The effects of parametric speaker sound on salivary hormones and a subjective evaluation.

OBJECTIVE Recently, a parametric speaker system has been developed. However, the safety of the parametric speaker for the human body has not yet been demonstrated. Therefore, we studied the effects of parametric speaker sound on salivary hormones and carried out a subjective evaluation. METHODS Nine male subjects participated in this study. They completed three consecutive sessions: a 20-min quiet period as a baseline, a 45-min mental task period with either a general or parametric speaker, and a 20-min recovery period. The subjects were evaluated by the salivary cortisol and chromogranin A (CgA) concentrations. In addition, they took the Kwansei-Gakuin sleepiness scale (KSS) test before and after the task and also a sound quality evaluation test after it. Two experiments, one with a general speaker (general condition) and the other with a parametric speaker (parametric condition), were conducted at the same time of day on separate days. To examine the effects of the parametric speaker, a two-way repeated measures ANOVA (speaker factor and time factor) was conducted. RESULTS The results showed that the cortisol concentration was significantly lower during the parametric condition than during the general condition. Furthermore, the sound quality evaluation found a "warm" sensation during the parametric condition to be lower than that during the general condition. A "noisy" sensation during the parametric condition tended to be higher than during the general speaker. However, the CgA concentration and the KSS score were not significantly different for either the speaker factor or the time factor. CONCLUSION The results suggested that the burden of the parametric speaker was smaller than that of general speaker, especially on the HPA-axis in the endocrine system.