Acoustics Australia最新文献

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.

The biosonar system of bats utilizes physical baffle shapes around the sites of ultrasound reception for diffraction-based amplitude modulation. Bat antitragus has been hypothesized to affect the bat biosonar. Using numerical methods, we show that the antitragus of a Chinese horseshoe bat has an effect on increasing the acoustic near field as well as enhancing the reflection coefficient of the external ear. The simulation result provides a direct link between the biosonar signal and the morphological structure. The underlying physical mechanism suggested by the properties of the effect is that standing waves are produced between the pinna and antitragus.

This study proposes a general half-analytical method to predict the sound absorption of multiple inhomogeneous resonators inspired by Sellers’ method with small calculation cost. In this method, the sound absorption coefficient of single units is calculated by the finite element method (FEM), and superposition is used to predict the sound absorption coefficient of the overall structure. Unlike existing fully analytical methods that have difficulties with complicated or novel constructions, we combine FEM and the analytical method called the half-analytical method (HAE), which predicts sound absorption performance with excellent results. Two example structures are tested and the absorption coefficients from the analytical method, FEM, present method, and experiment show excellent agreement. The novel HAE method is promising to accurately predict the sound absorption coefficient of multiple inhomogeneous structures.

In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and double-layer board with gradient structure. The physical, mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with appropriatemixture designexhibited almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3 MPa and 1 MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and disclose the mechanism of sound absorption and insulation in the material.

Sound as a ubiquitous energy in our surroundings is clean and sustainable, and carries abundant information in a wide frequency bandwidth. However, effectively harvesting and utilizing acoustic energy is still hindered by the limitations such as low energy density of acoustic energy and lack of novel application. In this paper, we successfully present a self-powered acoustic sensor, which is composed of an adjustable spacing structure and sound-driven triboelectric nanogenerator (TENG). The acoustic sensor exhibits excellent electric output properties because of the poriferous electrode structure, ultrathin vibrating membrane as well as high-quality triboelectric materials. The sensor can deliver a maximal output voltage of 6.28 V with the sound frequency of 350 Hz and sound pressure of 110 dB. In addition, the electric output frequency is closely related to the applied acoustic wave and the corresponding directional dependence pattern as a butterfly is highly symmetrical. Our approach presents a cost-effective strategy to develop self-powered acoustic sensor and shows great potentials in home automation, self-powered microphone, sensor network and artificial intelligence.

Dolphins have a diverse acoustic communication system which includes whistles necessary for their survival. Whistle variation in dolphins could be related to the group behaviour, group size, formation and also environmental factors such as water depth, tidal phases and location. Such information is relatively unknown for the dolphin populations in Malaysia. This study aims to understand the whistle variation in Indo-Pacific humpback dolphins found in two sites in northwestern Peninsular Malaysia and possible factors that influence their whistles. A total of 4971 whistles were detected with whistle rates and parameters analysed. A GLMM analysis showed that whistle rates in both sites and in differing group sizes had significant differences. Only the mean whistle frequency significantly differed in differing group formations. Indo-Pacific humpback dolphins in a loose and uniform group had a lower mean frequency compared to other group formations. Other parameters such as the whistle duration and coefficient of frequency modulation did not show significant differences in differing behaviour, size, formation, water depth, tidal phases and location. This study is important and particularly valuable for understanding the species’ bioacoustics in the wider region of Southeast Asia.