What is Noise?

Quick Links
- What is Noise?
- What is Noise Control?
- What is Noise Control Engineering?

What is Noise?

Noise is any sound that is unwanted.

Although "unwanted" is a subjective term, some sounds are typically accepted as being noise. These include:

  • Sound that interferes with one's hearing and comprehension of something, whether it's speech interference (conversation, safety, or teacher instruction), media or performance interference (listening to music or television), or other activity in which properly hearing the sound is essential.
  • Sound that is too loud or lasts too long such that it causes hearing loss or other health problems.
  • Sound that is disturbing – causing awakenings, disruption of concentration, or annoyance.
  • Sound that has negative connotations for a product – in many cases sound is tied to the sense of quality in products ranging from automobiles to dishwashers.

There are three basic dimensions of sound, where each dimension can contribute to the perception of noise:

  1. Magnitude (volume)
  2. Frequency (pitch)
  3. Time (duration and variation).
     

Typically, noise is measured or predicted as a sound pressure level, reported in decibels (dB). The measurements and noise metric applied is application-dependent, where magnitude, frequency, and time can be accounted for differently with different noise metrics. As an example, highway traffic noise is measured and reported as the loudest hour (sound energy averaged for the hour) in a 24-hour period, with a frequency weighting applied to account for human perception of sound. Another example is occupational noise where the impact of noise on hearing loss is a primary concern. In this case both the level and duration of sound is integrated to provide an exposure level that can be related to the potential for hearing loss of workers exposed to the sound over the period of exposure.
 

Note that we typically examine sound from pressure disturbances (vibrating particles) in air or water (for marine life), but structures can also vibrate, causing adverse effects. For some applications, vibration levels are measured or predicted and reported with the applicable vibration metric.
 

Sound and vibration are intimately related. Any vibrating surface or structure can radiate sound, so measures taken to reduce vibration will often lead to a reduction in noise level.  Examples of vibrating structures that radiate sound include engines, electric motors, many industrial machines, air conditioning or refrigeration compressors, exterior panels of dishwashers, and, of course, loudspeakers, which radiate sound on purpose.

The table below shows typical sound levels and human response for everyday sounds and noises.  Where not otherwise indicated, the sound levels shown are intended to reflect those heard by the operator of the device. Sound levels for common sound sources can be found at https://noiseawareness.org/info-center/common-noise-levels/

 

 

For more information about noise:
https://www.ccohs.ca/oshanswers/phys_agents/noise_basic.html
https://medlineplus.gov/noise.html
https://www.medicinenet.com/what_is_noise_or_what_is_noise_pollution/article.htm
- https://www.epd.gov.hk/epd/noise_education/young/eng_young_html/m1/m1.html
- https://www.faa.gov/noise/


What is Noise Control?

It is possible to control noise and vibration to reduce adverse effects. Noise and vibration control strategies vary by application, regulation, feasibility, and reasonableness, including consideration of cost and public opinion in some cases. There are many strategies currently available, and others being developed or improved.

Examples of noise control strategies include:

  • Constructing a noise wall between a noise source and the receiver of noise, to help block the sound as it propagates.
  • Applying sound-absorbing material to a surface to help reduce reflections.
  • Reducing the vibration of noise radiating surfaces.
  • Relocating the noise source so it is more remote from the receiver.
  • Eliminating any gaps or holes in any barrier between the noise source and receiver.
  • Constructing tuned resonators to reduce troubling tones resulting from flow noise.
  • Alter the speed, frequency, or modulation frequency for the operation of a machine to change the character or sound quality of the noise.
     

Examples of vibration control strategies include:

  • Inserting vibration dampers or vibration isolation mounts between a vibrating source and an adjoining structure.
  • Reducing forces generated within a machine that cause vibration.
  • Alter the speed, frequency, or modulation frequency for the operation of a machine to avoid exciting resonant frequencies of a structure.
  • Applying damping treatments to highly resonant surfaces such as sheet metal panels.
  • Applying tuned vibration absorbers to reduce vibration amplitude at resonant frequencies of a structure.
  • Stiffening a machine or structure to shift resonant frequencies outside the operating range.

 

For more information about noise control:
https://www.cdc.gov/niosh/topics/noisecontrol/default.html
https://www.safeopedia.com/definition/5982/noise-control
https://www.cdc.gov/niosh/topics/noise/reducenoiseexposure/noisecontrols.html
https://www.who.int/occupational_health/publications/noise10.pdf
https://www.ccohs.ca/oshanswers/phys_agents/noise_control.html


What is Noise Control Engineering?

 

 

Noise Control Engineering is the application of engineering methods to the scientific principles of acoustics, in order to achieve policy goals, improve customer satisfaction or to meet community expectations. Where noise is adversely affecting people or wildlife, Noise Control Engineers strive to reduce the noise (and vibration).

"Policy" here can mean legislation or regulation to protect citizens, workers, communities, and the environment, or market-driven objectives for products and processes.
 

Learning About Noise Control

A good introduction to the modern noise control and the issues currently faced is in the National Academy of Engineering publication The Bridge published in the fall 2007. This link will take you to the magazine: https://www.nae.edu/File.aspx?id=7411&v=13af7641.

A general resource for understanding how noise control is often thought of can be found at Wikipedia, https://en.wikipedia.org/wiki/Noise_control, which will also link to many other useful resources.
 

Noise Control Education and Training

While there are many paths to becoming a noise control engineer, the classical path involves undergraduate and often graduate degrees in specialized engineering disciplines.  For more information on noise control courses and training please go to the link below.

https://www.inceusa.org/careers-education/courses-and-training/
 

Noise Control Engineering Topics

Occupational Noise Control

The goal of occupational noise control is to minimize the hearing loss of workers. Many people with hearing loss associated with old age have hearing loss due to exposure to high levels of noise during their careers. For example miners are one of the most overexposed worker populations and experience high levels of hearing loss.  By age 60, 90% of miners have substantial hearing loss compared to a 10-15% loss expected from aging alone.

The National Institute for Occupational Safety and Health also has a series of documents providing a description of noise control measures. A good starting point is this document: https://www.cdc.gov/niosh/topics/noisecontrol/default.html. This is a very comprehensive resource with numerous links and the treatment of several aspects of noise control. It is focused on Occupational Noise, but there is still useful information for anyone thinking of noise control.

There are many sources of information on basics steps that can be taken in occupational noise control. One is a pamphlet prepared by the Georgia Tech Occupational Safety and Health Administration (OSHA) Program. This booklet can be download from this site: https://oshainfo.gatech.edu/wp-content/uploads/2019/03/Technical%20Guide%20for%20Noise%20Controls.pdf

The National Academy of Engineering (NAE) and National Institute of Occupational Safety and Health (NIOSH) provide valuable resources for noise control.  A practical guide to noise control from NA can be found at  https://www.nae.edu/File.aspx?id=7411&v=13af7641.  A comprehensive treatment of Controls for Noise Exposure are available from NIOSH at https://www.cdc.gov/niosh/topics/noisecontrol/default.html Where there are numerous links focusing on Occupational Noise.

 
Environmental Noise

More information coming soon!

 

Architectural

More information coming soon!

 

Product Noise

More information coming soon!

 

For more information on Noise Control Engineering:
https://www.who.int/docstore/peh/noise/Comnoise-5.pdf
https://oshainfo.gatech.edu/wp-content/uploads/2019/03/Technical%20Guide%20for%20Noise%20Controls.pdf
https://www.cdc.gov/niosh/mining/UserFiles/workshops/hlp1/08-YantekPracticalControls.pdf
https://www.inceusa.org/publications/noise-control-engineering-journal/
https://www.cedengineering.com/userfiles/An%20Introduction%20to%20Noise%20Control%20in%20Buildings%20R1.pdf

 

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