Electroacoustics – Simulators of human head and ear – Part 4: Occluded-ear simulator for the measurement of earphones coupled to the ear by means of ear inserts
|Publication Date:||1 January 2010|
|ICS Code (Electroacoustics):||17.140.50|
This part of IEC 60318 describes an occluded-ear simulator intended for the measurement of insert earphones in the frequency range from 100 Hz to 10 000 Hz. It is suitable for air conduction hearing aids and earphones, coupled to the ear by means of ear inserts e.g. ear moulds or similar devices. The occluded-ear simulator is also suitable as the basis for an extension intended to simulate the complete ear canal and the outer ear (for instance in head simulators).
The occluded-ear simulator simulates the acoustic transfer impedance for the occluded normal adult human ear. However, it does not simulate the leakage between an earmould and a human ear canal; therefore, the results obtained with the occluded-ear simulator may deviate from the performance of an insert earphone on a real ear, especially at low frequencies. Moreover, large performance variations among individual ears will occur which should be considered when using the ear simulator.
Above 10 kHz the device does not simulate a human ear, but can be used as an acoustic coupler at additional frequencies up to 16 kHz. Below 100 Hz, the device has not been verified to simulate a human ear, but can be used as an acoustic coupler at additional frequencies down to 20 Hz.
NOTE Due to resonances in the acoustic transfer impedance of the occluded-ear simulator above 10 kHz, high measurement uncertainties, e.g. in the order of 10 dB, can occur in earphone responses. Repeatable results mainly are obtained for insert earphones with high acoustic damping (used for instance in the extended high-frequency audiometry, see the earphones listed in ISO 389-6)1 coupled to the occluded-ear simulator by means of a simple, symmetrically designed and air tight coupling device.
1 Figures in square brackets refer to the Bibliography.