flow through the rotating bowl, which is integral to the function of the decanter, the exit ports should be designed so that the noise is produced within parts of the sound spectrum that have low noise levels.

This research thesis involves the measurement of the airborne sound insulation of road traffic noise barriers, with the goal of gaining a more in depth understanding of the factors that influence noise barrier performance. A measurement system is developed, based on EN 1793-6:2012, to quantify the airborne sound insulation of a noise barrier in situ. Validation testing is performed to ensure that the system meets the requirements of EN 1793-6:2012. MATLAB code is developed, incorporating all of the signal processing tasks into a single graphical user interface. The measurement system is then used to measure the airborne sound insulation of eight existing traffic noise barriers located around Auckland, New Zealand. The results from the Auckland field tests show that consistent single number ratings of airborne sound insulation can be achieved on different samples of the same noise barrier. The presence of air gaps and hidden defects will degrade the acoustic performance of a noise barrier, most significantly at the high frequencies. The comparison of single number ratings calculated with differing measurement frequency ranges is discussed, and some comments are made on the measurement standard itself.

No description available.

No description available.

No description available.

No description available.

No description available.