In designing acoustical systems, engineers must account for multiple physics and their interactions at multiple scales and frequencies.
By Mads J. Herring Jensen
To accurately model an acoustical system, engineers often must account for multiple physics as well as their couplings at different scales and frequencies.
With increasingly complex systems and tighter project deadlines, acoustical engineers are turning to numerical simulation software to get the job done. By using computational tools, design tasks can be accelerated and the need for costly and time-consuming physical prototypes can be reduced. Acoustics simulation also increases the understanding of a design, leading to better informed decisions and higher-quality products.
To reap the benefits, what capabilities are important in acoustics simulation? Applications often include the reproduction, propagation, and reception of sound signals under diverse conditions. This includes not only the interaction of the sound signal with structures, porous materials, and flow, but also modeling the transducers involved in the generation and detection of the sound signals. All these are multiphysics problems by nature that acousticians have to consider for the efficient development of new products and technologies. This places a critical requirement on the modeling software in terms of the ability to couple physics effects relevant to the full system.
Current Technological Challenges In Acoustics
Sound quality is a trending topic in many industries. This concerns the reproduction of sound inside, for example, car cabins (Figure 1) or the output from the exhaust and muffler systems. Other examples include the performance and optimization of headphones and loudspeakers or the speaker system of mobile devices. In all of these cases, a detailed understanding of both sound propagation and transducer behavior is necessary to optimize the systems. Clever digital signal processing is not enough anymore to make systems behave and “sound good.” For example, to improve the performance of hearing aids using adaptive feedback canceling, a coupling of a miniature loudspeaker vibroacoustics model with an acoustic and solid mechanics finite element (FE) model is needed for producing accurate simulation results.
In the loudspeaker industry, a standard driver design has reached the limit of where improvements can be done by simple trial-and-error testing (Figure 2). Optimization requires detailed numerical analysis. Miniature loudspeaker systems are now driven at such high sound pressure levels that distortion and attenuation due to nonlinearities are introduced. The same nonlinearities also play a significant role in liners in aerospace applications.
Another example involving a multiphysics coupling — electrostatics, structural membranes, and thermoviscous acoustics — is the modeling of condenser microphones. The physics are tightly coupled and all necessary for a correct prediction of the microphone sensitivity.
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