Audiometer Exhaustive Calibration: What ANSI S3.6 Actually Tests

An audiometer that passes its daily functional check and even its annual acoustic calibration can still be quietly out of spec in ways neither check is designed to catch. Exhaustive calibration exists for exactly that gap. It's a full electroacoustic workup against ANSI S3.6, and understanding what it actually measures explains why it's required on a schedule, not just when something obviously breaks.

What is exhaustive calibration checking that annual calibration doesn't?

Annual acoustic calibration confirms the audiometer's output level at each test frequency is within tolerance of a calibrated reference, using a sound level meter and coupler. Exhaustive calibration goes further, evaluating the instrument's internal circuitry and signal integrity in ways that a simple output check can miss entirely. An audiometer can produce a correct output level at 1000 Hz and still have a faulty attenuator that doesn't step down linearly, or crosstalk between channels that contaminates a masked threshold in the ear not being tested. Neither of those problems shows up on an annual spot-check of output levels, which is why OSHA's Appendix E schedule requires the deeper exhaustive check on its own separate interval.

What specific parameters does an exhaustive calibration measure?

A full ANSI S3.6 exhaustive calibration covers a defined list of electroacoustic properties, not a single pass/fail output check. It typically includes attenuator linearity across the tested range, frequency accuracy at each test tone, total harmonic distortion, rise and fall time and overshoot for the tone envelope, off-level and crosstalk between the left and right transducers, channel mixing error, and speech signal-to-noise ratio for instruments with speech testing capability. Each of these has a defined tolerance in the standard. Attenuator accuracy, for example, is generally required to fall within about 1.2 dB across the levels tested, frequency accuracy within roughly plus or minus 1 percent, and total harmonic distortion below about 2.5 percent for the pure tone signal.

Parameter	What it catches	Typical tolerance
Attenuator linearity	Uneven or non-linear steps in hearing level dial settings	Roughly 1.2 dB across tested levels
Frequency accuracy	Test tones drifting off their labeled frequency	Roughly plus or minus 1 percent
Harmonic distortion	Unwanted overtones distorting the pure tone signal	Below roughly 2.5 percent
Crosstalk / off-level	Signal bleeding into the non-test ear, corrupting masked thresholds	Standard-defined isolation limit
Rise/fall time and overshoot	Tone envelope shape that can cause a click artifact or false response	Standard-defined envelope timing

Why does this level of detail matter for a hearing conservation program?

Every one of these parameters can produce a wrong threshold without the operator or the employee noticing anything unusual during the test. A misbehaving attenuator can make an employee's actual threshold appear several decibels better or worse than it is, which matters directly for standard threshold shift determinations under a hearing conservation program. Crosstalk between channels can produce a false response in the non-test ear during masked testing, muddying a result that's supposed to isolate one ear's hearing. Because none of these failures are visible from the audiogram printout alone, the only way to catch them is the periodic exhaustive check itself, not a review of test results after the fact.

When is exhaustive calibration required outside the normal schedule?

Beyond the routine interval, commonly every two years for audiometers not used in mobile test vans, exhaustive calibration is triggered whenever the annual acoustic calibration shows a deviation the instrument can't be brought back into tolerance with a simple adjustment, or after any event that could plausibly have affected internal calibration, such as a hard drop, shipping damage, or an internal repair. An audiometer that has been serviced or had a component replaced should get an exhaustive calibration before returning to use, since a repair that fixes one output-level complaint can introduce a new problem in attenuator linearity or crosstalk that a quick spot-check won't reveal.

How Foster performs exhaustive calibration

Foster runs exhaustive calibration against ANSI S3.6 on industry-standard ACS calibration hardware and software, checking the full parameter list rather than stopping at output level once a unit is on the bench. We're a CMI authorized distributor and service center and our technicians are trained by CMI on the instruments we work on most, which matters here because attenuator and crosstalk failures often trace back to a specific model's known wear points rather than a generic fault. When a client's audiometer comes in for annual service and the output check shows a deviation we can't correct with adjustment, we move straight to the exhaustive workup rather than sending it back into service on a partial fix. Our calibration program tracks each unit's exhaustive interval separately from its annual date, so a client isn't relying on memory to know which check is due next. For the room side of the same compliance picture, see our related post on audiometer calibration and ANSI S3.1 booth requirements.

Frequently asked questions

Can an audiometer pass its annual acoustic calibration and still fail exhaustive calibration?

Yes. Annual acoustic calibration checks output level at each frequency against a reference. Exhaustive calibration checks additional parameters, such as attenuator linearity, crosstalk, and harmonic distortion, that an output-level check alone doesn't evaluate, so a unit can pass one and fail the other.

Does a repaired audiometer need exhaustive calibration even if it wasn't due yet?

A repair or component replacement is generally treated as its own trigger for exhaustive calibration, independent of the routine interval, since a fix addressing one symptom can affect other parameters the repair wasn't targeting.

What tolerance does ANSI S3.6 set for attenuator linearity?

Attenuator accuracy is generally required to stay within about 1.2 dB across the range of levels tested, though the exact figure depends on which edition of the standard a given audiometer is certified against.

How often does exhaustive calibration need to happen?

The common baseline is at least every two years for audiometers not used in mobile test vans, on top of triggers like a failed annual check or a repair, per OSHA's Appendix E calibration schedule under 1910.95.

Sources

• 29 CFR 1910.95 Appendix E, Calibration of audiometers (OSHA)
• Audiometer calibration requirements of the Hearing Conservation Amendment (OSHA standard interpretation, 1983)
• Have You Checked Your Audiometer Today? (CAOHC)

Foster Special Instruments provides audiometer calibration to ANSI S3.6, on-site and mail-in, across Ohio, Kentucky, Indiana, Illinois, and Michigan, plus hearing conservation testing and technician training. Schedule your next calibration.