D.C. Mun. Regs. tit. 20, r. 20-2999
The meanings ascribed to the definitions appearing in § 2799.1 of Chapter 27 of this subtitle shall apply to the terms in this chapter.
In addition to the definitions cited in Chapter 27, the following words shall have the meaning ascribed:
Ambient - the noise remaining when the source being measured is turned off.
Calibration, external - the testing under controlled conditions of the sound level monitoring system, by use of a calibration device, whose input sound pressure level and frequency are accurately known, for the purpose of ascertaining the accuracy of the system at the input level and frequency within the meaning of the Act. The system includes a microphone, microphone cable, and sound level meter and its internal components.
Descriptors, acoustical - the following descriptors are often used:
dB(A) - A-weighted sound level measured in decibels;
Ld - daytime equivalent A-weighted sound level between the hours of 0700 and 2100;
Ldn - day-night average sound level; the twenty-four hour (24) weighted equivalent sound level, with a ten (10) decibel penalty applied to nighttime levels;
Leq - equivalent A-weighted sound level over a given period of time;
Leq(1) - the Leq (1) is used in measuring construction noise and is the value of a steady state sound which has the same A-weighted average sound energy as that contained in a time varying sound. In this case, it is the equivalent sound level measured over a one (1) hour period. It is measured best with a statistical noise analyzer;
Ln - nighttime equivalent A-weighted sound level between the hours of 0700 and 2100; - maximum A-weighted sound level for a given time interval or event; and
Lmax - maximum A-weighted sound level for a given time interval or event; and
Lx - x percent sound level, the A-weighted sound level equaled or exceeded x% of time. For example: L10: sound level exceeded ten (10%) percent of time (usually the loudest level): L50: sound level exceeded fifty percent (50%) of time; and L90: sound level exceeded ninety percent (90%) of the time (usually the quietest level).
External Calibration - the testing under controlled conditions of the sound level monitoring system, by use of a calibration device, whose input sound pressure level and frequency are accurately known for the purpose of ascertaining the accuracy of the system at the input level and frequency within the meaning of the Act. The system includes a microphone, microphone cable, sound level meter and its internal components).
Intermittent noise - a noise that goes on and off but that is steady while it is on.
Large reflecting surface - a surface that may cause an interference with the noise measurements being taken (a wall, for example).
Pure tone - a single frequency that predominates to the extent that it is audible. Pure tones are characterized by the following: a hum, moan, howl, whine, or whistle, depending on their frequency.
Qualified - calibrated by an authorized acoustical standards laboratory or an authorized factory representative.
Quasi-steady noise - a rapid series of impulses that has the same effect on the sound level meter as a steady noise.
Qualification - a comprehensive series of tests (including calibration using the full frequency response of a microphone, plus meter, plus A-weighted network) demonstrating compliance with ANSI specifications in addition to, but not required, calibration within the meaning of the Act.
Rapidly fluctuating - continuous noise whose level varies rapidly over a range greater than three (3) dB(A) read on the fast scale during the course of the measurements.
Slowly fluctuating - continuous noise whose level varies slowly over a range greater than three (3) dB(A) read on the slow scale during the. course of the measurements.
Steady noise - a noise whose level varies less than three (3) dB(A) read on the slow scale during the course of the measurements.
Source of violation - consists of a single source, or of several distinct sources if all are being operated on the property from which the noise originates.
D.C. Mun. Regs. tit. 20, r. 20-2999