Method for determining the sound pressure level at the eardrum of an occluded ear
The sound pressure level at the eardrum may be determined by constructing an optimized model of the ear canal and then calculating the simulated sound pressure level at the eardrum. The model is obtained by comparing real-ear-to-coupler differences between the sound pressure level measured at a fixed distance from a hearing instrument and a simulation of the measurement, optimizing the model by varying the length and/or diameter of the canal model, repeating the simulation and determination of simulated real-ear-to-coupler difference until the differences between the measured and simulated values are minimized. The optimized real-ear-to-coupler difference at the eardrum may then be determined and in turn the sound pressure level at the eardrum may be calculated. The sound pressure level at the eardrum may then be used to acoustically fit the hearing instrument to the person.
1. A method for acoustically fitting a hearing instrument positioned in an ear canal, the hearing instrument comprising a tip and a sound tube comprising an end at the tip of the hearing instrument, comprising:
measuring the sound pressure level at a predetermined distance from the end of the sound tube of the hearing instrument positioned in the ear canal;
measuring the sound pressure level at the predetermined distance from the end of the sound tube of the hearing instrument positioned in a test coupler;
in response to measuring the sound pressure level in the ear canal and the test coupler, determining a measured real-ear-to-coupler difference at the predetermined distance from the end of the hearing instrument sound tube, where determining comprises calculating the difference between the measured sound pressure level in the ear canal and the measured sound pressure level in the test coupler;
simulating the sound pressure level at the predetermined distance from a model of a hearing instrument positioned in a model of the ear canal, where the ear canal model comprises a length and a diameter;
simulating the sound pressure level at the predetermined distance from the model of a hearing instrument positioned in a model of the test coupler;
in response to simulating the sound pressure level in the ear canal and the test coupler, determining a simulated real-ear-to-coupler difference at the predetermined distance from the model of a hearing instrument, where determining comprises calculating the difference between the simulated sound pressure level in the ear canal and the simulated sound pressure level in the test coupler;
optimizing the model of the ear canal, comprising
(a) varying the length and/or diameter of the model of the ear canal;
(b) simulating the sound pressure level at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising a varied length and/or diameter;
(c) determining the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising a varied length and/or diameter, where determining comprises calculating the difference between the simulated sound pressure level in the ear canal and the simulated sound pressure level in the test coupler;
(d) determining the error between the measured real-ear-to-coupler difference at the predetermined distance from the hearing instrument and the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument; and
iteratively repeating preceding steps (a) though (d) until the error is minimized to a predetermined, acceptable amount, yielding optimized values of length and diameter for the ear canal model;
simulating the sound pressure level at the eardrum generated by a model of the hearing instrument in the model of the ear canal comprising the optimized values of length and/or diameter; and
determining the optimized simulated real-ear-to-coupler difference at the eardrum, where determining comprises calculating the difference between the optimized simulated sound pressure level and the simulated sound pressure level in the test coupler.
2. A method as set forth in claim 1 , further comprising adding the optimized simulated real-ear-to-coupler difference at the eardrum to the sound pressure level measured in the test coupler.
3. A method as set forth in claim 1 , where the sound pressure level is measured and simulated over a range of frequencies f 1 -f 2 .
4. A method as set forth in claim 1 , where measuring the sound pressure level at a distance from a hearing instrument positioned in the ear canal comprises measuring the sound pressure level at a distance of 5 mm from the end of the hearing instrument sound tube.
5. A method as set forth in claim 1 , where measuring the sound pressure level at a predetermined distance from the hearing instrument positioned in a test coupler comprises measuring the sound pressure level in a test coupler comprising a volume of 0.4 cc.
6. A method as set forth in claim 1 , where the model of the ear canal comprises a taper from the hearing instrument towards the eardrum.
7. A method as set forth in claim 1 , where the model of the ear canal comprises a plurality of sections of decreasing diameter.
8. A method as set forth in claim 1 , where the model of the ear canal comprises a plurality of sections of varying diameter.
9. A method for creating an optimized model of an ear canal for a hearing instrument positioned in the ear canal, the hearing instrument comprising a tip and a sound tube comprising an end at the tip of the hearing instrument, comprising:
measuring the sound pressure level at a predetermined distance from the end of the sound tube of a hearing instrument positioned in the ear canal;
measuring the sound pressure level at the predetermined distance from the end of the sound tube of the hearing instrument positioned in a test coupler;
in response to measuring the sound pressure level in the ear canal and the test coupler, determining a measured real-ear-to-coupler difference at the predetermined distance from the end of the hearing instrument sound tube, where determining comprises calculating the difference between the sound pressure level measured in the ear canal and the sound pressure level measured in the test coupler;
simulating the sound pressure level at the predetermined distance from a model of a hearing instrument positioned in a model of the ear canal, where the ear canal model comprises a length and a diameter;
simulating the sound pressure level at the predetermined distance from the model of a hearing instrument positioned in a model of the test coupler;
in response to simulating the sound pressure level in the ear canal and the test coupler, determining a simulated real-ear-to-coupler difference at the predetermined distance from the model of a hearing instrument, where determining comprises calculating the difference between the simulated sound pressure level in the ear canal and the simulated sound pressure level in the test coupler; and
optimizing the model of the ear canal, comprising
(a) varying the length and/or diameter of the model of the ear canal;
(b) simulating the sound pressure level at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising the varied length and/or diameter;
(c) determining the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising a varied length and/or diameter, where determining comprises calculating the difference between the simulated sound pressure level in the ear canal and the simulated sound pressure level in the test coupler;
(d) determining the error between the measured real-ear-to-coupler difference at the predetermined distance from the hearing instrument and the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument; and
iteratively repeating preceding steps (a) though (d) until the error is minimized, yielding optimized values of length and diameter for the ear canal model.
10. A method for acoustically fitting a hearing instrument positioned in an ear canal, the hearing instrument comprising a tip and a sound tube comprising an end at the tip of the hearing instrument, comprising:
calculating a measured real-ear-to-coupler difference at a predetermined distance from the end of the hearing instrument sound tube, based upon the difference between the sound pressure level measured in the ear canal at the predetermined distance and the sound pressure level measured in the test coupler;
calculating a simulated real-ear-to-coupler difference at the predetermined distance from the end of the hearing instrument sound tube, based upon the difference between the sound pressure level simulated in a model of the ear canal, comprising a length and a diameter, at the predetermined distance and the sound pressure level simulated in the test coupler;
optimizing the model of the ear canal, comprising
(a) determining the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising a varied length and/or diameter, based upon the sound pressure level simulated at the predetermined distance from the model of the hearing instrument positioned in the model of the ear canal comprising a varied length and/or diameter;
(b) determining the error between the measured real-ear-to-coupler difference at the predetermined distance from the hearing instrument and the simulated real-ear-to-coupler difference at the predetermined distance from the model of the hearing instrument; and
iteratively repeating preceding steps (a) and (b) until the error is minimized, yielding optimized values of length and diameter for the ear canal model; and
calculating an optimized simulated real-ear-to-coupler difference at the eardrum, based upon the difference between the sound pressure level simulated at the eardrum generated by a model of the hearing instrument in the model of the ear canal comprising the optimized values of length and/or diameter, and the sound pressure level simulated in the test coupler.
11. A method as set forth in claim 10 , further comprising adding the optimized simulated real-ear-to-coupler difference at the eardrum to the sound pressure level measured in the test coupler.
12. A method for acoustically fitting a hearing instrument positioned in an ear canal, the hearing instrument comprising a tip and a sound tube comprising an end at the tip of the hearing instrument, comprising:
measuring the real-ear-to-coupler difference in the ear canal at a predetermined distance from the end of the hearing instrument sound tube;
simulating the real-ear-to-coupler difference at the predetermined distance from the end of a model of the hearing instrument in a model of the ear canal comprising a length and a diameter;
selecting values for the length and diameter of the model of the ear canal such that the differences between the measured and simulated real-ear-to-coupler differences at the predetermined distance are minimized to a predetermined level.
13. A method as set forth in claim 12 , further comprising calculating the simulated real-ear-to-coupler difference at the eardrum.
14. A method as set forth in claim 13 , further comprising calculating the sound pressure frequency response at the eardrum.