HARMAN Innovates Car Audio Systems Design Process with COMSOL Multiphysics

HARMAN Innovates Car Audio Systems Design Process with COMSOL Multiphysics

HARMAN team uses COMSOL Multiphysics to simulate microphone samples and to ease decision-making on the geometry of the acoustic path and the various acoustic impedances

  • 2068

The majority of newly manufactured vehicles come equipped with built-in microphones for various applications (hands-free communication, noise-canceling, e-call module), yet microphone design that upholds rigorous automotive standards and delivers the best user experience is quite challenging. With the support of the SciEngineer Consulting team, HARMAN Automotive—a global leader in providing the latest innovative automotive solutions for automakers—used COMSOL Multiphysics simulation software to take microphone quality and performance to the next level.

Challenge

Some of the most common challenges when designing automotive microphones are the strict physical design boundaries one must work with and the tuning of a good frequency response. Often, grill patterns and available space in the mounting position are specifications given by the customer and, thus, are non-negotiable. Due to the limited space for their installation, automotive microphones are usually no bigger than 3-4 cm (about 1.2-1.6 in), and the microelectromechanical systems (MEMS) microphone element is measured in millimeters. This makes for a short acoustic path with a dimensional change of 0.5 mm (about 0.02 in). Such a dimensional change, which is often given by a customer and has to be designed to be as close as possible to the desired outcome, can significantly impact the microphone’s frequency response.

Cross-section of an atomizer (with dimensions in mm).
Image 2. Cross-section of an atomizer (with dimensions in mm).

Based on the input of the acoustic engineering team and on the constraints coming from the automakers’ requirements, HARMAN engineers put together a CAD model of the microphone in question. To test it, the team identified 3D printing as the quickest and most cost-efficient way to create plastic housings and rubber seals for the prototypes. However, to get to the final design, multiple iterations need to be printed, measured, and changed.

Modifying the design model, printing, and cleaning all the samples make for an overall time-consuming process. In addition, when the printed parts are not immaculately clean or the printer makes a mistake, the measurements could give false positive results, making it extremely hard to backtrack the problem if a team happens to choose this particular sample design for the prototype.

Solution

With support from SciEngineer’ consulting, HARMAN Automotive introduced COMSOL Multiphysics simulation software to the team. The software helped to make the entire design process quicker, more efficient, and cheaper without sacrificing quality. It allowed the HARMAN team to improve the decision-making process regarding the geometry of the acoustic path and various acoustic impedances to tune the frequency response, and helped to eliminate the need for removing large amounts of mesh, felt, or any other covering material from all the possible sample variations.

The following image shows the three curves representing the simulated geometric response, with the simulation having corrected with the MEMS response and the design’s actual measurement result.

Simulated FR vs. measured FR
Image 2. Simulated FR vs. measured FR

To build the basic acoustic path, HARMAN Automotive created a COMSOL application enabling the team to build various basic geometries, change the impedance of the mesh, felt, or other covering materials, and even run a parametric sweep both on the geometry and the boundary conditions without any previous knowledge of COMSOL, as the physics and boundary conditions used for simulation are predefined.

Application for basic FR simulations
Image 3. Application for basic FR simulations

Now, with the help of COMSOL Multiphysics software, the team can simulate design modifications on the housing with a parametric sweep and only print out the best-performing solutions and reduce the number of print samples by 85%. On top of that, with 1 kg of resin and 1 kg of support costs running between USD 500-1000, the inclusion of a simulation phase resulted in a significant cost reduction.

The following table shows how simulation has impacted the number of 3D housing prints.

Full mic assembly weight  Total 3D printing material + support used  Approx. number of printed samples  Simulation 
Mic 1  22 g  9 kg  300  – 
Mic 2  4.2 g  0.5 kg  40 

For the in-car measurements, prior to COMSOL simulation use, the team was able to provide only an estimation of the microphone performance until testing of the microphone took place within the physical car itself. Now, with the help of the simulation, the team has been able to test out various scenarios, including the effects of wind, an air conditioner, or a rolled-down window, seeing their effects upon the performance of the internal microphone, even facilitating the location of the best microphone placement, as necessary according to the case. In addition, the team was able to extend the capabilities of the measurement system (plane wave tubes, couplers) so that they could continuously monitor and measure the improvement of sensors.

“Our goal for the near future is to be able to simulate the whole microphone – the electronics, mechanics, and acoustics. The knowledge of our engineers, coupled with relatively quick and cost-effective simulation results, helps us in our quest to create the highest-performing automotive microphones.”
– Balazs Varga, Acoustic Design Engineer at Harman/Becker Automotive Systems

Results

  • The number of printed samples and errors decreased. Including simulation eliminated the need to remove significant amounts of mesh, felt, or any covering materials from all the possible sample variations and allowed the team to print only the highest-performing samples, reducing their number by 85%.
  • The design process improved. The time the team needed to spend on modifying the model, printing, and cleaning of all the samples was decreased from several days to just a few hours.
  • Frequency response aligned with the target. Simulation facilitates decision-making regarding the geometry of the acoustic path and the various acoustic impedances needed to tune the frequency response.

Summary

Challenge

To improve the automotive microphone design process and frequency response tuning

Solution

Use COMSOL Multiphysics to simulate microphone samples and to ease decision-making on the geometry of the acoustic path and the various acoustic impedances

Results

  • Decrease in the number of printed samples and errors
  • Improvement of the design process
  • Frequency response aligns with the target

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About HARMAN

HARMAN is a global provider of connected technologies for the automotive, consumer, and enterprise markets. The company is known for its expertise in audio and infotainment systems, as well as connected car solutions. Learn more about HARMAN Automotive

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