Absatz

Antonio Stradivari required for his legendary violins, violas and cellos no more than a pound of wood, four strings and a bit of lacquer. Nevertheless, the 1000 instruments that were built in his workshop in Cremona in northern Italy are still considered to be unmatched today.

What is the secret of sound quality? Why does a Stradivarius sound more lively, voluminous, brighter than any other violin? Scientists worldwide have been trying to solve this mystery for years. Again and again theories are going on, especially regarding the material: the wood gives each violin a fingerprint, they stated. In micro-computer tomography performed by the musicologist Rudolf Hopfner from the University of Vienna, the violins were rayed in a slice-like manner. Nevertheless, the “Stradivari formula” could not be discovered in a 2,600-page study, writes the German journal Die Welt, division science. The sound of the Stradivarius still overwhelms listeners in the great concerts halls of our time.

Globally, prestigious concert halls are competing to count among the best concert halls. An announcement for the construction of the Elbphilharmonie in Hamburg, Germany, was: “the sound quality of the Grand Hall should make it to one of the ten best halls in the world”, an ambitious goal. The acoustics concept of the halls comes from the Japanese acoustician Yasuhisa Toyota, who has already created the concepts of more than fifty other concert halls. In Hamburg he wants to create his greatest masterpiece, writes the German journal Hamburger Abendblatt. The opening concerts will take place in January 2017. In the coming months, perhaps even years, we will see if Yasuhisa Toyota succeeded in creating his greatest masterpiece.

What distinguishes a good concert hall acoustically from one of the best concert halls? What makes it the Stradivarius made of concrete and wood? The acoustics experts have certainly calculated how sound waves spread, how early and late, direct and lateral reflections should run. But concert hall acoustics are complicated by the question of the shape of the hall, a classic rectangular shape, with the orchestra placed on the front of the stage or a hall where the orchestra is surrounded by the audience. Because of the size and their proportions, not all rooms are equally suitable for every repertoire. Halls which were built explicitly for the organization of concerts have a different character than all-round houses.  

What about the acoustics in vehicles? What transforms vehicles into a Stradivarius made of steel, aluminum, plastic and magnesium?  
The acoustics in the vehicle depend on a variety of factors. Acoustic experts are confronted with an extremely complex architecture in a greatly confined space. Through physical/mathematical parameters and the knowledge of psychoacoustics, MVOID tracks down sound collateral damages.

Decisive for an outstanding sound experience are the suitable position and the optimum integration of the loudspeakers into the vehicle cabin. Even a high-end loudspeaker in the wrong position or improperly integrated cannot reproduce its full potential. The expensive purchased sound quality fails. How is it possible to identify such sources of error?

What distinguishes a good vehicle acoustics and outstanding vehicle acoustics?
By using modern, multiphysical simulation applications, MVOID first analyzes the individual loudspeakers within the vehicle cabin. The distribution of the sound pressure as well as reflections caused by resonant panel members, windows and set covers are determined by means of mathematical/physical parameters into the utmost corner in the interior. For each loudspeaker the suitable position is found. The best possible components can be selected (tier level 1 – 3 of the MVOID methodology). The interaction of the entire system, the interaction of the individual loudspeakers, can only be investigated very tedious and extremely time-consuming via the simulation applications.

Why is this important? The human ear perceives all the loudspeakers as a whole in a vehicle. The analysis of the individual loudspeakers and their frequency behavior alone are insufficient. The task is to reproduce an outstanding sound of the overall system. An early analysis of the overall system can save costs and time. MVOID’s virtual tuning and auralization (levels 4 and 5 of the MVOID methodology) dedicate to these tasks.

MVOID’s virtual tuning and auralization (=  MVOID® VRtool) investigate the interactions between the loudspeakers. The sound system is audible in the virtual reality (= auralization).

Absatz
The consideration of the overall system is required, in particular to verify:

  • Where and how are which sound waves distributed in the overall system?

There may be areas within the complex architecture of the vehicle cabin in which sound waves cancel each other out. There may be constructive (addition) or destructive (subtractive cancellation) interferences. This means that each individual loudspeaker must be analyzed and rectified so that the acoustic energy at the relevant points in the vehicle is summed up in an optimal way and not subtracted.

  • What are the run-time and level differences of an audio signal between a loudspeaker and passengers in a vehicle?

The passengers are located near a loudspeaker and relatively far away and at a different angle to other loudspeakers in the vehicle. The loudspeaker in the driver’s door reach the driver much sooner than the loudspeaker integrated in the co-driver’s door. The sound does not arrive simultaneously. In addition, the level is different. These differences in the sound pressure level have to be balanced.

  • Are there any acoustic holes in spite of all the preventive measures?

At certain positions in the vehicle irregularities or resonances can occur: Frequencies may be too loud or too soft for the human ear. Frequency responses, for example, that show significant notches can be an indicator that certain frequencies – an essential part of music – are missing.

The “MVOID® VRtool” makes it possible to verify various scenarios. For example, to verify if it is possible to achieve the performance goal with a subwoofer that is playing up to 50 Hz and woofers in the front doors, that sound good from 70 Hz on. From our experience, this might pose a really big challenge. MVOID reliably predicts whether cost-intensive modifications in the hardware are required, i. e. changes to loudspeakers or their integration, or by means of tuning, i. e. with very low costs, an outstandingly good sound can be reproduced.

The acoustic experts use the MVOID® VRtool to analyze the interactions of all loudspeakers and tune the entire system virtually (virtual tuning based on virtual measures by means of tier level 1 – 3 of the MVOID methodology). In order to reproduce an outstanding sound experience every single seat has to be analyzed and disruptions must be eliminated. The acoustic experts find an ideal frequency response for each of the loudspeakers. 

An additional, significant bonus: using binaural reproduction techniques (auralization) the results are audible through headphones. Moreover, it is possible to evaluate and optimize the spatial reproduction of the sound system. For example, the acoustic experts verify the best loudspeaker position to transport the best stage setting or the influence of the center tweeter etc. Such questions can only be answered in final listening tests. For that purpose the acoustic experts use different sound signals and songs. If spatial attributes are not reproduced like the original event on the stage, the music loses its character. Associations, for example with a live experience, are lessened. The sound is distorted. The final sound results not solely on numbers, data, evaluations and graphics. Psychoacoustic effects are involved.

Due to the fact that the results are transported into the virtual reality – they are made audible – the acoustics experts and decision-makers are able to make safe and easy decisions for the further development of the sound system. Arguments are backed not only by graphical evaluations but also by the fact that they can listen to the sound systems.

In the following you will find two examples to demonstrate the power of the MVOID® VRtool:

Example 1:

In Example 1, the interaction of the right and left door woofers are analyzed. This analysis is even required for mono signal contents, like bass. The image shows the different sound pressure levels of both signals, that means of the left (red line) and right (white line) loudspeaker, at a seating location. The MVOIDÒ VRtool identifies the frequency response curve of the two channels and their overlay, the summation of both sound events (thick orange line). The example shows at the marked positions a bad summation of both loudspeakers. The consequence is a poor listening experience.  By means of an appropriate tuning, this interaction can now be significantly improved.

Example 2:

Example 2 shows the analysis of a complete system at a particular seating location. The analysis can indicate integration problems of individual loudspeakers, for example. If this is the case, the bandwidth of a channel could be shown significantly reduced. The MVOIDÒ VRtool analyzes whether the overall system can still fulfill the desired performance. Figure 2 shows a balanced acoustic energy distribution over all frequencies by a suitable virtual tuning. The result is a harmonious sound.

From the above descriptions, it becomes clear that not only the analysis of the individual loudspeakers and their frequency behavior are sufficient. The advantages of the analysis of the entire system are obvious:

  1. Early virtual analysis and optimization of the acoustic influences on system level to avoid cost-intensive modifications at a later time of development
  1. Early analysis whether problems are solvable by software (tuning process); Is it possible to minimize resonances, to adjust run-time differences and to eliminate acoustic holes?
  1. Early analysis whether design changes are necessary; Do the selected components reproduce at the defined positions, in the selected integration manner the desired sound or, in the worst case, is it necessary to modify hardware, i. e. to modify loudspeakers or their integration?

 

Virtual development of vehicle sound systems achieve the next level of development
As the interactions of all loudspeakers can be virtually analyzed, optimized, made audible – sound can be transported into the virtual reality – the virtual development of automotive sound systems has – in the opinion of the MVOID team – achieved the next level of development.

The experts and decision-makers of the automobile manufacturers now have the opportunity to analyze the overall vehicle sound system in the predevelopment phase from the first ideas to the final result – all in the virtual world. Hardly any single aspect remains left to analysis of the later real sound systems.

Acoustic experts and decision-makers can safely evaluate whether the sound system reproduces the desired harmonic sound – a Stradivarius made from steel, aluminum, plastic and magnesium.

References:
Photo Dr. A. Svobodnik: MVOID Technologies GmbH; Graphics: MVOID Technologies GmbH;
„Antonio Stradivari” Vol.1-8 , Jost Thöne Verlag – www.jost-thoene-verlag.de
welt.de/wissenschaft/article156561881/16.06.16; Abendblatt.de/hamburg/article207968035/30.07.16