Major Issues in First Fittings
Mueller (2015) reports that if you have an approximate idea of how much gain a patient needs, and if we were to somehow fix sound to have only one constant input level, there exists more than 1400 gain curve options available in today’s highly sophisticated hearing aids. Mueller notes that the “heavy lifting” associated with choosing the correct curve may be accomplished by choosing DSLv5 or NAL-NL2, as long as one verifies and validates that what the professional selects is actually being delivered!
Further, he cautions that the very best hearing aid on the market can be rendered fairly useless (i.e., “rendered worse than a PSAP…”) if programmed wrong. Mueller states that some 75 percent of all first fittings rely on manufacturer’s proprietary fittings, However, “...if you’re not using probe-mic measures to obtain the correct output in the ear canal, you’re not fitting to the targets….” Further, he reminds us that simply matching theoretical curves (on the manufacturer’s software programming screen) is unlikely to work, as there is no accounting for, or accommodation of, the patient’s actual ear canal. Unfortunately, the majority of first fittings are just plain wrong.
Taylor (2015) reported that hearing aids with basic technology fitted using a best-practice approach are likely to outperform premium products taken straight out of the box and placed onto a patient’s ears using a minimalist (i.e., first fit) approach.
Sanders et al (2015) compared real-ear output from multiple manufacturer’s versions of NAL-NL2 to the Audioscan Verifit version. They report that the NAL-NL2 option provided by the manufacturers offered less speech audibility than NAL-NL2. Four deviations were noted—(1) the manufacturers versions reduced gain for soft inputs, (2) they rolled-off high frequencies (above 2000 Hz), (2) they boosted gain in mid-tones (above NAL-NL2 prescription), and (4) they were more linear than NAL-NL2.
Sanders et al reported that “the dispensing professional cannot rely on the manufacturers” version of the software and of course, verification, validation, and real-ear must be performed to actually know what is really going on in the ear canal.
Leavitt and Flexer (2012) tested the premier instruments from the top six hearing aid manufacturers with regard to the QuickSIN SNR. They reported that variation from the manufacturer’s proprietary fitting to NAL-NL1 offered an improvement in QuickSIN SNR of approximately 7 dB across 4 of 6 instruments, and some 10 dB improvement for 2 of 6 instruments tested. That is, the manufacturer’s proprietary fitting performed substantially more poorly than did the NAL-NL2 option with regard to the QuickSIN SNR.
For More Information, References, and Recommendations
Leavitt R, Flexer C. (2012) The Importance of Audibility in Successful Amplification of Hearing Loss. Hearing Review 19(13):20-23.
Mueller HG. (2015) 20Q: Today’s Use of Validated Prescriptive Methods for Fitting Hearing Aids—What Would Denis Say? May.
Sanders J, Stoody TM, Webver JA, Mueller HG. (2015) Manufacturer’s NAL-NL2 Fittings Fail Real- Ear Verification. Hearing Review. March.
Taylor B. (2015) The “Good Enough” Era and Hearing Healthcare. Hearing Review. May:10,48.