Knowledge Centre · Understanding Noise
What is LA1?
LA1 can be thought of as the noise level exceeded for 1% of the measurement period — one of the most commonly used descriptors for assessing the loudest recurring noise levels.
Read time
2 minutes
Relevant to
Anyone reading a noise report or condition
What LA1 stands for
LA1 stands for: A-weighted Noise Level Exceeded for 1% of the Measurement Period.
Fortunately, it is much simpler than it sounds.
LA1 can be thought of as the noise level that is exceeded for only 1% of the measurement period. It is commonly used to describe the loudest recurring noise levels rather than a single maximum event.
A changing sound level, focusing on the loudest periods
Most environmental noise is constantly changing. A truck passes, then a quieter car, then perhaps a motorcycle. The noise level rises and falls throughout the measurement period.
LA1 identifies the noise level that is exceeded for only 1% of the time. Rather than recording the single loudest event like LAmax or averaging all noise levels like LAeq, LA1 represents the highest recurring noise levels during the measurement period.
If you measured traffic noise over one hour and recorded an LA1,1hour of 76 dB(A), this means the noise level exceeded 76 dB(A) for only 1% of that hour—approximately 36 seconds. It represents the louder traffic events that occurred during the measurement period.
Where LA1 is used
LAeq is one of the most commonly used noise descriptors in environmental acoustics and is used extensively for:
- Road traffic noise – assessing the louder traffic movements on busy roads.
- Environmental noise assessments – where planning policies or approval conditions require assessment of intrusive or higher-level noise.
- Industrial noise – assessing intermittent plant or machinery operating at higher noise levels.
- Mining operations – evaluating louder operational activities that occur throughout a shift.
- Community noise investigations – assessing noise that is regularly experienced rather than isolated peak events.
Related reading
Try the calculator
See how multiple sound levels combine logarithmically, not by ordinary addition.
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