In their recent "Community Newsletter" for the 1 Golden Lane project, Midgard present the following table:
On the face of it these sound levels look fine, you'd think. But look closer. Midgard are giving measures using LAeq10 Hours in plain old dB ... this is about the best way to hide noise nuisance while coming across as all clever and technical. But ...
LAeq (Equivalent Continuous Sound Level) is a flawed measure of sound nuisance which hides problematic peaks by averaging sound energy over long periods. The LAeq 10h measure used by Midgard averages over 10 hours, no doubt including the “Reduced impact hours” in the average.
Limitations of LAeq in more detail:
- Focuses on average energy: LAeq simply averages the sound pressure level over a specific time period. This doesn't account for fluctuations in the sound, which can be crucial for human perception of nuisance. A constant sound at a specific LAeq might be less bothersome than the same average level with frequent peaks or variations. The 1 Golden Lane work involves relatively brief bursts of extremely loud noise.
- Ignores frequency content: LAeq doesn't consider the frequency makeup of the sound. High-frequency sounds are generally perceived as more annoying than low-frequency sounds at the same LAeq level. For example, traffic noise with a lot of high-pitched engine sounds might be more bothersome than constant low-frequency hum from ventilation even if they have the same LAeq. The noise produced by the power tools in use on the 1 Golden Lane site is often of a high piercing frequency.
- Doesn't capture temporal aspects: LAeq doesn't consider how the sound changes over time. Sounds with sudden loud bursts or those that occur at night can be more disruptive than sounds with the same LAeq that are spread out evenly. Some of the noisiest work on the 1 Golden Lane site seems to be saved for the very start and very end of the permitted work times.
- Lmax: This metric measures the maximum sound pressure level during a specific period. It's a good way to identify potential for sudden loud noises that might be startling or disruptive.
- Leq,n: This metric represents the equivalent continuous sound level for specific time intervals within the measurement period (e.g., Leq,1h for hourly levels). It provides a more detailed picture of how sound levels fluctuate over time.
- Frequency weighting: Weighting scales like A-weighting (dBA) and C-weighting (dBC) prioritize frequencies that humans perceive more readily. This helps provide a better understanding of how annoying a sound might be.
