"Classroom Acoustics for Children with Hearing Impairment" is a wonderful example of a paper on child development. Information in classrooms is primarily transmitted verbally, and the proper transmission of this information is extremely vital. The acoustical characteristics of a classroom significantly affect the speech perception abilities of students. These characteristics include reverberation time, background noise, the relationship between the background noise and the teacher’ s voice, and the distance between students and teachers. In addition to the acoustical characteristics, the speech perception abilities of students are also affected adversely by diminished hearing sensitivity in students.
SNHL (sensorineural hearing loss) is the major cause of the reduction in speech perception abilities, especially in case of environments that have higher levels of noise and reverberation. Crandell and Smaldino thus discuss the acoustical characteristics of affecting speech perception ability of students in classrooms and the effects of these on the speech perception of children with normal hearing and those with SNHL. Background noise influences hearing ability by masking linguistic and acoustic cues in speech. It decreases consonant perception which in turn reduces speech perception. The noise that is generated within the enclosure, such as the noise made by talking children, is usually the greatest influence.
Others include low-frequency sounds and continuous noises such as the hum of air conditioners, heating systems, etc. The relationship between the intensity of background noise and the intensity of the signal (teacher’ s voice), which is referred to as SNR (signal to noise ratio) is a more important acoustic consideration than background noise or the type of noise. Studies have shown that SNRs in classrooms are in the range of +5 to -7 dB.
Favorable SNR is necessary for appropriate speech perception. Classroom noise has not only been shown to reduce academic performance but also teacher performance. In addition to these factors, reverberation time (RT) has also been found to affect speech perception. It is defined as “ time (in seconds) it takes for the sound from a source to decrease in level by 60 dB after the source has stopped” . Increase in-room volume, longer is the RT. The more the number of sound absorbers, the shorter is the RT. When a student is within the critical distance from the teacher (the direct sound field), reverberation is found to have very low effects on sound perception.
Speech perception ability can be increased by reducing the distance between teacher and student within the critical distance of the enclosure. Preferential seating however is not sufficient to create a proper listening environment for all students. Currently, there are no federal standards for classroom acoustics. For maximum communication, the SNRs should be more than +15dB and the unoccupied noise level should be less than 30-35 dB, reverberation should be not more than 0.4-0-. 6 seconds.