The Basics of Noise

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The Basics of Noise （This website is made by Osaka prefectural government, Japan.）
Contents:
1. The Basics of Sound 1.1 What Is Noise 1.2 The Three Elements of Sound 1.3 Frequency and Wavelength 1.4 Loudness Contour 1.5 Effects of Noise 2. Quantitative Assessment of Noise 2.1 Sound Pressure Level and A-weighted sound pressure level (noise level) 2.2 Percentile level (LAN, T) 2.3 Equivalent continuous A-weighted sound pressure level (LAeq) 2.4 Sound exposure level (LAE) 2.5 Weighted Equivalent Continuous Perceived Noise Level (WECPNL, Japan) 2.6 Types of Noise 3. Decibels 3.1 Definition and Logarithmic Calculation 3.2 Decibel Addition 3.3 Decibel Level Difference (Compensation for Background Noise) 3.4 Average Decibel Level (Average Power) 4. Sound Propagation 4.1 Sound power of a source and Sound Power Level 4.2 Sound Propagation 5. Frequency Analysis 5.1 Frequency Characteristics of Sound 5.2 Octave Band Analysis

1. The Basics of Sound
1.1 What Is Noise
Noise is defined as "unwanted sound that, for example, impedes the hearing of voices, music and so forth, or causes pain or obstructs lifestyle. (JIS Z 8106 [IEC60050-801] International electrotechnical vocabulary Chapter 801: Acoustical and electroacoustics)." Of other environmental pollution, noise pollution is special in that; [1] Personal and subjective judgment is a big part of recognizing a sound as noise pollution or not, and;
[2] The damage is localized and sporadic in comparison to water pollution and air pollution. (Aircraft noise is an exception here.)

In regards to characteristic [1] above, there is the problem of how to rank noise between the degree that an individual subjectively perceives as "loud" and an objectively measurable physical level. With characteristic [2], there is not a clear distinction between who is the aggressor and who is the victim, as often there are victims of nearby noise such as pianos and karaoke. Though there has been a decrease in the number of complaints registered with municipalities over the past few years, noise still accounts for a large proportion of civil complaints (Fig. 1-1).

Fig. 1-1 Complaints about pollution in Japan by type

Note: Complaints about land subsidence were omitted from the table as it was hard to represent.
Source: Environmental Dispute Coordination Commission

1.2 The Three Elements of Sound
When the keyboard of a piano is pressed, a person senses the "loudness", "pitch" and "tone" of the emitted sound. These are quantities that express the sensorial quality of sound and are known as the "three elements of sound".
As the physical quantities of "loudness", there are amplitude and sound pressure level. For "pitch", it is frequency. With "tone", there is a wide range of physical quantities, the trend today being to think of all that constitutes the character of the sound, including pitch, loudness and spectral distribution, as "tone".

1.3 Frequency and Wavelength
Think a moment about the particles that air is made of. Where these particles are dense, the air pressure increases, while, where they are sparse, pressure decreases. The phenomenon propagated by this change in pressure is a sound wave. A sound wave travels at the speed of sound in a wavelike motion. The distance between two geographical points (e.g., two points between which the maximum sound pressure of a pure sound is produced) distanced apart by only one period and which demonstrate the same sound pressure is called the "wavelength", expressed as (m). Then, if the sound pressure at an arbitrary point changes periodically, the number of times that this periodic fluctuation repeats in 1 sec is called "frequency", expressed as f (Hz, see Fig. 1-2). Sounds of high frequency are high-pitched, whereas low frequency sounds are low-pitched. The relationship of sound speed c (m/s), wavelength l and frequency f is expressed as follows.

c = f x The wavelength of audible sound is between a few centimeters and about 20 m. Most of the objects in our surroundings are within this range. The quality of a sound, which is effected by the roughness of reflecting surfaces, the height of fences and other factors, will differ as a ratio of the wavelength to the dimensions of the object, hence the issues are more complicated.

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1.5 Effects of Noise
Given the definition of noise of 1.1, if a sound disturbs reading or music listening, it is noise to that person even though others may not be bothered by it. Though the effects of sound have much to do with psychological and emotional factors, there are cases in which severe effects such as a loss of hearing are incurred because of the loudness of the A-weighted sound pressure level or the duration of exposure to the noise.

Table 1-1 Types of effects of noise Type Description Bodily effects Loss of hearing Noise induced temporary threshold shift, Noise induced permanent threshold shift Physiological effects Increase in discomfort or stress, increase in blood pressure, headaches, ringing Psychological effects Emotional disturbances Aggravation, distraction Lifestyle disturbances Sleep or rest disruption, loss of concentration when working, reading, etc. Hearing disturbances Impeding ability to hear TVs, radio, conversations, telephones, etc.

Noise Measurement
Contents:
1. Equipment Used in Measurement and Analysis 1.1 Noise levelmeter 1.2 Level Recorder 1.3 Audio Recorder 1.4 Frequency Analyzer 2. Combinations of Measuring Equipment 2.1 Recording A-weighted sound pressure level On-site 2.2 Making an Audio Recording of A-weighted sound pressure level 3. Noise Measurement Methods Specified by Japanese Law 3.1 Regulations 3.2 Measurement Method in Relation to Regulatory Standards 4. Noise Measurement Plans 4.1 formulating Measurement Plans 4.2 Measurement Preparations 4.3 Precautions in Measurement 5. Procedure for Measuring Factory or Business Site Noise for Imparting Guidance on Regulations or Countermeasures

The Basics of Vibrations and Vibration Measurement
Contents:
I. The Basics of Vibrations 1) Propagation of Vibrations (Ground Tremors) 2) Vibration Magnitude 3) Sound attenuation in distance 4) Physiological and Psychological Effects of Vibrations 5) Vibration Level and Psychological Effects 6) Effects on Buildings 7) Other II. Vibration Measurement 1) Equipment Used in Measurement and Analysis 2) Combinations of Measuring Equipment 3) Measurement Procedure 4) Measurements for Determining Compliance to Regulations

全部内容由Environmental Pollution Control Center, Osaka Prefecture提供
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