Lombard Effect

The Lombard effect is the involuntary tendency of speakers to increase their vocal effort in response to increasing background noise. Named after Étienne Lombard in 1911, the typical response is a 3–6 dB increase in voice level for every 10 dB increase in background noise. This creates a positive feedback loop in occupied spaces: as more people talk, noise levels rise, causing everyone to talk louder, further increasing noise. The Lombard effect is a major challenge in restaurants, open-plan offices, classrooms, and social venues. Acoustic design strategies to mitigate the Lombard effect include reducing reverberation time (less noise buildup), introducing sound masking (raising the threshold below which speech is detectable), and increasing absorption to reduce the overall reverberant sound level. Understanding the Lombard effect is essential for predicting realistic occupied noise levels, which can be 10–20 dB higher than unoccupied background levels.