Purpose: Sound pressure level (SPL), fundamental frequency (F0), time dose (Dt), cycle dose (Dc), and distance dose (Dd) are components affecting a vocal demand response. The study aimed to investigate the impact of sound field amplification systems (SFAS) on teachers' vocal parameters and determine the user comfort of SFAS use in teachers.
Methods: Twenty female teachers underwent long-term voice dosimetry with Vocal Holter Med (PR.O.Voice Srl) during everyday teaching activities. The SFAS PentaClassRuna (Certes) was installed in classrooms. Voice dosimetry was provided in two different acoustical conditions-without the use of SFAS (one to two days) and with SFAS (one to three days). Teachers underwent voice acoustic and laryngoscopic evaluation before voice dosimetry. Two teachers' groups were formed: teachers with and without vocal nodules. The visual analogue scale measured the user comfort of SFAS.
Results: There were no significant differences in vocal parameters and vocal doses between teachers with and without vocal nodules. Voice amplification significantly decreased average F0(-4.4 Hz), Dt%(-3.1%), Dc (-0.4 kcycles), and Dd (-1.3 m) in teachers without vocal nodules and F0 (-8.9 Hz) in teachers with vocal nodules. Vocal doses (Dt%, Dc, Dd) significantly decreased in classrooms with longer reverberation time. The user comfort of the SFAS during the lessons was high in both teachers groups.
Conclusions: SFAS was a mediator between the classroom's environment and the teacher's vocal demand response; it changed teachers' voice production parameters and reduced vocal demand response to satisfy the communication requirements. In addition, voice amplification was more beneficial for teachers without vocal fold lesions.
Keywords: Teachers; fundamental frequency; reverberation time; sound pressure level; vocal demand response; vocal dose; vocal nodules; voice amplification; voice dosimetry.