When devices such as telephone handsets, headsets, headphones, hearing aids and hearing protectors are electro-acoustically tested, mannequins known as Head and Torso Simulators (HATS) are used to replicate the upper part of the human body. They allow researchers to simulate Head Related Transfer Function, which is the process by which sounds are changed by the time they reach the human eardrum. The mannequins' calibrated pinna (outer ear) simulators have traditionally been represented through a series of two-dimensional cross-sectional profiles – this is the industry standard for pinnas on HATS. Now, as part of a revision of that standard, the Acoustics Team from the UK’s National Physical Laboratory (NPL) have created a three-dimensional pinna that overcomes the limitations of the 2D variety.
“Having a 2D pinna in an artificial ear has some inherent frequency limitations,” said NPL’s Ian Butterworth. “For example, when sound spreads through structures like narrow tubes, annular slits or over sharp corners, noticeable thermal and viscous effects take place causing further departure from the lumped parameter model. The new standard for the 3D model has been developed to give proper consideration to these effects.”
The model was created with a coordinate-measuring machine, that performed a laser scan of a physical model of a human ear. The data obtained by that machine can now be shared amongst HATS manufacturers, so that no matter where devices are tested, they will all be using a consistent, more accurate model.