• The objectives of vehicle NVH design
• Our NVH services
• Measures
• Methods

The objectives of vehicle NVH design

 

The objectives of vehicle acoustic and vibration design are nearly always shaped by human considerations with regards to the intended use of the vehicle. What does this mean? The driver is primarily interested in receiving clear acoustical information from the vehicle under operation. He or she wants to hear and feel the gears being shifted, the engine accelerating when the throttle is applied, the effects of applying brakes and the actuation of a turn indicator. The acoustic 'signature' of the engine should always provide the driver with unambiguous feedback regarding its operational status. A 'vibration signature' also provides the driver with vital information about e.g. the road surface.

The passengers may have other concerns:  They are probably most interested in having a comfortable ride – neither too noisy nor too bumpy. The passenger wants to be able to converse with the driver or a seatmate, even when the vehicle is travelling fast. This means that short-range speech intelligibility must be good. The air conditioning equipment should not be too loud, and reading or sightseeing should not be disadvantaged by annoying whistling, clapping or rumbling noises. At the same time, passengers sometime desire a certain amount of acoustical confidentiality - his or her conversations should not be heard by all the other passengers in the same carriage. For example; A lively conversation in a bus among the members of a bowling club can also be annoying for a solitary passenger three seats further up. Consequently, long-range speech intelligibility should not be too good in this case.

 

Last but not least, the “spectators” - to maintain our metaphor - play a part in determining the objectives of acoustic design. The spectators are the 'listening audience' and the people who live along the road or track where the vehicle travels. Since they are directly affected parties, they create the public opinion and affect the statutory regulations that become the 'scenery', which provides the interplay of social demands and expectations of environmental compatibility and mobility for the vehicle in question.

The vehicle manufacturer and buyer also have important supporting roles. A manufacturer would like to see their vehicles maintain profitability over its total life cycle. The buyer wants to see real value in return for his or her investment. This value encompasses not only a variety of technical aspects, along with sound quality,  riding comfort, cost-effectiveness and ease of maintenance, but also the 'image' of the vehicle in which sound and vibration quality is included.

 

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Our NVH services

A typical challenge is to consider the intended uses of the vehicle and its acoustic design that follow from these uses right from the start. An important prerequisite then is close collaboration among experts in the fields of psychoacoustics, technical acoustics and measurement technology. The available people and tools must be able to analyze the acoustic characteristics of the complex overall system represented by the vehicle and to recognize the various sources and generation mechanisms of sounds and vibrations. They must also have thorough mastery of research methods and computations related to the generation, transmission and radiation of airborne and structure-borne sound.

Müller-BBM has been a recognized partner of the motor vehicle industry and railway vehicle manufacturers for many years, as well as for purchasers, users and agencies. Our know-how is used during all stages of the development process as well as for vehicles in production. We assist manufacturers and purchasers with the definition of acoustic requirements, the formulation of target values and clear and unambiguous presentation of task descriptions related to vehicle NVH in requirement documents and individual parts specifications. Computer simulations and system-level feasibility studies can provide quantitative predictions with regard to the acoustic characteristics of the vehicle in early development phases.

We offer manufacturers and suppliers our services by making estimates and carrying out investigations for acceptance testing as well as for project management and quality control programs during the further development and production of a vehicle. Müller-BBM Scandinavia's experts may cooperate directly with the client's development teams or those of their suppliers, in order to deal with issues or special assignments. Our specialists can ensure that vehicle components, such as the gearbox, fuel pump or air-conditioning system, meet the requirements set by the vehicle manufacturer. Our investigations also help to ensure that the exhaust system will not drone, the brakes will not squeal and the chassis or body will not thrum.

 

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Measures

 

Our evaluations and tests provide problem diagnosis and the basis for development of remedial measures. As an independent consulting engineering company, we investigate and compare what is physically possible and technically feasible, and we also evaluate the cost-effectiveness of these options.

We can further investigate whether the use of active methods for sound suppression and vibration control would offer advantages in comparison to passive methods. This can be illustrated with a simple example;

“Every vehicle acoustics engineer is familiar with the problem of the second-order vibrations of four stroke four-cylinder engines. Instead of using expensive passive measures, such as special engine mounts or anti-drone materials, it is possible to obtain good active noise compensation in the vehicle interior over the full range of engine speeds using anti-phase sound. This approach is called 'active noise and vibration control'. It allows distinct weight savings to be realized in the overall vehicle structure. In addition, such active systems even allow design of the acoustics of the interior space by purpose - 'active noise and vibration design' - without any modifications to the mechanical structure”.

 

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Methods

 

We use methods in our work that are appropriate for our often complex assignments and that represent the very latest state of technical development. The standard tools of numerical acoustics regarding analytical aspects such as finite element method (FEM), boundary element method (BEM) and statistical energy analysis (SEA), are just as much a part of our toolbox as operational deflection shape analysis (ODS), experimental modal analysis, intensity analysis and transmission path analysis are on the testing side.

Furthermore, we have many special proprietary programs available. A few examples of these are our wheel-rail impedance model for the computation of roughness excitation of rail vehicles, ray-tracing programs for investigating sound propagation in rooms, special measurement techniques for determining speech intelligibility, measurement methods for in-situ investigation of absorption coefficients and measurement equipment that we have developed for determining the roughness of rails and railway vehicle wheels.

Our capabilities are not limited to presenting the results of computations and tests. These results are presented in comprehensive reports that also provide our clients with concise summary presentations, interpretations and evaluations. When appropriate, we deliver our results in audible form on digital storage media. For vehicle acoustics, audible examples are usually clearer and more convincing than visual illustrations. We assist our clients in making presentations and preparing publications. Our responsibility is to provide our client with a sound documentary basis for decision making regarding the acoustic properties of the product.

In most cases our test and analysis results are used as basis for design modifications of the vehicle or vehicle parts. We have long experience of providing “functional prototypes” for demonstrating the feasibility and practical effect of considered measures as well as assisting the design engineers of the OEMs or suppliers to find proper final solutions to NVH issues.

 

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