In a previous paper, a method was introduced to predict the sound transmission loss (STL) performance of multilayer panel constructions using a measurement-based transfer matrix method. The technique is unique because the characterization of the poro-elastic material is strictly measurement based and does not require modeling the material. In this paper, it is demonstrated how the technique is used to optimize the STL of lightweight, multi-layer panel constructions. Measured properties of several decoupler materials (shoddy and foam) are combined with sheet metal and barrier layers to find optimal combinations. The material properties are measured with the impedance tube per ASTM E2611.
An important factor contributing to a customer’s subjective perception of a vehicle, particularly at the point-of-purchase, is the sound created by the passenger doors during closure events. Although these sounds are very short in duration the key systems that control the sounds produced can be highly coupled. Similarly, the necessary efforts required to understand key design criteria affecting the sound can also be highly complex. Within this paper sub-systems affecting the door closure sound are evaluated to understand key structural properties and behaviors toward the contribution to the overall sound produced. This begins with the subjective preferences of typical sounds and the difficulties with both measuring and reproducing these sounds appropriately and leads directly to the target setting and target cascading process.
Introducing a new transducer concept has resulted in considerable reduction in setup time and at the same time improved accuracy and repeatability for engine bay noise transfer studies. The acoustic environment inside cars are one of the primary comfort parameters. This is made up of a number of contributions from drivetrain, auxiliary equipment, wind noise and tire noise, and all are influenced by the transfer from the source to the receiver. With the change from purely internal combustion engines to electrical or electrical assisted propulsion systems, a new set of noise sources are introduced in the engine compartment and this requires renewed focus on the transmission paths to the receivers inside the car cabin. Typically, one of the tools to study these mechanisms is by using a reverse transmission technique, placing a well-defined sound source in the receiver position inside the car and measure the resulting sound pressure levels in the engine compartment.
Theoretical modeling continues to play a larger role in noise and vibration engineering; however, until products are perfectly made, there will be a need to evaluate their end of line (EOL) performance. Manufacturing production of a wide range of items has classically involved some amount of subjective and/or evolved objective quality testing along the line or at the end of the line. This testing can have goals of determining product safety, durability, functionality, or the vibration/sound quality. A vibration-based measurement approach is often used for many of those goals. Often, many modern products utilize some combination of electric motors, internal combustion engines, and power transmission rotational components. The EOL testing for many of these rotational components is after many years now heavily refined in the measurement and analysis methods, and the separation of good, bad and marginally bad samples may not always be challenging.
The transmission of turbulent flow pressures through panels to the interior noise depends on the spatial matching of the pressure and vibration fields. Since the exterior pressure field on a moving vehicle includes both turbulent pressure and acoustic pressure, both need to be factored into a noise transmission loss calculation. However, these two exterior pressure fields have very different spatial patterns. This is further complicated when the exterior flow is separated from the surface due to an obstruction. This study uses wind tunnel and road tests to measure and model the wind noise transmission loss through the side glass of a vehicle. The results are seen to be very different from the traditional sound transmission loss curves for an acoustic pressure source.
Automakers have reported that passenger perception of vehicle interior wind noise is strongly correlated to the non-Gaussian and non-stationary character of the exterior aero-acoustic wind loading. It has been shown (Rouillard & Sek 2010) that leptokurtic non-Gaussian loading (Kurtosis κ>3) can be synthesized by non-stationary modulation of otherwise Gaussian random loading. This paper presents a transient statistical energy analysis (SEA) model for the aero-vibro acoustic transmission of non-stationary wind noise which uses the same approach - a modulation of otherwise Gaussian random fluctuating pressure loading, in each one third octave band. The authors have previously shown that the non-stationary character of random wind loading can be measured in a wind tunnel or on the road with a suitable surface pressure microphone array (Bremner et al SAE NVC 2017).
Internal combustion engines are increasingly being equipped with turbochargers to increase performance and reduce fuel consumption and emissions. Being part of exhaust and intake systems, the turbocharger strongly influences the orifice noise emission. Although 1D-CFD simulations are commonly used for the development of intake and exhaust systems, validated acoustic turbocharger models are not yet state-of-the-art. Consequently, the first aim of the paper is the investigation of the influence on the orifice noise and the development of an accurate 1D-CFD model. Firstly, active and passive acoustics of turbochargers are distinguished. Complex active turbocharger noise emissions were investigated on a turbocharger test rig and could be correlated with unstable rotating stall. Therefore critical acoustic operation can be identified in early engine development stages by comparison to other tested turbochargers.