Bone and air: the two paths of sound

Speakers' voices usually reach their own ears as air-borne and structure-borne sounds. The skull and jaw bones transmit the bone-conducted sound component to the inner ear, bypassing the middle ear. This phenomenon is familiar to anyone who has heard their own voice in sound recordings and then perceived it as different sounding – such recordings solely capture the air-borne sound but not the structure-borne sound perceived only by the speakers themselves. Modern in-ear headsets can use this structure-borne sound signal to significantly improve the transmission of a speaker's voice, especially in the presence of interfering noise. To do this, understanding how sound travels from the mouth to the ear is crucial. Like with air-borne sound, we can derive an average transmission characteristic for structure-borne sound based on test measurements on test persons.

An actuator in the artificial ear of an artificial head simulates realistic structure-borne sound for the measurement technology at a defined position in the ear canal. This is how we test the signal processing of in-ear headsets under natural conditions.