nappikuuloke_korvassa

Mechanical simulation improved the ergonomics of earbuds

When a Finnish start-up, SoundlyFit Oy, faced the challenge of improving the ergonomics of earbuds, they decided to look for solutions with PLM Group’s experts. This collaboration led to the introduction of mechanics simulation, which has proven to be an effective way to speed up the product development process and provide designers with clearer insights to optimize product comfort.

High-quality earbuds that feel comfortable and stay firmly in the ear place special demands on their design. In addition, these headphones need to offer first-class sound reproduction while being able to attenuate external sounds. Achieving this balance is not easy, as the ear cushion must seal perfectly in the ear canal to keep sounds inside and prevent external interference from entering. However, this requirement for tightness and comfort can pose conflicting challenges for designers.

korvatyyny_malli
Headset and 3D models of S, M, and L-size ear cushions ready for mechanical simulation.

On the one hand, a rigid ear cushion can provide a firm grip on the ear, but at the same time, it can put too much contact pressure on the delicate skin of the ear canal, which can feel uncomfortable after prolonged use. On the other hand, a softer ear cushion may feel almost imperceptible in the ear and conform perfectly to the shape of the ear canal, but at the same time, its surface pressure and friction may be insufficient to keep the device firmly in place in the ear.

The traditional design process is time-consuming

Traditionally, the design of earbuds and their ear cushions has followed a path of trial and error. During the development phase, prototypes are often created and subjected to subjective ergonomic tests. The test team members try different prototypes on their ears and rate them on comfort and usability. This process aims to identify the best solutions for further processing.

However, such a design process has its challenges: prototyping takes time and resources, getting a sufficient number of suitable test subjects, and collecting and analyzing test results are time-consuming tasks. In addition, the human sense of touch is not always accurate enough to discriminate subtle discomforts when using headphones, especially at points that may be uncomfortable.

HEADSET_KORVASSA
At the end of the mechanical simulation, the headset is in place in the ear.

How the process goes forward in the simulation-driven design?

The simulation process developed has two parts. The first is a mechanics simulation based on the elementary method (FEM) to determine the deformations of the earpiece and the cushion placed in the ear, and the contact pressures and strains they exert on the ear. When an external force is applied to the skin or cartilage of the ear, deformations and stresses occur, the magnitude of which depends on the magnitude of the external forces. In mechanical terms, therefore, the human ear, skin, and cartilage behave in the same way as industrial materials and products. The corresponding engineering calculations for different structures and materials based on the element method are therefore commonplace in product development in the engineering industry.

The physical results from the mechanical simulation are further processed using a comfort model developed by SoundlyFit, which brings in the human interpretation of the physical sensations and returns a user comfort rating for the device.

kuulokkeetKorvissa
3D model of the new headphone under review fitted to the ears of selected people. The ear population must be large enough to be statistically representative of the entire population of people under consideration.
Areas of discomfort are illustrated in black, making it easy for the designer to think about suggestions for improvement.

The material data and other properties of the laser-scanned ear models of real people are set so that the deformations of the ear under different loads match those measured in the real ear. The resulting library of virtual ears can now be used to select a suitable set of subjects for a virtual ergonomics test, for example, according to age, ethnicity, or gender. The 3D models of the earbud and ear cushions in the design phase will be fitted with material properties, after which the ergonomic test can be simulated.

Computational challenges in ear mechanics simulation include large deformations, contacts between different parts, and non-linear materials. The calculations have been performed using Abaqus/Explicit software from the Dassault Systèmes SIMULIA brand of the PLM Group, with automation built on top so that the calculation models for the desired ear-ear-cushion combinations can be easily built. By distributing the calculation task across 30 processor cores, one case can be calculated on a desktop computer in half an hour. This means that a virtual ergonomics test for 20 people, or 40 ears in total, can be completed in less than 24 hours. Compared to an ergonomics test on physical prototypes and real test subjects, this saves at least weeks and usually up to months.

 

This article was originally published in Tekniikka & Talous partner content 22.9.2023.