We have heard classical music aficionados tout the “glorious acoustics” of a particular concert hall, opera house, or theatre. These “acoustics” are the venue’s natural ability to support and enhance the musical or dramatic functions performed inside, without the need for an electronic sound system. Important parameters affecting room acoustics generally include geometric form, the appropriate quantity and location of acoustical materials, subdued noise from heating, air-conditioning and mechanical systems, and sound isolation from outdoors and adjacent spaces.
Acoustics are not only important to concert halls, however. The reason many (otherwise bashful) people break into song while in the shower is that the shower stall’s hard surface walls and geometric form provide intense resonance and reflective support for the human voice. The result is an impression that one’s voice is fuller, deeper and louder. Conversely, attempting to sing outdoors without a sound system usually is very difficult for untrained vocalists because of the lack of reflective support and high ambient noise levels.
The most commonly cited acoustical parameter for architectural spaces is Reverberation Time, or RT60. Reverberation refers to sound that is continuously reflected within a space, such that it continues for a period of time after the source has ceased. This is audible as a decaying “tail” following each syllable of speech, for example. We scientifically measure reverberation in terms of the length of time it takes this decaying sound to drop 60 decibels. Gothic cathedrals or other large hard-surfaced halls can have reverberation times greater than 3 seconds. The reverberation outdoors, without and buildings or sound-reflective surfaces nearby would be about 0 seconds. Reverberation can be beneficial to the performance of many different styles of music, but is often detrimental to clear speech intelligibility. It can lead to confused, hollow sounding, “echoing” speech.
It is vital to ensure a supportive acoustic environment for any critical listening space. The classroom serves as the acoustic venue for primary and secondary education. It must enhance and project the teacher’s voice, have a very subdued level of reverberation or late-arriving echoes, and prevent the intrusion of unwanted sound from building mechanical systems, adjacent spaces, and sources such as, children, lawnmowers, roadways, trains or airports.
Clear speech is essential to classroom function. About 60 percent of all classroom learning activities involve students listening to and participating in spoken communications with the teacher and other students, according to the Acoustical Society of America. Unfortunately, the presence of severe acoustical barriers is far too prevalent in American schools.
According to the United States General Accounting Office, millions of students attend schools with unsatisfactory acoustical conditions. 21,900 schools exhibit poor acoustics or noise control, affecting more than 11 million students. 28.1 percent of all schools reported unsatisfactory or very unsatisfactory environmental noise conditions. This was higher than ventilation (27.1 percent), physical security (24.2 percent), indoor air quality (19.2 percent), heating (18.9 percent), or lighting (15.6 percent).
The excessive noise levels and lack of support for speech in these classrooms have failed countless students and led to difficulties in learning and instruction. The impediment these classrooms pose to learning is often underappreciated by students, teachers and administrators. In some cases, problems caused by poor acoustic conditions may have been falsely attributed to other factors (teacher performance, socioeconomic factors, etc). This prevalence of poor listening conditions in classrooms results from a lack of understanding and awareness of the detrimental impact that noise and reverberation have on student learning.
A supportive and enhancing acoustic environment in the classroom will enable easier learning for students, with more retention, and less fatigue for teachers.
How Poor Acoustics Affect Students
The link between acoustical problems and academic achievement is demonstrated in dozens of studies from several scientific fields. Proper acoustical support is crucial to young children whose auditory and language faculties are still developing. According to the Acoustical Society of America:
“Young children are more susceptible than adults to the effects of background noise and reverberation on communication with spoken language. Because of this susceptibility, young children also require more favorable classroom signal-to-noise ratios and reverberation times to achieve the same level of speech intelligibility as adults do. Developmental status, linguistic and cognitive proficiency, temporary hearing impairments, and early receptive and expressive language disorders are all factors that affect the greater susceptibility of young children to background noise and reverberation.”
Adults and older children possess an ability to fill in missed or unintelligible words from a greater context. For example, consider the statement “Why ot so many old halls remain popular while shmu newer ewon have already undergone extensive renovation?” Our adult minds are easily able to fill in the meaning of unintelligible, but predictable words from the greater context and establish 100 percent of the meaning through 82 percent of the words. Younger children possess a less effective ability to discern these high predictability contexts than older children or teenagers. Additionally, missed words with low context predictability are disastrous for all students. Consider the following statement:
“An angle that has a measure less than a right angle (less than 90 degrees) is an sbtsu angle”
The presence of excessive noise or reverberation will lead to a greater percentage of missed words during classroom instruction. The affected words may be context predictable, or not.