Intensity of noise of the different sources, dB

Brief Theoretical Notes

High volumes of traffic characterize highly industrialized countries. Noise is perceived as a serious environmental nuisance. Noise reduces the “quality of life” and causes a significant health hazard. For example, people living nearby to busy roads tend to have higher blood pressure. In addition to the risks to human health, noise pollution has negative ecological impacts on species sensitive to noise.

Noise is defined as unwanted sound, it can be considered as the wrong sound in the wrong place at the wrong time.

Noise can be emitted from a point source, an areal source or a line source. Noise diffuses rapidly from its sources and at an adequate distance from the source. Noise pollution sources include

- traffic – the main source;

- industrial equipment;

- construction activities;

- sporting and crowd activities;

- low-flying aircraft.

Sound is defined as any pressure variation that the human ear can detect. Some of the elemential noise parameters are:

Amplitude (A) – the maximum or minimum pressure;

Wavelength (λ) – the distance between successive troughs or crests;

Period (P) – the time between successive troughs or crests;

Frequency (f) – the number of complete pressure variations or cycles per second;

Speed of sound (c).

Period and frequency are related by P=1/f.

Wavelength and frequency are related by λ=c/f.

The sound power level is estimated in decibels (dB). The hearing range extends from a frequency of about 20 to 20,000 Hz.

Intensity of noise of the different sources, dB

Source of noise	Level of noise, dB
Forest in winter, when the weather is calm
Whisper
Viladge
Library
Factory department
Salon of car
Mechanical pick
Heavy trucks
Music orchestra
Lightning
Jet plane at the distance 25 m
Start of space rocket

Sound can be classified as continuous, intermittent, and impulsive. A continuous sound is an uninterrupted sound level that varies less than 5dB during the period of observation. An intermittent sound is a continuous sound that lasts for more than one second but then is interrupted for more than one second. If a sound is of short duration, less than one second, it is classified as an impulsive sound.

Loudness is a person’s perception of a sound strength and to some extent it is subjective. Loudness varies with both the sound level pressure and frequency. It means that two sounds with the same sound pressure level in dB but at different frequencies will be heard as different loudness levels.

The hearing damage potential of a given noise source depends on its level and its duration. It is generally accepted that a sound environment below 75 dB is not harmful. A single sound above 140 dB may produce hearing damage. Between these two levels the amount of hearing damage varies with the sound level, the length of exposure and the individual’s susceptibility to noise.

Hearing loss may be either temporary or permanent. Exposure to high noise levels for a short period of time can result in a temporary loss of hearing that may last for several hours. Repeated exposure to high noise levels may result in permanent hearing damage. Environmental noises are seldom high enough to cause hearing damage.

Consequences of noise influence for human have a wild range of effects – from irritability to hearing loss. Noise disturb human rest, effective work, and can cause headache, fatigue. Noise influence has such possible effects as damages of nervous system, high blood pressure, heart problems and ischemia. Besides noise increase the development of disease, which already exist. Noise reduce the lifetime by 8-12 years. High level of noise can be reason of nervous exhaustion, psychical opression, neurosis, ulcer, changes in central nervous system.

At night the levels go from 35 dB (in suburban areas) to about 52 dB (in urban areas). Busy roads cause exposure of about 80 dB(A). The type of work or activity determines the noise exposure during daytime hours. This can range from 55 dB(A) in a quiet office, for example, to 90 dB(A) in noisy factories.

The European Economic Commission of UN defined the maximally permissible levels of noise: for passenger cars – 80 dB; for busses and trucks – 81 - 88 dB. So the scale of traffic noise levels matters from 0 dB to 150 dB and the noise of levels 0-80 dB are permissible and 80-150 dB are impermissible.

The values of harmful noise are legislatively set in Ukraine. The levels of noise are certain Technical instruction of protecting from noise (TI Noise, 1968) and State engineering’s norms for industries of building – SEN 18 005 (5, 1987) depending on character of territory:

Permissible levels of noise according to the character of territories (in Ukraine)

Character of territory	Permissible level of noise, dB
daily time (from 7 ^00 to 23 ^00)	night-time (from 23 ^00 to 7 ^00)
Industrial area
Living area
Central districts of the city
Rural area
Area of mass rest and tourism
Sanitary resort area
Preserves
Houses (inside) located near highways

Task

1. Calculate the level of noise at the distance for 7 m from the road by the formula:

V ₇=46+11,8*lg N + X_N + X_V + X_i + X_ТR, (dB)

where N - intensity of traffic on the road (vehicles/hour);

X_N – correction factor, which take into account share public and cargo transport (factor increase or decrease by 1 dB according to increasing/decreasing of 60% share by 10%);

X_V – correctionfactor, which take into account changes of speed of vehicles (increase for 1 dB per 4 km/hour from 40 km/hour);

X_i – correction factor, which take into account angle of road slope (increase by 1 dB per 2° of slope);

X_ТR – if the road have tram railway this correction factor = 3 dB.

(Р 2+ Р 3+ Р 4+ Р 5)*100%
XN, dB	-6	-5	-4	-3	-2	-1

Speed of vehicles, km/hour
XV, dB

Angle of road slope, °
Xi, dB			3,5

2. Compare received result with permissible level of noise, which is 80 dB according to the standards of the EEC of the UN (directly near the road).

3. Calculate the level of noise at the distance from the road that you interests (Vn)by the formula:

Vn = V₇ – X1 – Х2 – X3 – Х4, dB

where n – is a distanse, m;

V ₇ – a level of noise at the distance for 7 m from the road, dB;

X1 – correction factor, which take into account the decline of level of noise as a result of sound-waves distribution in the atmosphere

X1 = I0 of lg (n / 7), dB;

Х2 – correction factor, which take into account noise absorption by the earth surface

Х2 = Кs ∙ X1, dB

where Ks – coefficient of noise absorption by the earth surface (It is 0,9 for an asphalt, 1 – for open soil, 1,1 – for a lawn);

Х3 – correction factor, which take into account noise absorption by the green planting

X3 = Кp ∙ X1, dB

where Кp – coefficient of noise decline by the green planting (It is 0,7 for the bushes of middle closeness or trees grow rarely; 1,0 – for to the bushes of middle closeness and trees grow rarely; 1,2 – for strip of trees and bushes of middle closeness 6 m wide; 1,5 – for strip of bushes and trees height 7, tops of which closed up; 3 – for park and forest-park areas);

X4 – coefficient of noise absorption by the buildings (It is 25 dB).

4. Compare received result with permissible level of noise, which is 55 dB during the day and 45 dB at night for living districts of the city.

Дата добавления: 2015-10-31