Evaluation of the improvement in hearing Japanese speech while wearing earplugs advertised as enabling communication

Workers often refuse to wear earplugs because of the difficulty hearing conversations in noisy workplaces. Little research has been performed to explore whether multiple syllables of the Japanese language are difficult to hear through earplugs. New earplugs recently became available that could be used to communicate clearly in noisy workplaces and simultaneously prevent personal noise exposure. This study aimed to evaluate the hearing of speech using three types of earplugs in a noisy environment. The subjects were 10 people without hearing loss. We conducted this experiment in the anechoic room at the University of Occupational and Environmental Health, Japan. We set up a pink noise environment at 80 dBA, 85 dBA, and 90 dBA, and evaluated the hearing of speech with and without earplugs. The subjects were asked to distinguish standard Japanese words comprising two syllables recorded on a CD-ROM (TY-89) established for the evaluation of the fitness of hearing aids. If the speech level required for 90% inte...