Published on August 25, 2026 at 10:37 AM
A sound level meter doesn’t really measure sound. It measures a voltage that a microphone has produced from a change in air pressure — and how much voltage comes out depends on the condition of that microphone. A diaphragm that is exposed to humidity, dust, temperature swings and the occasional knock will not deliver the same reading for the same sound year after year.
That is why a serious noise measurement doesn’t begin with measuring, but with a known tone on the microphone.
What It’s About
An acoustic calibrator for checking and calibrating sound level meters.
- Generates 1 kHz at 94 dB
- Accuracy ±0.8 dB, frequency accurate to 5 percent
- For sound level meters with 0.5- and 1.0-inch microphones
- Battery test with status LED
- Rugged die-cast aluminum housing
- NIST certificate, five weeks lead time
Why 94 dB and 1 kHz in Particular
Both numbers are chosen, not found. The decibel scale for sound is referenced to 20 micropascals, the threshold of hearing. Calculating from there, a sound pressure of exactly one pascal corresponds to 94 dB. The calibrator therefore doesn’t produce an arbitrarily loud tone, but a physically round pressure — one pascal, directly at the microphone.
And 1 kHz is the point where the weighting curves pass through zero. The A-weighting used to assess noise in the workplace is defined so that it neither boosts nor attenuates at 1 kHz. The calibration is therefore unaffected by which weighting is set on the instrument — a detail that rules out an entire class of errors.
Why the Check Belongs in the Field
An acoustic calibrator checks the entire chain. The stimulus is sound, so it passes through the microphone, preamplifier, cable and meter — exactly the path the actual measurement takes. An electrical test signal generator would bypass the microphone and thus leave out precisely the component most likely to change.
That is why the check is performed before and after the measurement series. The check beforehand shows that the chain was correct. The check afterward shows that it stayed that way. If the two differ, you know the data in between is questionable — and that is far better than not knowing. For measurements documented for the assessment of noise exposure, this double check is the customary expectation anyway.
The microphone size is part of the definition. The calibrator couples to a cavity around the microphone capsule, and the size of that cavity affects the level generated. A half-inch microphone in an adapter for one inch therefore does not give the same value — and the error looks perfectly inconspicuous.
The battery test is not an accessory. A weak battery lowers the level generated without anything else indicating it. You would then adjust the meter to a wrong reference value — and subsequently every measurement of the day would be off by the same amount.
Three Typical Applications
- Occupational safety: Noise exposure measurements that are documented and, where necessary, challenged.
- Environmental noise: Measurements at facilities, construction sites and immission points with reporting obligations.
- Maintenance of measuring equipment: Regular functional checks of multiple sound level meters in your own inventory.
Why It Pays Off
A noise measurement is rarely made because someone is curious. It is made because a decision depends on it: hearing protection, operating hours, an investment in insulation, sometimes a dispute. That is exactly when the other side’s first question is whether the instrument demonstrably read correctly.
Without a calibration record, the measurement series is just an assertion, and the only remedy is to repeat it — with all the effort and lost time that entails. A calibrator costs a fraction of that repetition and makes it unnecessary.
