Insert earphones for audiometry
Patent 4677679 Issued on June 30, 1987. Estimated Expiration Date: 
July 5, 2004. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
July 5, 2004. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3811437 Damping element Transducer with improved armature and yoke construction Transducer coupling system Patent #: 4006321 InventorApplicationNo. 06/628009 filed on 07/05/1984US Classes:381/74, HEADPHONE CIRCUITS181/130, Auditory canal insert381/103, Having automatic equalizer circuit381/320, Spectral control381/328, Ear insert381/329, Device for manipulation381/382Sound conducting tubeExaminersPrimary: Rubinson, Gene Z.Assistant: Byrd, Danita R. Attorney, Agent or FirmInternational ClassesH04R 1/22 (20060101)H04R 1/10 (20060101) A61B 5/12 (20060101) AbstractInsert earphones, which are especially useful for audiometry applications include a transducer which is coupled to a resonance cancellation tube as well as to a main tube which is coupled to the ear, with series acoustic dampers in the tubes, operating in a known manner to obtain a smoothly varying frequency response characteristic. An electrical equalization network is coupled to the transducer, cooperating with the acoustic components to obtain a frequency response characteristic which is either flat or which matches that of the human ear. The dampers in series with the main and cancellation tubes have acoustic resistances which are respectively about 20% lower and 20% higher than the characteristic impedances of such tubes, operating to obtain a broadband increase in output.Other References
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