Acoustics Australia最新文献

Anthropogenic disturbance, including noise, is a major cause of biodiversity decline worldwide. Especially in anurans, the effect of noise pollution is known to have major consequences on their reproduction since acoustic communication is an essential part of this process. In this study, we tested the effect of three levels of traffic noise (55 dB, 65 dB, and 75 dB) corresponding to three different distances from the road (200, 100, and 50 m, respectively) on the Brazilian Mundo Novo treefrog (Boana marginata). The results of the playback experiments showed an effect on call type B. More specifically, there was a decrease in the advertisement call rate, a reduction in the number of pulses, and a lengthening of the interval between pulses, particularly at 65 dB. These findings suggest that at distances of up to 100 m, the masking effect significantly influences acoustic communication on the species. However, a 55 dB stimulus—equal to 200 m from the road edge—did not change the call in this species, suggesting a minimal distance to implement noise-inflicting infrastructures. We recommend that new studies adopt sampling methods from this distance to refine the threshold of the traffic noise effect.

This paper examines and compares methods of separating tonal and broadband components of the noise generated by small rotors as commonly found on small unmanned aerial systems (sUAS). Time synchronous analysis (TSA) methods with varying averaging algorithms, such as ensemble averaging (EA), exponential weighted moving averaging (EWMA) and Kalman filter averaging (KFA), are compared against themselves and against a cross-correlation-based method. The decomposition methods are used on noise measurements of a small isolated rotor under static operation and edgewise flight conditions at 10 m/s in the UNSW anechoic wind tunnel (UAT). The best method for isolating tones is TSA-EWMA and for isolating the broadband spectrum of noise is the cross-correlation method, based on the spectral reconstruction of the experimental data.

The train vibration levels at a receiver are primarily governed by the trackform and its offset from the tracks. For a given trackform and offset, however, there can still be a wide variation in vibration generated by trains depending on the wheel and rail surface conditions, composition of the fleet and train speeds. In Australia, policies for the assessment of ground-borne noise and vibration are generally focused on the 95th percentile of train pass-bys. The use of this statistical descriptor is equivalent to a 5% exceedance level, i.e. vibration from one in twenty trains can be expected to be greater. This paper analyses four vibration datasets measured in Australasia. Three sets were measured on busy metropolitan train networks with direct fixation tracks in tunnels, and one dataset was measured on a ballasted surface track. The study focuses on the calculation of 95th percentiles and the effect of dataset size on the resulting 95th percentile vibration levels. Statistical error bands are calculated as a function of the number of consecutive pass-bys used in the dataset which allows for estimating the potential risks associated with working with small datasets. The effect of different approaches for calculating the percentiles is also discussed.

The bogie region is one of the most important aerodynamic noise sources of high-speed trains. A thorough understanding of the generation mechanism and characteristics of bogie aerodynamic noise is the prerequisite for effective implementation of noise control measures. In this study, a delayed detached eddy simulation (DDES) is performed to solve the unsteady flow field around the bogie region, and an aerodynamic noise source identification method based on the integral solution of the Ffowcs Williams-Hawkings (FW-H) equation is adopted to determine the dipole and quadrupole sources distribution in the bogie region. The identification results of the two types of sources provide different understandings of the noise generation mechanism of the bogie region but determine the same flow structures closely associated with the bogie aerodynamic noise, which are the shear vortex structures formed at the rear edge of the cowcatcher and the front side edges of the bogie cavity. The flow field data obtained by DDES simulation is also used as input for the FW-H solver to calculate far-field noise, and the source contribution, spectrum characteristics and directivity of the far-field noise are analyzed. The results show that at a speed of 350 km/h, the aerodynamic noise in the bogie region is still dominated by dipole sources, and the contributions of the bogie itself and the bogie cavity to far-field noise are equally important despite the significant differences in their radiation characteristics.

The leading-edge and trailing-edge serrated guide vanes, inspired by the silent flight of owl wings, were designed to reduce the aerodynamic noise produced by elbows in cruise. Using the acoustic finite element approach in conjunction with the large eddy simulation model, the aerodynamic noise produced by the elbow is calculated. Using an air piping test platform, this hybrid simulation technique is validated. Further simulation results showed that these two bionic guide vanes contributed to the decrease in the aerodynamic noise by streamlining the airflow and lowering the formation of laminar flow separation bubbles. In particular, the leading-edge serrated guide vane reduced noise by 4.6 dB, whereas the trailing-edge serrated guide vane reduced noise by 3.4 dB.

Light rail vehicles will often idle with their air conditioners running at terminus locations that may be located near sensitive receivers due to network constraints. This creates a pseudo-stationary noise source with similar level and characteristics to industrial air conditioners that can result in disturbance and complaints from nearby sensitive receivers. However, in practice in the state of New South Wales (NSW), Australia, this pseudo-stationary noise source is commonly assessed against airborne noise criteria for transportation noise. This is due to the Conditions of Approval on the Sydney Inner West Light Rail Extension project explicitly delineating noise produced by light rail vehicles from other sources. This interpretation has been applied on all subsequent light rail projects in NSW, which have assessed this noise source at termini against the Rail Infrastructure Noise Guideline (RING) requirements. The Noise Policy for Industry (NPfI) has been applied to other noise sources on these projects, specifically fixed equipment at stops and all noise sources at stabling facilities (including light rail vehicle air conditioning noise and traffic movements within the boundary of the facility). This paper examines the policy overlap between the RING and the NPfI that makes both documents potentially applicable to noise from light rail air conditioners when idling at termini, depending on interpretation and specific project conditions of approval. It also presents a hypothetical assessment of typical light rail activities near termini against both the RING and NPfI, to demonstrate the potential differences in project outcomes between the applications of the two documents. An example of a compromise that acknowledges the pseudo-stationary nature of the noise source as well as the benefits that public infrastructure provides relative to industrial facilities is also suggested, in lieu of a separate threshold or policy for this very specific circumstance.

The impedance tube method is commonly employed to measure the acoustical properties of materials, but commercial versions are prohibitively expensive for researchers lacking access to well-funded acoustical laboratories. A significant expense in traditional impedance tube setups is the pressure field microphones. This study explores the feasibility of using low-cost consumer-grade electret microphones, which are substantially cheaper than their pressure field counterparts. Our impedance tube design was validated and tested with high-cost pressure field microphones, contrasting it with electret microphones priced under one US dollar (USD). The findings reveal that the sound absorption coefficient can still be effectively and accurately measured using inexpensive microphones, subject to suitable signal conditioning and accurate microphone calibration. The trade-off is a slight loss of accuracy for the low-end frequency range of < 250 Hz.