An Analysis of Open Fits, Noise-Reduction, and Directional Mics
Magnusson et al (2013) investigated word recognition scores in noise using open versus closed earmolds, as well as noise-reduction and directional microphones. Twenty adults (10 males and 10 females, mean age 57 years) with bilateral mild-moderate-severe sensorineural hearing loss (SNHL) and no previous hearing aid experience served as subjects. Each patient was fitted bilaterally with open-fitting hearing aids programmed to "first fit" with thin tubes or open domes, and fitted again with closed, unvented, acrylic shells, for the purposes of the experiment.
The authors determined omni microphones in noise did not improve word recognition scores compared to unaided conditions. However, performance was statistically significantly improved with directional microphones (fixed supercardioid pattern was selected for all directional trials) in noise and the advantage of directional microphones was enhanced using closed earmolds (4.4 dB SNR) as compared to open fittings (1.6 dB SNR) compared to unaided conditions. Of note, when using open fits, there was no advantage noted when using directional microphones and noise reduction in tandem. However, while using closed earmolds, a statistically advantageous listening improvement occurred when using noise reduction and directional microphones in tandem (0.8 dB SNR).
Magnusson et al reports that "people with normal hearing or a mild loss in the low-frequency region and a moderate loss in the high-frequency region will receive benefit from using open-fit hearing aids with directional microphones in noisy situations. On the contrary, open-fit hearing aids with omni-directional microphones do not improve performance…" in noise as compared to unaided performance. The authors concluded using open-fits in noise with omni mics does not enhance speech recognition as compared to unaided, using open-fits in noise with directional mics can significantly improve speech recognition, combining noise reduction and directional mics in noise with open-fits may not further improve speech recognition, the advantages of noise reduction and directional mics are significantly reduced via open-fits as compared to "conventional" earmolds, and successful auditory rehabilitation can be achieved via open-fit hearing aids (as was demonstrated via the IOI-HA questionnaire).
For More Information, References and Recommendations
Hall JW, Johnston KN, John AB, Kreisman NV, Crandell CC. (2010) Multiple Benefits of Phonak Edulink Use By Children With Auditory processing Disorder (APD).
Johnston KN, John AB, Kreisman NV, Hall JW, Crandell CC. (2009) Multiple benefits of Personal FM System Use By Children With Auditory Processing Disorder (APD). International Journal of Audiology 48:371-383.
Kim JS, Bryan MF. (2011) The Effects of Asymmetric Directional Microphone Fittings on the Acceptance of Background Noise. International Journal of Audiology, 50:290-296.
Kuk F. (2011) Hearing Aids For Children with Auditory Processing Disorders? Seminars in Hearing 32(2):189-195.
Magnusson L, laesson A, Persson M, Tengstrand T. (2013) Speech Recognition in Noise Using Bilateral Open-Fit Hearing Aids – The Limited benefit of Directioonal Microphones and Noise Reduction. International Journal of Audiology 52:29-36.