Models of bone-conducted sound in the chinchilla external ear.

Models and previously reported data are used to describe two hypothetical bone-conduction (BC) induced ear-canal sound-pressure (PEC) sources in chinchillas. Sound-pressure measurements and a middle-ear model are combined with new micro-computed tomography ear-canal measurements. The ear-canal models contain one ideal volume-velocity source in the cartilaginous canal walls and a second in the bony walls. Analyses suggest the following: (i) Vibrations of both the cartilaginous and bony walls contribute to BC-induced PEC. (ii) With an open ear canal, the BC-induced PEC is dominated by cartilaginous ear-canal vibrations at frequencies less than 3 kHz. (iii) The strengths of the two sources correlate with the surface areas of the two canal components. (iv) The cartilaginous walls move with nearly twice the magnitude of the bony walls. (v) The phases of motion of the bony and cartilaginous canal walls differ by 1/2 cycle between 2 and 8 kHz. This anti-phasic behavior leads to cancellation of the pressures produced by the two sources at some frequencies. (vi) The model predicts occlusion of the cartilaginous canal results in 20- to 30-dB increases in BC-induced PEC. These results are comparable to those from a similar model of human BC-induced PEC by Stenfelt and Reinfeldt [(2007). Int. J. Audiol. 46, 595-608].