The associations between voice ergonomic risk factors in 40 classrooms and the acoustic parameters of 40 schoolteachers' voices were investigated. The risk factors assessed were connected to participants' working practices, working postures, and the indoor air quality in their workplaces. The teachers recorded spontaneous speech and sustained /a/ before and after a working day. Fundamental frequency, sound pressure level, the slope of the spectrum, perturbation, and harmonic-to-noise ratio were analysed.The results showed that the more the voice ergonomic risk factors were involved, the louder the teachers' voices became. Working practices correlated most often with the acoustic parameters; associations were found especially before a working day. The results suggest that a risky voice ergonomic environment affects voice production.