The goal of industry is not noise reduction, but noise complaint reduction, or as it is known in acoustic circles, "acceptability."
Acceptability does not mean desirability. It means as loud as one can get away with. Acceptability means as noisy as possible with the fewest complaints.
The acceptability criterion punishes large numbers of human beings. Professor Raymond A. Bauer, of the Harvard School of Business Administration, an investigator of the sonic boom and other acoustic phenomena, reported that "the concept of 'tolerable' has a connotation that some may find intolerable. It implies a clear acceptance that the phenomenon involved is unpleasant, but not unpleasant beyond a certain point. In practice this has, in the past, meant the point at which citizen reaction has been intolerable to public officials...The National Academy of Engineering report suggests that perhaps one might want to substitute the concept of 'comfort' for that of tolerability...As an old hand at survey research, I can guarantee that if you ask people what level of noise they consider to be 'comfortable' and what level they consider to be 'tolerable,' the latter noise will have a higher level than the former."
One acoustician reports an increase in acceptability by creating a smooth-sounding and continuous artificial background noise level. There is something incongruous in this concept of minimizing some noise by creating constant noise. So little is known about the impact of noise on humans, how can we permit ourselves to be subjected to a lifetime of constant "low-level" noise?
Yet acceptability remains the goal, not a comfortable environment. And since a basic index of acceptability is complaint activity, a great deal of effort is devoted to techniques for reducing complaints. This goal protects the noisemaker from any significant economic burden.
One important technique of this sort is the social survey. People living in a delineated area are interviewed in an attempt to determine their reactions to specific noises in the area.
One of the first major surveys was conducted in the vicinity of London's Heathrow Airport in 1961. A sample was selected from the electoral registers (1,731 people) plus 178 people from a list of those who had complained. The 42-question questionnaire contained items designed to discover what the persons interviewed liked and disliked about their neighborhoods; the effect on them of aircraft, and other noise; their attitudes toward the airport and its importance locally; and their attitudes toward noise in general. Background information such as age, sex, and occupation was also obtained. Questions included:
Does the noise of aircraft bother you very much, moderately, a little, or not at all?
Does the noise of aircraft ever:
a) wake you up
b) interfere with listening to TV or radio
c) make the house vibrate or shake
d) interfere with conversation
e) interfere with or disturb any other activity, or bother, annoy, or disturb you in any other way?Have you ever felt like moving away from this area, and if so why?
Results of such tests are analyzed to show how much noise of a given kind the inhabitants of a given environment can take without serious complaints. Unfortunately, any guidelines developed from such surveys will not be based on a desirable acoustic environment, but on how much people will tolerate; in other words, "acceptability."
The Federal government sponsors community noise studies to collect attitudinal data from airport communities so that it may predict future reactions when existing airports intensify their activities, or when new airports are built. As part of the Federal jet noise alleviation program NASA is accumulating "behavioral psychometric data," which are personality profiles of people who live near airports. One contract was given to two University of North Carolina professors who analyzed residents according to characteristics such as:
noise sensitivity
worldly exposure (income, education, air travel experience)
high anxiety
anti-aviation
isolationist (negative attitude to growth and commerce)
pragmatist
passivity
phobia (generalized anxiety about flying and fear from sounds of aviation overhead)
idealist
conservative
imperturbable
complainer (tends to complain or protest about noise)
Are these two objective academics who are studying a problem of human beings, or—two investigators who started with a built-in prejudice that all who complain are "different" in some way?
The main purpose of these studies is to sharpen the tools for molding a positive attitude toward noise.
The test subjects, incidentally, were exposed to a noise level of 82 decibels because it was discovered that at a higher level—say, 90 decibels—virtually all subjects found the stimuli so annoying that ordinary psychological factors would cease to be part of the picture. In other words, whether one has a high or a low sensitivity—noise is noise.
United States government studies of public reaction to the sonic boom, supervised by NASA for the FAA, have been severely criticized. Oklahoma City, site of one of the major testing programs, is a center of aviation activity, with a direct stake in aviation development. FAA's Gordon M. Bain foresaw criticism of what appears to be a loaded sample. In his preface to the National Opinion Research Center report on the tests, he wrote: "Another objection to findings in this report may be based on the nature of the population of Oklahoma City. An estimated one-third of all residents have ties with aviation, and therefore might be presumed to possess an ingrained bias pertinent to this public reaction study. The report found that such connections did not appear to bias reactions to sonic boom, but there will inevitably be those who question this conclusion."
Not only is the sample suspect, so is the test itself. The booms were the less intense ones of the Air Force supersonic bombers, the shock was not unexpected, the public was carefully informed of the number of booms per day, it was given assurance of safety precautions, and finally the public knew that tests would be stopped, they would not go on for a lifetime.
In tests at Edwards Air Force Base, the subjects were paid by the hour to knit or read, and then, after a warning signal, told to record whether the subsonic or the supersonic flyover was more acceptable. Dr. Lundberg points out that the more appropriate phrasing of the question would have been, "Which noise is least acceptable."
When the FAA wanted to arrive at a goal for a lowered aircraft noise level it was aware that from the community response viewpoint the optimum reduction would be a level equal to that of the community's ambient (background noise level). Dismissing this goal as impractical at this time, the FAA decided to opt instead only for a 20 PNdB reduction. (PNdB, or Perceived Noise Decibel, is a calculated decibel that attempts to measure annoyance in terms of "noisiness") They arrived at this number by referring to the work of Bolt, Beranek and Newman which related changes in PNdBs to changes in the attitudes of people in the community. "Levels proposed by the FAA," reported an FAA official, "...should be sufficient to cause up to 50 per cent of the people to change from a "vigorous response" to a "no response" category...Residual noise will have to be handled by air traffic procedures and compatible land use planning."
Social surveys show a significant but minority number of complaints. Could one reason be that the noise victim has resigned himself to his fate? Such a defeated person, according to one noise survey specialist, "will often tell the investigator that he actually does not usually hear the noise." In other words, a good job of public relations preceding a survey virtually guarantees results pleasing to the noisemaker.