As used in this chapter, unless the context otherwise clearly indicates, certain words and phrases used herein are defined as follows:

(a) Ambient, Local. “Local ambient” is the all-encompassing noise associated with a given environment, being usually a composite of sounds from many sources, near and far. The ambient noise level is the level obtained when the noise level is averaged over a period of fifteen minutes without inclusion of noise from isolated identifiable sources, at the location and time of day near that at which a comparison is to be made. For the purpose of this chapter, in no case shall the local ambient be considered or determined to be less than:

(1) Thirty dBA for interior noise in section 13A-3 (b); or

(2) Forty dBA in application to all other sections hereof.

(b) dB. “dB” means decibel as herein defined.

(c) dBA. “dBA” means decibels measured on an A-weighted scale, as herein defined in subsection (f) entitled “Noise level measurement.”

(d) Decibel. The “decibel” is a unit measure of sound (noise) level relative to a standard reference sound on a logarithmic scale. The decibel level of a given sound is determined as twenty times the logarithm to the base ten of the ratio of the pressure in micronewtons per square meter of the sound being measured to the standard reference sound pressure of twenty micronewtons per square meter (0.0002 microbar).

(e) Emergencies. Essential activities necessary to restore, preserve, protect or save lives or property from imminent danger of loss or harm.

(f) Noise Level Measurement. For the purpose of enforcement of the provisions of this chapter, noise level shall be measured in decibels on the A-weighted scale with a sound level meter satisfying at least the applicable requirements for Type 1 or Type 2 sound-level meters as defined in the most :recent American National Standard Specifications. The meter shall be set for slow response speed, except that for impulse noises or rapidly varying sound levels, fast response speed may be used.

For outside measurements the microphone shall not be less than four feet above the ground, at least four and one-half feet distant from walls or similar large reflecting surfaces, and shall be protected from the effects of wind noises and other extraneous sounds by the use of screens, shields or other appropriate devices; for inside measurements, the microphone shall be at least three feet distant from any wall, and the average measurement of at least three microphone positions throughout the room shall be determined.

(g) Property Plane. A vertical plane including the property line which determines the property boundaries in space. (Ord. No. 1380, § 2.)