Acoustics Australia最新文献

This paper investigates the effect of blade rake angle on the tonal noise produced by contra-rotating rotor systems suitable for use on small multi-rotor unmanned aerial systems (UAS). This investigation utilises semi-analytical, numerical, and experimental methods to investigate the physics of the noise generation mechanisms, generated noise levels and the psychoacoustic characteristics of this noise. Computational fluid dynamics (CFD) simulations and semi-analytical models are employed to predict the periodic unsteady loading on the rotor blades, and the loading data are used to predict the radiated noise for rotor systems with different blade rake angles. Experimental measurements of the noise produced by a rotor system with no blade rake angle were used as a baseline case, and predictions were used to synthesise and auralise the sound produced by rotor systems with different rake angles for psychoacoustic analysis. The results show that increasing the blade rake angle generally reduces the amplitude of prominent interaction tones due to the reduction in the unsteady loading along the blade span caused by bound potential field interactions as the blade rake angle increases. This causes a reduction in the perceived tonal noise level.

Urban sound classification is essential for effective sound monitoring and mitigation strategies, which are critical to addressing the negative impacts of noise pollution on public health. While existing methods predominantly rely on Short-Term Fourier Transform (STFT)-based features like Mel-Frequency Cepstral Coefficients (MFCC), these approaches often struggle to identify the dominant sound in noisy environments. This gap in robustness limits the practical deployment of such systems in real-world urban settings, where noise levels are unpredictable and variable. Here, we introduce Smoothed Pseudo-Wigner–Ville Distribution-based MFCC (SPWVD-MFCC), a novel feature that merges SPWVD’s high time–frequency resolution with MFCC’s human-like auditory sensitivity. We further propose a dual-stream ResNet50-CNN-LSTM architecture to classify these features. Comprehensive experiments conducted on UrbanSound8K, UrbanSoundPlus, and DCASE2016 datasets demonstrate that the proposed SPWVD-MFCC significantly improves classification accuracy in noisy conditions, with an enhancement of up to 37.2% over traditional STFT-based methods and better robustness than existing approaches. These results indicate that the proposed approach addresses a critical gap in urban sound classification by providing enhanced robustness in low-SNR environments. This advancement improves the reliability of urban noise monitoring systems and contributes to the broader goal of creating healthier urban living environments by enabling more effective noise-control strategies.

Given the energy and size constraints of small and micro underwater unmanned platforms, along with the limited space gain available for acoustic systems and the challenge of detecting low-noise targets autonomously, this study introduces an improved histogram algorithm that relies on a single vector hydrophone. Additionally, a novel azimuth-based constant false alarm rate target autonomous detection method is developed to enhance the performance of target direction-finding and autonomous detection in scenarios characterized by low signal-to-noise ratio (SNR). Simulation results demonstrate that the modified histogram algorithm exhibits a narrower beamwidth and improved direction-finding accuracy. The SNR of −10 dB corresponds to a −3 dB beamwidth of 14° and direction-finding errors of 2.3°. Achieving a target autonomous detection probability of 100% simply requires an SNR of −16 dB. Experimental results in an anechoic pool show that the ameliorative histogram algorithm can effectively perform direction-finding and independent detection of sound sources at an SNR of −13 dB, with an average direction-finding error of approximately 4.8°. Sea testing data processing indicates that the improved histogram algorithm outperforms its predecessor in target direction-finding performance and enhances detection distance by approximately 2 times, validating the efficacy of the enhancement.

An alternating tone sequence may be perceptually integrated into one stream or segregated into two streams based on pitch and timbre differences between the tones (sequential stream segregation). However, the effect of the spectral dispersion of harmonic complex tones on sequential stream segregation has been largely unexplored. We introduced band tones that were harmonic complex tones divided into several frequency bands, in which frequency components in every other frequency band were removed. Here, we show that segregation was reported more often with fewer frequency bands and larger separation in fundamental frequency. Listeners generally responded to 2–8-band stimuli as segregated most of the time. However, the percentages of segregation responses for 16-band stimuli were generally dominated by fundamental frequency separations and whether the movements of fundamental frequencies and band-like spectral patterns were congruent or incongruent. The results suggest that the auditory system cannot organize rapidly alternating frequency component blocks spanning a wide frequency range into one stream.

In the post-COVID era, face masks have become a part of our daily lives. However, the effects of these masks on Mandarin speech production remain unclear. This study aimed to address this research gap by conducting a comprehensive investigation of the impact of surgical face masks on vowel production. Vowels produced in a continuous speech context were recorded for 61 native Mandarin-speaking adults, both with and without wearing a face mask. The acoustic parameters associated with three corner vowels /i/, /a/, and /u/ in Mandarin were measured. Significant changes were observed in the acoustic parameters under the masked condition, including an increase in F0 and a decrease in both F1 and F2 of vowel /a/, as well as tVSA, F1RR, and F2RR. However, no significant changes were found in duration and FCR. The patterns exhibited similarities between male and female speakers. The observed differences in vowel production can be attributed to the acoustic and physical consequences of wearing face masks. These differences, which may indirectly lead to reduced speech intelligibility, highlight the necessity of adopting adaptive strategies when face masks are present in various communication settings.

Transfer function method impedance tube measurement is a well-known approach used for determining acoustical properties of mostly porous materials. This paper presents a prototype of impedance tube together with the software solution published under open-source license. The prototype is developed specifically for experimental design of Helmholtz resonators. For room acoustic purposes, these are difficult to sufficiently characterize by other methods because of their highly frequency dependent complex-valued pressure reflection factor resulting in large phase shifts happening upon reflection. The main benefits of the presented method are the movable rigid termination operated by a stepper motor and the use of open-source libraries as well as widely available hardware for the whole measurement.

Multi-zone sound field reproduction uses the loudspeaker array to divide the space into different zones, which is a sound field control method to meet the different requirements of listeners in each zone. Since the vehicle interior is a small and enclosed space, the disturbance of acoustic transfer function (ATF) caused by scattering and reverberation in the acoustic environment and external noise will greatly affect the control effect. Certain predictable and measurable disturbances of ATF can be solved through error modeling or active control. However, due to the presence of disturbances that cannot be measured in advance, the effect of multi-zone sound field reproduction is barely satisfactory. In this paper, the maximum normalized recovery control (MNRC) is proposed to improve the robustness of multi-zone sound field reproduction. By measuring ATF in the actual car and calculating the expected ATF, the magnitude variation range of ATF is confirmed. Then, through normalizing the maximum value of the ATF matrix before being disturbed, the transmission characteristics are preserved, allowing for good multi-zone sound field reproduction performance even in the presence of unpredictable disturbances. The MNRC method does not require any error parameters of uncertain disturbance except for its amplitude variation range, reducing the preliminary preparation work for multi-zone sound field reproduction. Through simulation and experimental verification, the results show that when controlling the disturbed sound field, the MNRC method has a significant improvement compared to classic multi-zone sound field reproduction method. Furthermore, the performance in certain frequency bands is even better than the effect before being disturbed.

Traction induction motors (TIMs) are widely used in electrically powered railway vehicles. TIMs can generate significant noise during operation, which has become one of the primary noise sources for railway vehicles. In this paper, a purposely designed experiment was conducted to characterize the acoustic performance of a TIM based on the comparison of speed up and power off conditions. It was found that aerodynamic noise was dominant at speeds higher than 3000 r/min (3000 rotations per minute) and the main component of the aerodynamic noise was the 48th order (48 times the rotation frequency), which was related to the 48 conductors in the air-gap. To simulate the aerodynamic noise of the TIM, a computational fluid dynamics model was developed to calculate the flow field of the TIM. Lighthill acoustic analogy was then applied to calculate the noise due to the acoustic sources induced by the flow. Compared to the method with Ffowcs Williams–Hawkings acoustic analogy, the proposed method improved the accuracy in predicting the aerodynamic noise, and allowed to quantify the contribution to the aerodynamic noise of TIMs from a variety of acoustic excitation sources. The results showed that the excitation sources adjacent to the rotational air gap contributed the most to the motor’s aerodynamic noise. The proposed method was proven to be an efficient approach for optimal design of the TIM aerodynamic noise by identifying the main excitation sources and offered valuable insights for prediction of aerodynamic noise of other types of induction motors.