Industrial Noise and Vibration Control (Second Edition)

Author: Xu Shiqin / et al.
Editor-in-Chief: Zhang Weizhen
Publisher:
Publish Date: 2005-09-21
Features:
Content Summary This book is divided into eight chapters, with main content including the basic concepts, evaluation, standards, measurement methods, and control technologies of noise and vibration, as well as engineering design. It is suitable for grassroots leaders in industrial plants and mines, environmental protection, occupational health and safety, and relevant technical personnel and workers.
Excerpt:
Chapter 1 Basic Concepts of Noise and Vibration
Section 1 Noise and Industrial Noise
Human existence is accompanied by various sounds, such as speech, music, and the roar of machinery. Generally, these sounds can be divided into music and noise. From a physics perspective, rhythmic and harmonious sounds are called music, while chaotic and dissonant sounds are referred to as noise. From a psychology perspective, noise and music are difficult to distinguish, as their concepts are subjective and relative. Therefore, it classifies any sound that is irritating, unpleasant, or unnecessary as noise. Common sense tells us that in certain situations, noise can indeed become a useful sound, and music can also become annoying. For example, experienced workers can judge whether equipment is operating normally based on the size of the mechanical noise; ball mill workers can estimate the degree of ore crushing by the size of the noise generated when steel balls grind the ore. Similarly, when you need to rest or study, melodious and pleasant singing can also become irritating interference noise. Under normal circumstances, noise is certainly unwelcome, but people do not necessarily demand absolute silence or the absence of any sound. In an environment with a certain background noise, people can still work, study, and rest well. Since people's requirements for sound are very complex, in today's world, some scientists are actively engaged in noise control work, while others are developing various devices that can emit sleep-inducing noise. It is clear that to benefit humanity, noise not only needs to be controlled but can also be utilized.
I. Noise
Sound is the reaction of the human ear or other receivers to the propagation of vibrations of objects in a medium. Noise is a type of sound and possesses all the characteristics of sound waves. We refer to objects that can produce sound as sound sources, and objects or machinery that generate noise as noise sources. Sound sources can be solid, gaseous, or liquid. Between the sound source and the human ear, the energy of object vibrations must be transmitted through a medium. We know that air can transmit sound. In addition to air, other gases, liquids, and solids can also transmit sound. We call the substances that can transmit sound media for sound transmission. Due to different media for sound transmission, noise propagation can be divided into air noise, solid noise, and water noise, among others. If there is only a sound source without a medium for sound transmission, the human ear will not hear any sound. For example, in 1969, when the U.S. Apollo spacecraft first carried humans to the moon, the astronauts did not hear any sound because there was no air or other medium for sound transmission on the moon.
When sound waves enter the human ear, they cause the eardrum to vibrate, stimulate the auditory nerve, and produce the sensation of hearing. Therefore, not all vibrations transmitted through a medium can be perceived by the human ear. The lowest sound pressure (threshold of hearing sound pressure) that the human ear can perceive is 2×10^-5 Pa, and the frequency range of audible sound (audible sound) is 20 to 20,000 Hz. Sound waves with frequencies below 20 Hz are called infrasound, and those above 20 kHz are called ultrasound. Infrasound and ultrasound are both sound waves that the human ear cannot hear. Generally, noise does not include infrasound and ultrasound but refers to sound waves within the audible range.
II. Sources of Noise
Noise comes in many varieties, differing based on the conditions under which it is produced. Noise on Earth primarily originates from natural noise and noise generated by human activities. Natural noise includes air sounds, thunder, ground sounds, water sounds, and wind sounds produced by natural phenomena such as volcanic eruptions, earthquakes, tides, rain, and wind. Noise generated by human activities includes traffic noise, industrial noise, construction noise, and social life noise.
(1) Industrial Noise
Industrial noise generally refers to the sounds produced by the operation of machinery during industrial production. With the development of modern industry, the control of industrial noise has become increasingly important. Industrial noise mainly includes three types: aerodynamic noise, mechanical noise, and electromagnetic noise.