Measurement of the acoustic output of headphones, telephone handsets, hearing aids and many other devices designed to be directly coupled (or closely coupled) to the ear, are usually carried out using ear simulators. Ear simulators are devices that enable the acoustic output of a transducer to be measured objectively, while providing an acoustic load that approximates that of a nominal human (adult) ear. A range of different ear simulators are available commercially, each designed to suit a particular class of transducer and the variety of configurations used to couple them to a real ear. They can simulate either the whole outer ear or a closed (occluded) ear canal, down to the eardrum, and may or may not need to have the correct anatomical form, depending on the application. Two widely used ear simulators, often referred to as the artificial ear and the occluded ear simulator, are standardised by the International Electrotechnical Commission (IEC); in IEC 60318-1 and IEC 60711, respectively (IEC 60711 will be re-numbered as IEC 60318-4 when the current revision is complete). While this paper focuses on the artificial ear, the principles in determining acoustical impedance to be described, apply equally to the occluded ear simulator.
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