4

Conclusions and Recommendations

The working group's major conclusions and recommendations are as follows:

  1. The weight of accumulated evidence since publication of CHABA (1981) makes it inadvisable to continue to rely on the dosage-response relationship recommended in that earlier report. However, information currently available does not support construction of a single dosage-response relationship that is fully appropriate in all circumstances of impulsive noise exposure.

  2. Two alternative procedures are therefore recommended, for use in circumstances described in Table 4:

Method 1 (adaptation of Green and Fidell, 1991, model): The prevalence of a consequential degree of annoyance due to high-energy impulsive noise exposure may be predicted from CDNL values as shown in Eq. 24

where D is the constant 61.1 chosen to minimize the variance of the set of available field observations of the annoyance of high-energy impulsive noise exposure. Note that CSEL values of individual events that are summed to form CDNL must exceed 85 dB (75 dB at night) to avoid overpredicting community response to nonhigh-energy impulsive sounds.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 33
Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 4 Conclusions and Recommendations The working group's major conclusions and recommendations are as follows: The weight of accumulated evidence since publication of CHABA (1981) makes it inadvisable to continue to rely on the dosage-response relationship recommended in that earlier report. However, information currently available does not support construction of a single dosage-response relationship that is fully appropriate in all circumstances of impulsive noise exposure. Two alternative procedures are therefore recommended, for use in circumstances described in Table 4: Method 1 (adaptation of Green and Fidell, 1991, model): The prevalence of a consequential degree of annoyance due to high-energy impulsive noise exposure may be predicted from CDNL values as shown in Eq. 24 where D is the constant 61.1 chosen to minimize the variance of the set of available field observations of the annoyance of high-energy impulsive noise exposure. Note that CSEL values of individual events that are summed to form CDNL must exceed 85 dB (75 dB at night) to avoid overpredicting community response to nonhigh-energy impulsive sounds.

OCR for page 33
Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 TABLE 4 Circumstances Favoring Alternate Methods of Predicting the Prevalence of Impulse-Noise-Induced Annoyance in Communities Circumstances and Knowledge of Noise Exposure Recommended Prediction Method No measurements or other information available about range or variance of distribution of impulsive sound levels (as when CSEL values of individual impulses are not captured or preserved, or cannot be reliably or cost-effectively recovered) No alternative to reliance on equal energy hypothesis; base predictions on Method 1 (using CDNL as a predictor variable) Small range/little variability in distribution of impulsive sound levels (as from a single, nearly constant source of impulse noise little affected by long-range propagation) Equal-energy hypothesis is adequate; predictions may be based on Method 1; predictions made by Method 2 (based on CIDNL) may not differ greatly Detailed knowledge of individual impulsive noise event levels, and/or large variability (σ ≥ 5 dB) in distribution of impulsive sound levels (as from multiple or complex impulsive noise sources, or from impulses greatly affected by long-range propagation) Predictions preferably based on Method 2; predictions may differ considerably from those based on CDNL, depending on absolute levels and variance of CSEL values Highly variable noise environment containing a mixture of impulsive and nonimpulsive sounds; measurements or other information available about levels of individual impulsive noise events Predictions preferably based on Method 2; predictions may differ considerably from those of Method 1, depending on absolute levels and variance of CSEL values Method 2 (level-dependent summation): The prevalence of a consequential degree of annoyance due to high-energy impulsive noise exposure may alternately be predicted by cumulating CSELs of individual impulsive sounds in a manner consistent with the annoyance weighting identified in Chapter 3, in the section on the level-dependent summation approach. Community response to sonic booms can be assessed using either of the above two procedures. Method 2 is preferable for assessment of community response to explosive noises from artillery or mining noise, especially when more detailed information is available about the distribution of CSEL values of individual high-energy noise events.

OCR for page 33
Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 Since neither of the above predictive relationships is known to be causal, both should be regarded as interim expedients. DIRECTIONS FOR RESEARCH The most obvious remedy for the paucity of information about community response to high-energy impulsive noise exposure is the conduct of additional large-scale social surveys. This is an unlikely remedy for several reasons. First, opportunities for conducting large-scale field studies involving intentional exposure of entire communities to sonic booms or other high-energy impulsive sounds have been all but foreclosed in the United States since passage of the National Environmental Policy Act of 1969. Second, opportunities to conduct surveys of adventitious exposure to high-energy impulsive noise are limited. Because no civil aircraft fly supersonically over land, and because the military confines its overland supersonic operations to areas of relatively low population density, only small populations have yet experienced relatively high levels of exposure to sonic booms on a regular, long-term basis. Blasting, artillery training, and other sources of nonaircraft, high-energy impulsive noise are also generally experienced only by localized populations. Third, it is unlikely that information about effects of sonic booms in the high-exposure ranges of CDNL can ever be collected. CDNL values in studies of community response to high-energy impulsive noise exposure that have been conducted to date are all confined to the region below LCdn = 70 dB. No community experiences the numbers of daily supersonic flights necessary to produce greater long-term impulsive noise exposure, nor is it practical to create or credibly simulate such exposure in the long term. Greater Precision in Measurement of Noise Exposure Uncertainties about the characterization of high-energy impulsive noise exposure are one of the major limitations on the ability of purely acoustic variables to account for large amounts of variance in community response. Future studies would profit greatly from: Direct empirical measurements of noise exposure in preference to predictive modeling of exposure; Collection of information about the distribution of individual impulsive noise events in addition to CDNL values; Measurements of characteristic indoor noise levels associated with time-averaged cumulations of outdoor exposure; and To the extent possible, characterization of personal as well as place-oriented noise exposure.

OCR for page 33
Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 Improved Study Designs Several measures would improve the utility of data collected in studies in which test participants are asked to judge the immediate annoyance of individual noise events: Careful attention should be given to sound reproduction capabilities and listening environments so that the very low-frequency content of high-energy impulsive sounds is accurately presented for judgment; so that spectra of test signals covary appropriately with level; and so that valid estimates of at-ear sound levels can be made; Secondary emissions (rattling sounds) should be fully controlled and accurately measured at test participants' ears; and Judgments of the annoyance of both impulsive and nonimpulsive sounds should be solicited over a wide range of levels. FURTHER ANALYTIC EFFORTS These recommendations should be reviewed as additional information about the annoyance of high-energy impulsive noise exposure (preferably from field studies) becomes available. They should also be reviewed from other theoretical perspectives as advances are made in understanding the origins of noise-induced annoyance. It is possible, for example, that nonacoustic predictor variables might account for useful amounts of variance in community response to infrequent, individually memorable episodes of high-energy impulsive noise exposure.