Kurt Heutschi

A SIMPLE METHOD TO EVALUATE THE INCREASE OF TRAFFIC NOISE EMISSION LEVEL DUE TO BUILDINGS, FOR A LONG STRAIGHT STREET

Abstract A new method is presented to calculate the sound increase of traffic noise due to reflections between buildings. The new approach is a result of numerous ray tracing simulations to model the sound propagation in street gorges. The application of the method is based on look-up tables, thus yielding rapid results. The situation parameters ‘width of the street’, ‘height of the facades’, ‘distance from the receiver to the traffic lane’ and ‘width and position of gaps’ are taken into account. Measurements of the influence of buildings in real situations and predictions by the new method were compared and showed good agreement.

Detection and tracking of drones using advanced acoustic cameras

Recent events of drones flying over city centers, official buildings and nuclear installations stressed the growing threat of uncontrolled drone proliferation and the lack of real countermeasure. Indeed, detecting and tracking them can be difficult with traditional techniques. A system to acoustically detect and track small moving objects, such as drones or ground robots, using acoustic cameras is presented. The described sensor, is completely passive, and composed of a 120-element microphone array and a video camera. The acoustic imaging algorithm determines in real-time the sound power level coming from all directions, using the phase of the sound signals. A tracking algorithm is then able to follow the sound sources. Additionally, a beamforming algorithm selectively extracts the sound coming from each tracked sound source. This extracted sound signal can be used to identify sound signatures and determine the type of object. The described techniques can detect and track any object that produces noise (engines, propellers, tires, etc). It is a good complementary approach to more traditional techniques such as (i) optical and infrared cameras, for which the object may only represent few pixels and may be hidden by the blooming of a bright background, and (ii) radar or other echo-localization techniques, suffering from the weakness of the echo signal coming back to the sensor. The distance of detection depends on the type (frequency range) and volume of the noise emitted by the object, and on the background noise of the environment. Detection range and resilience to background noise were tested in both, laboratory environments and outdoor conditions. It was determined that drones can be tracked up to 160 to 250 meters, depending on their type. Speech extraction was also experimentally investigated: the speech signal of a person being 80 to 100 meters away can be captured with acceptable speech intelligibility.

Developing a GIS-Based Visual-Acoustic 3D Simulation for Wind Farm Assessment

Public landscape impact assessment of renewable energy installations is crucial for their acceptance. Thus, a sound assessment basis is crucial in the implementation process. For valuing landscape perception, the visual sense is the dominant human sensory component. However, the visual sense provides only partial information about our environment. Especially when it comes to wind farm assessments, noise produced by the rotating turbine blades is another major impact factor. Therefore, an integrated visual and acoustic assessment of wind farm projects is needed to allow lay people to perceive their impact adequately. This paper presents an approach of linking spatially referenced auralizations to a GIS-based virtual 3D landscape model. We demonstrate how to utilize a game engine for 3D visualization of wind parks, using geodata as a modeling basis. In particular, the controlling and recording of specific parameters in the game engine is shown in order to establish a link to the acoustical model. The resulting prototype has high potential to complement conventional tools for an improved public impact assessment of wind farms.

Calculation of Reflections in an Urban Environment

Sound propagation in an urban environment is often significantly influenced by reflections at building facades. The facades are typically structured in depth in the order of magnitude of decimeters up to meters. Low frequency reflections tend thus to be mirror like while at high frequencies they get a more and more diffuse or scattering character. A model is presented to calculate the effects of both type of reflections. After a discretization of the boundaries into grid cells, the sound pressure and energy exchange between the patches is calculated step by step. A coherent model is established to handle specular reflections. It solves a Kirchhoff-Helmholtz formulation by a time iterative process. The incoherent model for diffuse reflections assumes energy conservation and Lambert distribution for the reflections. The advantage of the model - which is part of the new Swiss railway noise calculation scheme sonRAIL - is its continuous behavior and the ability to take into account the reflector size. The model for specular reflections was validated extensively and proofed to reproduce scale model experiments as well as numerical FDTD simulations with good accuracy.

Short-term annoyance reactions to stationary and time-varying wind turbine and road traffic noise: A laboratory studya)

Current literature suggests that wind turbine noise is more annoying than transportation noise. To date, however, it is not known which acoustic characteristics of wind turbines alone, i.e., without effect modifiers such as visibility, are associated with annoyance. The objective of this study was therefore to investigate and compare the short-term noise annoyance reactions to wind turbines and road traffic in controlled laboratory listening tests. A set of acoustic scenarios was created which, combined with the factorial design of the listening tests, allowed separating the individual associations of three acoustic characteristics with annoyance, namely, source type (wind turbine, road traffic), A-weighted sound pressure level, and amplitude modulation (without, periodic, random). Sixty participants rated their annoyance to the sounds. At the same A-weighted sound pressure level, wind turbine noise was found to be associated with higher annoyance than road traffic noise, particularly with amplitude modulation. The increased annoyance to amplitude modulation of wind turbines is not related to its periodicity, but seems to depend on the modulation frequency range. The study discloses a direct link of different acoustic characteristics to annoyance, yet the generalizability to long-term exposure in the field still needs to be verified.

Sound Propagation over Ballast Surfaces

Sound emission measurements of railway vehicles are usually performed with microphones close to the railway line. In case of double-track lines and vehicles on the distant track ground reflections develop mainly above the ballast bed. The uncertainty of estimated sound power based on microphone signals depends on the accuracy of considered propagation effects. It is found that ground reflection over ballast has to be understood as an extended-reaction process. With the application of a simple geometrical model for a ballast structure good agreement between measurement and calculation could be achieved. The model was validated for a large set of loudspeaker measurements conducted at the occasion of the development work of sonRAIL, the new Swiss railway noise calculation model.

Outdoor sound propagation measurements using an MLS technique

Abstract The maximum length sequence (MLS) technique has been applied to the investigation of outdoor sound propagation. MLS leads to a significant increase in the signal-to-noise ratio compared to conventional, stationary excitation. In addition, it offers the advantage that the travel time of the signal is known for each of the pulse sequences. This aids in correlating the measured excess attenuation to the momentary wind speed. First results have been obtained at propagation distances of 50, 100 and 200 m for flat, grassy terrain. For a neutral atmosphere, the experimental results are in excellent agreement with theoretical expectations. In the presence of a positive or negative sound gradient, comparison is difficult because the appropriate value of the sound gradient is unknown.

Modelling parallel assemblies of porous materials using the equivalent circuit method.

Recently, the accuracy of the parallel transfer matrix method (P-TMM) and the admittance sum method (ASM) in the prediction of the absorption properties of parallel assemblies of materials was investigated [Verdière, Panneton, Elkoun, Dupont, and Leclaire, J. Acoust. Soc. Am. 136, EL90-EL95 (2014)]. It was demonstrated that P-TMM is more versatile than ASM, as a larger variety of different backing configurations can be handled. Here it will be shown that the same universality is offered by the equivalent circuit method.

Generating sequences of acoustic scintillations

Spatial and temporal inhomogeneities in temperature and wind velocity affect sound propagation resulting in amplitude and phase fluctuations called scintillations. A computationally efficient method is presented to generate sequences of scintillations. The method, already used in the field of wireless communication to predict the performance of wireless communication links, could be used in the field of acoustics to create more perceptually valid auralizations. A Gaussian spectrum and a spherical wavefront is considered, but the method can also be used in combination with other spectra like the Von Karman spectrum as well as plane waves. Two examples are given, one is a pure tone affected by the scintillations and the other is an auralization of an aircraft fly-over. The effect of the transverse speed of the source is demonstrated as well.

Modelling sound propagation in the presence of atmospheric turbulence for the auralization of aircraft noise

A new tool for the auralization of aircraft noise in an urban environment is in development. When listening to aircraft noise sound level fluctuations caused by atmospheric turbulence are clearly audible. Therefore, to create a realistic auralization of aircraft noise, atmospheric turbulence needs to be included. Due to spatial inhomogeneities of the wind velocity and temperature in the atmosphere acoustic scattering occurs, affecting the transfer function between source and receiver. Both these inhomogeneities and the aircraft position are time-dependent, and therefore the transfer function varies with time resulting in the audible fluctuations. Assuming a stationary (frozen) atmosphere, the movement of the aircraft alone gives rise to fluctuations. A simplified model describing the influence of turbulence on a moving elevated source is developed, which can then be used to simulate the influence of atmospheric turbulence in the auralization of aircraft noise.