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As customer awareness of product sound grows, the need exists to ensure that product sound quality is maintained in the manufacturing process. To this end in-process controls that employ a variety of traditional acoustical and alternate sound quality metrics are utilized, usually partly or wholly housed in a test enclosure. Often times these test cells are required to attenuate the background noise in the manufacturing facility so that the device under test can be accurately assessed. While design guidelines exist the mere size and cost of such booths make an iterative build and test approach costly in terms of materials as well as engineering and testing time. In order to expedite the design process and minimize the number of confirmation prototypes, SEA can be utilized to predict the transmission loss based upon material selection and booth construction techniques.

Statistical Energy Analysis (SEA) is an effective tool for evaluating the acoustic performance of a vehicle structure and sound package. SEA is typically used to predict both interior noise levels and to set noise reduction targets for various components. A typical full vehicle SEA model includes acoustic loads from airborne sources such as engine, tire and exhaust noise [1]. Each source is typically spatially compact (for example, a tire contact patch) but the source radiates sound that then propagates across the entire exterior surface of the vehicle. In order to characterize a source it is therefore necessary to know both the sound pressure level in the vicinity of the source and also the way in which sound from the source diffracts around the vehicle. A companion paper has investigated the numerical prediction of the diffraction of acoustic sources around a vehicle using the Fast Multipole Boundary Element Method [2].

Attenuation of noise from the rear of a vehicle was evaluated for different trunk insulation systems using a combination of poro-elastic material modeling and a full vehicle SEA model. The model considered the interaction between the trunk and the passenger cabin. The sound absorption coefficients and acoustic impedance for each of the material systems used in the trunk were measured and the poro-elastic Biot properties were calculated to define the acoustic treatments in the SEA model. Several levels of acoustical treatment for the trunk were studied ranging from a trunk with no decorative liner to a trunk with a liner and maximum acoustical treatment. The results show the contribution of the trunk material in reducing cabin noise for different levels of noise originating at the rear of the vehicle. These results demonstrate the value of combining poro-elastic material modeling and SEA models for selecting efficient material systems early in a vehicle design.

The application of SEA (Statistical Energy Analysis) to the sound package design for a convertible is presented. SEA modeling was used optimize the soft-top construction and the acoustic insulation in the top-stack area (where the soft-top is stored) which were shown to be important transmission paths for tire noise. Correlation between measurement data and predictions from the SEA model is presented and good agreement shown. It is concluded that SEA can be applied to determine the special sound package requirements for convertible vehicles.

For the assessment of vehicle acoustics in the early design stages of a vehicle program, the use of full vehicle SEA models is becoming the standard analysis method in the US automotive industry. One benefit is that OEM's and Tier 1 suppliers are able to cascade lower level acoustic performance targets for NVH systems and components. Detailed SEA system level models can be used to assess the performance of systems such as dash panels, floors and doors, however, the results will be questionable until test data Is available. Correlation can be accomplished with buck testing, which is a common practice in the automotive industry for assessing the STL (sound transmission loss) of vehicle level components. The opportunity to conduct buck testing can be limited by the availability of representative bodies to be cut into bucks and the availability of a transmission loss suite with a suitably large opening.

Interior noise has become a significant performance attribute in modern passenger vehicles and this is extremely important in the luxury market segment where a quiet interior is the price of entry. With the elimination of early prototype vehicles to reduce development costs, high frequency analytical SEA models are used to design the vehicle sound package to meet targets for interior noise quality. This function is important before representative NVH prototypes are available, and later to support parameter variation investigations that would be cost prohibitive in a hardware test. This paper presents the application of an analytical full vehicle SEA model for the development of the acoustic package of a cross over luxury utility vehicle. The development concerns addressed were airborne powertrain noise and road noise. Power flow analysis was used to identify the major noise paths to the interior of the vehicle.

The excitation of structural modes of vehicle roofs due to structure-borne excitations from the road and powertrain can generate boom and noise issues inside the passenger cabin. The use of elastomeric foams between the roof bows and roof panel can provide significant damping to the roof and reduce the vibration. If computer-aided engineering (CAE) can be used to predict the effect of elastomeric foams accurately on vibration and noise, then it would be possible to optimize the properties and placement of foam materials on the roof to attenuate vibration. The properties of the different foam materials were characterized in laboratory tests and then applied to a flat test panel and a vehicle body-in-white. This paper presents the results of an investigation into the testing and CAE analysis of the vibration and radiated sound power of flat steel panels and the roof from the BIW of an SUV with anti-flutter foam and Terophon® high damping foam (HDF) materials.

At certain key stages in the vehicle development process, prototype vehicles are available for NVH testing. This testing fulfills two functions: primarily it is used to assess the status of the vehicle to the program NVH performance targets, but it also provides an opportunity to validate the vehicle SEA model. These single vehicle test events provide a snapshot of the NVH performance but do not provide any understanding of the variability of the NVH performance, which is due to many factors: components, build or assembly and test setup variability. SEA models can be used to estimate the vehicle level variability, if the variability of the interior components is understood, but there is limited data available to confirm the accuracy of these predictions. In this paper we examine the repeatability and reproducibility through a standard gage R&R study of Engine Noise Reduction (engine NR) and Tire NR testing.

In this paper the application of Statistical Energy Analysis (SEA) to the sound package design for a fuel cell powered sedan is presented. Fuel cell vehicles represent a different challenge to a vehicle with a conventional powertrain. With the replacement of the internal combustion engine (ICE), a principal source of airborne and structure-borne powertrain noise, the expectation is that the cabin noise levels would be significantly reduced as the main noise sources would be road and wind noise. A fuel cell powertrain, however, has a number of mechanical sources on the body structure that will radiate airborne noise and may transmit significant structure-borne noise to the vehicle interior. With this alternative power train, much of the conventional wisdom on vehicle sound package developed from experience with ICE's must be reconsidered.

The interior noise in a vehicle that is due to flow over the exterior of the vehicle is often referred to as ‘windnoise’. In order to predict interior windnoise it is necessary to characterize the fluctuating surface pressures on the exterior of the vehicle along with vibro-acoustic transmission to the vehicle interior. For example, for greenhouse sources, flow over the A-pillar and side-view mirror typically induces both turbulence and local aeroacoustic sources which then excite the glass, and window seals. These components then transmit noise and vibration to the vehicle interior. Previous studies by the authors have demonstrated validated CFD (Computational Fluid Dynamics) techniques which give insight into the flow-noise source mechanisms. The studies also made use of post-processing based on temporal and spatial Fourier analysis in order to quantify the amount of energy in the flow at convective and acoustic wavenumbers.

A reactive aftermarket automotive style muffler was considered for development and validation of a procedure to numerically predict and experimentally validate acoustic performance. A CAD model of the silencer was created and meshed. The silencer interior included two sections of perforated pipe, which were included in the cavity mesh. A hybrid FE-SEA (Statistical Energy Analysis) numerical model consisting of a finite element acoustic cavity excited by a diffuse acoustic field at the inlet and coupled via hybrid junctions to SEA semi-infinite fluids on both the inlet and outlet. The hybrid FE-SEA model solves very rapidly on a desktop PC making iterative numerical design a realistic option. To validate the predictions, an experimental setup was created to directly measure the muffler insertion loss. This was done by using a broadband acoustic source piped into a hemi-anechoic chamber.

Automotive interior noise at mid and high frequencies is typically dominated by the airborne noise from acoustic sources that are spatially distributed around a vehicle. Each source is typically spatially compact (for example, a tire contact patch) but the source radiates sound that then propagates across the entire exterior surface of the vehicle. To characterize a source it is therefore necessary to know both the sound pressure level in the vicinity of the source and also the way in which sound from the source diffracts around the vehicle. The former depends on the details of the source, the latter typically depends on the overall vehicle geometry. When creating Statistical Energy Analysis (SEA) models of interior noise, the diffraction of airborne loads around a vehicle is often measured experimentally.