Acoustics Australia最新文献

The widespread adoption of face masks is now a standard public health response to the 2020 pandemic. Although studies have shown that wearing a face mask interferes with speech and intelligibility, relating the acoustic response of the mask to design parameters such as fabric choice, number of layers and mask geometry is not well understood. Using a dummy head mounted with a loudspeaker at its mouth generating a broadband signal, we report the acoustic response associated with 10 different masks (different material/design) and the effect of material layers; a small number of masks were found to be almost acoustically transparent (minimal losses). While different mask material and design result in different frequency responses, we find that material selection has somewhat greater influence on transmission characteristics than mask design or geometry choices.

The underwater glider is a new type of unpowered, unmanned, moving observational platform with advantages of low-noise level, long operation time, far sustainable range, and high cost-effectiveness. In the paper, based on the underwater glider platform integrated with single vector acoustic sensor, an underwater acoustic glider platform is developed with the ability to detect target direction and observe the ambient noise. The acoustic measurement system and the self-noise of the glider platform under each working condition are tested to analyze the self-noise levels of the acoustic system and the primary noise sources of the platform, and conduct the vibration and noise reduction processing of the platform and optimize the working mode of the acoustic system. The test result shows that the underwater acoustic glider with the optimization has the ability to observe the ambient noise only on the pressure hydrophone channel. With the data sampled from one of the underwater gliders of the sea trial organized in a certain area of the South China Sea in August 2019, authors analyze the variation of spectrum levels of the ambient noise with the depth and the time at the center of seven frequency points (63 Hz, 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1.6 kHz and 3.15 kHz) and discuss the influence of the sailing vessel close to the glider on it. The experimental result shows that the underwater acoustic glider, as an unscrewed moving platform, can be well used to monitor the ambient noise properties over a long term.

The detection and recognition of quiet, small objects in shallow water is one of the challenges in underwater acoustic signal processing, especially for buried objects. The seafloor strongly absorbs sound waves, while the object echo signals are weak, which makes the detection of the buried objects more difficult. Realizing object echo signal enhancement in a seafloor reverberation background and improving the signal-to-reverberation ratio (SRR) are critical problems. Based on the difference in energy aggregation between object echo signals and reverberation in the optimal fractional Fourier domain, a blind separation algorithm in the spatial fractional Fourier domain is presented. Expressions of the object rigid scattering components and the reverberation in the fractional Fourier domain are derived, and the energy distribution characteristics of both are analyzed. The objective function is constructed by the generalized correlation matrix of the multiple array signals in the optimal fractional Fourier domain, and the object rigid scattering components are obtained by approximate joint diagonalization. The simulation and data processing results show that the spatial fractional domain blind separation algorithm (FRFTBSS) can improve the signal-to-reverberation ratio. Compared with time–frequency domain blind separation (TFBSS), the proposed algorithm avoids the cross-item interference and performs better at lower SRR.

The aim of this research project was to investigate the scattering acoustic field by a rigid cavity in a rigid plane insonified by an arbitrary deterministic incident field. The Kobayashi potential method was used in order to derive the scattered acoustic field in a modal form. A previous model was developed using the same method for an incident plane wave (Khanfir et al. in J Sound Vib 361:251, 2016). The incident spherical source was then decomposed into plane waves. The total scattered field was determined by summing all the elementary scattered fields. In this paper, we present a new technique allowing the scattered acoustic field determination without using the decomposition into plane waves technique. This new model was compared to numerical results obtained using the previous model, the boundary element modeling method and experimental results for two rectangular cavities insonified by a spherical source. A good agreement between numerical and experimental results was obtained supporting the validity of the model.

The challenge in the acoustics design of the traditional mosque is twofold. First, the interior atmosphere of the space should create a sacred feeling on the users' holistic and phenomenological spatial perception, which is generally recognized as a direct effect of increased reverberation time (T30) and low clarity (C80). Second, speech should be adequately intelligible, which requires a low T30 and high speech clarity, contradicting the initial concern of the sacred atmosphere. We hypothesize that in Islamic architecture, wooden hypostyle mosques may comply better with the reverberation time requirements of speech intelligibility, while maintaining the sacred feeling, due to their comparatively absorptive surface finishing materials and structural elements. The Aslanhane Mosque is a unique sacred structure within its era of construction, well-known with its wooden columns and ceiling. It is an important case for room acoustics analysis of such holy spaces. This study aimed to analyze the room acoustic measurement results of the Aslanhane Mosque, evaluating the intelligibility of speech and interpreting the sacred feeling created by reverberance, envelopment, and spaciousness, which are all crucial in such holy structures. It is revealed that although the Aslanhane Mosque's subjective rating for speech intelligibility is “good,” the overall low volume of the mosque and the lack of surface reflections decrease the sacred sensation. Additionally, the intelligibility of speech is vulnerable to obstacles within the line of sight, such as load-bearing columns. Lastly, it was observed that the increase in T30 at low frequencies improved the sacred sensation, envelopment, and spaciousness, without any profound negative impact on the intelligibility of speech.

A design of the sonic crystal (SC), called the gradient-based sonic crystal (GBSC), that uses the gradient of properties of the SC array is proposed as an improvement over the traditional design of SCs. The gradient of properties is obtained by changing the resonator dimensions and the distance between them throughout the array instead of keeping them uniform. Because of this non-uniformity, the supercell approximation was used to handle the non-ideal periodic conditions it induces in the array. GBSCs in non-uniform rectangular and triangular lattices were designed and analyzed using the finite element method. The results show that the GBSCs widen existing bandgaps, create new bandgaps, induce high acoustical losses compared to the uniform SCs of Helmholtz resonators (HR) or hollow scatterers (HS) and have similar space requirements. Therefore, the GBSCs can be used for acoustic attenuation in low-mid-high frequency bands. Parameters such as increasing or decreasing order of the resonator size and distance, and the resonator orientation were found to influence the attenuation by the GBSCs. Experiments were conducted on the traditional uniform HS sonic crystals and HR sonic crystals and their finite element (FE) models were developed which were later useful for developing robust FE models of the GBSCs.

Sound radiation from thin metal plates has consistently been recognized as a severe noise problem. One of the most popular approaches to suppressing this noise is applying viscoelastic layers, also called free layer damping (FLD), on the plate surface, which can damp the structural motion and minimize the radiated sound. The thickness of the FLD is an important parameter. It needs to be optimized for the target acoustic limits through numerical simulations, as the total mass and the costs may rise unnecessarily. This paper investigates the sound radiation from thin metals of particular sizes with different thickness values of FLD. A unique test setup was established to measure vibration and sound for three different sized plates, with each one having three different FLD thicknesses, namely, 0.5 mm, 0.75 mm, and 1 mm. In parallel, vibro-acoustic analyses were performed for the same configurations using the finite element method. The damping of the FLD was defined using the Rayleigh damping model, of which coefficients were obtained through a prediction formula developed earlier by the authors. After validating the model with the test, the effect of FLD on the extended acoustic parameters (radiated sound power, directivity) was also analyzed.

Acoustic attenuation of a hybrid sonic crystal made with periodic cylindrical scatterers and cascaded porous panels in a broad frequency range is endeavoured in this paper. It is observed via simulations that, the insertion loss (IL) of hybrid configuration is larger than the summation of IL of individual contributors such as periodic scatterers and parallel porous panels in post first Bragg resonance frequency band. The key finding of the research is that the passband in post first Bragg resonance is turning to stopband on introducing the cascaded porous panels within scatterers. Other configurations such as periodic array of cylindrical scatterers in series with porous panels in upstream, downstream and bounded with porous panels are examined and compared. The potential of said claim is shown by investigating a multi-resonant array of scatterers with cascaded porous panels. Finally, the experimental results are presented to authenticate the observed findings of simulations.

The number of research papers dealing with vibration-based condition monitoring has been exponentially growing in recent decades. As a consequence, one may identify some trends that emerge from this vast literature. The present paper delineates a methodology that can be recognized in several research works, which is rooted in a succession of three stages. The first stage embodies a linear transform of the data, typically in the form of a filterbank, the second stage reduces the dimension of the data through a nonlinear functional, typically in the form of health indicators, and the last stage supplies a statistical decision. Although several variants of this methodology exist, its fundamental principles seem to have converged to a general consensus, at least implicitly. This paper provides a critical overview of this methodology. It discusses its working assumptions under some typical scenarios and formulates several caveats. It also provides a few prospects that may nourish future research.