The L90 statistical descriptor in noise measurement is primarily used to represent
- AThe maximum peak noise recorded during the interval.
- BThe average energy level of the noise.
- CThe background or ambient noise level.Correct
- DThe impulsive noise from construction activities.
Solution
Concept
Background ambient noise metric L90
Formula
NONE
Step-by-step solution
1. Statistical noise levels (Lx) indicate the sound pressure level exceeded for x% of the total measurement interval. 2. L10 denotes peak or traffic noise, as it is exceeded only 10% of the time. 3. L50 represents median noise level (exceeded 50% of the time). 4. L90 represents the level exceeded 90% of the time, capturing continuous residual background or ambient noise between intrusive events. Answer: C
Explanation
In environmental acoustic surveys, statistical percentiles denote noise levels exceeded for specific percentages of observation time. The L90 descriptor signifies the sound pressure level exceeded during 90% of the monitoring duration, functioning universally as the benchmark metric for residual or ambient background noise in an area.
Why the other options are wrong
A) Maximum peak noise recorded during an interval is designated by Lmax or L1. B) Average acoustic energy level integrated over time is designated as Leq (equivalent continuous sound level). D) Impulsive construction noise occurs sporadically and is characterized by L10 or peak impact metrics.
Shortcut
L10 = Peak noise (10% exceeded); L50 = Median noise; L90 = Background/ambient noise (90% exceeded).
Common mistake
Mistaking L90 for 90% of maximum peak noise rather than 90% time exceeded.
Correct answer: C) The background or ambient noise level.