Dr. Gunther Lehmann, former director of the Max Planck Institute, in Dortmund, West Germany, has warned that what threatens man is not the likelihood of auditory troubles or loss of hearing due to noise, "but an incessant disturbance, which under certain conditions creates an intolerable strain."
The effects of noise other than damage to hearing are called extra-auditory effects. Most of the science of acoustics has been applied to measuring only one category of extra-auditory response, described by the catch-all term of annoyance. Annoyance is probably the most widespread and one of the more complex responses to noise.
The acoustician approaches the annoyance reaction by attempting to separate the acoustic or physical factors (pitch, intensity, duration) from the extra-auditory factors. Of the acoustic factors, loudness has been selected as a key consideration. All other things being equal, the louder the sound, the more annoying it is. Loudness distracts. Loud shouting and yelling—from Indian war whoops to the Japanese banzai—have been used in battle to demoralize, confuse, and frighten.
Though loudness is related to the intensity of the sound, the more decibels the louder, other factors can influence loudness. For example, a given sound appears louder at night, if the background level is lower than during the day.
If one has been shielded from loud noise, sudden exposure is uncomfortable, and can prove startling. People who have had ear surgery find everyday noises inordinately discomfiting. Before the Belgian Congo got its independence, one of its government agencies placed an order for silencers for construction machines being shipped from Europe. It had been observed that Congolese workmen would run away from the construction sites because they could not stand the unmuffled noise.
Extremes of pitch are annoying. Illustrations are sirens (high pitch) and fog horns or boat whistles (low pitch). These intense sounds intrude over the background noise.
Annoyance appears to be a matter of degree and circumstance. For example, irregularity, lack of pattern, makes sound ugly and annoying. The unexpected, unpatterned sounds of jackhammers, auto horns, and helicopters cause unpleasant internal responses. Almost paradoxically, regularity, too, can irritate. The constant roar of an air compressor or a loud air conditioner is not soothing.
A sound which repeatedly changes its point of origin is annoying. When a noisy truck passes another vehicle on the highway, the overtaken driver is immersed in and consequently disoriented by the intense sound that seems to be coming from all directions at once.
Sounds can be annoying even if they are not loud. Proponents of center city heliports claim that helicopters are not as loud as jets, therefore not as annoying. But the distinctive drone and chop-chop of a helicopter is irritating. It is also terribly disturbing to have a relatively low-decibel background noise at night punctured by the clicking of heels on the floor overhead, the hammering in water pipes, the neighbor's TV.
Sound becomes noise for many non-acoustical reasons. Canned music in a restaurant or an elevator is noise to a man who is preoccupied. This is an invasion of privacy. According to the British Wilson Committee* annoyance can be "essentially the resentment we feel at an intrusion into the physical privacy which we have for the moment marked out as our own, or into our thoughts or actions."
The fight for a quieter world becomes obscured when feelings about a noise are divorced from the noise itself. We are told that how we react to a given noise may be influenced by our attitude towards the noise source, our state of health and well-being, our personalities, education, income, previous exposure, ad nauseum. Does the transportation noise problem disappear if we all learn to love driving and flying, or the industries that make these activities possible? Would I have been less disturbed by the subway project if I appreciated what the TA was doing for progress? Is a 90-decibel jackhammer really less of a noise because it takes place during the day, or because I've heard one before? It is relatively simple to measure the physical quality of the noise signal, its decibel level, frequency distribution, duration, number of occurrences per unit time, etc. It is virtually impossible to measure the significant human response to noise. Schemes for predicting complaints and evaluating annoyance responses are crude guidelines, their effectiveness questioned even by noise specialists.
A number of schemes have been developed to predict the response to a new noise in a given environment, or the response to a noise from a given source. According to acoustician Lew Goodfriend, "All currently used noise rating techniques are based not on what the optimum environment for man should be, but on what the public as a group will put up with."
One of these noise rating tools is the Composite Noise Rating, or CNR. It supposedly predicts whether a given noise will lead to no response, or provoke a rising degree of protest, culminating in vigorous legal action. "The objective," states Goodfriend, "is not to produce an enjoyable or even a suitable environment, It is merely to prevent complaints."
Another example of a noise rating system based on what people will tolerate is the family of "Noise Criteria" curves. Ratings obtained by means of these curves are aimed at "determining the maximum level of noise at which office personnel feel they can accomplish their duties without loss of efficiency." For secretarial areas (typing) and accounting areas (business machines), the recommended rating is NC-50 to NC-55. The environment for communication at this level is described as "unsatisfactory for conferences of more than two or three people; use of telephone slightly difficult; normal voice one to two feet; raised voice three to six feet."
Goodfriend is evolving a scheme using computers to obtain a statistical picture of the noise within a community. "From this information it should be possible by mathematical analysis to describe the optimum environment." Unfortunately for human beings, they do not lend themselves to formulae and equations.
We can measure sound; we can only guesstimate noise. But we know how to reduce noise and noise exposure (Chapter 8). Why not do so? Each day we avoid design for quiet we pay an unreasonable price for progress.