Virtual product development using the example of sound systems in vehicles
A vehicle delivers one of the most difficult environments to reproduce sound. The structure of a vehicle is complex. In vehicles the installation space is highly limited. Several individual woofers, midrange speakers and tweeters have to be integrated in an ideal way. In addition, vehicle and road noise may add additional coloration of the reproduced sound.
For the virtual product development of sound systems in vehicles MVOID couples five tier levels.
When all five MVOID tier levels are applied, we can refer to a complete virtual product development environment that enables a realistic listening environment of the virtual system. This is unprecedented.
Tier Level 1: Multiphysical Modeling of Loudspeakers
Within the first tier level the point is to create a multiphysical model of the loudspeakers. Electromagnetism, mechanics, acoustics (sometimes thermal transfer and fluid dynamics) and its bi-directionally interactions are analyzed. Besides, we have to deal with path dependent dynamic effects and nonlinearities (including instabilities) in each domain.
1D-Lumped parameter models, and 2D/3D finite element models are used for multiphysical simulations.
Tier Level 2: Multiphysical loudspeaker model attached to enclosure
In order to achieve an outstanding sound performance not only the quality of the transducer is important. Of particular importance is the mechanical and acoustical integration of the loudspeakers into the vehicle. The simulation model of the loudspeaker of tier level 1 is extended to its integration (including also an enclosure).
Spurious vibrations of enclosures and structural parts are discovered quickly by MVOID analyses. By using MVOID in the pre-development phase complete new ways of integration can be followed. For example the use of cavities of the vehicle structure as enclosures (resonance volume) for speakers, because loudspeakers require an enclosure as resonance volume in order to reproduce low frequencies.
Tier Level 3: Full System Model including the listening space
In tier level three the car cabin is to be integrated into the simulation model. The car cabin has an important impact on the perception of the reproduced sound and acoustical comfort. Within the multiphysical simulation model the distribution of the sound, the 3D sound field, can be determined right into the farthest corners by physical/mathematic parameters. All major factors that affect the sound in the interior are taken into account.
The mix of materials in the car cabin is particularly important, like trim components, carpets, glass etc. They have to be integrated in the model. The various materials with totally different behavior and different joining techniques require detailed descriptions of the material properties in the electrical and structural domain. This is provided by the MVOID database, which provides realistic models and their parameters based on specifically developed measurement methods.
Tier Level 4: Virtual Tuning
The authentic listening experience can only be achieved by adjusting the sound to the individual vehicle type and sound system at hand – the acoustic tuning process.
The virtual tuning in tier level four enables a computer-based adjustment that integrates the knowledge of psychoacoustics, the subjective sound perception in order to reproduce a perfect sound experience for all passengers.
Extensive virtual measurements of tier level three are required. On the basis of these measurements, each channel as well as the summation of the individual channels are tuned. The results show whether costly modifications of the hardware are required or if cost-effective improvements can be achieved by software (by means of applying a proper tuning).
The essential tasks of the virtual tuning include:
1. Minimize resonances caused by the listening space
2. Adjust run-time and level differences due to different distances of the loudspeakers
Optimize the summation of different speakers
Tier level 5: Auralization
In the phase of auralization the acoustics experts finally evaluate the audio performance on the multidisciplinary simulation model. Listening tests in terms of spatial reproduction are carried out. When we speak about auralization it comes to the width and height of the stage – the music is to be reproduced according to a life performance. The singers are usually found in front of the stage in the middle, next to the bassist, guitarist, saxophonist, the drums are mostly towards the back. If the spatiality is not reproduced like the original event on the stage, the music loses its character.
Using binaural reproduction techniques the acoustic experts are able to reproduce spatiality similar to the real situation in the vehicle.