A framework for geometry acquisition, 3-D printing, simulation, and measurement of head-related transfer functions with a focus on hearing-assistive devices

Abstract

Individual head-related transfer functions (HRTFs) are essential in applications like fitting hearing-assistive devices (HADs) for providing accurate sound localization performance. Individual HRTFs are usually obtained through intricate acoustic measurements. This paper investigates the use of a three-dimensional (3D) head model for acquisition of individual HRTFs. Two aspects were investigated; whether a 3D-printed model can replace measurements on a human listener and whether numerical simulations can replace acoustic measurements. For this purpose, HRTFs were acoustically measured for four human listeners and for a 3D printed head model of one of these listeners. Further, HRTFs were simulated by applying the finite element method to the 3D head model. The monaural spectral features and spectral distortions were very similar between re-measurements and between human and printed measurements, however larger deviations were observed between measurement and simulation. The binaural cues were in agreement among all HRTFs of the same listener, indicating that the 3D model is able to provide localization cues potentially accessible to HAD users. Hence, the pipeline of geometry acquisition, printing, and acoustic measurements or simulations, seems to be a promising step forward towards in-silico design of HADs.

Keywords: 3D head model; 3D printing; Acoustical measurements; Acoustical simulations; CAD modeling; Head-related transfer functions.

Fig. 1

Head-and-ear model. (a) Acquired geometry (b) Model used for printing (c) Printed model mounted on a torso simulator.

Fig. 2

Geometry layers used for HRTF simulation. From inside to out: empty space shaped as the head and torso, inner air box, and perfectly matched layer.

Fig. 3

Right-ear HRTF magnitudes for the frontal position in the horizontal plane.

Fig. 4

Right-ear HRTF magnitude spectra in the horizontal plane (elevation angle of 0°) and the azimuth angle of 90, 45, 0, −45 and −90°.

Fig. 5

HRTF magnitude spectra in the median plane (as function of elevation angle). Color encodes the relative magnitude in dB. F, T, R describe directions in front, top, and rear of the listener. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Spatial correlation between HRTF magnitudes for NH167 and NH167 remeasured, NH167 printed and NH167 simulated, respectively. Solid line: right ear, dashed line: left ear.

Fig. 7

ITDs in the horizontal plane (as function of azimuth angle). The right panel shows a zoom around the most lateral directions shown in the left panel.