Measurements · Noise
Max Level (Lmax)
Also known as maximum noise level
Maximum sound level over the interval.
What it is
What is Lmax (maximum sound level)?
Lmax is the highest time-weighted sound level reached during a measurement period. As noise rises and falls, the meter tracks the level with a chosen time weighting (Fast or Slow), and Lmax records the loudest value that weighted level reached. It is almost always A-weighted, so it is written LAFmax or LASmax to show both the frequency and time weighting, because the same event yields a higher Lmax under Fast than under Slow. Lmax is not the true instantaneous peak sound pressure; that is a separate metric, Lpeak, measured without any time weighting.
Where Leq captures the average energy over a whole period, Lmax captures the single loudest moment within it. The two answer different questions about the same noise.
Band resolution: reported broadband plus 1/1 octave and 1/3 octave. The metric and its frequency band are independent. Check the sound-capable devices below for what each one reports.
Health and operational effects
Single loud events are what wake people at night and provoke complaints, even when the average level over the night is modest. A truck reversing, a door slamming, a dog barking, or an aircraft passing can each produce a brief peak that disturbs sleep or startles people, and Lmax quantifies these events. For this reason many night-time noise conditions and planning limits are written against a maximum-level criterion in addition to an average, guarding specifically against the loudest occurrences rather than the overall exposure.
For a site operator or event organizer, Lmax is therefore the metric that governs individual disruptive events, complementing the Leq that governs cumulative impact.
Limits
Max Level (Lmax) Limit Values
The published values, by averaging period; each links to the standard that sets it.
Ceiling (at any time)
- MSHA noise 115 dBA: without adjustment for hearing protectors
Lmax is reported in decibels, normally dB(A), with its time weighting stated. Interpret it as the loudest single event in the period, not a running average: one exceptional pass-by can set the Lmax for a whole night without much affecting the Leq. Nighttime and event limits are frequently expressed as a maximum level not to be exceeded, and the applicable values appear in the limit table on this page. Read Lmax together with Leq so that both the peaks and the overall exposure are assessed.
How it is measured
How Max Level (Lmax) Is Measured
Lmax is derived by a sound level meter built to the IEC 61672 standard, which continuously tracks the time-weighted level and holds the highest value reached over the logging interval. Because full acoustic assessment needs more than the built-in metrics of an ambient sensor, precision Lmax measurement uses an external IEC 61672 Class 1 or Class 2 instrument logged on a Thiamis gateway, reporting Lmax alongside the anchor metric Leq and related values such as Lpeak and the statistical levels. The time weighting must be recorded with the value, since Fast and Slow give different maxima.
An instrument on Thiamis1
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing noise monitors
For environmental Lmax monitoring the microphone is placed at the affected receptor or the site boundary, at a standard height, clear of reflecting surfaces, and fitted with a windshield. Wind gusts across the diaphragm can register as false maxima and are a common cause of spurious Lmax readings. Continuous unattended logging is important because the significant events are unpredictable and short, so the monitor must be watching whenever they occur to catch the true maximum rather than a value from a brief attended survey.
Every device and option that measures Max Level (Lmax) 1
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 TSI · SP-SE-1, SP-SE-1-1/1, SP-SE-1-1/3… | Noise Monitors | Thiamis |
Where it is monitored
Solutions That Monitor Max Level (Lmax)
Each one links to the solution page showing what that industry measures it for.
Noise Monitoring
Often addedEnvironmental and occupational sound levels
Perimeter Monitoring
Often addedSite boundary dust, silica, and noise compliance
Related
More in Noise
Questions
Max Level (Lmax) FAQ
What is the difference between Lmax and Lpeak?
Lmax is the highest time-weighted level, measured with a Fast or Slow time constant, while Lpeak is the true instantaneous peak sound pressure measured with no time weighting at all. Lpeak is always higher and is used for sudden impulsive noise and hearing-damage risk, whereas Lmax characterizes the loudest sustained moment of an event.
How does Lmax differ from Leq?
Leq is the energy-average level over the whole period; Lmax is the single loudest time-weighted level within it. A quiet night with one loud truck pass can have a low Leq but a high Lmax, which is why nighttime limits often specify both.
Why does the time weighting matter for Lmax?
Because Fast responds more quickly than Slow, it captures brief rises that Slow smooths over, so the same event gives a higher LAFmax than LASmax. The weighting is therefore always stated with the value, and the correct one depends on the standard or condition being assessed.
How do I monitor Lmax?
Full acoustic metrics beyond the built-in Aethair sound reading need an external IEC 61672 sound level meter on a Thiamis gateway, logging Lmax continuously alongside Leq. Use the configurator to combine noise with dust and the other parameters your site permit requires you to monitor.
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