Replication of human head movements in 3 dimensions by a mechanical joint
Listeners in 3D sound systems frequently focus on sounds coming from vertical positions deviating from the horizontal plane by moving their viewing direction towards them. Additionally, binaural room-impulse response measurements in small rooms like car cabins require an averaging of measurements at multiple positions to overcome comb-filter effects, caused by sound reflections at surrounding surfaces. For these purposes, in the project depicted here a mechatronic construction was developed to carry out head movements in the three rotatory degrees of freedom yaw (azimuth), pitch (frontal elevation) and roll (lateral elevation) by a dummy head. The kinematic system simulates head and neck movements as close as possible to real human movements in the 3 rotational degrees of freedom. Thereby the human neck's 7 cervicals are represented by a mechanical compression spring which allows a range of motion of ±30° for pitch and roll. Four stepper motors are used to tilt a base board holding the dummy head in which two microphones in the ear-canals are incorporated for binaural measurements. This construction is placed on a rotatory actuator, a combination of stepper motor and turntable. For the rotation in the horizontal plane a full turn would be possible, however it is limited by software to ±90°. The whole system is integrated into a human torso which guarantees that shoulder reflections are taken into account while processing acoustic measurements. The construction's accurateness is <1° in the horizontal plane and 2° for the tilt angles.