How Often Must an Audiometer Be Calibrated?

How often does an audiometer need calibration?

An audiometer used for OSHA hearing conservation testing needs calibration checks at three different intervals: a functional (biological) check before use each day it's used, an annual acoustic calibration at least once a year, and an exhaustive calibration whenever the annual acoustic check reveals problems the instrument can't be adjusted to correct, or after any event that could have damaged the instrument — a hard drop, transport damage, or a failed functional check that a simple adjustment doesn't fix. Skipping any of these three isn't just a maintenance lapse; 29 CFR 1910.95 requires the audiometric test record to state the date of the instrument's last acoustic or exhaustive calibration, so a lapsed calibration invalidates the paperwork for every test run on that instrument.

What is a daily functional (biological) check?

Before an audiometer is used each testing day, the operator runs a quick biological check: a known-hearing person listens through the earphones at each frequency the device tests, at a low hearing level, and confirms the tones are audible, clear, and free of distortion, and that the attenuator dial and talk-back circuit work correctly. This isn't a formal calibration — it doesn't require reference equipment — but it catches gross failures like a dead earphone or a stuck dial before a technician tests dozens of employees on a broken instrument and has to retest all of them.

What is annual acoustic calibration?

Once a year, the audiometer's output at each test frequency is checked against a calibrated reference (a sound level meter and artificial ear or coupler) to confirm actual output matches the dial reading within the tolerance set by ANSI S3.6, the American National Standard for audiometers. This check catches drift that a functional check can't — an instrument can sound fine to the ear and still be off by several decibels at a specific frequency. Results and adjustments get logged, and that log date is what goes on the employee's audiometric record per 1910.95.

When is exhaustive calibration required?

Exhaustive calibration is a full electroacoustic evaluation against ANSI S3.6 specifications — checking not just output level but linearity, frequency accuracy, harmonic distortion, and attenuator function across the full range. It's required when the annual acoustic check shows the instrument is out of tolerance and can't be brought back into spec with a simple adjustment, after any repair, or on whatever multi-year interval (commonly every two years) a program has set as a baseline regardless of interim results. An instrument that fails exhaustive calibration standards gets taken out of service, not patched.

Check type	Frequency	What it verifies
Functional (biological)	Each day of use	Audible, clear tones at each frequency; dial and controls work
Annual acoustic	At least once per year	Output level accuracy vs. ANSI S3.6 tolerance at each frequency
Exhaustive	After failed acoustic check, repair, or set multi-year interval	Full electroacoustic spec: level, linearity, distortion, attenuator

What does Foster's annual acoustic calibration visit involve?

A Foster cal tech brings a reference sound level meter and coupler to the customer's audiometer rather than shipping the unit out, so the instrument is back in service the same day. The tech runs each test frequency through the coupler, compares actual output to the dial reading at each step, and checks attenuator linearity across the range rather than just spot-checking one or two frequencies. Any frequency reading outside ANSI S3.6 tolerance gets adjusted on the spot if it's a routine drift; if the unit needs parts or shows distortion the field kit can't fix, it goes back to the shop and the customer gets a loaner audiometer so scheduled annual testing doesn't slip. The tech leaves a dated calibration certificate that lists every frequency checked, which is the document that has to match the date printed on each employee's audiometric record.

What causes an audiometer to fail calibration that a daily check misses?

The most common failure a functional check can't catch is gradual output drift at one or two specific frequencies — the tones still sound clear to a listener, but the actual decibel output at, say, 4000 Hz has crept several dB off the dial reading over months of use. Earphone cushions that have hardened or lost their seal are another quiet failure mode: they don't sound obviously wrong but change the acoustic coupling enough to shift readings. Transport damage is the third common cause, especially for units that travel between job sites in a vehicle without a hard case — a dropped audiometer can pass a same-day functional check and still be out of spec on the next acoustic calibration.

Frequently Asked Questions

What standard governs audiometer calibration tolerance?

ANSI S3.6, the American National Standard Specification for Audiometers, sets the accuracy tolerances that annual and exhaustive calibration are checked against.

Does a missed annual calibration invalidate audiograms taken that year?

It creates a recordkeeping and defensibility gap — 1910.95 requires the calibration date on the audiometric record, and testing on an instrument past its calibration due date is difficult to defend if a threshold shift determination is later challenged.

Can the same technician who tests employees also run the functional check?

Yes — the daily functional check is designed to be run by the testing technician as a quick pre-use verification, not a separate certified calibration event.

Foster Special Instruments performs audiometer calibration to ANSI S3.6 and supports on-site hearing testing programs. For the full 1910.95 program requirements, see the OSHA hearing conservation checklist.