The Impact of Ear Canal Geometry: New Article by Brian Johansen, Per Rasmussen and Morten Pedersen
In this Whitepaper, we examine another important factor besides frequency response when testing in-ear headphones.
Understanding how ear canal geometry affects in-ear headphone testing is crucial for achieving consistent and reliable results. In this article, GRAS experts Brian Johansen, Per Rasmussen, and Morten Høgholm Pedersen explore how pressure fields, insertion depth, and leakage influence test outcomes, emphasizing the need for precise positioning in ear simulators. If you’re looking to optimize the accuracy of your headphone assessments, these insights are invaluable.
Introduction
As expectations for in-ear headphone sound quality continue to rise, the development of advanced solutions has accelerated, necessitating the use of increasingly sophisticated measurement equipment.
To address these needs, a range of ear simulators has been introduced by various vendors, designed to cover the entire human audible frequency spectrum.Among these are the 60318-4 IEC standard Ear Simulator (100 Hz – 10 kHz),the GRAS “711” High-Frequency Ear Simulator (100 Hz – 20 kHz), and the ITU-T recommended Type 4.3 Ear Simulator (20 Hz – 20 kHz). There is growing interest in the high-frequency spectrum within the human ear canal, as well as an emerging focus on factors like leakage and placement, which are crucial for both device performance and accurate measurement.
While efforts have been made to design a “one size fits all” ear simulator, which essentially reflects an “average ear” geometry, there is an often-overlooked dimension at play. Research indicates that the success of headphones, particularly in-ear models, is not solely determined by assessing the frequency response between the in-ear transducer and the ear simulator. Instead, the listening experience is significantly shaped by how the pressure field develops within the semi- or fully enclosed ear simulator, making factors such as leakage and insertion position critical.
As a result, addressing immediate issues can lead to new challenges, complicating efforts to ensure consistency and repeatability when characterizing in-ear devices. To evaluate the impact of various ear canal geometries, Pressure Acoustics frequency domain simulations are performed using the COMSOL Type 4.3 Ear Simulator. The simulations begin with the specific geometry outlined in ITU-T Rec. P.57 Type 4.3, assuming the in-ear headphone is placed inside the ear canal, but not extending beyond the reference plane for practical reasons.