ANSI Overview Hearing Aid Testing and Verification What is ANSI? Distortion Feedback SSPL-90 Bandwidth (Frequency Range) Frequency Response Equivalent Input Noise (EIN) Battery Drain

Hearing Aid Tests Conducted to measure the quality and quantity of sounds produced by the hearing aid. Normally conducted by attaching the hearing aid to a coupler that simulates the size and shape of a human ear canal. Creating a soundproof seal between the hearing aid and the coupler is imperative. The hearing aid and coupler are placed into a soundproof test box.

What is ANSI ANSI stands for the American National Standards Institute. Specifications for hearing aid characteristics are covered under ANSI standard 3.22 (S3.22) Many hearing aid test systems will automatically run the ANSI tests with the push of a button. ANSI recommendations are updated periodically. The date of the standards will be listed along with the standard number (e.g., S3.22-2003).

Total Harmonic Distortion Occurs when new frequencies that are not present in the input are generated in the output. An output that is free of audible distortion is referred to as “clean.” Most hearing aids will amplify normal speech cleanly, but loud sounds and background noise may produce distortion. Using a hearing aid analyzer, simply set the gain control to the reference-test position, present the test signals, and read the percent total harmonic distortion (%THD) presented on the display.

Feedback Feedback occurs when amplified sound returns to the hearing aid input and is re-amplified. Two types of feedback: internal and external. Internal feedback is caused by a feedback loop inside the hearing aid case. External feedback occurs when amplified sound from the hearing aid escapes the acoustic seal and returns to the hearing aid’s microphone to be re-amplified. To test for feedback, seal the hearing aid to a 2 cc coupler, set the hearing aid to the use-gain level, and the analyzer to the spectrum mode. Input noise may be necessary to produce feedback. Internal feedback will produce oscillation on the display. If no feedback is detected, place the hearing aid in the patient’s ear, set the volume control to use-gain and listen for feedback. If feedback is heard, it is external feedback.

Measuring SSPL-90 SSPL-90 stands for saturation sound pressure level-90. It is also referred to as OSPL-90 (output sound pressure level-90). It is a measurement of the intensity of the output of the hearing aid when the hearing aid is in its full-on position and a 90 dB input is present. This test determines how well the output-limiting circuitry keeps the output within the patient’s comfortable listening range. Set the trim controls and gain control to the broadest and most powerful response, set the input level, and run a pure tone frequency response. Read the maximum SPL at any given frequency from the graph.

Frequency Response Most hearing aids are used well below the full-on position the use curve may not be the same as the full-on curve. This normal use curve is referred to as the frequency response curve. To determine this curve, secure the hearing aid to the appropriate coupler and place it in the test box. Set the gain control of the hearing aid to within ±1.5 dB of the reference test position Set the input level to 60 dB SPL and run the frequency response test.

Bandwidth Bandwidth refers to the frequency range of inputs in which a hearing aid could be considered effective. Determine the bandwidth by finding the high frequency average (HFA) and subtracting 20 dB from that average. This number is called the response limit of the hearing aid. Example: HFA = 100 dB, Response limit = 80 dB (100 dB – 20 dB = 80 dB).

Finding f1and f2

Equivalent Input Noise Equivalent input noise (EIN) is produced by the hearing aid circuitry and can be loud enough to be perceptible to the wearer. Subtract the HFA value from the HFA gain value with a 50 dB input. The resulting number is the EIN of the hearing aid.

Battery Drain Use battery simulation device with the hearing aid analyzer. Set the gain control to the reference test position Use an input signal of 1000 Hz and 65 dB SPL. Compare your results to those stated by the manufacturer.