INTRODUCTION TO NOISE CONTROL By APOCALYPSE ACOUSTICS SCIENCES CORP
Definitions and Background
What is Noise? Noise is disagreeable or unwanted sound. In many instances, noise is a relative definition of a sound since one person’s music may be another person’s noise. It is difficult to give a very clear definition of an irritating noise. Generally, noise is an unwanted sound, regardless of its intensity or duration.
Noise Pollution has been recognized as a major threat to human well being. Much discussion and legislation has evolved in an attempt to recognize and combat the problem of noise pollution. It has been recognized that noise, of sufficient intensity, can damage hearing and be classified as a hazard.
In combating the problem of noise pollution it is necessary to use a means of measuring noise levels and a system of classification. The decibel is a number which relates sound intensity or sound pressure. When most people use the term decibel or discuss noise levels in decibels they are referring to decibels as related to the “A-weighted” scale or, dBA. The A-weighted scale parallels the sensitivity of the human ear and uses the lowest audible sound that the human ear can detect as the reference point for determining the decibel level of a noise.
The reference intensities used above represent the threshold of audibility where sound is just loud enough to be heard. At 140 decibels or more acute pain is experienced. Some common noise values are as follows:
- Ordinary conversation – 60 dBA.
- Heavy traffic – 80 dBA.
- Cocktail Party – 90 dBA.
- Moving subway train – 100 dBA.
- Riveting gun – 130 dBA.
- Hard rock band – 100 to 138 dBA.
- Jet plane heard at close range – 150 dBA
Any noise rating above 80 dBA produces physiological effects and any long term exposures at much or above 90 or 100 decibels will cause permanent damage to a person’s hearing. An increase of 10 dBA is a doubling of loudness with respect to the human ear.
Noise generally consists of many tones with varying rates of vibration or frequency. The frequency expressed in cycles per sound or hertz (HZ) usually is in the range of 20 to 20,000 cycles per second. The ear is not very responsive to very low or very high tones as it is to the tones of medium frequency.
The dBA scale matches the response of the ear, and is therefore well suited for evaluating noise as it relates to human beings.
For More Information on Noise Control or Noise Mitigation:
Apocalypse Acoustic Sciences Corp
#605, 6th Floor, Vani Nilayam,
Sebastian Road, Secunderabad-3.
Ph: +91-40-30621266. Fax: +91-40-27531331.