In 2026, 151 of 287 audiometers arrived with an earphone output outside the calibration tolerance

How far outside tolerance were they?

The median audiometer’s largest deviation was 4.2 dB, and the 90th percentile was 10.9 dB. Deviation is measured minus target at each ear and test frequency before any adjustment, and the largest absolute value per audiometer is used. Readings above 40 dB were treated as measurement artifacts and dropped.

Which frequencies and which ear were most often outside tolerance?

500 Hz, at 21.3% of points. The right ear was outside tolerance more often than the left: 17% (378 of 2,221 points) against 13.2% (293 of 2,214 points).

Each point is one ear at one frequency. 250, 750 and 1500 Hz were measured only on some older units and are not shown.

Did audiometers calibrated about a year apart still arrive outside tolerance?

Often. Of 143 audiometers calibrated 300 to 430 days after a prior Foster calibration, 73 (51%) arrived with at least one point outside tolerance. The earlier calibration was issued as verified within tolerance, but its as-left values were not re-checked for this comparison, so this is not a measured drift rate.

What tolerance limits were used?

OSHA 29 CFR 1910.95 Appendix E sets 3 dB at 500 to 3000 Hz, 4 dB at 4000 Hz and 5 dB at 6000 Hz. Beyond a limit, the appendix says an exhaustive calibration is advised. It is not a pass or fail test, and the appendix makes an exhaustive calibration required at deviations of 15 dB or greater. The 8000 Hz limit of 5 dB comes from ANSI S3.6, not OSHA.

Did the test rooms measured at calibration exceed OSHA Table D-1 levels?

No 1/3-octave reading did. Of 328 calibrations with a usable room reading, none showed a reading above the Table D-1 level at 500, 1000, 2000, 4000 or 8000 Hz. The median A-weighted room level was 32.5 dBA and the 90th percentile was 42.3 dBA.

This is not a compliance finding. Table D-1 in Appendix D sets octave-band limits (40 dB at 500 Hz, 40 dB at 1000 Hz, 47 dB at 2000 Hz, 57 dB at 4000 Hz, 62 dB at 8000 Hz) for readings taken with specified sound level meter and filter equipment, and the calibration certificate reports 1/3-octave readings. A 1/3-octave reading under the limit does not show the octave band is under it. Summing the 1/3-octave bands into octave bands gives an estimate above Table D-1 in at least one band for 8 of 328 (2.4%) of these calibrations. The room readings come from calibrations dated 2025 (133), 2026 (186) and earlier years (9), and the certificate does not record the measurement conditions.

What this data is and is not

• It covers Foster customers only, mostly in the Ohio, Kentucky and Indiana region plus mail-in units.
• It is not a national sample and does not estimate how many audiometers in use are outside tolerance.
• The as-found results cover 2026 calibrations only. There is no year-over-year trend.
• As-found readings were recorded on 287 of the 437 audiometers in the records.
• Output level is the only measurement counted. Distortion, attenuator linearity and tone timing are not included.
• Every audiometer was adjusted and verified within tolerance before it left Foster.

How to cite this

Foster Special Instruments. “2026 audiometer calibration findings.” Foster Instruments, published 2026-11-10. https://fosterinstruments.com/research/audiometer-calibration-findings-2026