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Task 6.6. Noise reduction methods




Calculate efficiency of the acoustic screen (find input data in Table F.6), using Interactive Sound Level Calculator (MAS Environmental - http://www.masenv.co.uk/noisecalculator2) or other available software. Compare calculated noise levels with maximum permissible levels.

Methodological guidelines for doing the task

Limitation of noise pollution. Environmental noise, also known as noise pollution, is among the most frequent sources of complaint regarding environmental issues in Europe, especially in densely populated urban areas and residential areas near highways, railways and airports. In comparison to other pollutants, the control of environmental noise has been hampered by insufficient knowledge of its effects on humans and of exposure–response relationships, as well as a lack of defined criteria.

The European Parliament and Council adopted Directive 2002/49/EC of 25 June 2002 with the main aim of providing a common basis for tackling noise problems across the EU. This Directive defines environmental noise as unwanted or harmful outdoor sound created by human activities, including noise from road traffic, railway traffic airports and industrial sites, and focuses on three action areas: the determination of exposure to environmental noise through noise mapping, based on common assessment methods; the adoption of action plans by the Member States based on noise-mapping results; and public access to information on environmental noise and its effects.

The principles of the Directive 2002/49/EC are similar to those underpinning other overarching environment policies (such as air or waste), i.e.:

· Monitoring the environmental problem; by requiring competent authorities in Member States to draw up "strategic noise maps" for major roads, railways, airports and agglomerations, using harmonized noise indicators Lden (day-evening-night equivalent level) and Lnight (night equivalent level). These maps will be used to assess the number of people annoyed and sleep-disturbed respectively throughout Europe

· Informing and consulting the public about noise exposure, its effects, and the measures considered to address noise, in line with the principles of the Aarhus Convention

· Addressing local noise issues by requiring competent authorities to draw up action plans to reduce noise where necessary and maintain environmental noise quality where it is good. The directive does not set any limit value, nor does it prescribe the measures to be used in the action plans, which remain at the discretion of the competent authorities.

· Developing a long-term EU strategy, which includes objectives to reduce the number of people affected by noise in the longer term, and provides a framework for developing existing Community policy on noise reduction from source.

Among the various effects of environmental noise, health effects are a growing concern of both the general public and policy-makers in the Member Status in Europe.

Most of the assessments performed so far to evaluate the impact of environmental noise have been based on the annoyance it causes. Its consideration as a public health problem with measurable health outcomes has been limited.

Considering the scientific evidence on the threshold of night noise exposure indicated by Lnight as defined in Directive 2002/49/EC, and Lnight value of 40 dB should be the target of the night noise guidelines to protect the public, including the most vulnerable groups such as children, the chronically ill and the elderly. Lnight value of 55 dB is recommended as an interim target for countries that cannot follow night noise guidelines in the short term for various reasons and where policy-makers choose to adopt a stepwise approach.

A constitutionally guaranteed right for environmental protection was reflected in the Law of Ukraine on the protection of atmospheric air (ЗУ “Про охорону атмосферного повітря”). In article 21 “Prevention and abatement noise” domestic and environmental noise measures for control the major sources of noise: transport, aviation, and railway are concerned

Steady noise is restricted in accordance with Sanitary norms of permissible noise in residential and public buildings and in the residential area (Санитарные нормы допустимого шума в помещениях жилых и общественных зданий и на территории жилой застройки, 03.08.1984 № 3077-84) by means of sound pressure levels in octave bands: 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz. For additional evaluation of noise A-weighted sound level LA is used. Equivalent sound level recommended for application in case sounds vary irregularly in level.

According to the State Sanitary Rules of planning and development of populated localities (Державні санітарні правила планування та забудови населених пунктів від 19 червня 1996 р. N 173) the maximum permissible level of equivalent and maximum noise levels were defined within the residential areas and in the vicinity of airports (Table F.4 and F.5).In the vicinity of airports the maximum permissible levels depend on the type of residential area: «A» – all types of building, including apartment houses, policlinics, schools and other educational institutions;«Б» and «B» - office building and hotels only;«Г» - office building only with additional acoustic treatment of the building.

The methods of noise control include:

- reduction of noise at source (development of new more environmentally friendly types of transport);

- reducing noise on the path of propagation (noise barriers, Fig. F.1);

- reduction of noise by soundproofing and sound absorption;

- active noise reduction methods;

- individual methods of noise protection (earplugs, earmuffs) urban planning.

The efficiency of acoustic barriers can be assessed in accordance with specific methodologies. Different approximate calculation tools for efficiency of acoustic screens on different distances were developed to simplify this process. One of them is the Interactive Sound Level Calculator, which is free for educational purposes and available on-line.

NOTE: Sound waves propagate as a sphere and follow the "inverse square law" of level reduction. A general rule is that the level reduces by 6dB per doubling of distance.

As sound waves travel through the air a small portion of the energy is converted into heat depending upon the atmospheric temperature and humidity, however the amount is only significant with high frequencies and long distances.

Sound waves will be reflected or absorbed by the ground depending upon the frequency of the sound wave and how porous the ground is (indicated by the "Ground Factor" value G). Barrier insertion will take precedence over ground effect, the effect is not cumulative.

For "Hard Ground" G = 0. Hard ground is assumed to reflect all sound waves. Examples include roads and paved areas.

For "Soft Ground" G = 1. Soft ground is porous and is assumed to absorb all sound waves. Examples include grass, trees and other vegetation.

For "Mixed Ground" use a value for G between 0 and 1 that represents the fraction of the ground that is soft.

Sound waves are reduced by a barrier depending upon the frequency of the sound wave, lower frequencies are less affected. A general rule is that a barrier at eye level with a source and receiver will reduce the level by approximately 5dB.

How to use the Interactive Sound Level Calculator:

1. Download the Interactive Sound Level Calculator (http://www.masenv.co.uk/noisecalculator2)

2. Choose between "Single Frequency" for tonal single sources.

3. Enter values for distances & sound levels or click and drag the items in the diagram to modify their position. Click "scale ratio" to reset the diagram for best viewing.

a. Enter T=20°C, Humidity – 50% and Ground Factor – 1 (Soft) for all variants. b. Enter input data from Table F.6 in accordance with the number of your variant.

Example of calculation

For the following input data:T=15°C, Humidity – 90% and Ground Factor – 0 (Hard);Height of the sourse – 0.9 m; Distance to the barrier – 2.5 m;Height of the barrier – 1.9 m;Distance to the receiver – 6 m;Height of the receiver – 2 m;Frequency – 500 Hz;Sound Power Level – 55 dB.The Resulting sound pressure level is equal to 31.4 dB (Fig. F.2). c. Copy resulting sound pressure level (dB) and compare with permissible sound levels LAmax within the residential area (Table F.4). For variants 1-15 – you should choose permissible sound levels for area in the vicinity of residential houses (day time), for variants 16-30 - for area in the vicinity of hospitals, health resorts (night time).

4. Move the barrier top to change its position, click the barrier body to toggle on/off.

5. In "Single Frequency" mode click Σ for a breakdown of the calculation steps.

6. Copy values reduction of sound pressure levels in third-octave frequencies band for the examined screen and total sound levels.






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