Acoustics Australia最新文献

This paper explores the possibility to use statistical energy analysis (SEA)-based computations to synthesize sounds that can be used in a subjective evaluation of the unpleasantness of exterior noises transmitted in the car compartment through the glazing. A medium family car (C-segment car) was placed in a reverberation room. A sound source was placed outside the car. The resulting noise was measured at the driver’s position for nineteen different configurations of glazing. The transmission loss (TL) of each car window was computed using an in-house software and used in a SEA-based vibroacoustic synthesis model. The nineteen corresponding configurations were simulated. A listening test experiment was conducted to compare the signals synthesized from the measurements and from the simulations. The results showed a good agreement between the unpleasantness ratings of each glazing configuration. However, in the case of tempered glasses, a slight difference in the ratings was detected. Further analysis showed that this was due to an inaccurate prediction of the TL of the glazing, around its coincidence frequency. Additional measurements proved that this could be related to an underestimation of the damping. More precisely, because the intrinsic damping of a tempered glass is very low, the additional damping brought by the window seals must be taken into account. Further measurements were made to estimate the TL of a tempered glass mounted on a gasket. The use of these new values in the SEA calculation allowed for the correction of these difference in subjective ratings. The SEA computations can thus be used in the acoustic design process of cars.

Acoustic data from the Perth Canyon, Western Australia, were collected for the 2017 northern migration allowing for detailed acoustic analysis of eastern Indian Ocean pygmy blue (EIOPB) whale songs within a migratory season to explore fine-scale variability in song production. An algorithm was used to follow the unit II signal in time, tracking the change in frequency over the duration of the signal and enabling a comparison of song unit production within and between singing bouts. The results of this analysis indicate that units from within the same song event have relatively consistent characteristics but vary between song events, suggesting it is possible that individual whales may have distinct vocal characteristics. The presence of breaks within a unit was identified as a significant level of variability in song production within the 2017 data set and was seen to increase throughout the season. It is hypothesised that unit breaks may play a role in intra-species communication as well as represent a novel variation to song production that increases song complexity and thus may increase individual fitness through sexual selection.

Metro running causes wheel/rail rolling radiation noise and reflects multiple times between the tunnel wall and the car body. Reverberation in a tunnel increases the interior noise and reduces riding comfort. A statistical energy analysis (SEA) model for a metro train in a tunnel is proposed to predict interior noise and improve ride comfort. The model considers the acoustic excitation caused by wheel/rail rolling, the damping/coupling loss factors, reverberation time in the tunnel/coach, and the equivalent panels. The results show that the error between the simulation and the measured is 3–6 dB; the SEA model is available. The mechanical wave of symmetrical loading may cancel out on the plane of symmetry. At low frequencies, the difference between the internal and external noise is slight (10 dBA), the transmission is robust, and the sound insulation of the car body is weak. In contrast, at high frequencies, the difference is significant (25 dBA). The tunnel reverberation effect increases the sound pressure inside the car by 8–12 dBA than the open-line, and the reverberation will reduce the spatial distribution gradient of the interior noise. Applying noise control treatment on the tunnel’s inner wall can reduce the noise by 5–10 dBA.

The impact of cutting the f-holes in a completed violin was investigated based on two measurable characteristics of the instrument. One of these aspects focused on the signature modes, while the other involved monitoring the graph of the bridge mobility. A particular emphasis was placed on analyzing this graph due to existing literature suggesting the connection of the bridge hill to the presence of f-holes. In the case of two real violins, bridge mobility was measured using an ultra-miniature accelerometer and an impact hammer. Concurrently, signature modes were recorded using Electronic Speckle Pattern Interferometry, an optical technique that performs well on rough surfaces; hence, the violins employed were intentionally left unvarnished. One of the violins lacked f-holes but included the rest of the structural elements. It was measured in stages as the f-holes were cut. The second violin adhered to a standard design but featured slightly wider f-holes, serving as a reference. Additionally, bridge mobility and signature modes were simulated for a finite element violin soundbox both with and without f-holes. Contrary to expectations, both the experiments and simulations revealed the emergence of the Bridge Hill even in the absence of f-holes. However, the alteration of the middle and high-frequency response was evident during the f-hole cutting process, accompanied by the observation of CBR as well as (B_1^-) and (B_1^+) modes.

Due to the increasing noise pollution, noise control has drawn more and more public attention. Different from traditional methods to reduce noise energy such as active and passive noise control, suppressing noise annoyance through adding sounds is another choice. In previous studies, water sounds are usually used to adjust the annoyance of traffic noise, but the suppression effect of the water sounds varies from person to person. Low-frequency tonal noise is one kind of typical and common mechanical noise, i.e., substation noise, whose annoyance is caused by tonal perception and higher energy in low frequency is difficult to suppress even though adding sounds. In this study, different controllable sounds (water sounds and narrow-band color noises) with different masker-to-noise ratios (MNRs) were added to low-frequency tonal noise to investigate the annoyance suppression effect through listening tests. Furthermore, in order to evaluate the quantitative suppression effect, the standard sample method (SSM) was applied in the listening tests to convert the annoyance difference into the difference of equivalent sound pressure level of 1 kHz and 70 dB pure tone ((Delta SPL_{1kHz,70dB})). Results show that different kinds of water sounds and narrow-band color noises effectively reduce noise annoyance. The optimal result comes from adding one kind of water sound, which reduces the annoyance of substation noise by 27.24%, equivalent to reducing (Delta SPL_{1kHz,70dB}) by 6.5 dB. Finally, the annoyance prediction model of combined noises is established to choose controllable sounds and predict the suppression effect of annoyance.

The fundamental objective of acoustic barriers is to preserve the inhabitants of nearby areas from the high noise generated by road traffic. It is possible to significantly improve the performance of conventional acoustic barriers by attaching small acoustic diffusers on their upper part (caps) that do not imply an appreciable height increase of the barrier, thereby adhering to any height regulation or restriction. This work deepens and yields findings in the study of the acoustic performance of barriers with diffusers of different shapes, number and arrangement through the calculation of their insertion losses (IL). In this research, a design of four Y-shaped diffusing elements arranged according to the well-known fractal pattern called Cantor set is presented and validated through two types of traffic noise sources (‘Car’ and ‘Ambulance’), one listener and a wide frequency band up to 10 kHz. The results demonstrate that the proposed diffuser provides a significant increase in acoustic losses compared to the results obtained in previous works without raising the height of the barrier. To the best of the authors’ knowledge, there are no diffuser structures like the one presented here that have been installed or even proposed/analysed.

With the increasing demand for household appliances, people are putting forward higher requirements for their sound quality. In this paper, we apply the theory of acoustic metamaterials to a bladeless fan and propose a curly space-type acoustic metamaterial (CSAM) to optimize the sound quality while ensuring the airflow of the bladeless fan. The acoustic transmission loss of CSAM is calculated by numerical simulations. Based on the hybrid approach to calculating aerodynamic acoustics (CAA) to calculate the aerodynamic noise of the bladeless fan, the ICFD module of Actran is used to convert the CFD simulated data into sound field data. The internal flow field and sound field of the bladeless fan with or without CSAM are compared and analyzed. Finally, an experimental test is done to verify the noise reduction effect and air velocity change after adding CSAM. The analysis shows that the change in the air velocity of the bladeless fan by adding CSAM is not apparent, and the sound pressure level at the monitoring point is reduced. The experimental results show that the noise of the bladeless fan is reduced by 4.9 dB after adding CSAM, and the wind speed at the location of the monitoring point is increased by 0.08 m/s. Without affecting the air velocity, CSAM can change the intensity of the sound source inside the bladeless fan and effectively suppress the aerodynamic noise. It demonstrates the feasibility of acoustic metamaterials to reduce aerodynamic noise.

This study used accelerometers and hydrophones to measure the vibration and underwater noise from two different types of offshore wind turbine installed near the East China Sea Bridge (Shanghai). Wind speed and rotor speed were also monitored synchronously. The spectrograms of the vibration and underwater noise signals display well-defined spectral lines that are easily distinguishable. Line-component spectra of both vibration and underwater noise signals were synchronously extracted through filtering and correlation analysis. On this basis, relationships between the intensity and frequency of wind turbine vibration and underwater noise line-component spectra, rotor speed, and wind speed were analyzed. Results indicate that rotor speed is positively correlated with wind speed, and that the peak vibration frequencies and intensities of both types of turbine are positively correlated with rotor speed. Consequently, it can be concluded that the frequency and intensity of turbine-generated underwater noise are closely related to wind speed. Additionally, the vibration mechanism and the characterization of underwater noise of the wind turbines have been revealed.