6.2 Electroacoustic Analysis & ANSI S3.22 Standards

Purpose of ANSI S3.22

The American National Standards Institute (ANSI) S3.22 (2014/R2020, most recently revised as ASA/ANSI S3.22-2024) defines the methods for specifying the electroacoustic performance of hearing aids. Its primary purpose is quality control: confirming that a hearing aid performs according to the manufacturer's published specifications before it is fitted to a patient, and re-confirming performance whenever a device's history raises doubt about that performance.

When Electroacoustic (EA) Analysis Is Performed

EA testing is not a one-time event tied only to a new fitting. Dispensers routinely run a full test-box analysis at several points in a device's life:

• Incoming stock QC: when new hearing aids arrive from the manufacturer, to catch factory defects or shipping damage before a patient ever wears the device.
• Initial fitting: to document baseline performance against the manufacturer's spec sheet.
• After any repair: whether performed in-house or returned from the manufacturer, to confirm the repair actually restored normal performance before the aid goes back to the patient.
• Following a performance complaint: weak output, distortion, or excessive noise that cannot be explained by an obvious mechanical cause, since EA testing objectively distinguishes a device malfunction from an acoustic or fitting problem.

Test Box Setup and Couplers

Electroacoustic analysis is performed in a specialized, sound-isolated test box. The hearing aid is attached to a standard 2cc coupler, which approximates the volume of an average adult ear canal with an earmold in place.

• HA-1 Coupler: Used for custom hearing aids (ITE, ITC, CIC) and receiver-in-canal (RIC) aids directly attached to the coupler with putty.
• HA-2 Coupler: Used for behind-the-ear (BTE) hearing aids, utilizing standard tubing attached to the coupler.

Measured Parameters and Tolerances

The ANSI standard defines specific parameters that must be measured, along with the acceptable tolerance window around the manufacturer's published spec — the range a device must fall within to pass QC.

Output Sound Pressure Level (OSPL90)

Measured with a 90 dB SPL input signal with the hearing aid volume full on, OSPL90 determines the maximum output capability of the hearing aid. The HFA-OSPL90 is the High-Frequency Average, calculated from the output at 1000, 1600, and 2500 Hz, and is the single most exam-tested electroacoustic value because it defines the loudest sound a device can ever deliver to a patient's ear — a critical safety ceiling.

Gain Measurements

Full-On Gain (FOG) HFA is the high-frequency average gain measured with a 50 dB SPL input and the volume control full on. Reference Test Gain (RTG) instead sets the volume control to a specific, calculated output level (HFA-OSPL90 minus 77 dB) with a 60 dB SPL input, approximating a typical real-world use setting rather than the full-on extreme.

Other Key Measurements

• Frequency Response Curve: A plot of output across frequencies, typically measured with a 60 dB SPL input at the Reference Test Position, confirming the overall shape of the response matches the spec sheet curve rather than just a single-point average.
• Total Harmonic Distortion (THD): Measures distortion introduced by the hearing aid at 500, 800, and 1600 Hz; must not exceed the manufacturer's specified percentage, commonly under 5% for standard channels.
• Equivalent Input Noise (EIN): The internal noise generated by the device's own microphone and amplifier chain — essentially the noise floor a patient hears in an otherwise silent room.
• Battery Current Drain: Milliamps drawn from a substitute power source in place of the real battery, used to diagnose complaints of unexpectedly short battery life.

Battery Current Drain Testing in Detail

Because short battery life is one of the most common patient complaints, candidates should know the basic procedure. A battery pill — a dummy battery connected by wire to a regulated power supply — replaces the real battery so the test system can measure current draw without depleting a consumable cell. Two values are typically captured: quiescent current, measured with the gain control at the Reference Test Setting and no acoustic input signal present, representing the device idling; and maximum battery current, measured with a 90 dB SPL input at the three HFA frequencies and averaged, representing worst-case draw during loud sound processing. A device drawing well above its rated current, especially at quiescent, no-sound conditions, points to a hardware fault such as a shorted component or a failing wireless radio, rather than normal use, and explains a pattern of batteries dying in days rather than weeks.

IEC 60118: The International Counterpart

Outside the United States, hearing aid electroacoustic testing is governed by the IEC 60118 series (Electroacoustics – Hearing Aids), published by the International Electrotechnical Commission. IEC 60118-0 covers the broader research-and-development frequency range of 200 Hz to 8,000 Hz. Since a 2022 revision folded the former production-test standard, IEC 60118-7, into it, IEC 60118-0 now also serves the narrower production-QC range of 200 Hz to 5,000 Hz that closely parallels ANSI S3.22. The two standards have been deliberately harmonized so that a device tested to one framework produces results consistent with the other, which matters for internationally distributed hearing aids and for candidates who may encounter manufacturer spec sheets referencing either standard.