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Indoor vehicle pass-by noise applications deal with measuring the exterior noise from a vehicle fixed on a chassis dynamometer in a large hemi-anechoic room. During a standardised acceleration test, the noise is measured with an array of microphones placed in the far-field, and the overall noise level versus vehicle position can be simulated. The indoor facility allows controlled and repeatable measurements independent of weather. For engineering purposes, pass-by contribution analysis can be included in the test leading to information about the pass-by noise contribution from major noise sources. This work presents a novel application of blind source separation to vehicle measurements from an indoor pass-by measurement campaign. In contrast to the classical transfer path approach using point sources for modelling vehicle noise sources and combining an operational measurement with transfer functions, the blind approach does not consider a specific noise source model.

This work presents an application of airborne source path contribution analysis with emphasis on prediction of wideband sounds inside a cabin from measurements made around a stand-alone engine. The heart of the method is a time domain source path receiver technique wherein the engine surface is modeled as a number of source points. Nearfield microphone measurements and transfer functions are used to quantify the source strengths at these points. This acoustic engine model is then used in combination with source-to-receiver transfer functions to calculate sound levels at other positions, such as at the driver's ear position. When combining all the data, the in-cabin engine sound can be synthesized even before the engine is physically installed into the vehicle. The method has been validated using a powertrain structure artificially excited by several shakers playing band-limited noise so as to produce a complicated vibration pattern on the surface.

The simulated indoor pass-by noise measurement system is the measurement tool to evaluate the pass-by noise at the test laboratory, without doing measurement at the field. This measurement system can overcome the limitations of the field measurement, i.e. weather conditions, reproducibility. In this measurement, microphone array is located around the car on chassis dyno. The measured time-domain signals are synchronized with one signal, which is equivalent to the signal recorded in the field representing the moving source effect. By using FRF between indicator and receiver microphones, which are representing source strength and evaluation points correspondingly, source path contribution analysis is performed at 7.5m apart from the centerline of car. In this paper, the measurement and signal processing on top of the theoretical background would be discussed with the measurement example.

Microphone array-based Panel Contribution Analysis (PCA) is a new technique used for Sound Package design optimization for commercial vehicles. The technique allows for noise control performance and cost optimization. This technique ranks the contribution of fully trimmed structural panels (e.g. floor, roof, etc.) and leaks in a vehicle cabin to the noise levels experienced by a driver while the vehicle is in cruising operation. Often the noise and vibration sources (engine, transmission, exhaust, aerodynamic noise, tires, etc) cannot be easily modified, thus the only practical action to solve noise problems is to design the noise control treatments applied to the vehicle panels. Panels that have a large contribution to the noise levels at the driver's ear are heavily treated with noise control materials, whereas panels with low contribution get little to no treatment.

In this paper a time-domain version of source-path-contribution analysis is investigated using a controllable source, an engine noise and vibration simulator installed into a trimmed vehicle, and compared to the results obtained using a more traditional frequency-domain source-path-contribution analysis. Both airborne and structure-borne inputs are investigated and the matrix method is used to calculate source contributions as sounds at a listeners' position inside the cabin. Operating data from a simulated run-up/run-down and sets of transfer functions (FRFs) are firstly used to estimate the strength of some defined point sources, acoustically and mechanically. Secondly the operating source strengths are combined with acoustic or vibro-acoustic FRFs to predict contributions at a receiver. In this work it is attempted to make the airborne and structure-borne models as simple as possible, and predicted contributions are validated against actual measured data.

Patterned tires can not be build that are less than 1-3 dB(A) louder than smooth tires. Further reduction of tire excitation by tread pattern optimization cannot be expected. For further lowering the tire/road noise the tire construction and the excitation by road needs to be addressed. In the EC funded project SILENCE a subproject looks for further reduction possibilities of tire/road noise. For a straightforward improvement of tire/road noise the vibration pattern on the surface of a rolling tire must be known. In the project the tire vibrations of rolling tires were identified with indirect methods. Two new approaches will be presented in the paper: The framework for numerical optimization of point source positions and source strengths has been tested on a real tire rolling at 80 km/h. Models with one two to six sources have been produced, covering frequencies up to 1 kHz.

The present paper focuses on methods for estimating equivalent source positions or “hot spots” on an object to be modelled acoustically. This procedure is the first step in the derivation of an acoustic equivalent source model to be used e.g. in connection with measured acoustic transfer paths. Methods based on Near-field Acoustic Holography as well as the Inverse Boundary Element Method are described and compared. The use of the different methods is illustrated by actual measurements and calculations on a real passenger car exhaust line system.