Issue: Apr 2015

Virtual audio system reduces time to production

by Nick Palmen

Virtual product development of audio systems in vehicles and the reduction of noise is becoming an increasingly vital part of the automotive design process in order to improve the levels of comfort enjoyed by the occupants.

Devices such as MP3 players, smartphones and PC-Tablets have changed our private and professional lives. They allow us to hear our favorite music everywhere. Consumers expect to be able to listen to music of highest sound quality and not to be disturbed by extraneous noise. As the car becomes more than a means of transport the industry is looking for new ways to help motorists to enjoy the drive. Outstanding sound performance and acoustic comfort are essential components for driving enjoyment.

Automotive Industries (AI) asked Dr. Alfred J. Svobodnik, Managing Director Konzept-X, and expert in identifying and resolving acoustic challenges in vehicles, how virtual simulation helps automakers to solve acoustic challenges. Svobodnik: The noise of vehicles and the acoustic performance of audio systems is a development priority of all automakers, both in terms of customer perceived comfort and sound radiation. The concept and design of the components as well as the evaluation of the systems with modern simulation methods in the early phase of product development are becoming increasingly important.

Konzept-X has developed a process model to simulate the complete vehicle acoustics using vehicle CAD data called Multidisciplinary virtually optimized industrial Design (M-voiD®).

M-voiD couples all electro-mechanical-acoustic characteristics on the basis of appropriate numerical schemes and thus indicates its fully virtualized product development environment. The major advantage of M-voiD is that acoustic problems can be identified and resolved in the virtual domain before any prototype is built. Sound characteristics are measurable and assessable and can be optimized using the virtual model. It is not just limited to the graphical reproduction. You can listen to the virtual sound system. By optimizing vibration levels and acoustics in an early stage of development, we pave the way for outstanding sound performance and acoustic comfort for pure driving enjoyment. Companies also benefit from M-voiD in that they can make design decisions already on the virtual model. Consequently development cycles can be shortened and project risks as well as project costs can be reduced.

AI: What are some of the challenges that you face? Svobodnik: A car is one of the most difficult environments in which to achieve good sound quality. Let me explain: In order to achieve an outstanding sound performance, not only the quality of the speakers is important. Of particular importance is the mechanical and acoustic integration of the loudspeakers in the vehicle. For developers, the space requirements of speakers are particularly challenging. In the past, this integration has been evaluated mainly with real prototypes at a late stage of development. It took a lot of time and money and also bore a risk in the progress of the project.

Using CAE-based simulation tools the speaker integration can be optimized in the design phase. As a result, errors can be avoided. The oscillations of enclosures and structural parts as well as complete new ways of integration can be taken into account. An example is the use of cavities of the vehicle structure to enhance the resonance volume of speakers.

However, these enclosures (cavities) often have a very complex geometry. Consequently these enclosures require an expansion of the electromagnetics, mechanics and acoustic domain in the simulation model. In this context the term multiphysical simulation is used. Right now we are just talking about loudspeakers. In order to create a holistic simulation model, it is necessary to examine the complete subsystem.

In doing so it is necessary to consider all involved subsystems and to investigate their reciprocal interaction as it will demonstrate their impact. The overall system is significantly more than a speaker and amplifier: Head Unit, bus system, amplifier, different number of speakers and their integration in the vehicle (various enclosures), cabin acoustics, and the perception of sound by humans. Everything has to be taken into account.

Besides strongly coupled different physical domains, like electromagnetics, mechanics, acoustics, thermal transport and fluid dynamics, we also have to deal with path dependent dynamic effects and nonlinearities (including instabilities) in each domain. Additionally, materials with totally different behavior and different joining techniques for each component are used in the construction of the car.

AI: How does M-voiD simulate all this? Svobodnik: The Konzept-X’s M-voiD simulation process contains currently five different levels for linear models, which are coupled with each other.

1. Multiphysical modeling of loudspeakers A finite element model is used that fully couples the motor system (electromagnetism), the vibration system (mechanics) as well as the surrounding air (acoustic).

2. Multiphysical loudspeaker model attached  to enclosure The integration of loudspeakers is very challenging. For example,  in order to reproduce low frequencies, speakers require an enclosure as resonance volume. By limitations of available space these enclosures often have a complex geometry and also important influence on the sound. The previously designed multiphysics model of the speakers has to be extended. The enclosures have to be integrated and provided with mechanical and acoustic characteristics.

3. Full system model After integrating the speakers and speaker enclosures into the virtual model, the next step is to extend the simulation model by the car cabin, which has an important impact on the perception of the sound. The mechanical and acoustic characteristics of the car cabin have to be considered in the simulation model. Due to the mix of materials, like different kinds of leather, plastic, textiles, etc. a hybrid approach is used in order to calculate the mechanical and acoustic characteristics.

It must be mentioned here that the coupled model alone will not automatically lead to realistic simulations. In addition we need to accurately describe their material properties in the electrical and structural domain. Thus, a key aspect here is material measurement procedures specifically designed to measure electrical and mechanical parameters as well.

4. Virtual tuning of audio systems In the perception and evaluation of a sound different psychoacoustic characteristics and properties are important. Through careful virtual tuning irregularities and resonances in frequency response will be compensated. The frequency response of all channels must be coordinated. It is also necessary to compensate acoustically the proximity of the seats to the loudspeakers and the varying distances to the individual sound transducers.

5. Auralization of Audio systems After extensive tests and measurements with modern techniques, the sound systems must finally undergo analysis by the human ear. These listening tests are necessary to finally evaluate the audio performance, especially in terms of spatial reproduction. When all five M-voiD tier levels are applied we can refer to a complete virtual product development environment. The result is a virtual mock-up to be used from the concept development of the next generation of vehicles till SOP. Various system architectures and system content as well as positions of speakers can be analyzed and optimized during the whole development cycle. Konzept-X is continuously improving the accuracy and efficiency of multiphysical calculations. Thus we are currently working to capture non-linear models and their behavior on different levels, to identify even more possible disruptions of the listening experience. In future work we will add more and more physical effects, e.g. road noise or thermal effects.

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