Acoustics Australia最新文献

Tyre cavity resonance noise is one kind of low-frequency and narrow-band noise that particularly affects the passengers inside the cabin of vehicle, especially when driving at a medium speed. In this paper, a noise reduction structure made of multiple resonators is proposed to reduce this type of noise. Based on the local resonance principle, the dimension of the resonator unit is determined by the tyre cavity resonance frequency. In order to obtain this characteristic frequency and the acoustic feature, the acoustic-structure coupling model of the tyre and cavity is established by the finite element method (FEM), and the modal frequency and shape of the tyre cavity are calculated and validated by the experimental results. Based on these analyses, the geometric and material parameters of the sound reduction structure are calculated to match the resonant frequency of the tyre cavity. A long belt filled with multiple resonators is designed to fit the profile of the tyre cavity, and simulations and experimental tests are conducted to investigate the noise reduction performance. The results show that the multiple resonators can significantly reduce the sound pressure inside the tyre cavity due to the vibroacoustic coupling effect. This paper provides a novel solution for reducing tyre cavity resonance noise.

Classrooms are important learning spaces, however, the acoustic conditions in these spaces can often be suboptimal. The aim of this scoping review, which used the PRISMA-ScR protocol, was to understand what is known from the literature about the effect of classroom acoustic treatment on students’ listening, learning, and well-being. Thirteen papers from the database searches were deemed relevant for the review. Information on the years of publication of the papers, the population studied, the types of acoustic treatment used, the measures and methods used to assess the effect of acoustic treatment, and the outcomes of the papers was gathered. Seven of the 13 studies reported positive effects of classroom acoustic treatment on student’s speech perception, attention, and well-being. Five studies reported both positive effects and no effect depending on the measure, condition, or population. The remaining study reported a negative effect of classroom acoustic treatment on children’s speech perception and listening effort. These findings suggest that the effect of ceiling and/or wall absorbers/diffusers on sound and reverberation in the room can help students’ speech perception, attention, reading, and well-being, but they may also reduce the speech transmission index resulting in increased listening effort. The limitations of the reviewed studies and avenues for future research on the effect of acoustic treatment on a broader range of listening, learning, and well-being outcomes for students are discussed.

Active control of road noise has been widely recognized as a promising technology. For a feed-forward active road noise control system, the proper selection of the reference vibration signals is very important. It determines the theoretically optimal effect that the system can achieve. In order to achieve a reasonable selection of reference signals, a modified signal selection method is proposed in this paper. A test on road noise data acquisition and relevant analysis is conducted to decide the target frequency band for noise control. After that, an initial reference signal set is established and it is expanded by iteratively calculating the Fisher information matrix and the amount of new correlation information so that a reference signal set that has optimal multiple coherence with road noise is obtained. In the case study, a comparison between the traditional method and the proposed method is conducted. The results show that the proposed method can reach a higher average coherence coefficient and better noise reduction performance than the traditional method.

This paper investigated the effect of wall compliance on the noise attenuation performance of a water muffler. Firstly, the sound transmission loss (TL) of an expansion chamber with a piston-spring element located at one end wall of the chamber was derived using the transfer matrix method. It is found that transmission loss of a water-filled expansion chamber can be noticeably improved by introducing a reacting element, especially for the low-frequency range and frequency range around the resonance of the reacting element. A further lumped model established using acoustical–electrical analogy reveals that the reacting element functions as a volume amplifier of the expansion chamber for the low-frequency range, while the resonant behavior is dominated by the area and impedance of the reacting element. Then, the model was extended by replacing the piston-spring element with a circular plate. A 1.5-dimensional model was developed in which the fluid–structure interaction was regarded as an added mass effect, and a FEM model was used to verify the accuracy of the theoretical model. Finally, the effects of material properties, thickness, radius, boundary conditions, surface area, and length of the expansion chamber on the sound attenuation performance of reacting expansion chamber mufflers have been examined and discussed.

Matched Field Processing (MFP) is an inversion technique often employed in source localization applications. Conventional MFP approaches are incapable of producing precise results in the presence of extremely impulsive noises, which are typically present in actual applications such as underwater acoustics. This is because the covariance matrix for this category of noises does not converge. Moreover, impulsive noise suppression algorithms fail to provide accurate results. Particularly, fractional lower order moment (FLOM)-based approaches have an unbounded output, and data trimming methods introduce uncertainty into the estimation covariance matrix. In this study, a novel MFP method employing the empirical characteristic function (ECF) is developed. The desirable properties of the characteristic function (CF) result in a robust localization method that is ideally suited for extremely strong tailed noise environments. Using the CF array output, a new covariance-like matrix that can be used in MFP methods has been constructed. To demonstrate the efficiency of the ECF-MFP technique, experiments are conducted in a water tank. Experimental results reveal that this method is very robust in the presence of very heavy tailed noise, a low signal-to-noise ratio, and a tiny sample size. Additionally, it outperforms previous approaches in terms of resolution probability.

Transcranial focused ultrasound stimulation is a promising brain stimulation technique for its noninvasiveness and higher spatial resolutions and is used for various neuromodulation applications. As the skull is the primary barrier to delivering ultrasound to the deep brain region, it induces unpredictable ultrasound exposure. The objective of the study is to design customised transducers and assess the effects of the skull on ultrasound wave propagation. Computational skull models were constructed using computerised tomography scans. A full-wave finite-difference time-domain simulation platform, Sim4Life, was then used to design and simulate ultrasound wave propagation. In addition, the impacts of the skull were assessed through sensitivity analysis in the intracranial intensity, pressure, full width at half maximum, and energy deposition. Compared to the intracranial intensity distribution when the transducer is placed over the top area of the skull, the peak intensity increased by 23.4% for transmission through the temporal window. The temporal window, the thinnest part of the skull, provides a site for intracranial peak intensity and optimal focal spot area using focused ultrasound. The numerical investigation in this study provided a guideline for targeting and dosing, accounting for and lessening variability in studies addressing transcranial focused ultrasound applications.

The Ear of Dionysius cavern has frequently been explored for its unique acoustic properties. According to legend, it amplifies whispers and soft sounds so that they can be heard through a narrow tunnel 35 m above the ground. The legend refers to Dionysius, who ruled Syracuse between 432 and 376 BC and was supposedly able to hear the whispered secrets of prisoners chained in the cave. Acoustic measurements, simulations, and intelligibility listening tests were conducted to investigate the validity of this legend. The results were analyzed and compared to evaluate the definition (D₅₀) and speech transmission index at different locations in the cave. The results show that speech intelligibility in the Ear of Dionysius cavern is rated “fair” overall according to the ISO 9921 criteria, with better values in the central zone of the space. This fair rating suggests that the legend of the tyrant Dionysius eavesdropping on prisoners’ conversations may not be based in reality.

The sonar self-noise characteristics of an acoustic window made from multilayer functionally gradient materials (FGMs) under external turbulent pulsating pressure excitation were theoretically modeled using the multilayer plate (MLP) transfer function method and the turbulent pulsating pressure wavenumber–frequency spectrum. An MLP transfer matrix was used to determine acoustic transmission loss of the multilayer FGM plate under plane wave excitation. The theoretical model was verified by the finite element method. The FGM was fabricated from rubber and fiberglass-reinforced plastics (FRP)/carbon fiber. The acoustical transmission loss of the multilayer FGM plate and noise reduction patterns of the multilayer FGM acoustic windows were assessed at different gradients. The acoustic effect of the window on external sound waves and its spatial filtering effect on external turbulent fluctuation excitations can be adjusted by regulating the proportions of rubber and FRP, which changes the gradient variation pattern.

Obtaining adequate numeracy skills and listening comprehension skills at primary school are vital for children’s future success. However, classrooms are often noisy and reverberant which may interfere with learning these skills. Two scoping reviews were conducted to synthesise research assessing the effect of different classroom acoustic conditions on (1) children’s numeracy performance and (2) children’s listening comprehension and to identify areas for future research. The PRISMA-ScR protocol was used for these scoping reviews. A comprehensive search of four online databases was conducted in September 2021 using the search term classroom AND (noise OR reverberation OR acoustics) AND (numeracy OR math* OR arithmetic) for the first scoping review, and in May 2022 using the search term classroom AND (acoustic* OR noise OR reverb*) AND ("listening comprehension" OR "auditory comprehension" OR "spoken language comprehension" OR "speech comprehension”) for the second scoping review. The effect of the acoustic conditions on children’s numeracy was varied with most studies showing a negative or no effect of noise, but two showed a positive effect. Therefore, future research is needed to better understand the effect of different classroom acoustic conditions on children’s numeracy performance. For listening comprehension overall, signal-to-noise ratios below + 10 dB mostly had a negative effect on children’s listening comprehension compared to quiet conditions; however, variables such as the noise type, signal-to-noise ratio tested, the listening comprehension domain examined, the population studied, and the voice used for the stimuli affected this. Future research avenues to better understand these effects are proposed.

Hydrate blockage and pipeline leakage are two common factors that threaten the safety of natural gas pipelines. However, most of the current research focuses on nonintrusive, passive-like techniques that can only detect one of these abnormal events, with occasional attention to identification technique. This paper introduces an active method to simultaneously detect hydrate blockage and pipeline leakage using intrusive sensors, and further presents a deep forest-based classification method for two types of abnormal events, which aims to avoid the problem that the classification of traditional deep learning depends on huge number of hard-to-acquire samples. Besides, network structure and parameters in deep learning affect the classification performance, and deep forest is just a better solution to this problem. The parameter tuning experiments results of deep forest show that the classification accuracies are mostly 100% whatever in training and testing, proving that different parameter settings have little effect on the classification accuracy. The stability and portability of the classification method are tested, and it is verified that this classification method is easy to implement and has strong universality, which is expected to be applied to other types of natural gas pipeline event classification.