Acoustics Australia最新文献

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.

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.

The experimental characterization of the acoustic characteristics of engine exhaust devices is usually carried out through measurements in cold conditions, due to the intrinsic difficulties associated with proper temperature control in an acoustic rig. While those measurements may be sufficiently indicative for the cold end of the exhaust (the silencing elements) their significance for the hot end (the aftertreatment system) is more doubtful, as a result of the high temperatures and, eventually, the higher amplitude of pressure waves acting on the system. In this paper, a direct assessment is provided on the significance of acoustic measurements in cold conditions for representing the actual behaviour of an aftertreatment system in a hot pulsating, engine-like flow. Making use of wave decomposition techniques, the measured characterization was convoluted with the hot-flow excitation and the device responses were directly compared. The results indicate that, while it is not possible to fully reproduce the behaviour observed in hot pulsating flow, the tendencies are reproduced, at least qualitatively. In particular, the effect of soot loading is fairly reproduced.

This study aimed to determine if self-complete at-home recordings could produce audio samples of sufficient quality for use in voice analysis software, and if audio samples of similar or sufficient quality could be extracted from audio-recorded naturalistic phone interviews. Data were obtained from 31 adults aged 18 years and over who smoked. The /a/ sound segment was manually isolated, and analysis functions were used to produce the following values: fundamental frequency, jitter, shimmer, noise ratio, formant 3, and formant 4. The /a/ sound segment was then manually isolated from audio recordings of naturalistic interviews previously conducted by phone. These were analysed in the same way and compared for quality against Evistr-recorded audio samples from the same participants. A third audio sample consisted of an Evistr or phone-recorded sustained phonation of the /a/ sound. Means and standard deviations were calculated for the target vocal parameters. Statistical comparisons for quality of sound segment were conducted for readings, interviews, and vowel phonation and for sound signals extracted via both recording methods. Self-recording by adults who smoked provided audio samples of sufficient quality for analysis of vocal features that have been associated with a clinical outcome. The values obtained for sustained phonation audio samples displayed the least perturbation and noise for the vocal parameters surveyed. Sound signals recorded with smartphones appeared to be affected by electronic interference but have potential for use in diagnostic tools for measuring vocal parameters.

The Sarasvati Veena is an Indian stringed musical instrument with a curved bridge having a parabolic equation. We study the effect of such a bridge on the timbre of the instrument. We model the interaction of the vibrating string with the bridge as frictionless impact. So we implemented an energy-conserving method where string–bridge interaction is modelled with a penalty approach. We solve the resulting Hamilton’s equations numerically. Simulations are performed with different values of bridge parameters, namely slope and curvature. The numerical model is validated by comparison with experimental analysis. We isolate the contribution of the bridge by mounting it on the sonometer in place of one of its knife-edges and a mechanism is provided on the sonometer to change the bridge slope. We mounted the sonometer on foam to minimize the effect of other structural parameters. The typical Veena timbre shows sustain of most harmonics and the revival of higher harmonics with time. These features are attributed to the shape of the metallic layer at the top of the Veena bridge, its slope and curvature. Our model also shows these features, which are further corroborated by the experiment.

Most of the continental shelf area is a weakly range-dependent shallow-water environment. Compared with range-independent Bayesian geoacoustic inversion, range-dependent inversion usually has problems with the complex forward model and low efficiency for posterior analysis. According to the adiabatic normal-mode theory, the weakly range-dependent shallow-water environment can be divided into a series of range-independent segments; thus, this paper proposes a dual-source modal dispersion inversion method for local geoacoustic parameters of a segment based on a range-independent forward model. In addition, considering that the computational cost of the forward model limits the application of sampling-based methods for posterior analysis, a novel approximate variational inference, namely variational Bayesian Monte Carlo, is applied in this study. It has superior efficiency and shows similar accuracy compared with Markov Chain Monte Carlo sampling. This work is demonstrated in the shallow-water experiment in the continental shelf area of the East China Sea, and the results indicate that the local and range-dependent geoacoustic parameters are well-estimated.