Excessive background noise in a classroom can originate from outside the building (aircraft and traffic noise, lawnmowers and leaf blowing) or from within the building (heating, ventilation, air-conditioning, plumbing systems, noise from adjacent classrooms or hallways, gymnasiums or music rooms) or noise from the students themselves. However, it is important to note that the level of residual noise from the students is strongly related to the general level of ambient noise in the room. That is, student chatter will increase as the general level of ambient noise increases, an example of the Lombard effect (Junqua, 1996).
Speech perception studies have investigated how interference from noise and reverberation influences the perception of syllables, words, or sentences in classrooms. The importance of ambient noise levels is mostly related to speech-to-noise ratios. Kindergarten and first and second grades are the primary years in which children learn to break down written words into their phonetic components and acquire the ability to read. This requires careful listening to develop the ability to discriminate among minor differences in words such as pet, pit, pot, put, and pat (Anderson, 2004). Such differences can be lost in a noisy environment, and hence younger children require higher signal-to-noise ratios corresponding to quieter conditions.
The impacts of excessive noise vary according to the age of the students because
the ability to focus on speech is a developmental skill that evolves with maturation of the brain and mastery of language. Because the auditory mechanism does not fully mature until age 13 to 15 years, young children … require better acoustical environments than do adult listeners to achieve equivalent word recognition scores. (Anderson, 2004, p. 119)
For that reason, a student’s difficulty in understanding speech in noisy situations may not be recognized by teachers, building designers, or other adults. Said another way, adults cannot recognize the level of children’s difficulty by using their own ability to perceive speech under the same adverse listening conditions. Elliott et al. (1979) found that the ability to recognize sentences in noisy environments improves systematically with age for children ages 7, 9, 11, 13, 15, and 17 years. This has recently been shown in extensive studies in actual classrooms (Bradley and Sato, 2004).
There are also studies suggesting that the negative effects of excessive reverberation are more acute for younger listeners (Nábĕlek and Robinson, 1982), but the requirements for children of various ages have not been determined. Although most standards (e.g., ANSI S12.60) recommend approximately a 0.6-s reverberation time, some studies have suggested that much shorter reverberation times would be better (Nábĕlek and Picket, 1974). However, some of these studies are flawed and their results cannot be relied upon. These experimental results are incomplete because they include only the negative effects of increased reverberation but not the positive benefits (i.e., increased speech levels). Further research is required to more precisely confirm optimum reverberation times for children of various ages.
Since the 1970s, a number of studies have been conducted that compare the reading skills of students in schools exposed to transportation noise with the reading skills of students in schools in quieter areas. A study in the early 1970s looked at the performance of children in a New York school that was parallel to the tracks of an elevated train. During a 3-year