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OCR for page 46
Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 APPENDIX C Glossary Abbreviations and mathematical symbols used in this report follow the practices of American National Standard S1.4-1944 Acoustical Terminology. Abbreviations are usually a sequence of capital letters used in text to shorten the reference to frequently used acoustical terms. Mathematical symbols are the letter symbols used for these terms in equations. Thus, sound exposure level is abbreviated as SEL, while its mathematical symbol is LAE. With no additional modifier, the words “sound exposure level” and its abbreviation “SEL” are usually understood to be A-weighted sound exposure level. This report makes such frequent reference to both A-weighted and C-weighted sound exposure levels that the abbreviations ASEL and CSEL are used throughout to minimize confusion. day average sound level: Time-average sound level between 0700 and 2200 hours. Unit, decibel (dB); abbreviation, DL; symbol, Ld. Note: Day average sound level in decibels is related to the corresponding day sound exposure level, LEd, according to: Ld = LEd − 10 log (54,000/1) where 54,000 is the number of seconds in a 15-hour day.
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 day-night average sound level: Twenty-four hour average sound level for a given day, after addition of 10 decibels to levels from 0000 to 0700 hours and from 2200 (10 p.m.) to 2400 hours. Unit, decibel (dB); abbreviation, DNL; symbol, Ldn. Notes: Day-night average sound level in decibels is related to the corresponding day-night sound exposure level, LEdn, according to: Ldn = LEdn − 10 log (86,400/1) where 86,400 is the number of seconds in a 24-hour day. A-frequency weighting is understood, unless another frequency weighting is specified explicitly. instantaneous sound pressure: Total instantaneous pressure at a point in a medium minus the static pressure at that point. Unit, pascal (Pa); symbol, p. loudness level: Of a sound, the median sound pressure level, in a specified number of trials, of a free progressive wave having a frequency of 1,000 Hz that is judged as loud as the unknown sound when presented to listeners with normal hearing who are facing the source. Unit, phon. Note: The manner of listening to the unknown sound must be specified. maximum sound level; maximum frequency-weighted sound pressure level: Greatest fast (125 ms) A-weighted sound level within a stated time interval. Alternatively, slow (1,000 ms) time-weighting and C-frequency-weighting may be specified. Unit, decibel (dB); abbreviation, MXFA; symbol, LAFmx (or C and S). night average sound level: Time-average sound level between 0000 and 0700 hours and 2200 and 2400 hours. Unit, decibel (dB); abbreviation, NL; symbol, Ln. Note: Night average sound level in decibels is related to the corresponding night sound exposure level, LEn, according to:
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 Ln = LEn − 10 log (32,400/1) where 32,400 is the number of seconds in a 9-hour night. one-hour average sound level: Time-average sound level during a time period of one hour. Unit, decibel (dB); abbreviation, 1HL; symbol, L1h. Note: One-hour average sound level in decibels is related to the corresponding one-hour sound exposure level, LE1h, according to: L1h = LE1h − 10 log (3,600/1) where 3,600 is the number of seconds in one hour, 1 s is the reference duration for sound exposure, and sound exposure E is in pascal-squared seconds. peak sound pressure: Greatest absolute instantaneous sound pressure within a specified time interval. Unit, pascal (Pa). Note: Peak sound pressure may be measured with a standard frequency weighting. peak sound pressure level; peak frequency-weighted sound pressure level: Level of peak sound pressure with stated frequency weighting, within a stated time interval. Unit, decibel (dB); example abbreviation, PKA; symbol, LApk. perceived noise level: Frequency-weighted sound pressure level obtained by a stated procedure that combines the sound pressure levels in the 24 one-third octave bands with midband frequencies from 50 Hz to 10 kHz. Unit, decibel (dB); abbreviation, PNL; symbol, LPN. Note: Procedures for computing perceived noise level are stated in Federal Aviation Regulation Part 36, Noise Standards: Aircraft Type and Airworthiness Certification, Appendix B, and in International Civil Aviation Organization Annex 16, Volume 1, Aircraft Noise, Third Edition, July 1993. sound exposure: Time integral of squared, instantaneous frequency-weighted
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 sound pressure over a stated time interval or event. Unit: pascal-squared second; symbol, E. Notes: If frequency weighting is not specified, A-frequency weighting is understood. If other than A-frequency weighting is used, such as C-frequency weighting, an appropriate subscript should be added to the symbol; e.g., EC. Duration of integration is implicitly included in the time integral and need not be reported explicitly. For the sound exposure measured over a specified time interval such as one hour, a 15-hour day, or a 9-hour night, the duration should be indicated by the abbreviation or letter symbol, for example 1-hour sound exposure (1HSE or E1h) for a particular hour; day sound exposure (DSE or Ed) from 0700 to 2200 hours; and night sound exposure (NSE or En) from 0000 to 0700 hours plus from 2200 to 2400 hours. Day-night sound exposure (DNSE or Edn) for a 24-hour day is the sum of the day sound exposure and 10 times the night sound exposure. Unless otherwise stated, the normal unit for sound exposure is the pascal-squared second. sound exposure level: Ten times the logarithm to the base ten of the ratio of a given time integral of squared instantaneous A-weighted sound pressure, over a stated time interval or event, to the product of the squared reference sound pressure of 20 micropascals and reference duration of 1 second. The frequency weighting and reference sound exposure may be otherwise if stated explicitly. Unit, decibel (dB); abbreviation, SEL; symbol, LAE. Note: In symbols, (A-weighted) sound exposure level is: where p2A is the squared instantaneous A-weighted sound pressure, a func
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 tion of time t; for gases p0 = 20 µPa; t0 = 1 s; E is sound exposure; E0 = p02t0 = (20 µPa)2s is reference sound exposure. sound level; weighted sound pressure level: Ten times the logarithm to the base ten of the ratio of A-weighted squared sound pressure to the squared reference sound pressure of 20 µPa, the squared sound pressure being obtained with fast (F) (125 ms) exponentially weighted time-averaging. Alternatively, slow (S) (1000 ms) exponentially weighted time-averaging may be specified; also C-frequency weighting. Unit, decibel (dB); symbol LA, LC. Notes: In symbols, A-weighted sound level LAτ(t) at running time t is: where τ is the exponential time constant in seconds, ξ is a dummy variable of integration, pA2(ξ) is the squared, instantaneous, time-varying, A-weighted sound pressure in pascals, and p0 is the reference sound pressure of 20 µPa. Division by time constant τ yields the running time average of the exponential-time-weighted, squared sound-pressure signal. Initiation of the running time average from some time in the past is indicated by −∞ for the beginning of the integral. ANSI S 1.4-1983, American National Standard Specification for Sound Level Meters, gives standard frequency weightings A and C and standard exponential time weightings fast (F) and slow (S). sound pressure amplitude: Absolute instantaneous pressure in any given cycle of a sound wave at some specified time. Unit, pascal (Pa). sound pressure; effective sound pressure: Root-mean-square instantaneous sound pressure at a point, during a given time interval. Unit, pascal (Pa). Note: In the case of periodic sound pressures, the interval is an integral number of periods or an interval that is long compared with a period. In the case of nonperiodic sound pressures, the interval should be long enough to make the measured sound pressure essentially independent of small changes in the duration of the interval.
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 sound pressure level: Ten times the logarithm to the base ten of the ratio of the time-mean-square pressure of a sound, in a stated frequency band, to the square of the reference sound pressure in gases of 20 µPa. Unit, decibel (dB); abbreviation, SPL; symbol, Lp. static pressure: Pressure that would exist at a point in the absence of a sound wave. Unit, pascal (Pa); symbol, ps. Note: One pascal is equal to one newton per square meter. The static pressure in air at sea level on a standard day is 101.325 kilopascals (2,116 pounds per square foot; 1 atmosphere). time-average sound level; time-interval equivalent continuous sound level; time-interval equivalent continuous A-weighted sound pressure level; equivalent continuous sound level: Ten times the logarithm to the base ten of the ratio of time-mean-square instantaneous A-weighted sound pressure, during a stated time interval T, to the square of the standard reference sound pressure. Unit, decibel (dB); respective abbreviations, TAV and TEQ; respective symbols, LAT and LaeqT. Note: A frequency weighting other than the standard A-weighting may be employed if specified explicitly. The frequency weighting that is essentially constant between limits specified by a manufacturer is called flat. In symbols, time-average (time-interval equivalent continuous) A-weighted sound level in decibels is: where p2A is the squared instantaneous A-weighted sound pressure signal, a function of elapsed time t; in gases reference sound pressure p0 = 20 µPa; T is a stated time interval. In principle, the sound pressure signal is not exponentially time-weighted, either before or after squaring.
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Community Response to High-Energy Impulsive Sounds: An Assessment of the Field Since 1981 ADDITIONAL TERMS C-weighted sound exposure level: Sound exposure level, as defined above, where C-weighted sound pressure is used instead of A-weighted sound pressure. Unit, decibel; abbreviation, CSEL; symbol, LCE. energy average: Colloquial term for time-mean-square average of the sound pressures for a series of sound signals. energy summation: Colloquial term loosely used to indicate addition of non-coherent sound signals by the sum of the squares of their sound pressures or the sum of their sound exposures. peak overpressure: Maximum positive pressure produced by an impulsive sound. Often used to describe the magnitude of a sonic boom, in pounds per square foot (psf). One pound per square foot is equal to 47.89 pascals or a flat sound pressure level of 127.6 decibels.
Representative terms from entire chapter: