FINAL WORD | Van Vliet | December 2013 Hearing Review
Diary of a Cricket Hunter: Localization and Mic Location Can Be Important
By Dennis Van Vliet, AuD
The chirps of field crickets are a common part of the nocturnal sounds in summer and fall in Southern California. One evening this fall as the air was getting chillier, we were sitting at home reading. My wife, audiologist Alison Grimes, suddenly looked up and reported that she thought one cricket in particular sounded like it was generating a song inside rather than outside of the house.
It turns out that crickets are interesting and well-studied. The chirp is created by their forewings, or tegmina, rubbing together with the plectrum (modified edge of the forewing acting like a guitar pick) of one wing scraping across teeth-like protrusions of the other wing, creating a very regular oscillating motion that sets areas of the tegmina into vibration. These areas, known as “harps,” serve as the principal sound radiators. The male crickets are the noisemakers, looking to attract a suitable mate. The fundamental frequency of the chirp varies by species, but is often reported as 5 kHz and higher.
The melody of crickets outside is natural and soothing to me. Inside the house, however, it is as annoying as tinnitus. I set out on a search to find this cricket that was looking in the wrong place for a mate. As I went downstairs, he stopped chirping until I was still for a few moments. When he started back up, I had a tough time localizing where the sound was coming from. I was making some pretty gross errors because the frequency of his chirp made it necessary to rely on intensity alone. I was not able to tell much by moving my head.
I finally found him lurking under the recesses of a textured sisal rug in front of the exterior door. I was successful more by employing a logical visual search than relying on acoustical cues.
Hunting Other Acoustic Targets
My struggles reminded me that the frequencies above 4 kHz are often not easy targets for hearing aid fittings. Yet, as my hunting expedition reminded me, they are valuable for spatialization as well as for speech.
Stelmachowicz et al1 illustrated the problems with limited bandwidth in hearing aids a decade ago, and offered frequency lowering strategies as one option to help overcome high frequency deficits. The potential benefits of frequency lowering are well documented, but if there is residual hearing that can be aided without frequency lowering, it seems best to strive for the least distortion when possible.
In this time of quick-and-easy fittings with receiver-in-canal (RIC) and thin-tube hearing instruments, it can be easy to overlook custom hearing aid fittings as an option. One exceptional benefit from a custom in-the-canal (ITC), completely-in-the-canal (CIC), or invisible-in-the-canal (IIC) fitting is the microphone location effect. As described by Best et al,2 the pinna and concha resonances offer “free” high frequency enhancements and improved directivity indexes when compared to the “above the pinna” microphone locations of standard products.
I participated as a subject for mic location effect studies not long ago, and was quickly convinced of the differences in spatialization as I tried to locate the source of sounds with BTE mic locations. Many of us can remember anecdotal reports from patients who reported a dramatic difference with a custom product compared to a standard BTE worn instrument—in spite of the fact that our in-office testing revealed little differences.
The Final Word?
It is unlikely that we’ll list “cricket hunters” as a vital patient profile in our future hearing aid user demographics. However, it is important to remember that custom hearing instruments should still have a prominent place in the options for what we can offer to our patients. A product inquiry may start with a cosmetic or convenience motivation, but excellent benefit may end up as an important part of the outcome.
References
1. Stelmachowicz PG, Pittman AL, Hoover BM, Lewis DE, Moeller MP. The importance of high-frequency audibility in the speech and language development of children with hearing loss. Arch Otolaryngol Head Neck Surg. 2004;130:556-562.
2. Best V, Kalluri S, McLachlan S, Valentine S, Edwards B, Carlile S. A comparison of CIC and BTE hearing aids for three-dimensional localization of speech. Int J Audiol. 2010;49(10):723-32. doi: 10.3109/14992027.2010.484827. w
Dennis Van Vliet, AuD, has been a prominent clinician, columnist, educator, and leader in the hearing healthcare field for nearly 40 years, and his professional experience includes working as an educational audiologist, a private-practice owner, and VP of audiology for a large dispensing network. He currently serves as the senior director of professional relations for Starkey Technologies, Eden Prairie, Minn. Correspondence can be addressed to HR or: [email protected]
Original citation for this article: Van Vliet, D. Diary of a cricket hunter: localization and mic location can be important. Hearing Review. 2013, December: 78.
