The Effect of the Frequency and Energetic Content of Broadband Noise on the Lombard Effect and Speech Intelligibility

The Lombard effect is an unconscious reflex of speakers to increase vocal effort when disturbed by noise, aiming to enhance speech intelligibility. This study aims to evaluate the effect of noise with different energetic content and levels at various frequencies on the Lombard effect, communication disturbance, vocal comfort, and speech intelligibility. Twenty university students participated in the study, reading a six-sentence excerpt and performing an intelligibility test under 12 randomized noise conditions. These conditions included noises at low (20–500 Hz), medium (500–4000 Hz), and high frequencies (4000–20,000 Hz), at four levels (45 dB, 55 dB, 65 dB, 75 dB). After each condition, participants rated their perceived communication disturbance and vocal discomfort. The results indicated that noise with energetic content at medium frequencies produced the highest Lombard effect, produced the most detrimental effect on communication disturbance and vocal comfort, and caused the strongest decrease in speech intelligibility, whereas it was minimally affected by low- and high-frequency noise. In conclusion, this study highlights that medium-frequency noise has the greatest impact on vocal effort, communication disturbance, and vocal comfort, while low- and high-frequency noise has minimal effect on speech intelligibility.