Changes on Speech Transmission Characteristics by Types of Mask

Purpose: Given the increased levels of fine and ultrafine dust, as well as the spread of COVID-19, current opinion is that most people will wear a face mask such a KF94 mask for a long time. To test speech transmission through the face masks, various types of masks including dust masks available in the market at the time of the study were tested under laboratory conditions. Methods: Fourteen types of masks worn on a head and torso simulator (HATS) and test signals were played on a speaker installed in the mouse position of the HATS. Speech Transmission Index (STI) and the speech level in the octave band were measured at distances of 1 m and 2 m. Results: STI at a distance of 2 m was decreased to 3.4-5.7% and speech levels in the octave band at 4 kHz or higher were also decreased when wearing disposable masks and a cotton mask. KF80 and KF94 masks showed decreased STI similar to those of disposable masks; however, a decrease in the speech level was observed at the octave bands of above 2 kHz. Dust masks and single-cartridge half-face respirators showed approximately 11.2% and 33.7% to 39.3% decreases in STI levels, respectively. Conclusion: When wearing masks, STI and the speech level was decreased in the high-frequency bands. However, speech level differences at high frequencies may be related to the increased voice level of the speaker and the understanding of consonants with the masks for several hours in living and working environments.