Community Noise Equivalent Level Research Articles

Detailed CNEL/Ldn roadway noise calculations vs. estimation methods

Roadway traffic noise calculations of the community noise equivalent level (CNEL) and the day-night average sound level (Ldn) metrics are sometimes required for various federal, state, and local government permitting requirements. To complete calculations of these metrics, detailed hourly traffic data is needed and obtaining this data can sometimes be a challenge. This paper explores various estimation strategies that are sometimes employed for situations where this data is not available and compares the estimates against calculations using detailed hourly traffic data to assess their validity. Project examples are provided of various permitting efforts such as those in support of California Environmental Quality Act (CEQA) documents, roadway projects at airports for Federal Aviation Administration (FAA) National Environmental Policy Act (NEPA) documents, and other local permitting requirements.

Variations of road traffic noise in residential areas

The ability to predict road noise in urban area is important. The community noise equivalent level (L(den)) varies from day to day (weekdays, weekends, holidays, etc.). There is a need to compromise between the accuracy in the determination of L(den) and limited resources of input data, the measuring equipment, and time. The problem can be managed using the method proposed in this study. It requires only one short-term measurement of the time-average sound level, L(Aeq,T).

Assessing noise impacts on wildlife under the National Environmental Policy Act.

Under the National Environmental Policy Act, authors must address environmental impacts of various anthropogenic actions on wildlife. One such impact of increasing awareness and concern is effect noise on wildlife, both during construction and operation of the project. However, biologists often have difficulty in understanding the fundamentals of acoustics and noise analysts often have difficulty in understanding the biological implications of increased noise on wildlife. As a result, inappropriate weighting metrics (such as A-weighted decibel) or time descriptors (e.g., community noise equivalent level) are often used erroneously to assess noise impacts on wildlife. Noise exposure thresholds on wildlife exist for marine mammals and fish, as mandated by the National Marine Fisheries Service. However, no such thresholds exist for terrestrial wildlife. This talk provides specific examples of how noise impacts on wildlife have been assessed using GIS-based technology, industry-accepted noise propagation models, and peer-reviewed literature in the absence of management guidelines. Examples include assessing construction noise impacts on the California coastal gnatcatcher in southern California, aircraft noise impacts on sage grouse in central California, and helicopter disturbance on caribou in Alaska.

Noise codes for residential spaces in Los Angeles

The State of California is rather unique in using the community noise equivalent level (CNEL) rating to assess the amount of environmental noise transmission into buildings, not just to apply this index to gauge airport noise. When residential housing units in Los Angeles undergo construction or renovation, a certificate of housing compliance must be obtained before tenants or condominium owners are allowed to move in, in accordance with the provisions of Section 91.0318 of the Los Angeles municipal code. As a part of the application procedure for the certificate, a licensed acoustical engineer must prepare an acoustical report that describes the type of construction between dwelling units and the general sound attenuating properties of such construction, including hard numbers for sound attenuation between dwelling units. A field sound transmission class (FSTC) test is mandated, with a minimum required FSTC rating of 45 between the walls of adjacent units. If the FSTC test is not passed, remedial action must be taken so that the proper amount of acoustic insulation is achieved between the dwelling units.

CNEL at two sites in Del Mar, due to a hundred helicopter flybys

In the Settlement Agreement in early 1999 of a lawsuit about helicopter noise, in which the City of Del Mar was one of the plaintiffs and the Marine Corps was one of the Federal defendants, there was a requirement that the community noise equivalent level (CNEL) be included as a standard for measuring noise significance. This is a preliminary report about CNEL measured continually at two sites in south Del Mar, California. In both cases the residents had filed official complaints about the noise of helicopters. These residences are distance from heavily traveled streets and highways. The automatic noise monitor consists of a Computer Engineering, Ltd., 493-2 integrating sound-level meter feeding a CEL-238 secondary processor, all in a weather-proof case. The outfit prints, and puts in memory, the one-hour average sound level during a preceding hour and at the end of a day the 24-hour average sound level (24 HL), the day–night average sound level (DNL), and the CNEL. At 22839 Via Grimaldi, Friday to Wednesday 5–10 May 99, the CNELs were 55.8, 55.5, 54.6, 55.9, 58.7, and 58.7 dB. At 421 Ocean Drive, Tuesday to Saturday 11–15 May 99, the CNELs were 58.4, 56.5, 59.6, 58.6, and 60.5 dB.

Six months of continuous measurement of one‐hour average sound levels, one mile sidewise from NAS Miramar, San Diego

From 18 July 1994 to 17 December 1994, 1‐h average sound level was measured continuously by Computer Engineering Ltd. model 493 integrating sound level meter feeding model 238A secondary processor. The time‐mean‐square average level printed automatically on the hour, and recorded in an RS232C memory for later analysis, is that during the hour preceeding the hour printed. The site of noise monitoring is the roof 7084 Miramar Road, San Diego, about a mile sidewise north of Runway 6L‐24R, NAS Miramar. After adjustments to remove steady ventilating and compressor noise, aircraft noise was tabulated for each day as community noise equivalent level (CNEL), the day‐evening‐night weighted 24‐h average level specified for California airports. The 148‐day average CNEL was 69 dB. In one week CNEL varied from 58 dB on Sunday to 75 dB on Tuesday. Such noise variability is being investigated in relation to future movement of Navy aircraft from Miramar to NAS Lemoore, and Marine aircraft from MCAS El Toro to Miramar. Also being here reported for 7084 Miramar Road are the A‐weighted sound exposure levels (ASEL) in excess of 100 dB; the greatest thus far is 116 dB.

Noise control: Experimental research in Kuwait

Abstract Environmental noise has been found in many experimental research studies in Kuwait, to be a prominent factor which influences the level of satisfaction with a particular residential environment. This can be seen also as a consequence of the higher level of awareness today about the adverse effects of excess noise on human beings and their environment. The effects of noise, criteria, community noise in Kuwait, aircraft noise impact on the airport environs, and fuzzy set concepts for evaluating noise interference models, are the topics of this paper. Review of the experimental research and results of the analysis show that the community noise equivalent level [CNEL] was significantly correlated with both the prevalence of the complaints and their severity. The airport management should set up a noise abatement committee to develop procedures that are mutually acceptable and will have the least objectionable noise impact on urbanized areas. Recommendations for further studies are also presented.

Residential noise insulation for mild climates

Since 1974 the California Building Standards Law has required that new multifamily housing, hotels, and motels be designed to prevent the intrusion of exterior noise above a community noise equivalent level of 45 dB. At about the same time, the State also adopted energy insulation standards which require low air infiltration rates for new dwellings. While these requirements seem to be complementary from the standpoint of noise insulation, the relatively mild climate of costal communities often obviates the need for air conditioning or even mechanical ventilation. This paper discusses some of the design, cost, and enforcement conflicts between adequate ventilation and noise insulation for areas with mild climates.

Administering a “noise budget” for a civil airport

“Noise budgets” offer air carrier airports a means for achieving noise control without imposing rigid restrictions of numbers of operations or types of aircraft. This paper describes the application of noise budget concepts to actual administration of operations at a medium size air carrier airport. The airport's noise budget is based upon consideration of the noise‐incompatible land use areas within a specified community noise equivalent level (CNEL) contour. However, budget controls for air carriers are expressed in terms of the “equivalent numbers of operations” where the equivalent number is based upon the number of opertions per day, evening, and night periods and the relative noise levels produced by different aircraft. The relative noise levels are derived from data from the airport's permanent noise monitoring system. Samples of the budget analyses that are undertaken to evaluate changes in air carrier schedules will be presented.

Noise‐insulation requirements for multi‐family dwellings

Noise insulation standards are part of the California Administrative Code (Title 25, Section 1092). These standards apply to all new multi‐family dwelling units such as hotels, apartments, duplexes, townhouses, and condominium units. Detached single‐family dwellings are specifically excluded. The standards establish minimum requirements for the isolation of interior spaces from exterior noise and set minimum ratings for noise insulation of partitions between dwelling units. A community noise equivalent level (CNEL) of 45 dB is set as the maximum for intrusive noise from exterior sources such as rail or road traffic, or aircraft operations. American Society for Testing and Materials (ASTM) testing procedures for party wall and floor/ceiling system sound transmission provide the basis for setting minimum acceptable performance for separations between units. As a consultant to builders, planners, and architects, the site planning and design of residential projects have been examined and field evaluations have been performed on completed projects. Building designs and the selection of suitable building elements (wall construction composites, window assemblies, vent configurations, etc.) which assure compliance with the standards have been identified. The paper provides a brief description of the standards, their enforcement pitfalls, and an assessment of their impact on residential construction in California.

Temporal sampling requirements for estimation of long-term average sound levels in the vicinity of airports

Community noise temporal sampling requirements in general, and in the vicinity of airports or other large noise producers in particular, are not well understood. Frequently, the purpose is to sample and estimate the true yearly Day/Night Average Sound Level (DNL) or Community Noise Equivalent Level (CNEL). This being the case, it is important to note that day-to-day samples are not independent, but, in fact, the time series formed by these day-to-day samples exhibits an autocorrelated structure. For this reason, sampling requirements are 4 to 8 times larger than are calculated by assuming purely random day-to-day data. Moreover, the data may exhibit weekly and yearly deterministic trends. As a result of those factors, the analysis herein shows that sampling requirements sufficient to achieve a precision of +2 to −3 dB of the true yearly CNEL or DNL value with a 95% confidence level can be summarized as 14 days of totally random sampling throughout the year, or 3–4 weeks of quasi-random sampling taken one week at a time, or at least 30 days of totally continuous sampling.

Development of temporal sampling strategies for monitoring noise

This paper addresses the problem of the estimation of the long term (yearly) mean of the Community Noise Equivalent Level (CNEL) or day/night average sound level (LDN). Examination of daily average noise levels (either in mean‐square pressure or in decibel units) shows that while the data may be stationary with respect to mean level over a several month period, they exhibit a strong pattern of autocorrelation in which positive correlation predominates. As a result, the sample sizes required to achieve a desired level of precision in the sample‐mean estimate are much larger than they would otherwise be if the data were uncorrelated serially in time. For the data examined, to obtain an estimate of the mean level within a 5‐dB range (±50% of the mean in mean‐square‐pressure units), sample sizes in the range of 20 to 50 consecutive daily averages would be required. If the daily averages were uncorrelated in time, only 5 to 15 consecutive daily averages would be required. The data used in this study were obtained from continuous monitoring at a number of sites in the vicinity of a busy Naval Air Station. Some data obtained from a large commercial airport were also analyzed and found to have even stronger positive autocorrelation and therefore requiring even larger sample sizes for mean‐value estimation.

Development of temporal sampling strategies for monitoring noise

This paper addresses the problem of the estimation of the long-term (yearly) mean of the Community Noise Equivalent Level (CNEL) or day/night average sound level (LDN). Recent environmental noise standards have emphasized the significance of this problem. While it is possible to continually monitor the noise level, it is not necessarily desirable or practical. It is desirable to sample the level over a relatively short period of time and use this information to draw reliable inferences about the long term mean level. Examination of daily average noise levels (either in mean square pressure or in decibel units) shows that while the data may be stationary with respect to mean level over a several month period, they exhibit a strong pattern of autocorrelation in which positive correlation predominates. As a result, the sample sizes required to achieve a desired level of precision in the sample mean estimate are much larger than they would otherwise be if the data were uncorrelated serially in time. To assess the level of autocorrelation in the data, autoregressive-moving average (ARMA) models are developed for the noise data via the Dynamic Data System (DDS) approach to time series analysis. These models are then used to derive estimates of the sample mean variance and therefore to establish sampling strategies. For the data examined, to obtain an estimate of the mean level within a 5-dB range (±50% of the mean in mean square pressure units), sample sizes in the range of 20–50 consecutive daily averages would be required. If the daily averages were uncorrelated in time, only 5–15 consecutive daily averages would be required. The data used in this study were obtain from continuous monitoring at a number of sites in the vicinity of a busy Naval Air Station. Some data obtained from a large commercial airport were also analyzed and found to have even stronger positive autocorrelation, and therefore requiring even larger sample sizes for mean value estimation.

Development of an integrated airport noise model

A set of computer programs, called Integrated Noise Model (INM), has been developed to compute noise exposure values due to aircraft at various locations around airports. The INM evolved from an earlier computer model used for investigating noise around 23 U. S. airports in terms of NEF. The INM consists of three independent routines: (1) Contour Analysis Model, (2) Grid Analysis Model, and (3) Contour Plotting Pack.age. INM will compute noise exposure values for the following: Noise Exposure Forecast (NEF); Day—Night Average Sound Level (Ldn); Community Noise Equivalent Level (CNEL); Aircraft Sound Description System (ASDS); and Daily Overall Sound Exposure (DOSE, an experimental noise metric). The calculations are sensitive to details of fleet mix data and flight operational procedures. The Contour Analysis Model develops points on curves of equal noise exposure. The Grid Analysis Model computes exposure levels at user‐specified points. Optional output allows examination of the noise contribution from each flight. The Contour Plotting Package retrieves contour point locations from mass storage and plots them. [Work supported by U. S. Department of Transportation.]

Development of airport noise contours by extensive noise monitoring and analytical modeling

This paper describes one of the first known efforts to combine analytical modeling techniques and extensive field noise monitoring to produce airport noise contours. The objective was to produce community noise equivalent level (CNEL) contours whose accuracy could be enhanced and defended by field measurements. An advanced computer simulation model (developed for the U. S. Air Force) was used in concert with 24-h noise monitor data at 44 locations surrounding Miramar Naval Air Station at San Diego, CA. A three-phase study was undertaken to satisfy the objective: (1) develop a preliminary set of contours using the analytical model and the best available data base, (2) use contours to select noise monitor locations and acquire monitor data, and (3) normalize monitor data to typical flying conditions and update noise contours. The paper discusses the variables involved in generating the contours, their ability to be reliably measured at reasonable cost, and their relative impact on contour accuracy.

Variability in the day‐to‐day noise environment near airports

The 24‐h noise data now being acquired at a number of airports are providing information on the day‐to‐day variations in noise environment. Community noise equivalent level (CNEL) data acquired at four airports (three civil and one military), based on measurements at 16 positions and for periods ranging from 13 to 193 days, show trends that may be useful for planning purposes. Plots of the standard deviation for the daily values (weekdays only for the military airport) versus the logarithm of a typical distance from the aircraft to the monitoring position show that the variability increases slowly with distance from the aircraft. The standard deviations at positions under the landing path (distances of approximately 400 ft) are of the order of 2 dB. The standard deviations increase to the order of 3 dB at a distance of 3000 feet. The weekday and weekend noise environment near the military airport shows distinct differences reflecting the large reduction of operations on weekends. Correlation of daily nois...

Automatic Airport Noise Monitoring System

The acoustical parameters which have to be considered in a noise monitoring system are examined. Individual aircraft operations are characterized by the parameter single event noise exposure level. community exposure is characterized by values of hourly noise level and community noise equivalent level. A general description is given of an aircraft noise monitoring system which was designed and built to performance specifications prepared by the airport engineering department in accordance with state requirements.

A Building Code for Exterior-Noise Isolation

A building code has been formulated to describe various constructions to cause a specified noise-level reduction in a given noise zone in the city of San Diego. Noise-level reduction means reduction in average A-weighted sound level from outside to inside a building. The average noise level is that called the annual community noise equivalent level according to now effective “Noise Regulations for California Airports”; this average is a mean-square A-weighted sound-pressure level obtained with the noise levels existing between 7 p.m. and 10 p.m. increased by five decibels and the noise levels between 10 p.m. and 7 a.m. increased by 10 decibels. A noise zone is an area of the city bounded by contours of annual community noise equivalent level, at intervals of five decibels. Noise-level reduction is required by the code such as to limit to 45 decibels the average noise level inside a residential building due to outside noise of whatever source. For calculating noise-level reduction from room size and construction materials, a noise spectrum is specified that is typical of aircraft and other noise in one of the noise zones. If needed to verify compliance with the building code, a simple test of noise-level reduction is provided that can be performed with noise generally prevailing outside the building.

Industrial Noise in the Community—Current Views

Noise from industrial plants has continued to be a problem for both the plant managements and their neighbors. Several recent studies have indicated that the majority of persons in residential areas are exposed to ambients set by transportation noise sources. This is of little comfort to the immediate neighbors of an industrial plant whose noise dominates a small region surrounding the plant. Recent acceptance of the A-weighted sound level to rate noise, results of several Federal studies, and an evaluation of the Normalized Community Noise Equivalent Level (NCNEL) have changed the community-industry situation little, but prepare the way to develop workable methods for rating noise situations in a manner similar to the earlier Composite Noise Rating, but without measurement of the spectrum. Furthermore, the interrelationship of a community and its industrial neighbors appears to play a major part in the acceptance of the noise levels surrounding the plant. This leads to the conclusion that there is no universal method of rating community noise that will satisfy any given percentage of neighbors in a community without first determining attitudinal factors that can be applied in the noise evaluation as weighing factors. Further research is currently under way. This effort is critical since current work to reduce transportation noise may lead to a situation where industrial noise becomes dominant in the major portion of many more communities.

Instrumentation for the California Airport Noise Standards

California law requires measurement of both hourly noise level (HNL) and total daily noise exposure (Community Noise Equivalent Level, or CNEL) in the vicinity of airports. The 24-h total is determined by a formula which adds greater weight to evening and nighttime noise because of the additional annoyance experienced during those hours. An instrument is described for determining these noise levels. The hourly noise computation is performed by sampling, squaring, digitizing, and storing in memory a cumulative sum-of-the-squares of voltages proportional to the sound-pressure level. The 24-h total is obtained by additional pre-scaling, chosen to give the required evening and night weightings. The contents of both the HNL and CNEL memory registers are converted to decibels for the final output. Recently developed MOS integrated circuits make possible battery operation with very low average power drain. A novel printing head consisting of resistors deposited on glass “burns” the answers into thermochromic paper once each hour, with an additional printout at midnight for the daily CNEL. Sample measurements obtained near Logan Airport, Boston, are presented.