When does sound become noise?
There is no simple answer to this question, any more than there is a simple answer to the question of what is an optimum acoustic environment. We can only hope to approximate an answer.
In general, sound is noise when its physical components disturb the relationship between man and his fellow man, and man and his environment. Or, when the acoustic energy causes undue stress and actual physiological damage.
In conventional terms, sound may be classified as noise when it damages the hearing mechanism, causes other bodily effects detrimental to health and safety, disturbs sleep and rest, interferes with conversation or other forms of communication, annoys or irritates.
Some authorities say that the most obvious effect of noise on man is an interference with the ability to communicate. Sound becomes noise when it masks sounds one wants to hear. Nonetheless, this problem is not necessarily obvious to the victim as a noise problem.
"Speak up," judges often tell lawyers and witnesses. Sometimes this signifies a hearing problem on the judge's part; sometimes it means that outside noises are penetrating the halls of justice. A member of London's Scientific Advisory staff told me that one of the older judges came to him for a hearing test, explaining with embarrassment that he was having difficulty hearing his cases. Shortly thereafter another judge came up to the acoustic lab, and then another. Puzzled, the acoustic scientist did a noise level survey of the courtrooms, and discovered that speech was being masked by intrusive street noises.
Ironically, the masking effect of sound starts a spiral of other objectionable sounds. Fire and police departments, for example, justify making sirens louder and louder, to overcome increasingly higher street noises. Continuous masking is experienced in homes because of noisy air conditioners, appliances, and passing traffic, and perhaps this is one reason why neighbors play radios and TV at high volume.
One way of judging what noise does to behavior is by seeing what happens when it is removed. Researchers at the Ford Foundation's Educational Facilities Laboratories believe that disruptive noise influences both the dignity and the effectiveness of the teaching process. Donald Barr, headmaster of New York's Dalton School, has observed that 8- and 9-year-olds—noisy and unruly in the typical noise-box classroom-calmed down and concentrated in that school's first sound-treated classrooms. Noise and dignity seem interlinked.
Noise-induced hearing damage is described in Chapter 3.