Acoustics Australia最新文献

Effective communication between teachers and students is vital for successful learning, but outdoor noise can disrupt classroom acoustics and hinder this process. Despite growing research on classroom acoustics, gaps remain in understanding how factors like environmental noise, building design, and classroom acoustics interact to affect learning environments. This scoping review aims to systematically synthesize existing literature on the transmission of outdoor noise into classrooms. It explores the sources and factors that contribute to noise transmission, examines how the classroom acoustic properties that influence the impact of transmitted noise on occupants, and reviews effective mitigation strategies. The review analysed 33 peer-reviewed papers from 2003 to 2023, retrieved from Web of Science and Science Direct using the keywords Classroom acoustics AND Outdoor noise. Included studies that met criteria such as focusing on outdoor noise in mainstream classrooms and being published in English peer-reviewed journals. Traffic, aircraft, and railway noise were identified as major sources, with traffic peaking in the morning and afternoon. Building design, façade insulation, and ventilation influenced noise transmission exacerbated by proximity to noise sources. Poor acoustic properties like high reverberation time reduce speech clarity and increase background noise, affecting students' cognitive performance and teachers' vocal health. Mitigating strategies for noise include improved façade insulation, noise barriers, and window placement. This review also identifies gaps in current research, particularly regarding the combined effects of architectural elements such as building shape, height, and façade ratio. Future studies should explore how these factors interact to develop more effective noise management strategies in school. Implementing these strategies will enhance classroom acoustics, benefiting its occupants.

The variation in the acoustic response of the Karadeniz kemenche, a bowed string musical instrument, depending on the thickness of the soundboard is investigated. The most important challenge in obtaining an updated model for the musical instruments is the uncertainties arising from the orthotropic wood materials used. A model update procedure is implemented to resolve uncertainties in the mechanical properties of materials. The model is updated and complemented through an experimental modal analysis study. An analytical solution for the calculation of acoustic mode frequencies is implemented. A vibroacoustic analysis is performed to model the fluid–structure interaction. An acoustic response analysis is conducted by applying the experimentally measured nonlinear triaxial acceleration signal to the bridge of the musical instrument to simulate the slip–stick behaviour of the bow. Finally, the effect of soundboard thickness on the amplitude of acoustic pressure is examined. It is revealed that the amplitude of acoustic pressure substantially increases at the resonances that appeared at 340 Hz and 900 Hz, when the thickness of soundboard is 2.1 mm, and the amplitudes of pitch frequencies are observed to be higher in a broadband range. When the thickness of the soundboard of the instrument is 1.7 mm, it is seen that the amplitude of the pitch frequency of 1040 Hz increases significantly, and thus, it can produce a higher-pitched sound. When the soundboard thickness of the instrument is 2.9 mm, a strong pitch frequency of around 700 Hz can be obtained, according to the results of the studied model.

Assessments of vibration signals measured on surfaces of piping systems are essential in prevention of vibration-induced failures. Magnets, piezoelectric accelerometers, and hand-held vibration analysers are typically used for those assessments. ISO 5348–2021 “Mechanical Vibration and Shock—Mechanical mounting of accelerometers” provides a guideline of the correct mounting of accelerometers on flat surfaces. However, it offers limited information regarding the mounting of accelerometers on curved surfaces. This technical note focusses on the mounting of accelerometers on 20-mm-diameter curved surfaces. Experimental studies with sinusoidal signals were conducted using magnetic and non-magnetic metallic materials, small and large accelerometers and six common mounting methods, i.e. beeswax, cyanoacrylate glue, dual-rail magnet, flat magnet, hand-held and thin double-sided tape. For each mounting method, a frequency response plot of the relative sensitivity of the test accelerometer with respect to the reference accelerometers was obtained for frequencies ranging from 2 Hz to 10 kHz. The plots were used to determine mounting frequency limits by identifying points that deviate more than 3 dB from the reference sensitivity. For magnetic curved surfaces, the dual-rail magnet and glue methods exhibited the highest frequency limits. For non-magnetic curved surfaces, a thin strip of double-sided tape was required, but it only worked for small accelerometers. Hand holding an accelerometer is not recommended. Future work is needed for transient signals.

With the rapid advancement of modern railway technology, remote monitoring of rail safety has become increasingly important. The acoustic signal in the rail has become a key method for remote monitoring due to its long propagation distance and high speed. However, these acoustic signals face the challenge of large data volumes before transmission, necessitating effective compression. In this study, an innovative acoustic signal data dimension reduction method is proposed for acoustic emission signals with periodic pulse characteristics and narrow-band frequency domain features generated by wheel damage. It integrates sparse decomposition and kurtosis-guided resampling to compress these signals. The aim is to reduce the training time and dimensionality of the learning dictionary, thereby achieving sparse representation of the acoustic signal in the rail. In this method, the impact interval is determined using sliding window technology, and the data between adjacent impacts are down-sampled to significantly reduce the amount of signal data while retaining key impact characteristics. Furthermore, a Hankel matrix is used to organize the data after dimensionality reduction to optimize the subsequent sparse decomposition process. Using finite element simulation and experimental verification of service lines, this study systematically discusses the influence of various parameters on sparse decomposition and signal reconstruction. The experimental results show that, compared to the discrete cosine transform, wavelet compression algorithm, and piecewise aggregate approximation method, the proposed method not only retains the impact characteristics of the original acoustic signal but also achieves a higher compression ratio, demonstrating excellent performance and broad engineering application prospects. This study provides a novel and efficient signal processing technology for rail safety monitoring, contributing to the further development of railway safety monitoring technology.

The abundance distribution pattern of zooplankton associated with the pre-upwelling and late-upwelling phase is assessed for the eastern Arabian Sea (EAS) summer system, using vessel-mounted moving Acoustic Doppler current profiler (ADCP) and the in situ zooplankton samples collected using plankton nets. The distribution pattern of zooplankton is observed to be regulated by physical factors such as coastal upwelling, circulation patterns, mesoscale eddies, regional stratification, the presence of subsurface chlorophyll-a maximum, etc. during different phases of the upwelling cycle. The volume backscattering strength, a proximate factor for the zooplankton biomass, is computed after deriving the appropriate sound absorption coefficient, slant range, and backscatter noise. The linear relation derived by enumerating the backscatter-to-zooplankton biomass relationship was stronger during the pre-upwelling phase (r = 0.58) but weaker during the late-upwelling phase (r = 0.25). The findings underscore the potential of ADCP backscatter as a reliable indicator of zooplankton biomass within the mixed layer depth of the EAS, especially in the stable, calm, early summer season. The derived equations for estimating biomass are log(B) = 5.39 + 0.05  Sv for pre-upwelling and log(B) = 3.10 + 0.02  Sv for late-upwelling. The reduced correlation later suggests that environmental changes, such as zooplankton size and composition shifts, may affect ADCP’s detection threshold, necessitating careful interpretation. The study shows fish larvae act as dominant scatterers due to their gas-bearing properties, reliably indicating proxies for zooplankton abundance across both upwelling phases. Fluid-like and elastic-shelled scatterers vary between phases, reflecting shifts in zooplankton composition and their impact on acoustic backscatter. The analysis of ADCP backscatter data tracks diel vertical migration (DVM) of zooplankton with significant concentrations at depths of up to approximately 80 m during night-time. This study identifies distinct vertical migration velocities with zooplankton ascending in the range of 7.2 cm/s during dusk and descending at 7.7 cm/s during dawn.

The development of unmanned aerial vehicles continues to progress at pace. While these devices have been primarily used in research and hobby applications to date, there are increasing development efforts by companies interested in commercial applications where ‘drones’ would more commonly be deployed and encountered in the community. This paper considers the regulation of drone noise in the context of New Zealand’s Resource Management Act and seeks to examine how well the approaches traditionally used by acoustical engineers to quantify and manage environmental noise will cope with the widespread commercial use of drones. Drawing on recent experience providing advice to the aerospace sector in New Zealand, examples of the types of vertical and horizonal take-off drones which appear set for relatively imminent commercial use in New Zealand are discussed in general terms, along with indicative sound power levels and applications for these devices. How those situations may be managed in a typical District Plan context is then examined, along with the relevance of the concepts outlined in NZS6802:2008 Acoustics—Environmental Noise, NZS6805:1992 Airport Noise Management and Land Use Planning, NZS6807:1994 Noise Management and Land Use Planning for Helicopter Landing Areas, and case law such as Dome Valley District Residents’ Society v Rodney District Council.

Anthropogenic disturbance, including noise, is a major cause of biodiversity decline worldwide. Especially in anurans, the effect of noise pollution is known to have major consequences on their reproduction since acoustic communication is an essential part of this process. In this study, we tested the effect of three levels of traffic noise (55 dB, 65 dB, and 75 dB) corresponding to three different distances from the road (200, 100, and 50 m, respectively) on the Brazilian Mundo Novo treefrog (Boana marginata). The results of the playback experiments showed an effect on call type B. More specifically, there was a decrease in the advertisement call rate, a reduction in the number of pulses, and a lengthening of the interval between pulses, particularly at 65 dB. These findings suggest that at distances of up to 100 m, the masking effect significantly influences acoustic communication on the species. However, a 55 dB stimulus—equal to 200 m from the road edge—did not change the call in this species, suggesting a minimal distance to implement noise-inflicting infrastructures. We recommend that new studies adopt sampling methods from this distance to refine the threshold of the traffic noise effect.

The train vibration levels at a receiver are primarily governed by the trackform and its offset from the tracks. For a given trackform and offset, however, there can still be a wide variation in vibration generated by trains depending on the wheel and rail surface conditions, composition of the fleet and train speeds. In Australia, policies for the assessment of ground-borne noise and vibration are generally focused on the 95th percentile of train pass-bys. The use of this statistical descriptor is equivalent to a 5% exceedance level, i.e. vibration from one in twenty trains can be expected to be greater. This paper analyses four vibration datasets measured in Australasia. Three sets were measured on busy metropolitan train networks with direct fixation tracks in tunnels, and one dataset was measured on a ballasted surface track. The study focuses on the calculation of 95th percentiles and the effect of dataset size on the resulting 95th percentile vibration levels. Statistical error bands are calculated as a function of the number of consecutive pass-bys used in the dataset which allows for estimating the potential risks associated with working with small datasets. The effect of different approaches for calculating the percentiles is also discussed.