Abstract
Several tests designed to assess the effects of increased noise levels created by the Concorde supersonic aircraft were administered to 48 residents living around Dulles International Airport and 31 persons not living near an airport. Results of a pretest questionnaire and lack of significant changes in annoyance levels and time estimations indicate that, while airport-area residents may be more conscious of aircraft noise, changes in the perceived intensities of sounds may not occur.
On May 24, 1976, limited flight operations by the Concorde supersonic transport aircraft were begun into and out of Dulles International Airport, located approximately 20 miles west of Washington, D. C. The initiation of these flights marked the first time that commercial aircraft capable of supersonic speeds had been permitted to operate within the boundaries of the United States. Preliminary government studies indicated that not only would the aircraft be noisier than existing subsonic aircraft, e.g., Boeing 707, Boeing 747, but that a significantly greater area would be subjected to noise levels above 100 EPNdb as well (Federal Aviation Administration, 1975). Because of the one-time nature of this event, a unique opportunity to study its impact upon citizens living in the airport area became available. In an effort to assess the effects of the increased noise levels, several tests were conducted on volunteer subjects living in communities surrounding the airport.
One test, an annoyance level test, was designed to investigate the extent to which a person's tolerance for loud sounds changes following repeated exposure to increased aircraft noise. In this test annoyance levels in db(A)s for tones at six different frequencies and white noise were obtained from subjects both before and after the initiation of Concorde service into the area. Of particular interest was whether comparable changes in annoyance levels would occur at different sound frequencies and with broad-spectrum noise.
A second test, involving time estimation, required subjects to make several estimates of intervals filled with tones differing in frequency and duration. Although it was not possible to obtain before and after measurements with this test, it was felt that when compared with control-area subjects, estimates by airport-area residents would tend to be overestimated. Such an explanation was based in part on findings of previous laboratory studies investigating the relationships between the perceived intensity of a tone and estimates of tonal duration (Needham, 1935; Zelkind & Ulehla, 1963). A positive relationship between experienced duration and intensity has been the usual finding.
In addition to the objective measures, subjects were asked to respond to a brief questionaire designed to assess their general attitudes about aircraft, noise, etc., as well as their personal sensitivity to noises of various kinds. Also, to assure that the hearing of participants was comparable at the start of the study, a simple hearing test was administered.
Method
Subjects
Seventy-nine volunteer subjects participated. Subjects were obtained by canvassing neighborhoods three to four weeks before testing was to begin. Ages of participants ranged from 12 to 52 yr. Forty-eight of the subjects living in four residential areas adjacent to Dulles International Airport served as experimental subjects. The areas (Greenbriar, Brookfield, Centreville, and Sterling Park) are located from 1 to 3 nautical miles from the airport and are generally situated in its flight paths. Thirty-one subjects, who did not live near the airport, formed a control group. As nearly as possible, groups were balanced for age, sex, and occupation. Also, all subjects must have lived at their current address for at least a year prior to the testing.
Procedure
Pre- and posttesting of annoyance levels were administered about 2 wk. before and 1½ mo. after Concorde landings began, whereas time estimation tests were conducted about 2 mo. after the landings. Questionnaires and tests of basal hearing were administered 2 wk. prior to Concorde activity. Also, with only a few exceptions, testing was accomplished in subjects’ homes.
Hearing Tests
Basal hearing of each subject was checked using a portable audiometer (Beltone, Model 10D). Hearing levels at 125, 250, 500, 1000, 2000, and 4000 Hz were determined by the method of limits. One ascending and one descending series of trials was given at each frequency. Mean thresholds were recorded in db(A)s. During testing, subjects sat with their backs to the experimenter and acknowledged hearing a tone by raising their hand.
Questionnaire 2
Questions used in present study were selected from a larger questionnaire developed and used by Dr. P. N. Borsky, Columbia University. The author would like to thank Dr. Borsky for permission to use these materials.
Eighteen questions aimed at assessing subjects’ sensitivity to and attitudes concerning noise (including aircraft) were answered by all participants at the start of testing. Many could be answered with a simple yes or no; however, others required evaluations to be made on a 7-point scale.
Annoyance Level Tests
In this test the intensity in db(A)s at which a tone or white noise became uncomfortable for a subject was determined. Tones and noise were binaurally presented to subjects with a portable audiometer (Beltone, Model 10D). Subjects were tested at six frequencies (125, 250, 500, 1000, 2000, and 4000 Hz) and with white noise. Two trials were given with each sound and a random order of presentation was used. Annoyance levels were determined by increasing the volume until the subject raised his hand to indicate that the sound was “uncomfortable at that level.” The sound level was then recorded, and a new trial begun.
Time Estimation Tests
Three methods were used to assess subjects’ perceptions of sound durations, viz., by reproduction, production, and direct estimation. Sounds and durations were controlled and measured by means of a portable tone generator/timer which was specially constructed for the study. Sounds were presented over a pair of stereo headphones, and during testing, subjects sat with their backs to the experimenter.
In the reproduction test subjects were required to match the duration of a target sound by reproducing it. Two frequencies (400 Hz and 4000 Hz) and two durations (3 and 17 sec.) were used. Sound levels averaged 70 db(A) at the ear. Since each tone-duration combination was presented twice, a total of 8 matches were required. Order of presentation was random.
Immediately after the reproduction test, subjects were asked verbally to estimate how long they felt the durations were during the reproduction test (direct estimation test).
Finally, subjects were asked to produce sounds of 1, 5, 10, and 25 sec. duration. Subjects produced these estimates by holding down a hand-held button which simultaneously activated the 400-Hz tone and a hidden timer.
Results and Discussion
An examination of hearing test scores and responses to the questionnaire gave the following picture of the subjects tested in the study. Apart from a slight tendency for control subjects to hear less well at 125 and 250 Hz (t = 2.12, df = 58, p < .04, and t = 2.04, df = 58, p < .05, respectively), over-all hearing levels of airport- and nonairport-area subjects did not differ significantly.
Also, an examination of responses to the questionnaire indicated that airport-area residents were much more likely to be bothered by aircraft noise during the day, evening, and night than their control-area counterparts (χ2 = 5.47, p < .01; χ2 = 8.96, p < .001; and χ2 = 6.64,p < .01, respectively). In addition, airport subjects felt that aircraft noise was more harmful to one's health (7-point scale) than did nonairport residents (t = 2.29, df = 76, p <.03; M = 4.13, SD = 1.57 and M = 3.29, SD = 1.60, respectively). Curiously, however, while airport-area subjects appeared to be more sensitive to aircraft-type noise, control subjects tended to find other kinds of noise such as “whistling-out-of-tune,” “door-banging,” typewriters, dripping faucets, lawnmowers, a knife-scraping-on-a-plate, scraping-on-a-blackboard, pneumatic drills, and musical instruments-at-practice, etc., more bothersome than airport residents (see Table 1).
Percentages of Subjects Bothered or Annoyed by Different Sounds
n = 48. †n = 31.
Since one of the primary aims of the present testing was to see whether annoyance levels for airport residents would change following initiation of Concorde flights, several analyses were performed on the measures of annoyance level taken before and after supersonic service began. The results of these analyses can be summarized rather briefly. That is, no significant differences were found between groups either before or after landings began, or when change scores (pretest scores minus posttest scores) were examined, and this was true for all frequencies and white noise (p > .05). There was a tendency for subjects in both groups to tolerate slightly higher db(A) levels during post-testing however, but these increases were not significantly different from pretest scores (Table 2).
Annoyance Levels in db (A)s of Airport and Control-area Residents
Comparisons of time estimates yielded no significant differences between control and airport subjects regardless of method used, i.e., production, reproduction, or direct estimate (p > .05). Except for direct verbal estimations, estimates were almost always underestimated by subjects in both groups. Thus, if the perceived intensities of the 400- and 4000-Hz tones by airport-area residents was different from that of control subjects, no evidence of this was demonstrated (Table 3).
Time Estimates by Airport and Control-area Subjects
To examine possible significant relationships between hearing, annoyance levels, time estimations, and subjects’ subjective responses concerning their general hearing and noise sensitivity, several correlations were performed on the data from control and airport-area residents (separately and combined). For control group subjects, significant negative correlations between ratings of personal sensitivity to noise and before and after annoyance level scores were found (r s ranged from -.40 to -.67, ps < .04). That is, if a subject felt he was more sensitive to noises than most people, his annoyance level scores at the various frequencies and with white noise were relatively low, and vice versa. Although a similar correlation was not obtained for airport-area residents, the extent to which annoyance levels changed after Concorde service was negatively correlated with ratings of noise sensitivity. That is, greater changes were observed in airport residents who felt they were less sensitive to noise than most people, and vice versa (r s ranged from -.36 to -.56, ps < .04).
Finally, no correlation was found between subjects’ time estimates and annoyance levels.
Thus, the results indicate that, despite higher exposure to aircraft noise in general and increases due to supersonic transport flights, tolerances for intense sounds by airport-area residents may not differ significantly from those of persons not living near an airport. Indeed, both before and after Concorde landings, annoyance levels of airport residents were quite similar to those of their control counterparts. While annoyance levels did change for both groups, the higher levels observed were not significantly different (either within or between groups) from before-test levels.
Further evidence to suggest that mere exposure to high levels of aircraft noise may not be sufficient to produce changes in the perceived intensity of sounds was indicated by the fact that time estimations by airport and nonairport groups were not significantly different. However, it should be noted that only one relatively high intensity level, 70 db(A), was represented in the tests. It is possible that a more definitive conclusion would have been forthcoming had additional levels been examined.
These results suggest that, while persons who live around airports may be more sensitive to aircraft noise, this sensitivity may be manifested more in terms of differential attitude than any change in the perceived intensity of sounds.