Revisiting speech interference in classrooms

A review of the effects of ambient noise and reverberation on speech intell igibility in classrooms has been completed because of the longstanding lack of agreement on preferred acoustical criteria for unconstrained speech acc essibility and communication in educational facilities. An overwhelming bod y of evidence has been collected to suggest that noise levels in particular are usually far in excess of any reasonable prescription for optimal condi tions for understanding speech in classrooms. Quite surprisingly, poor clas sroom on acoustics seem to be the prevailing condition for both normally-he aring and hearing-impaired students with reported A-weighted ambient noise levels 4-37 dB above values currently agreed upon to provide optimal unders tanding. Revision of currently proposed room acoustic performance criteria to ensure speech accessibility for all students indicates the need for a gu ideline weighted for age and one for more vulnerable groups. For teens (12- year-olds and older) and young adults having normal speech processing in no ise, ambient noise levels not exceeding 40 dBA are suggested as acceptable, and reverberation times of about 0.5 s are concluded to be optimum. Younge r students, having normal speech processing in noise for their age, would r equire noise levels ranging from 39 dBA for 10-11-year-olds to only 28.5 dB A for 6-7-year-olds. By contrast, groups suspected of delayed speech proces sing in noise may require levels as low as only 21.5 dBA at age 6-7. As one would expect, these more vulnerable students would include the hearing-imp aired in the course of language development and non-native listeners.