2003-06-11 CC Packet - Laserfiche WebLink

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.~ 389.30 MINNEAPOLIS CODE dump truck, front end loader, bobcat, crane or backhoe used in a construction project which has a defined beginning and end. Cycles per second: A measure of frequency numerically equivalent to hertz. Daytime: 6:00 a.m. to 6:00 p.m. of the same day. dB(A): Composite abbreviation for decibel and A-weighted sound level. The weighted sound pres- sure level by the use of the A metering character- istic and weighting specified in ANSI Specifica- tion of Sound Level Meters, 81.4-1983. dB(A) is used as a measure of'human response to sound. Disturbing, excessive or offensive noise: Any sound or noise conflicting with the criteria or levels set forth in this article. Equivalent A-weighted sound level (Leq): The constant sound level that, in a given time period, would convey the same sound energy as the actual time-varying A-weighted sound level. Hearing: The subjective human response to sound. Hearing level: A measured threshold of hearing at a specified frequency, expressed in decibels relative to a specified standard of normal hearing. The deviation in decibels of an individual's thresh- old from the zero reference of the audiometer. Hertz (Hz): Unit of measurement of frequency, numerically equal to cycles per second. Impact sound: The sound produced by the collision of two (2) solid objects. Typical sources are footsteps, dropped objects, etc., on an interior surface (wall, floor, or ceiling) of a building. Impulsive noise: Impulsive noise means a sound of short duration, usually one second or less with abrupt onset and rapid decay. Impulsive noises include but are not limited to metal impacts, hammers, gunshots, explosions, and drop forge impacts. Intensity: The sound energy flow through a unit area in a unit time. L10: The sound level, expressed in dB(A), which is exceeded ten (10) percent of the time for a one Supp. No. 16 hour survey, as measured by test procedures approved by the commissioner of the Minnesota Pollution Control Agency. L50: The sound level, expressed in dB(A), which is exceeded fifty (50) percent of the time for a one hour survey, as measured by test procedures a pproved by the commissioner of the Minnesota Pollution Control Agency. Level: The logarithm of the ratio of a quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be specified. Logarithm: The exponent that indicates the power to which a number must be raised to produce a given number. For example, for the base ten (10) logarithm, used in acoustics, two (2) is the logarithm of one hundred (100). Loudness: The subjective judgment of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure, a tenfold increase in acoustical energy, or, ten (10) dB(A) to produce a doubling of loudness. Loudness level: Measured in phones it is nu- merically equal to the median sound pressure level (dB) of a free progressive one thousand (1,000) Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud. Masking: 1. The process by which the threshold of audibility for a sound is raised by the presence of another (masking) sound. 2. The amount by which the threshold of audibility of a sound is raised by the presence of another (masking) sound. Masking noise: A noise that is intense enough to render inaudible or unintelligible another sound that is also present. Medium: A substance carrying a sound wave. Noise: Any sound which is unwanted, or does not occur in the natural environment (e.g., air- 1654.2