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NIST System for Measuring the Directivity Index of Hearing Aids under Simulated Real-Ear Conditions.

Wagner RP - J Res Natl Inst Stand Technol (2013)

Bottom Line: Since this response is different for a hearing aid worn on a person as compared to when it is in a free field, directivity index measurements of hearing aids are usually done under simulated real-ear conditions.Omnidirectional, cardioid, and bidirectional response patterns were measured.Results are presented comparing the NIST data with the reference values calculated from the data reported by all participating laboratories.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-8223.

ABSTRACT
The directivity index is a parameter that is commonly used to characterize the performance of directional hearing aids, and is determined from the measured directional response. Since this response is different for a hearing aid worn on a person as compared to when it is in a free field, directivity index measurements of hearing aids are usually done under simulated real-ear conditions. Details are provided regarding the NIST system for measuring the hearing aid directivity index under these conditions and how this system is used to implement a standardized procedure for performing such measurements. This procedure involves a sampling method that utilizes sound source locations distributed in a semi-aligned zone array on an imaginary spherical surface surrounding a standardized acoustical test manikin. The capabilities of the system were demonstrated over the frequency range of one-third-octave bands with center frequencies from 200 Hz to 8000 Hz through NIST participation in an interlaboratory comparison. This comparison was conducted between eight different laboratories of members of Working Group S3/WG48, Hearing Aids, established by Accredited Standards Committee S3, Bioacoustics, which is administered by the Acoustical Society of America and accredited by the American National Standards Institute. Directivity measurements were made for a total of six programmed memories in two different hearing aids and for the unaided manikin with the manikin right pinna accompanying the aids. Omnidirectional, cardioid, and bidirectional response patterns were measured. Results are presented comparing the NIST data with the reference values calculated from the data reported by all participating laboratories.

No MeSH data available.


Geometric diagram that shows the triangle and the parameters used with the law of cosines to determine the stay wire length l required to set the sound source at a given elevation angle α. (Not to scale)
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f3-jres.118.005: Geometric diagram that shows the triangle and the parameters used with the law of cosines to determine the stay wire length l required to set the sound source at a given elevation angle α. (Not to scale)

Mentions: Adjustment of the elevation angle is done with a vertical positioning system that moves the loudspeaker used as the sound source on the path of a circular arc. The arc has a 1 m radius and is centered on the test point so that the 1 m distance required from the sound source to the test point is maintained at all elevation angles. The loudspeaker is mounted at the center of a swing arm, which is attached to poles fixed to separate ends of the wooden support. A weight and pulley system elevates the swing arm and loudspeaker, which is fixed at a given elevation angle by a thin steel stay wire attached to the wooden support at one end and to a cable fixed to the swing arm at the other end. The elevation angle is determined by the stay wire length l. By applying the law of cosines, the value of l required for each elevation angle was calculated using(4)l=[x2+y2−2xycos(α+β)]12−d,where x is the distance from the test point to the sound source, y is the distance from the test point to where the stay wire attaches to the wooden support, d is the distance from the sound source to where the stay wire attaches to the swing arm cable, and β is a fixed angle. Figure 3 is a geometric diagram that shows the triangle used with the law of cosines and the parameters of Eq. (4).


NIST System for Measuring the Directivity Index of Hearing Aids under Simulated Real-Ear Conditions.

Wagner RP - J Res Natl Inst Stand Technol (2013)

Geometric diagram that shows the triangle and the parameters used with the law of cosines to determine the stay wire length l required to set the sound source at a given elevation angle α. (Not to scale)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4487306&req=5

f3-jres.118.005: Geometric diagram that shows the triangle and the parameters used with the law of cosines to determine the stay wire length l required to set the sound source at a given elevation angle α. (Not to scale)
Mentions: Adjustment of the elevation angle is done with a vertical positioning system that moves the loudspeaker used as the sound source on the path of a circular arc. The arc has a 1 m radius and is centered on the test point so that the 1 m distance required from the sound source to the test point is maintained at all elevation angles. The loudspeaker is mounted at the center of a swing arm, which is attached to poles fixed to separate ends of the wooden support. A weight and pulley system elevates the swing arm and loudspeaker, which is fixed at a given elevation angle by a thin steel stay wire attached to the wooden support at one end and to a cable fixed to the swing arm at the other end. The elevation angle is determined by the stay wire length l. By applying the law of cosines, the value of l required for each elevation angle was calculated using(4)l=[x2+y2−2xycos(α+β)]12−d,where x is the distance from the test point to the sound source, y is the distance from the test point to where the stay wire attaches to the wooden support, d is the distance from the sound source to where the stay wire attaches to the swing arm cable, and β is a fixed angle. Figure 3 is a geometric diagram that shows the triangle used with the law of cosines and the parameters of Eq. (4).

Bottom Line: Since this response is different for a hearing aid worn on a person as compared to when it is in a free field, directivity index measurements of hearing aids are usually done under simulated real-ear conditions.Omnidirectional, cardioid, and bidirectional response patterns were measured.Results are presented comparing the NIST data with the reference values calculated from the data reported by all participating laboratories.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-8223.

ABSTRACT
The directivity index is a parameter that is commonly used to characterize the performance of directional hearing aids, and is determined from the measured directional response. Since this response is different for a hearing aid worn on a person as compared to when it is in a free field, directivity index measurements of hearing aids are usually done under simulated real-ear conditions. Details are provided regarding the NIST system for measuring the hearing aid directivity index under these conditions and how this system is used to implement a standardized procedure for performing such measurements. This procedure involves a sampling method that utilizes sound source locations distributed in a semi-aligned zone array on an imaginary spherical surface surrounding a standardized acoustical test manikin. The capabilities of the system were demonstrated over the frequency range of one-third-octave bands with center frequencies from 200 Hz to 8000 Hz through NIST participation in an interlaboratory comparison. This comparison was conducted between eight different laboratories of members of Working Group S3/WG48, Hearing Aids, established by Accredited Standards Committee S3, Bioacoustics, which is administered by the Acoustical Society of America and accredited by the American National Standards Institute. Directivity measurements were made for a total of six programmed memories in two different hearing aids and for the unaided manikin with the manikin right pinna accompanying the aids. Omnidirectional, cardioid, and bidirectional response patterns were measured. Results are presented comparing the NIST data with the reference values calculated from the data reported by all participating laboratories.

No MeSH data available.