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Airborne sound transmission through vehicle panels is the main contributor to interior noise in high frequencies. This transmission can be reduced by the application of sound insulation materials. An insulator typically used in the dash panel treatment comprises a porous material layer bonded to a limp dense material. This porous layer dissipates sound energy mainly by viscous effects and reduces sound transmission. An accurate prediction of the insulator performance depends on the porous material model adopted and input material properties. Some simplified models take into account only a single longitudinal wave propagating in the porous medium since it is represented by an equivalent fluid with effective properties. More complex models, based on Biot's theory, also consider waves whose properties are more connected to the porous material frame. In this paper one-wave, two-wave and three-wave models are presented.

The noise emitted by the heating, ventilation and air conditioning system (HVAC) has a great influence on the car acoustical comfort and quality perception. To improve its sound quality, physical properties which determine the subjective perception have to be identified. The HVAC-noise of twelve cars in different arrangements of fan speed and direction of air flow was recorded for later objective and subjective analysis. All cars were of the same model, but with three different types of HVAC-systems, and had just been manufactured. Objective analysis with sound quality software and subjective evaluations was carried out. Using multiple linear regressions on the subjective data, relations between subjective results and psychoacoustic metrics were determined and models to predict subjective response to HVAC sounds are proposed. It is shown that the annoyance caused by the HVAC-noise can be satisfactorily described by Zwicker's stationary loudness model.

For the automotive industry, the sound quality inside the vehicles is very important. This importance has increased significantly in the last years within the globally competitive automotive market. The interior vibroacoustic behavior depends on the dynamic characteristics of the car body. Several treatments are used to reduce the structural energy of the body panels. For instance, it may be applied passive damping technology, by use of viscoelastic materials, to control their noise and vibrations. This paper presents a comparison of the vibroacoustic characteristics of two firewall panels, made with normal and quiet steel. Experimental and numerical (FEM and BEM) techniques are used to get modal and acoustic data.

This paper addresses the effect of environmental humidity and temperature on friction level and squeal noise propensity of friction materials when measured in dynamometers at laboratory controlled test conditions. The present work investigates the influence of the environment conditions on the result of noise and friction evaluation of friction material for disc brakes. The relationship among environmental conditions and squeal noise propensity has been studied before by a few authors [1] and is still an open issue when concerns to standard evaluation performed at laboratory controlled conditions. The effect of two main environmental properties for dynamometer testing, cooling air temperature (between 10 and 30°C) and humidity (between 25 to 85%), on friction level and noise were evaluated using a front disc brake. A test matrix, based on SAE J2521, was developed to adequately evaluate these two variables separately into a NVH environmental chamber equipped dynamometer.

During the last decades, the application of noise control treatments in vehicles has targeted the main noise transmission paths to interior noise. These paths include vehicle body panels such as dash panel, doors and floor. Many improvements have been achieved on these areas, and, as a consequence, other transmission paths once thought as secondary became relevant. This is the case of the sound transmission through door seals and others sealing elements at mid and high frequencies. In this paper, the interest lies on the prediction of the transmission loss of door seals. A full nonlinear deformation/contact analysis is used to estimate the deformed geometry of a door seal in real conditions. The geometry is then used in a vibro-acoustic analysis to predict the in-situ transmission loss of the seal using a local Hybrid FE-SEA model. The channel between the door and the car structure where the seal is located is also included in the analysis.

The general spiral equation is an excellent tool in array development. However, some modifications can improve the array response for a certain range of frequencies. This work describes a different approach to the spiral equation aiming the project of a high frequency array (20 k - 35 k Hz). By constraining some of the array and measurements parameters, a geometry is proposed intending to maximize the dynamic range response at a focal point. The steps of this approach are discussed showing the results of the simulations for different parameters of this equation. Some of these parameters were fixed and for some others a parameter sweep was performed. The final geometry is intended to work with ultrasound applications, such as measurements of scale models, and also with the acoustic frequency range.

In many cases the in situ measurement of the absorption coefficient requires an iterative method for the correct calculation of the surface impedance of a sample. This happens because when spherical waves reflect on a sample's surface the pressure field above it is a function of the sample's surface impedance. As the pressure field involves an integral term, numerical integration is required in the iterative algorithm, which can be time consuming. The aim of this paper is to present an iterative approach based on Pony's method, which instead of numerical integration uses a series expansion with a few terms. Therefore the time of processing is decreased. Besides the description of the method, simulations and measurements (with a p-u probe inside an office room and a car) are presented. A comparison, with numerical integration, regarding the accuracy and the time of processing of Pony's method is also discussed.

In this paper, four different configurations of plug type muffler are investigated. Three different evaluations methods are used; Finite Element Method, Transfer Matrix Method and experimental measurements. The results obtained for the transmission loss of each muffler are compared. No flow and temperature variation are considered.

The use of a microphone array for acoustic measurements in wind tunnels is known to degrade the sound pressure levels and dynamic range of the acoustic image, due to the decorrelation between each pair of microphones, after the acoustic wave has crossed the turbulent boundary layer of the wind tunnel. Based on a large number of studies in the areas of radiophysics, underwater acoustics and atmospheric science, this paper describes research on a physical model of wave propagation in a turbulent medium and its stochastic solution, obtaining as a solution the statistical momentum of the wave signal after it has propagated through the turbulent medium. The parabolic equation for acoustic wave propagation is considered and the Markov approximation is assumed for the stochastic solution of the wave. The signal coherence between each pair of microphones is the amount considered responsible for the decorrelation of the signals.

There is a great lack of Brazilian laboratory and field measurements on of noise generated by the interaction between tyre and road surface. In this study the tyre-road noise interaction on Brazilian roads through the CPX method with a wheeled trailer with enclosure that simulates a light vehicle of 700 kg equipped with two tyres and two microphones for each tyre is evaluated. Two types of sections of the road with different surfaces characteristics were evaluated with the trailer at speed of 80 km/h. The first section road is comprised of a rubberized asphalt mixture about 30 months of age and the other surface is composed of an ordinary dense asphalt mixes with approximately 10 years of age. The noise generated by the tyre-road showed that the sound pressure levels are concentrated between 630 and 1600 Hz and the differences in the sound levels are related with the characteristics and ages of the road surface.