Type 0, Type 1, and Type 2
ANSI S1.4, "Specifications for Sound Level Meters", sets performance and accuracy tolerances at three levels of precision:
- Type 0: used in laboratories.
- Type 1: precision measurements in the field, accurate to ±1 dBA. Oregon OSHA prefers it for readings used to design noise controls.
- Type 2: general-purpose measurements, accurate to ±2 dBA. It is the most widely used meter for workplace evaluations and the minimum precision Oregon OSHA accepts for noise measurements.
Because of that ±2 dBA tolerance, Oregon OSHA only counts an overexposure measured with Type 2 equipment when the 8-hour average is at least 2 dBA over the limit.
Class 1 vs Class 2 in IEC 61672
Many meters state a class from the international standard IEC 61672-1 instead of an ANSI type. It has two performance categories, class 1 and class 2. The acceptance limits for class 2 are the same as or wider than those for class 1, so class 1 is the stricter grade.
A meter that names neither a type nor a class has not been shown to meet either standard.
Time-Weighting, Integrating, and Dosimeters
IEC 61672-1 covers three kinds of sound level meter:
- Time-weighting meters show the level as it changes, smoothed by a fast or slow time weighting.
- Integrating-averaging meters give the average level over a measurement period.
- Integrating meters give the total sound exposure over the period.
Oregon OSHA notes that meters set to integrate or average sound don't use the fast or slow time constant: they sample many times per second.
A noise dosimeter is worn by the worker. Its microphone clips near the ear, on the shoulder or lapel, and the meter clips to the belt. It averages exposure over the shift and reports an 8-hour average or a percentage of the permissible limit. Most dosimeters have the accuracy of a Type 2 meter, and Oregon OSHA calls the dosimeter the primary instrument for compliance measurements. Oregon OSHA sets them up with a 5 dB exchange rate, A-weighting, the slow response, and a threshold of 80 dBA for hearing conservation or 90 dBA for noise controls.
Octave Band Analyzers
An octave band analyzer splits a sound into frequency bands and measures the level in each one. It attaches to a Type 1 meter or is built into it. Knowing which frequencies dominate helps choose the materials that will block a noise best.
Phone Apps and Unrated Meters
Some meters meet neither the Type 1 nor the Type 2 requirements. Oregon OSHA says these modestly priced meters are useful for finding noisy places and tracking improvements, but they can't document compliance. It says the same of smartphone apps: a rough estimate of the noise level, not a compliance reading.
For everyday checks, the decibel meter on this site runs in your browser. See how accurate a phone decibel meter is and how calibrating it helps.
Calibration
Every Type 1 or Type 2 meter and dosimeter needs two kinds of calibration, according to Oregon OSHA:
- Periodic factory calibration every 12 months, with a certificate. The acoustic calibrator itself also needs calibrating every year.
- A check with the calibrator before and after each use, for example at 114 dB at 1,000 Hz, recorded each time.
Its manual names a weak battery as the most common reason a meter fails its pre- or post-use check.
Which Type to Use
- A quick check at home, at a concert, or in a classroom: a phone meter gives an estimate.
- A noise complaint or regular checks at work: a Class 2 handheld meter. Our guide to handheld sound level meters compares three.
- Workplace compliance: a Type 2 or better meter, or a dosimeter for a full shift. The workplace noise meter shows how long a level is safe while you decide.
- Designing noise controls: a Type 1 meter with an octave band analyzer.
For what the A in dBA means and when to switch weightings, see what dBA is.