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MAY 1994 BL I I I IIII AMERICAN PLANNING ASSOCIATION How to Draft an Effective Noise Ordinance £y James Cowa, Most municipalities include noise ordinances in their adminis- trative and/or zoning codes. Man)', however, are worded in ways that render them unenforceable or ineffective. This issue of Zoni,g News provides the key points to include in a noise ordinance to ensure its maximum effectiveness and enforceabiL it'3.'. First, however, it is important to understand the effects of noise on people to establish the need for effective noise codes. Although the one noise-induced impact most people would name first is hearing loss, this usually results from sound levels that are much higher than those commonly found in communi- ties. Common environmental noise sources, however, have been linked by researchers to several stress-related illnesses, most notably cardiac and circulator), diseases. Noise can also compro- mise concentration, communica6on, and sleep, creating anything from annoyance to potentially hazardous situations. Acoustic Terminology Definitions are important if an ordinance is to be enforceable. The most common technical terms used to describe noise are decibels and octave band levels. Decibels are the units normally used to assess the loudness of a noise source. A decibel has meaning only if related to some me. asured ouantiw such as pressure or power. In noise analyses, sound pressure is the usual qua.ntit7 referenced, and the decibel level is then calied a sound pressure level (SPD. SPL varies with distance from a DOJSe SOUTCC, SO, readings must be identified in terms of their locations. SPL typically is monitored in terms of overall readings that provide a single decibel value taking into account all frequencies or pitches. But certain cases in noise analysis require a more detailed look at sound levels in terms of frequency segments. These segments, rypically called bands, allow a researcher to view the frequen%, content ora sound signal. This can be a useful tool for noise-control engineers or acousticians but can easily introduce complexities into the enforcement process for those with little technical background in the acoustical field. The most common frequency bands are known as octave band-s, which are standardized frequency bands. Each band contains frequencies that are t~,ice the value associated with the preceding band. An SPL associated with each band is known as an octave band level, as is typically used in equalizers on stereo equipment. Avoid Ineffective Ordinance Language Many noise ordinances have enforcement criteria that are too technical or complex in nature for average officers to understand. Such codes require complex monitoring using man), locations, orientations, and data values. A common example is the limitation in terms of octave band sound tevels. instruments that measure sound levels in terms of octave bands known as octave band analyzers, can be complicated to operate, and the results can easily be misinterpreted by people who have minimal experience in their use. A.n appropriate rule is that the more complicated the measurements are ro perr%rm, the better the chance for misinterpretation. To make matters worse, many ordinances that specify the use of octave bands use antiquated nomenclature. Before the earl), 1970s, octave bands were described in terms of a range of frequencies, as shown in Table 1. New York CiD, and Chicago still use such octave band designation for their manufacturing district limits. Current standards, according to the American National Standards institute (ANSI) and the International Organization for Standardization, require the designation of octave bands in terms of a single geometric center frequency, also shown in Table 1. These frequencies correspond to a frequency range, but it is not the same as the old range shown in the table. Octave band analyzers manufactured since the 1970s are based on these current center frequencies. Therefore, an analyzer manuhcrured within the last 20 years probably would not measure levels conforming with the old frequency ranges. Correction factors would have to be added to all data gathered from instruments that conform with current standards, compounding the complexity of the enforcement process. Most of the time, The $o..m?act size of this Type 2 Sound Level M'e're~? ~ak~s 4~q.,good choice for industrial, militaO';~l~w enforcement, and envi~3~;enral applicariom.