bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and analysis of tire road noise, finite element results and validation
Authors: Brinkmeier Maik , Nackenhorst Udo , Biermann Jan , Von Estorff Otto
Published: May 2008

This presentation shows the methods and results of the German research project "Silent Traffic". The main topics are the simulation of tire road noise as well as the validation of the methods and finite element models. The target is to understand the mechanisms of sound generation and to get suggestions to reduce the traffic noise resulting from the virtual system. The investigations are based on a physical modeling of the tire road system rather then on the processing of statistical data. The simulation procedure can be decomposed into four steps: The computation of non-linear stationary rolling, the eigenvalue analysis in the deformed state, the analysis of road surface textures, and the calculation of the noise radiation including a modal superposition approach with an excitation by deterministic functions. Thereby, the numerical model enables for a detailed analysis of certain effects of the sound generation and radiation that contribute to the overall tire road noise. The simulation results are compared to measurements, both for structural dynamics and acoustics, to show the quality of the model und to indicate possible improvements for further development.
A multiple regression model for predicting rattle noise subjective rating from in-car microphones measurements
Authors: Gauduin Benoı̂t , Noel Christophe , Meillier Jean-Louis , Boussard Patrick
Published: May 2008

In some situations when the road is deformed, the shock absorbers of vehicles may produce a specific sound, called rattle noise. It may be perceived by the driver and wrongly considered as a malfunction of the vehicle. This sound is part of the global acoustic comfort of the vehicle and hence is studied by RENAULT. The approach presented here aims at predicting the rattle noise subjective rating given by a RENAULT expert on a scale from 0 to 10, by developing a model based on in-car binaural microphones measurements in the ears if the driver. First, a set of 11 metrics has been build, related to temporal aspects, spectral components and time-frequency information of the rattle noise recorded. The corpus is made of 19 different configurations of shock absorbers of a given car. The method used to select the most relevant metrics for the multiple regression model is presented. This selection is based on a statistical robustness estimation of the model. Hence, it appears that only 6 metrics are sufficient to build the model. Finally, the performance of the model is evaluated on 5 new configurations of shock absorbers.
Impulsive occupational exposure for workers in drop-forge foundries
Authors: Zechmann Edward L. , Brueck Scott , Murphy William J.
Published: May 2008

Occupational noise exposure limits for impulsive sounds in the United States are established by the Occupational Safety and Health Administration and recommended by the National Institute for Occupational Safety and Health to permit no impulsive exposure in excess of 140 dB peak SPL. Peak pressure levels in excess of this limit can be found in industrial sectors such as construction, law enforcement and manufacturing. Taylor et al. [J. Acoust. Soc. Am 76:807-819, 1984] reported equivalent A-weighted levels, LAeq, of 108 dB for forge operators sampled in seven drop-forge foundries in the United Kingdom. In a recent study of noise exposure at two drop-forge manufacturing plants in the U.S., peak impulse levels were measured in a range of 117 to 154 dB peak SPL and 8-hour equivalent A-weighted levels, LAeq8, for forge operators between 95 and 116 dB and for press operators between 95 and 105 dB. Kurtosis, A, B C and D-durations were assessed for the impulsive and continuous noise samples. This paper will present the results of measurement and analysis of noise exposures typical for a drop-forge facility.
Frequency loci veering in deformed rotating tyres
Authors: Van Doorn Ruud , Lopez Ines , Van Der Steen René , Roozen N.b. , Nijmeijer Henk
Published: May 2008

In previous work [1] a methodology to model tyre vibrations has been developed, which exploits a modal base determined in a standard FE package and includes rotational effects by a coordinate transformation. In the present paper, the effect of rotation on the eigenfrequencies of a deformed tyre is examined. It is well-known that rotation splits the eigenfrequencies of an undeformed tyre symmetrically around the eigenfrequencies of the non-rotating tyre, where the slope of the eigenfrequency-lines is determined by the circumferential wave number and tyre radius only. However, the eigenfrequency-lines of a deformed tyre demonstrate a fascinating mutual repulsion behaviour if the velocity is increased. This phenomenon is known as frequency loci veering and is induced by the a-periodicity resulting from the tyre deformation. Besides the effect of veering on the eigenfrequencies, the corresponding eigenmodes interact in the transition zones and finally interchange. The effects of veering are extremely intensified by the high modal density of the tyre structure, which results in a decreasing eigenfrequency distribution when the rotational velocity increases. [1] I. Lopez et al, JSV 307, 481-494, (2007)
A model to evaluate the importance of tangential contact forces for tyre/road noise generation
Authors: Sabiniarz Patrick , Kropp Wolfgang
Published: May 2008

The interaction between tyre and road is a complex non-linear process including radial and tangential contact forces between tyre and road surface. During recent years models have been developed which allow for predicting radial forces as function of surface and tyre properties. These models can be used to quantify the influence of radial forces on the noise generation. Whereas in many cases time varying radial forces are the main reason for the generation of tyre noise, in some cases other mechanisms seem to be dominant. This paper aims on understanding the influence of tangential contact on tyre/road noise generation. For this reason the model developed by the Chalmers Tyre Road Noise Group has been extended to also include tangential interaction. The model is based on the same concept as that used by McIntyre and Woodhouse for modelling string/bow contact of musical instruments. It computes the time varying normal and tangential contact forces for a tyre rolling over a rough surface at constant speed. A small selection of simulation results are presented aiming at showing the effect of different parameters, such as friction coefficient and normal load, on the occurrence of instability phenomena such as stick/slip vibrations.
A single wheel trailer for tire/road noise measurements enabling both the CPX- and pass-by methods
Authors: Höjer Martin , Nilsson Nils-Åke
Published: May 2008

A single wheel trailer for tyre/road noise measurements has been developed. It has a towing beam, up to 8 m long, which ensures low background noise from support wheels and towing vehicle. Shielding hood is not necessary. The single wheel trailer can thus be used both for CPX-measurements with on-board carried microphones and pass-by measurements using stationary road-side microphones. The advantage of measuring in the free field with a minimum influence from the suspension attachments etc. is that the emission frequency spectra will be almost undisturbed. It can thus be more easily compared to the sound levels at road-side residents. Due to the long towing beam, tyre prototypes >10 dB quieter can be studied without disturbing background noise. The trailer has been specially designed to ensure stable vehicle dynamics, even though the normally loaded measurement tyre is rolling up to 8 meters behind the support trailer. Another interesting feature is the telescopic design of the towing beam, which enable compaction of the trailer so that the measurement wheel is landed on the trailer support part, enabling convenient transportation to the measurement site.
Experimental investigation of wind turbine noise
Authors: Leroux Maud , Gervais Yves , Borée Jacques , Ménoret Arnaud
Published: May 2008

Broadband noise is nowadays the major contribution to the total spectrum of noise generated by wind turbines. The mechanisms that generate airfoil self-noise have been studied through years and many authors agree that dominant noise comes from inflow turbulence, and interaction between turbulent boundary layer and trailing edge of the airfoil. This study presents results from combined experimental techniques in order to better identify and predict noise issuing from a NACA 0012. Noise from trailing edge is most investigated in a 2D configuration in an anechoic wind tunnel, using microphone array (far field measurements), wall pressure fluctuations, hot wire. The data base turns out to be useful in order to improve extensions of Amiet and Brooks models. Some aspects of noise mechanisms and their characteristics are better identified and refined when wind tunnel results are compared to measurements of noise on full scale wind turbines. Measurements in situ achieved with a microphone array of 30 meters wide are used to provide complementary informations on 3D rotating source in terms of localisation and specific directivity.
Stationary structures in acoustically active nonequilibrium media with one relaxation process
Authors: Galimov Rinat , Molevich Nonna
Published: May 2008

Chemical active mixtures with irreversible reactions, vibrationally excited gases, and nonisothermal plasmas are examples of acoustically active nonequilibrium media. In such media it is possible the existence of stationary nonlinear structures that are different from the step-wise shock wave structures. In the first part of the present paper it is investigated the solutions of a general acoustical equation, describing in the second order perturbation theory a nonlinear evolution of wide spectrum acoustical disturbances in nonequilibrium media with one relaxation process. Its low- and high- frequency limits correspond to Kuramoto-Sivashinsky equation and the Burgers equation with a source, respectively. Stationary structures of general equation, the conditions of their establishment and all their parameters are found analytically and numerically. In acoustically active media it is predicted the existence of the stationary solitary pulse. Then, we consider 1-D relaxing gas dynamics system of equations with simple Landau-Teller model of relaxation. The possible stationary profiles are shown in nonequilibrium degree- stationary wave speed bifurcation diagram. The boundaries of this diagram are obtained in analytical forms. The field of weak shock wave instability is shown in this bifurcation diagram. Unstable shock wave disintegrates into the sequence of solitary pulses described by the general acoustical equation.
Observation of induced shear acoustic phonons by Brillouin scattering
Authors: Yoshida Taisuke , Murata Sigeo , Yanagitani Takahiko , Matsukawa Mami
Published: May 2008

The Brillouin scattering measurement is an efficient nondestructive and noncontact method which enables the simultaneous measurement of longitudinal and shear wave velocities at hypersonic frequencies. However, the measurement accuracy of shear wave velocities is low because of the weak Brillouin scattering from the thermal phonons. In this study, therefore, we have tried to overcome this problem by making use of the induced coherent shear phonons. We have adopted the Reflection Induced θA (RIθA) scattering geometry for Brillouin scattering measurement. To induce shear acoustic phonons, we used an uniaxially aligned ZnO film transducer developed in our laboratory, which can be fabricated on any solid materials without the epitaxy technique. As a result, we obtained the intense Stokes peak in case of silica glass sample which is larger than that obtained from the thermal phonons. It means that observation of induced shear acoustic phonons was achieved. Because the RIθA geometry enables the simultaneous measurement of longitudinal and shear phonons in plane, this technique opens the new feature for the nondestructive elasticity measurement.
Adjusting the phase of the signals transmitted from dual frequency probe for reducing second harmonic during propagation
Authors: Mirza Pasovic , Cachard Christian , Matte Guillaume , Van Der Steen René , De Jong Nico , Basset Olivier
Published: May 2008

During propagation of the ultrasound wave, nonlinearities of the medium, causes rise of higher harmonics that are seen in amplitude spectrum. In ultrasound contrast harmonic imaging this is unwanted effect, since it is expected to image only higher harmonics produced by contrast agents. In previous studies Christopher, Krishnan and Shen proposed transmitting either an inverted signal (collected by hydrophone), transmitting 2nd harmonic with broadband transducer or transmitting third harmonic to reduce the second harmonic at measurement point. Our study uses a dual frequency probe which transmits one wave at frequency f0 and one wave at double frequency 2f0 named second harmonic reduction signal (SHRS) for reducing the second harmonic in the propagating signal. The hardest task is the appropriate adjustment of the phase of the SHRS to reduce second harmonic during propagation in the focal area. We outline how to set phase and established that the phase of the SHRS in not affected by the nonlinear parameter B/A and excitation pressure P0 but rather by the excitation frequency and the ultrasound system geometry (transducer size and distance to focal area). A reduction of 25dB has been obtained in simulation (Po=100kPa, fo=2.25 MHz). Experiments in water tank, have shown the reduction of 2nd harmonic by 30dB.
A route to chaotic state on an electrodynamic loudspeaker
Authors: Petosic Antonio , Djurek Ivan , Danijel Djurek
Published: May 2008

The low frequency electrodynamic loudspeaker (EDL) unit has been measured and analyzed in terms of chaotic behavior. It was found that an electrodynamic loudspeaker can function as a chaotic system. Loudspeaker impedance and vibration amplitude as function of driving frequency were measured at various driving currents, and well-know cut-off effect from nonlinear dynamical systems has been noticed. In the frequency region near cut-off and at higher driving currents the period doubling and later chaotic state occur. The experimentally obtained chaotic state was confirmed theoretically solving nonlinear equation of motion with strong nonlinear effective stiffness spatial dependency. It was found that statically measured suspension effective stiffness does not enables chaotic state when included in differential equation, and it has been concluded that membrane viscoelastic properties enhance the restoring force far enough to obtain chaos. The nonlinear equation describing anharmonic periodically driven oscillator has been solved numerically and the theoretical results were compared to experimental results.
Analysis of the effects of the oscillations of a rigid sphere inside a cylindrical cavity containing a standing acoustic wave
Authors: Torres Edgar A. , Santillan Arturo
Published: May 2008

Under certain driving conditions of a single-axis acoustic levitation device, a suspended sample leaves its stability state and starts to oscillate vertically around the initial equilibrium position. A published theory on such instabilities [J. Rudnick and M. Barmatz, "Oscillational instabilities in single-mode acoustic levitators," J. Acoust. Soc. Am., 87(1), 81-92, 1990] predicts the occurrence of time delays between the response of the cavity of the device and the motion of the sample inside it. In this paper, a theoretical and experimental investigation on similar time delay effects will be described. A solid sphere was moved in a controlled way inside a closed cylindrical cavity by means of a rod connecting the object to the outside of the system. A standing wave was generated inside the cavity by using a speaker. In this way, oscillations of the sphere were produced and the response of the sound field to such movement was studied. The effect of the frequency of the oscillations of the sphere on the time delay between the sound pressure and the movement of that object will be reported. In addition, the relations between the obtained results and the published theory on oscillational instabilities will be discussed.
Dual frequency ultrasound- A pulse-echo technique for analysis of layered material
Authors: Riekkinen Ossi , Hakulinen Mikko , Töyräs Juha , Jurvelin Jukka
Published: May 2008

Ultrasound (US) thickness gauges typically analyse layered materials by utilizing ultrasound reflections between different layers and prior knowledge for the material order within the layered structure. In this study, a dual frequency ultrasound (DFUS) technique is applied to eliminate the effect of overlying layered structure on the measurements of the object of interest without prior knowledge of the order of materials within the multilayered structure. DFUS technique utilizes prior knowledge on US attenuation coefficient and speed at two frequencies in multilayered materials, consisting of two different material types. Then, US reflection from the front (first) and the back (last) surfaces of the multilayered structure is measured using two different US frequencies. No reflections from the internal interfaces are needed. The technique was validated using several elastomer samples and their combinations, measured at 2.25 MHz and 5.0 MHz. DFUS reduced the mean error, induced by the overlying elastomers, in reflection from the object of interest from 103.6 - 289.4% to -15.9 - 5.6% and from 37.5 - 77.5% to -12.0 - 4.9% with 5.0 MHz and 2.25 MHz, respectively. Based on these results, DFUS is a straightforward technique to analyse the multilayered structure without the need for echoes from internal interfaces.
Structural Health Monitoring using cross-correlation of an ambient noise field
Authors: Abou Leyla Najib , Moulin Emmanuel , Assaad Jamal , Grondel Sébastien , Poussot Pascal
Published: May 2008

Theoretical and experimental studies in underwater acoustic, seismology and more recently ultrasonic have demonstrated that an estimate of the Time Domain Green Function (TDGF) between two receivers could be obtained from the cross-correlation of a diffuse acoustic noise field of these two receivers. The aim of the work is to exploit this technique in order to characterize Structural Health Monitoring (SHM) of aeronautic structures without the use of active sources. In this case, the aero-acoustic and/or mechanical sources (engine) generate an ambient noise field with some imperfections for the application. Indeed, source concentrations, source directivity and non-random components in time can appear which leads to an erroneous estimate of the TDGF. A key point to the study is thus to understand the influence of such imperfections. Therefore, experimental measurements have been performed using different types of acoustic noise sources (localized or diffuse). Cross-correlation results obtained in each case are then compared and theoretically interpreted. Finally, the potential of this technique in terms of damage detection is verified.
Comparison of headphones and equalization for virtual auditory source localization
Authors: Schonstein David , Ferré Laurent , Katz Brian F.
Published: May 2008

This study investigates the variation in localization performance between different headphone styles. Eight different headphones (including various in-ear, circumaural open and closed, and bone conduction headphones) were tested. In addition, the effect of headphone equalization (aiming to produce an approximately flat frequency response) was investigated. Localization was examined for 24 locations distributed on a sphere surrounding the listener. A single subject participated in the study using a single chosen non-individual HRTF set. Each location was repeated 6 times, resulting in a total of 144 localization reports. Overall, results were relatively consistent for 3 out of the 8 headphones tested. For these headphones, there was no significant difference in lateral angle error, associated with ITD and ILD cues. Polar angle errors, associated with the cone of confusion, however did vary significantly for these headphones. The headphone equalization had varying effects on localization accuracy depending on the headphone. Globally, headphone equalization showed no significant effect on localization accuracy. The results serve as a preliminary investigation, highlighting consistent results for only a select group of headphones tested for effective sound rendering in virtual auditory space. In addition, the results suggest that headphone equalization has a minimal influence on localization accuracy under these conditions.
Underwater vehicle attitude estimation using Hough transformation
Authors: Shiba Hisashi
Published: May 2008

In these decades various imaging sonar systems have been developed. They are very effective for underwater investigations such as geologies, fisheries, resource surveys and securities. To extend these system abilities we studied new imaging sonar applications and found they are also useful in underwater vehicle navigations. In this presentation I propose a new method of estimating vehicle attitude parameters relative to the ocean surface or the seafloor by the onboard imaging sonar. The ocean surface or the seafloor is often obtained as a plane in sonar images. However, the images are sometimes too noisy to identify the plane locations because of ambient noise and reverberations by texture patterns on the planes. The new method describes these planes with plane equation parameters connected to attitude parameters, and searches the most appropriate parameter sets using a voting procedure which is a three dimensional expansion of the Hough transformation widely applied in line detections on noisy two dimensional images. The method provides the plane location and attitude parameters simultaneously without other sensors. After the algorithm explanation multi-beam imaging sonar simulations are shown and accuracies are evaluated.
Acoustical and optical measurements on a mixture of air microbubbles in water
Authors: Duro Vincent , Rajoana Dominique , Decultot Dominique , Maze Gerard
Published: May 2008

An important challenge for current naval research is the modernization of battleships. Their target detection system must be increasingly efficient and they must be increasingly undetectable. Due to turbulent flows and bubbles, ship wakes are a detectable acoustic signature and ship bow waves disturb sonar detection. In this work, we study sound propagation through bubble clouds in water. We have developed an experimental set-up which permits us to acquire, in synchronization, acoustical signals and optical images. The phenomenon of bubble monopole resonance in very low frequency, related to bubble size, provokes effects of strong sound damping and sound speed dispersion. These experimental results, related to theoretical results, permit to estimated sizes and concentrations of bubbles. The acquired bubble images permit to know the real bubble sizes and concentrations, in order to correlate with the experimental acoustical results. Air bubbles are generated with a high pressure water jet introduced into the host liquid medium. A hydrodynamic study is done to characterize the bubble jet. We present in this work, theoretical results establishing a complex effective wave number characterizing the sound propagation in an effective medium. All results are discussed and compared with results of others papers on this subject.
Observation of sub-bottom sediments in the Southern Baltic by means of nonlinear acoustic method
Authors: Grelowska Grazyna , Kozaczka Eugeniusz , Gloza Ignacy
Published: May 2008

The aim of the paper is to present results of preliminary experimental investigation using parametric echosounder in natural conditions for profiling the subbottom sediments in the Gulf of Gdansk. The ability to predict seabed properties: seafloor roughness, sub-bottom structure and discrete scatterers laying on the seafloor or buried into sediments, from remotely sensed data is important especially in regions that need permanent monitoring. Precise determination of seabed structure or localisation of buried objects in the sand requires the use of a low frequency signal to penetrate the sediment and a narrow beam to provide high-resolution data. Both requirements can be achieved with a parametric (nonlinear) technique. The special experimental setup has been arranged allowing penetration of bottom sediments as well as precise positioning and following a given route. Measurements were conducted exactly along given routes, for that geological profiles have bean taken by means of another method. It allow as to compare detailed date obtained by means of parametric echosounding to ones given at geological map. In all investigations the primary frequency of the array was of 100 kHz, whereas the secondary frequency changed in range 5 kHz - 15 kHz.
Experimental study of parametric transmission: Simultaneous generation of two beams
Authors: Amate Maud , Cervenka Pierre , Marchal Jacques
Published: May 2008

In order to respond to the buried mines threat, an approach of GESMA (Groupe d'Etudes Sous-Marines de l'Atlantique) is to take advantage of the parametric transmission in sonar imagery. This technique allows producing narrow beamwidths at low frequencies. Such a parametric transmitter has been designed and calibrated in collaboration with an academic laboratory of Paris VI, and the targeted benchmark is fulfilled: 2° @ 20 kHz, with sufficient source level. The design of the complete sonar system is based on a sequential multibeam transmission associated with a synthetic aperture technique at receive. However, the shortfall of the sweeping technique lies in the timing limitation. One solution to increase the coverage rate is the simultaneous generation of several parametric beams in different directions. Experimentations have been conducted in a tank with different signals: CW, LFM, Ricker. This presentation addresses the results of these experimentations in the context of buried mines detection and classification.
General impedance boundary conditions in pseudospectral time-domain methods for room acoustics
Authors: Spa Carlos , Mateos Toni , Garriga Adan
Published: May 2008

Finite-differences in the time domain (FDTD) are among the most accurate numerical techniques to simulate wave phenomena. The main drawback of FDTD numerical schemes is their computational cost in large scale simulations. The recently developed Fourier pseudospectral time-domain (PSTD) techniques, by approximating the spatial derivatives more efficiently, have improved significantly the accuracy and time costs of the simulations of electromagnetic fields. As a step towards applying PSTD techniques to room acoustic problems, we present here a framework to properly deal with material modeling in terms of generic impedance boundary conditions, beyond the common perfectly matched layer absorbing boundaries. We apply our results to a few representative cases (simple but reverberant rooms) and analyse its performance in terms of accuracy and computational resources. In particular we analyse whether the mild constraints that PSTD imposes on space-time discretization lead to good enough results in room acoustic simulations.
On the implementation of room acoustics modeling software using Digital Waveguide Mesh
Authors: Lopez José J. , Escolano José , Pueo Basilio
Published: May 2008

The Digital Waveguide Mesh (DWM) method for room acoustic simulation has been introduced in the last years to solve sound propagation problems numerically. However, the huge computer power needed in the modeling of large rooms and the complexity to incorporate realistic boundary conditions has delayed their general use, being restricted to the validation of theoretical concepts using simple and small rooms. This paper presents a complete DWM implementation where all the stages needed to analyze a room are discussed. The software starts the analysis from the architectural model of the room importing its geometry directly from a CAD file. After that, it generates the rectangular mesh of individual cells that conforms the volume to be simulated. Next, the time domain recursion is carried out using parallel computer techniques. Also the software includes a serious treatment of boundary conditions using different material with frequency dependence characteristics. Finally, the software can export the results. Additionally, some room simulation examples are presented and analyzed in detail. The work carried out demonstrate how it is possible, with the current power of the personal computer, to start to simulate real rooms with high amount of geometric details and frequency dependent boundary.
The drying process influence on the brick walls sound reduction index: laboratory evaluations and theoretical analysis
Authors: Scrosati Chiara , Scamoni Fabio , Valentini Fabrizio
Published: May 2008

This paper presents experimental results showing the sound reduction index of different types of brick walls; the analysis was in particular carried out on double walls, single walls, and single walls with external lining. Its main purpose is to find the minimum drying time of the structure necessary to obtain the sound reduction indexes of brick walls as close as possible to laboratory real values. Moreover, it aims at making results of different laboratories as comparable as possible in terms of repeatability and reproducibility. All the fundamental quantities, such as the sound reduction index (R), the weighted sound reduction index (R_{w}), the spectrum adaptation terms C and C_{tr}, and temperature (T) and relative moisture, have been analyzed. A qualitative analysis of the curves slope of the sound reduction index versus frequency has been conducted for each drying time for each type of evaluated wall. The measurements were carried out in the acoustic laboratory of ITC-CNR (the Construction Technologies Institute of the Italian National Research Council) in Milan, according to the procedures of ISO 140 part 3.
Lightweight system Technostar specified in the CCTV tower Beijing
Authors: Koster Andrew
Published: May 2008

The role and possibilities of lightweight mineral wool is known for quite some years, acting as the optimum spring in a mass spring mass system one can reach high acoustic values. Compared to the massive constructions (e.g., concrete) the use of a mass spring mass construction has also other advantages (e.g., logistic, dimension of foundation and labour costs). Saint-Gobain Isover developed a wall system called Technostar, originally defined for cinema walls. In this construction an optimal mass spring mass construction is created. The theory of mass spring mass systems will shortly come up. All elements of the system are described. The acoustical performance of the Technostar construction is calculated with acoustic software (Stiff) and compared with laboratory measurements; the influence of different parameters on the measured acoustical performance will be shown. The practical use of the Technostar wall will be shown on the basis of the project CCTV tower in Beijing. For this project the acoustic requirements, the translation in terms of the wall construction with the specific details will be shown. The system will be build in March 2008.
Impact sound insulating performance of access floors
Authors: Asdrubali Francesco , D'Alessandro Francesco
Published: May 2008

Access floor are raised floor systems consisting of modular panels supported by posts at a certain height to create a gap below the floor surface. Electrical wires and pipes can be placed inside the gap in order to avoid exposed installations and to simplify operations involving the inspection, repair, changing, or adding of system elements. This paper presents the results of the measurement campaign carried out on seven different access floor configurations, obtained by changing different floor elements: panels, surface finishes, damping materials under the posts base. Impact sound insulating properties of access floors combined with false ceilings were also tested and are reported in the paper. The tests were executed in two overlapping reverberating rooms available at the Acoustics Laboratory of the University of Perugia using the procedures given by ISO 140-6 Standard. The results are expressed in terms of normalized sound impact pressure level Ln and of the corresponding single number index Ln,W.
Influence of flanking transmission in typical Italian constructions
Authors: Secchi Simone , Cellai Gianfranco , Nannipieri Elisa
Published: May 2008

Actually acoustic performance of building components are analysed with reference to standardised conditions, in laboratories with suppressed flanking transmission. Laboratory results often show values of the performances quite different from those measured in real buildings, as a consequence of flanking transmission and of different conditions of realisation in situ. Moreover, in spite of all efforts aimed to standardise laboratory test conditions, often we find different certified performances of same building components obtained in different laboratory. In some cases, these differences may be very relevant. Besides, the Italian decree on acoustic requirement of buildings prescribes limiting values to be measured in situ. For these reasons, many producers of building materials and components more frequently presents in their depliants both laboratory values and in situ values of acoustic performances of their products. The paper shows the preliminary results of an research aimed to verify acoustic performances of partition walls and floors in a laboratory which respect conditions of ISO 140-1, but with the presence of relevant flanking transmission, similar to real buildings. The relevance of the flanking transmission has also been modified by means of a lining applied to the ceiling of the receiving room of the laboratory.
Converging evidence in evaluating acoustical intimacy
Authors: Gibbs Bobby E. , Braasch Jonas , Krueger Ted
Published: May 2008

Previously, we presented a novel interactive pilot experiment in which participants modified parameters in a virtual acoustical environment so that they corresponded to three intimacy settings: low, medium, and high. Additionally, participants were asked to rank the -- yet unknown -- parameters (volume, direct-to-reverberant energy ratio, frequency attenuation, and room size) in terms of the importance in making their judgments. Based on a larger body of data, the direct-to-reverberant energy ratio emerges as the strongest acoustical correlate of intimacy. A repeated-measures test revealed that the “preservation” of this parameter (the degree to which a participant changed the value from an optimum setting) varies the least across intimacy levels and across levels of previous training. Additionally, this parameter is consistently ranked as being the most important in the ranking portion of the test. We also found that salience of some of the other parameters varied significantly across intimacy levels, possibly suggesting a weighting system is warranted. These results are compared with binaural measurements of the virtual system. In particular, we will address disparities from the pilot experiment and recent data that resulted from differences in measuring the direct-to-reverberant energy ratio. [Work supported by RPI HAAS Fellowship and ASA Minority Fellowship.]
Acoustic production mechanisms in pinnipeds
Authors: Spasikova Marija , Fitch William T. , Reichmuth Colleen , Schusterman Ronald J.
Published: May 2008

The ability to develop articulate speech relies on capabilities that became available to our ancestors through changes in both peripheral mechanisms (vocal acoustics and anatomy) and neural mechanisms (vocal control and imitation). Few distantly related species (cetaceans, birds and pinnipeds) have shown the ability of vocal imitation, but of the three, only the pinnipeds use the same vocal tract as us humans. For this reason we choose to study two closely related pinniped species: the harbour seal (Phoca Vitulina), a good vocal imitator (capable of complex vocal learning), and the Californian sea lion (Zalophus californicus), a close relative with very limited vocal imitation capabilities (no evidence of complex vocal learning) to look at the acoustical production mechanisms of the species as well as the neural mechanisms underlying the same. Using previously acquired data gathered in California at the Long Marine Lab, we performed video and acoustic analysis to show correlation between jaw opening and formants frequencies in the harbour seal (Phoca Vitulina), in speech like vocalisations. We are examining the involvement of tongue movement during these vocalisations, hypothesising that it will account for the remaining residuals in the correlation between the formants excursions and the jaw movements.
Automated acoustic identification of beetle larvae in imported goods using time domain analysis
Authors: Schofield James , Chesmore David
Published: May 2008

The detection of insect pests in imported goods is of considerable economic importance and the automation of this process is becoming more viable both technologically and financially. As a result, the Department for Environment, Food and Rural Affairs in the UK has funded a research project to develop instrumentation facilitating real-time acoustic detection of the feeding activity of insect larvae inside imported goods, such as timber. The instrumentation will also be capable of species-level identification. Previous work at York has shown that detection of beetle larvae in wood is possible using low cost piezoelectric sensors. The project described here extends this work by investigating a number of signal analysis methods for robust detection of biting events, including fractal dimension analysis. Identification is currently being carried out using time domain signal coding and artificial neural networks. This paper will concentrate on the results of various algorithms for the estimation of fractal dimension and their relative suitability for bite detection. The effects of varying sampling rates, threshold levels and signal-to-noise ratio on the detection rate will be demonstrated.
Advances in the tracking of partials for the sinusoidal modeling of musical sounds
Authors: Marchand Sylvain
Published: May 2008

Whereas sinusoidal modeling is widely used for sounds, polynomial models are still used for the model parameters, which can hardly handle modulations (vibrato and tremolo) present in musical sounds. Moreover, the partial tracking algorithms are often designed under stationarity assumptions. Advances in partial tracking may come out of the modeling of the partials themselves. We consider their parameters (frequencies and amplitudes) as predictable and slow time varying: First, the future of any partial can be determined from its past evolutions; second, no audible frequency should appear in the spectral content of these evolutions, otherwise it would question the perceptive consistency of the model. We then choose to handle nonstationary sinusoidal modeling by a deterministic approach based on linear prediction of the partial evolutions and partial discrimination based on the spectral properties of these evolutions. The underlying model for each partial is now a sum of sinusoids, thus leading to a two-level sinusoidal modeling, well suited for musical sounds, where modulations are important. The enhanced partial tracking algorithm also handles the case of crossing partials, without the need for any probabilistic approach. Better modeling the deterministic part of polyphonic sounds leads to enhanced source separation and time scaling algorithms.
Applicability of advanced measurement techniques to soundscape studies
Authors: Fiebig André , Genuit Klaus
Published: May 2008

A wide range of measurement systems and analysis techniques were applied in previous soundscape studies to document and describe the physical conditions of the scrutinized area. Monaural and binaural recording systems positioned at different measurement points are frequently used, and the collected recordings are played back with headphones or sophisticated loudspeaker arrangements in specific surroundings for further analyses. In the paper, an overview of measurement and playback technologies applied in soundscape studies will be given and the immanent problems related to certain recording and playback systems will be discussed, e.g., measurement accuracy and expense, costs, etc. Furthermore, soundscape researchers have started to establish more and more a pool of specific analyses, which allows - at least partially - the detection of relevant (acoustical) patterns and features as well as a first classification of soundscapes. This allows even the detection of positively experienced environments. However, varying measurement technologies and procedures used in different soundscape studies lead to the problem that the studies and the obtained analysis results are often difficult to compare. The present paper takes up this problem and deals with developing a common basis of measurement techniques and procedures.
Advanced acoustical material tuned for low frequency noise reduction: a case study
Authors: Kondylas Kathleen , Levit Natalia , King Joseph A. , Fuller Chris R.
Published: May 2008

Low frequency noise is a significant annoyance at very low amplitudes, particularly when outdoor community noise from mechanical equipment penetrates commercial and residential building structures. Mid and high frequencies are selectively attenuated by the exterior walls. However, mitigation of the low frequency noise has been very challenging due to the longer wavelength and higher energy. This work presents case studies of an advanced acoustical material in typical metal panels to mitigate community noise from outdoor mechanical equipment. These advanced materials were developed with a unique combination of patented acoustical and vibration absorbing technology, based of distributed absorbers, layered with standard acoustic materials. The materials provide enhanced low frequency noise (below 300 Hz) over state of the art 10 cm metal panels filled with the fiberglass absorber. The case studies demonstrate superior acoustic performance in low frequency without substantial increase in weight.
Vibration case study - design challenges for meeting medical imaging manufacturer specifications
Authors: Papadimos Chris
Published: May 2008

Manufacturer vibration specifications for medical imaging equipment impose formidable challenges particularly when locating such equipment on elevated floors, which is increasingly desirable for work flow and proximity to operating rooms and other support spaces in healthcare facilities. Urban sites can further complicate matters as such sites tend to often be near busy roads that are sources of vibration. Other internal sources of vibration that must be taken into consideration include occupant activities and operating building mechanical systems. All these conflicting interests need to be properly balanced and clearly evaluated; developing solutions requires a diligent and experienced design team. Some of the challenges that had to be overcome in order to develop vibration designs to accommodate medical imaging equipment such as CT Scanners and MRI's on elevated floors of a new healthcare facility are presented in this paper. Extensive site testing to evaluate design constraints and pre-existing conditions, avoidance of incompatible adjacencies and proper considerations in terms of space layouts, development of specialized floor designs and a clear understanding of imaging equipment manufacturer specifications are the key elements addressed in this paper.
NMR sensitivity to floor vibration
Authors: Ben-Dov Yuval , Heiland Peter , Rajan Srinivasan
Published: May 2008

NMR is widely used in the determination of molecular structures in solution. Floor vibrations interfere with the NMR measurements and are coupled with the signal of interest. To minimize the effect of floor vibrations, NMR spectrometers are typically installed on a solid floor with minimal structurally induced vibrations. However, in some cases this is not possible, and the tool is exposed to structural vibrations. We study the NMR sensitivity to floor vibrations. A Bruker 500 MHz installed on IDE active isolation platform is used. By exciting the platform in a controlled manner we can measure the noise as observed in the NMR spectrum due to the platform vibrations. The sensitivity highly depends on the excitation frequency, and is not well reflected in a typical requirements specification. Revised requirements are presented for the floor vibration both for a tool installed as is, and for a tool on top of our isolation platform.
Acoustic performance of membrane based multilayered systems with improved thermal inertia characteristics
Authors: Guigou-Carter Catherine , Sallee Hebert , Normand Xavier
Published: May 2008

In this paper the development of double membrane based systems, including phase change materials (denoted-PCM) is discussed. The cavity between the two membranes is filled with a new type of absorbing material: a 3D, nonwoven, complex structure made of two or three fibrous mats that allows the inclusion of small granulated particles while being fabricated. Granulated phase change materials are therefore included in this 3D, nonwoven structure in order to increase thermal properties by the heat storage/restoring principle. The PCMs introduced in this nonwoven structure act to store part of the heat when it is in excess, and then, to restore it when the temperature inside the room is too low. The intermediate temperature chosen to correspond to a desired comfort temperature (for example around 20 °C) corresponds to the phase transition temperature of the PCM. Lightweight membranes are then fixed on each side of this complex 3D, nonwoven structure, including the PCMs. The acoustic performance of such systems is investigated in terms of the sound transmission loss, both experimentally and analytically. The thermal performance is also briefly presented.
Real time evaluation of soft microphones on a local active noise control system
Authors: Potirakis Stelios M. , Rangoussi Maria , Savvaidis Stylianos , Zafeiropoulos Nikos
Published: May 2008

Systems for the active control of acoustic noise (ANC) rely on measurements of the noise signal in order to produce the required “quiet zone.” Soft microphones (SM) are a virtual microphone alternative already proposed by the authors, employing estimates rather than measurements of the noise signal obtained from room impulse responses based on measurements. Therefore, a single microphone can be used to estimate the noise signal at multiple points. This has already been successfully applied on single microphone noise mapping. In the present work, the SM method is evaluated on a real time local ANC system. The proposed scheme is a filtered-s least mean square (FXLMS) based control structure, incorporating SM. Following the proposed system design-simulation with Matlab-Simulink, a three-dimensional enclosure (office-simulating) and a real electroacoustic ANC system based on a TI® TMS320C6713 DSP, developed for this purpose, were built in the laboratory to carry out the experiments. Different options of estimating the SM signals and exploiting them into the control structure are experimentally evaluated as to their ability to enlarge the silence zone and their noise reduction performance around the listener ear zone (using a head and torso simulator) and compared to the standard FXLMS solution.