Quality control operating specifications have been around for a long time. The U.S. Food and Drug Administration (FDA) has used the American National Standards Institute (ANSI) specifications to govern hearing aid quality since 1976. Manufacturers are required to test and report the results of specific standards before device shipment. However, standardized testing is not needed by the dispensing professional. Modern hearing aids add a layer of complexity to electroacoustic evaluation and advanced features, and programming can make it challenging to determine the exact protocol for electroacoustic purposes. Recently, Holder et al. (2016) examined the extent to which modern hearing aids meet ANSI standards. Also, the functionality of features such directional processing was studied.
The group tested 73 new behind-the-ear (BTE) style hearing aids from four different manufacturers. Specific testing protocols were employed based on individual manufacturer’s protocols for ANSI testing. Audioscan Verifit and Frye’s Fonix 8000 test box systems were both used to cross check measures. BTE instruments were coupled to the HA-2 coupler using a 10-mm length of heavy wall no. 13 earmold tubing. Receiver-in-the-canal instruments were coupled to the HA-1 coupler using putty as recommended by the manufacturer. The hearing aids were position in the test box for the ANSI automatic gain control (AGC) per system manual.
The AGC includes the following components:
- Max OSPL90 (maximum output with a 90 dB SPL input with full on gain)
- High-frequency average (HFA)-OSPL90 (average output at three frequencies with full on gain)
- HFA-FOG (average gain for a moderate level input at three frequencies with full on gain)
- Total harmonic distortion (THD)
- Equivalent internal noise (EIN)
- Attack and release times (time required for amplitude compression to activate or deactivate)
The battery current and telecoil tests were not included in the evaluation. Each measurement was compared to the ANSI specified tolerance and assigned a “pass” or “fail.” Directionality was assessed with the Audioscan Verifit. Directional processing is assessed by pure tones that are interleaved between a front facing and rear facing loudspeaker in the test box. The hearing aids were programmed to the manufacturer’s first fit for a 60 dBHL flat hearing loss. The hearing aid was then set to be in a fixed full directional setting without any additional features. Front to back separation was calculated for 16 different 1/12th octave center frequencies from 200 to 6300 Hz. No standards exist for comparison, rather the range and variability for each hearing aid brand was evaluated.
The results showed of the 73 hearing aids tested, none were within the allowable tolerance for every specification. Only Max OSPL90 had no instance of noncompliance. The vast majority of devices were within specifications for THD, however not a single device was within specification for EIN. The results for EIN were tested system dependent. Attack and release times showed significant variability across brands. Finally, directional processing was found to be functional for all devices with an average separation of 4 dB per instrument.
The authors discuss the findings and systematic versus unsystematic noncompliance issues. Also, they point to the importance of manufacturers including ranges of expected value and where mechanical dysfunction is expected. Well-defined quality control protocols that are easily accessed and clinician use of ANSI testing were encouraged.
Holder J, Picou E, Gruenwald J, Ricketts T. (2016) Do Modern Hearing Aids Meets ANSI Standards? J Am Acad Audiol 27(8):619–627.
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