Effect of low-frequency tones and turbulent-boundary-layer noise on annoyance

A laboratory study was conducted to examine annoyance to combinations of low-frequency tones and turbulent-boundary-layer noise. A total of 240 sounds, containing tones in the range from 80 to 315 Hz, were rated by 108 test subjects in an anechoic chamber. The results indicated that tone penalties (defines as the failure of a noise metric to account for the presence of pure tones) are highly dependent on the choice of noise metric. A-weighted sound pressure level underpredicted annoyance by as much as the equivalent of 5 db and unweighted sound pressure level overpredicted by as much as the equivalent of db. Tone penalties were observed to be dependent on the shape of the turbulent boundary-layer noise spectrum

Identification of major noise donors, a sure way to abating noise

A Study was conducted to ascertain the specific noise emitted by presumed noisy environments. This was achieved by direct measurement of the noise with the use of an integrated sound level meter in which a built-in frequency filter or weighting network is incorporated. Ten (10) environments were selected in Ilorin and Akure towns in Nigeria, in which sixty (60) readings were taken at intervals of 30 seconds for 30minutes separately at each location. This amounted to an overall reading of six hundred (600) readings. The results show that the Lawn Mower emits noise with the highest Equivalent sound level

Theoretical study of stimulated and spontaneous Hawking effects from an acoustic black hole in a hydrodynamically flowing fluid of light

We propose an experiment to detect and characterize the analog Hawking radiation in an analog model of gravity consisting of a flowing exciton-polariton condensate. Under a suitably designed coherent pump configuration, the condensate features an acoustic event horizon for sound waves that at the semiclassical level is equivalent to an astrophysical black hole horizon. We show that a continuous-wave pump-and-probe spectroscopy experiment allows to measure the analog Hawking temperature from the dependence of the stimulated Hawking effect on the pump-probe detuning. We anticipate the appearance of an emergent resonant cavity for sound waves between the pump beam and the horizon, which results in marked oscillations on top of an overall exponential frequency dependence. We finally analyze the spatial correlation function of density fluctuations and identify the hallmark features of the correlated pairs of Bogoliubov excitations created by the spontaneous Hawking process, as well as novel signatures characterizing the emergent cavity

Aircraft wing trailing-edge noise

The mechanism and sound pressure level of the trailing-edge noise for two-dimensional turbulent boundary layer flow was examined. Experiment is compared with current theory. A NACA 0012 airfoil of 0.61 m chord and 0.46 m span was immersed in the laminar flow of a low turbulence open jet. A 2.54 cm width roughness strip was placed at 15 percent chord from the leading edge on both sides of the airfoil as a boundary layer trip so that two separate but statistically equivalent turbulent boundary layers were formed. Tests were performed with several trailing-edge geometries with the upstream velocity U sub infinity ranging from a value of 30.9 m/s up to 73.4 m/s. Properties of the boundary layer for the airfoil and pressure fluctuations in the vicinity of the trailing-edge were examined. A scattered pressure field due to the presence of the trailing-edge was observed and is suggested as a possible sound producing mechanism for the trailing-edge noise

Measurement of noise events in road traffic streams: initial results from a simulation study

A key question for road traffic noise management is whether prediction of human response to noise, including sleep quality, could be improved over the use of conventional energy equivalent, or percentile, measures, by accounting for noise events in road traffic streams. This paper reports initial results from a noise-events investigation into event-based indicators over an exhaustive set of traffic flow, traffic composition, and propagation distance, conditions in unshielded locations in proximity to roadways. We simulate the time-varying noise level histories at various distances from roadways using a dynamic micro-traffic model and a distribution of sound power levels of individual vehicles. We then develop a comprehensive set of noise event indicators, extrapolated from those suggested in the literature, and use them to count noise events in these simulated time histories. We report the noise-event algorithms that produce realistic, and reliable, counts of noise events for one-hour measurement periods, then reduce redundancy in the indicator set by suggesting a small number of representative event indicators. Later work will report the traffic composition and distance conditions under which noise event measures provide information uncorrelated with conventional road traffic noise indicators — and which thus may prove useful as supplementary indicators to energy-equivalent measures for road traffic noise

Aeroacoustics of a coaxial rotor in level flight

The aeroacoustic characteristics of a coaxial system with teetering rotors in level forward °ight are com- pared to those of an equivalent articulated single rotor with the same solidity. A lifting line representation of the blade aerodynamics is coupled to Brown's Vorticity Transport Model to simulate the aerodynam- ics of the rotor systems. The acoustic ¯eld is determined using the Ffowcs Williams-Hawkings equation. Acoustic analysis shows that the principal contribution to noise radiated by both the coaxial and equivalent single rotor systems is at the fundamental blade passage frequency, but that the coaxial rotor generates higher sound pressure levels (by 10 dB for the evaluated con¯gurations) than the equivalent single rotor at all °ight speeds. The sources of blade vortex interaction (BVI) noise are investigated and the principal BVI events are identi¯ed. For the coaxial rotor, the most intense impulsive noise is seen to be generated by the inter-rotor BVI on the advancing side of the lower rotor. The impulsive noise that is generated by blade vortex interactions for the equivalent single rotor reduces in amplitude as the strength of BVI events on the rotor decreases with forward speed. Conversely, the BVI noise of the coaxial rotor intensi¯es with increasing °ight speed due to the increasing strength of the interaction between the wake of the upper rotor and the blades of the lower rotor. The impulsive noise due to BVI for the coaxial rotor is found to be higher by 20{35 dB compared to the equivalent single rotor. The overall and impulsive noise characteristics of the coaxial system are found to be weakly sensitive to changes in rotor separation and the relative phasing of the rotors

Measurement of Field Complex Noise Using a Novel Acoustic Detection System

This paper represents our recent experimental measurement study of the complex noise in industrial fields, using a novel acoustic detection system and wavelet transform algorithms. Noise induced hearing loss (NIHL) continues to be one of the most prevalent occupational hazards in the United States. Number of research on NIHL showed a complex noise could produce more hearing loss than an energy-equivalent continuous or impulsive noise alone. Many workplaces in varied industries are subjected to the high level complex noise (i.e., high-level impulsive noise mixed with continuous Gaussian noise). The current noise measurement guidelines and devices (e.g., conventional sound level meters) are based on the equal energy hypothesis (EEH), which states that loss of hearing by exposure to noise is proportional to the total acoustic energy of the exposure. However, the EEH does not accurately rate the impulsive noise and the complex noise. Therefore, the conventional sound level meter may not be able to accurately assess the complex noise in industrial fields. In this project, a new waveform profile based noise measurement system has been developed for evaluation of the high level complex noise in industrial fields. The system consists of four ½” condenser microphones, and it can simultaneously detect and record four waveforms of the complex noise with high sampling rate (125 KHz). In addition, a wavelet transform based signal analysis algorithm has been modified and implemented to characterize the complex noise. Pilot field measurements have been conducted in selected local coal mining fields (e.g., wet coal preparation plant and dry coal handling plant) using the developed system. The preliminary results showed that the system successfully detected and recorded waveforms of complex noise in industrial fields. The modified algorithm can decomposed the complex noise signals and display the detailed features in the time-frequency joint domain. The key parameters of complex noise can be determined, and the hazardous complex noise in industrial fields can be identified. In addition, when measuring the equivalent A-weighted averaged sound pressure level, the developed system is comparable to a conventional sound level meter

Assessment Of Noise Impact: A Case Study Dueto Aircraft Activities

This paper presents the results obtained from an environmental noise measurement at a selected location in Malaysia in order to establish the impact of noise to human at residential area. The measurement site was situated less than three kilometers from the nearest airport and any major activities can be expected to be heard. The noise measurement was carried out for 24 hours monitoring for 30 days by using integrated B&K SLM equipments to obtain the equivalent sound level (Leq), L10 and L90 so that the exposure of noise to community can be assessed. Maximum sound level (Lmax) and sound exposure level have been measured as specified by the Federal Aviation Administration (FAA) for aviation noise assessment. The results revealed that the overall noise level exceeded the requirement of standard which is stated at 65dBA.These finding are very useful to be used as reference and guideline for future regulations on noise limit to be implemented for urban areas in Malaysia not only to human but also for wildlife and building structure

Modelling of a city canyon problem in a turbulent atmosphere using an equivalent sources approach

The sound propagation into a courtyard shielded from direct exposure is predicted using an equivalent sources approach. The problem is simplified into that of a two-dimensional city canyon. A set of equivalent sources are used to couple the free half-space above the canyon to the cavity inside the canyon. Atmospheric turbulence causes an increase in the expected value of the sound pressure level compared to a homogeneous case. The level increase is estimated using a von Kármán turbulence model and the mutual coherences of all equivalent sources' contributions. For low frequencies the increase is negligible, but at 1.6 kHz it reaches 2–5 dB for the geometries and turbulence parameters used here. A comparison with a ray-based model shows reasonably good agreement