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What Is a Sound Level Meter?

A sound level meter measures sound pressure and reports it in decibels, usually A-weighted to match hearing. The class of the meter, its weighting and its time response decide whether the number means anything against a noise limit.

By the Akermin Editorial Team · 3 min read

A sound level meter measures sound pressure with a calibrated microphone and reports it in decibels. It applies a frequency weighting (usually A, to mimic hearing), a time response (fast or slow), and on better meters an integrating function that averages energy over a period (Leq). Meters are built to IEC 61672 as Class 1 or Class 2, which defines how accurately they must read across frequencies. That standard is what separates a measurement that can be compared with a noise limit from a number on a phone screen.

What it measures

Sound pressure level (SPL) in decibels relative to 20 micropascals, the threshold of hearing. The scale is logarithmic: +10 dB is ten times the sound energy and roughly twice the perceived loudness; +3 dB is double the energy and barely noticeable. Typical values: a quiet bedroom 30 dBA, conversation 60 dBA, a vacuum cleaner 70 to 75 dBA, a busy road 80 dBA, a chainsaw 100 to 110 dBA.

The parts that matter

  • Microphone. A condenser capsule with a flat response. Cheap meters use electret capsules with more variation.
  • Weighting. A-weighting follows the ear’s sensitivity and is used for almost all limits; C-weighting is nearly flat and is used for peak levels and low-frequency noise. See what dBA means.
  • Time response. Fast (125 ms) follows fluctuations; slow (1 s) smooths them. Limits specify which.
  • Integration. Leq is the constant level with the same energy as the fluctuating sound over a period; it is the basis of workplace exposure limits. Lmax, Lmin and percentiles (L90 for background) are related statistics.
  • Range. Typically 30 to 130 dB; some meters switch ranges.
  • Calibration. An acoustic calibrator (a 94 or 114 dB reference tone at 1 kHz) checks the meter before and after a measurement session. Class 1 and 2 meters accept one; many consumer meters do not.

Class 1 and Class 2

Class 1 Class 2
Tolerance at 1 kHz ±1.1 dB ±1.4 dB
Frequency range with stated tolerance 16 Hz to 16 kHz 20 Hz to 8 kHz
Required for Environmental noise, legal evidence, research Workplace noise surveys, general checks
Cost High Moderate

Consumer meters that do not claim a class are unclassified; treat their readings as indicative. Meters such as the Extech SL510 state Class 2 and accept a calibrator.

Common uses

  • Workplace noise exposure against 85 dBA daily limits.
  • Checking HVAC, generators and pumps against equipment specifications.
  • Neighbor and venue noise complaints, where Class 1 and a calibration record are usually needed.
  • Home theaters and studios, where a meter sets speaker levels.
  • Sleep and study environments, where a logging meter shows what a night sounds like.

Measuring properly

  1. Calibrate with an acoustic calibrator before and after.
  2. Hold the meter at arm’s length or on a tripod, microphone toward the source, away from walls and your body.
  3. Use the weighting and response the limit specifies, usually A and slow or Leq.
  4. Measure long enough to capture the pattern; a 15-minute Leq for steady noise, longer for intermittent.
  5. Record background level with the source off.

Sound meters appear alongside anemometers and light meters in multifunction environmental instruments; see the environmental monitoring category.

Extech SL510 Sound Level Meter, 35-130 dB, Class 2

Extech SL510 Sound Level Meter, 35-130 dB, Class 2

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Decibel Meter, TopTes TS-501B Sound Level Meter with 2.25” Backlit LCD Screen, Portable SPL Tester with A/C Weighted, Range 30-130dB, MAX/MIN, Data Hold, Use for Home, Noisy Neighbor, Factory - Orange

Decibel Meter, TopTes TS-501B Sound Level Meter with 2.25” Backlit

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

What is the difference between a Class 1 and Class 2 sound level meter?

Both follow IEC 61672. Class 1 has tighter tolerances across a wider frequency range and is required for legal and environmental measurements; Class 2 is accepted for general workplace and screening use.

Is a phone app as good as a sound level meter?

No. Phone microphones are not calibrated, roll off at low and high frequencies, and vary between models. Apps can indicate roughly loud versus quiet; they cannot support a measurement against a limit.

What does dBA mean?

Decibels with A-weighting, a filter that reduces low and very high frequencies the way human hearing does. Nearly all noise limits are in dBA.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.