November 1, 2011 Audiology

Improving Hearing Aid Function in Noisy Situations

see also

Even with today's sophisticated hearing aid advances in microphone directionality and noise-reduction circuitry (Chung, 2010), hearing-instrument users still experience difficulties in some challenging environments, such as in restaurants and at parties. Almost half of hearing-aid users who return their devices cite problems with hearing over background noise (Kochkin, 2007). It is no surprise that use in noisy situations is listed as one of the top 10 factors pertaining to hearing aid user dissatisfaction (Kochkin, 2010).

Innovative approaches to facilitating hearing in noise, therefore, may further increase hearing-
instrument users' satisfaction. These approaches include strategic microphone placement in non-
directional devices and the use of wireless accessories that stream the speaker's voice directly to the listener's hearing aids.

Microphone Placement 

Strategic microphone placement taps the natural physical characteristics of the external ear to improve speech intelligibility. Outer ear structures have been shown to contribute to greater directivity toward the front than the rear (Ricketts, 2000; Shaw, 1974), which may translate to better speech understanding in noise in situations where the listener is facing the speaker. Conversely, when the microphone of a hearing instrument is positioned behind the ear, all pinna effects—including the ear's natural directivity and protection from wind noise—are obliterated. However, moving the microphone inside the ear canal or even within the bowl of the concha maintains some of these favorable pinna effects, thereby naturally restoring some of the ear's physiological ability to help the listener discriminate speech from noise.

A relatively new hearing aid model on the market takes advantage of natural pinna effects (Figure 1 [PDF], left panel). This form factor is similar to a conventional custom in-the-canal (ITC) device (right panel), except the microphone is removed from the shell and extends into the upper part of the concha. Removal of the microphone from the shell may allow for a smaller device or a larger vent. Yet since the microphone is still secured within the ear, natural directivity and spectral cues provided by the pinna are maintained (Van den Bogaert, Carette, & Wouters, 2011). A study at Walter Reed Army Medical Center revealed no significant difference in hearing-in-noise test results between this new custom form factor and a directional behind-the-ear hearing instrument (Cord & Block, 2011). In addition, the natural protection afforded by locating the microphone in the crevices of the outer ear (the concha) reduces the intensity of wind noise. Figure 2 [PDF] shows a spectrogram of wind noise measured in a hearing instrument with the microphone located within the concha (left panel) and with the microphone behind the ear (right panel). Red areas indicate the areas of highest energy across the frequency range due to wind noise.

Accessories 

Another approach to improving speech in noise is the use of wireless accessories to stream the speaker's voice directly to the hearing instruments. One of these approaches is a wireless hearing aid accessory that communicates through Bluetooth technology to the mobile phone (or Bluetooth-enabled landline phone). Bluetooth is an open technology that uses radio frequencies in the 2.4-GHz range to send data wirelessly over a limited distance. After pairing the accessory to the Bluetooth-ready phone and the hearing aids, the user is able to conduct phone conversations at a more favorable signal-to-noise ratio than without the accessory. In addition, the conversation is streamed simultaneously to both hearing aids, providing the additional benefit of binaural listening adjusted to the user's hearing thresholds for each ear.

Another wireless accessory is a personal wireless microphone that speakers can clip onto their clothing. Akin to a separate FM system that uses a transmitter and a receiver or boots that attach to the hearing instrument(s), this technology effectively improves the signal-to-noise ratio for the listener, especially in an environment with background noise. New direct wireless transmission, however, requires no additional boots or receivers for the listener. This technological advancement means reduced cost and hassle for the hearing-instrument user.

Additional methods of promoting speech intelligibility in noise—in addition to hearing aid algorithms—may be necessary to reduce the return rate and the number of hearing aids stored in the drawer. With strategic microphone placement, which allows for natural directivity and wind noise protection in non-directional hearing instruments, and wireless technology that directly streams a more favorable signal-to-noise ratio, hearing in noise may become easier for hearing-instrument users.

Tamara Stender, AuD, CCC-A, is a senior audiologist in Global Audiology for GN ReSound Group. Her research interests include hearing aid benefit and satisfaction, and the use of signal processing and other methods to improve speech discrimination in noise. Contact her at tstender@gnresound.com.

cite as: Stender, T. (2011, November 01). Improving Hearing Aid Function in Noisy Situations . The ASHA Leader.

References

Bluetooth. (2011, June 20). In Wikipedia, The Free Encyclopedia. Retrieved 15:41, June 21, 2011, from http://en.wikipedia.org/w/index.php?title=Bluetooth&oldid=435265724.

Chung, K. (2010). Reducing noise interference: Strategies to enhance hearing aid performance. The ASHA Leader, 15(4), 10–13.

Cord, M., & Block, K. (2011, March). Efficacy of the remote microphone hearing aid for novice hearing aid users. Presented at Joint Defense Veteran Audiology Conference (JDVAC), San Diego, CA.

Hearing Industries Association (HIA) (2010). Statistical reporting program. Washington, DC.

Kochkin, S. (2010). MarkeTrak VIII: Customer satisfaction with hearing aids is slowly increasing. Hearing Journal, 63(1), 11–19.

Kochkin, S. (2007). MarkeTrak VII: Obstacles to adult non-user adoption of hearing aids. Hearing Journal, 60(4), 27–43.

Nilsson, M., Soli, S. D., & Sullivan, J. A. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America, 95(2), 1085–1099.

Ricketts, T. (2000). Directivity quantification in hearing aids: fitting and measurements effects. Ear & Hearing, 21(1), 45-58.

Shaw, E. A. G. (1974). Transformation of sound pressure level from the free field to the eardrum in the horizontal plane. Journal of the Acoustical Society of America, 56(6), 1848–1861.

Van den Bogaert, T., Carette, E., & Wouters, J. (2011). Sound source localization using hearing aids with microphones placed behind-the-ear, in-the-canal, and in-the-pinna. International Journal of Audiology, 50(3), 164–176.



  

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