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Explanation of Noise Reduction of Sound - Succeed in Physical Science. Also refer to physics, acoustics, gasoline engines, muffler, combustion, music, loudness, filtering, acoustical materials, absorption, white noise, masking, Ron Kurtus, School for Champions. Copyright © Restrictions

Noise Reduction of Sound

by Ron Kurtus (revised 21 February 2007)

Noise reduction consists of reducing unwanted—and often irritating—sounds from your environment. One method is to reduce the noise from the source. Another method to reduce noise is to use sound absorbing acoustical materials. You can also get relief from some noise by masking the sounds.

Questions you may have include:

• How can noise be reduced at the source?
• What are sound absorbing materials?
• How can noise be masked?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

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Reducing noise at source

The first line of defense against excessive noise is to reduce or stop the noise at its source.

Gasoline engines

Gasoline engines can be very noisy due to the combustion or explosion of the fuel. Automobiles and most other machine that use gasoline engines are equipped with mufflers that greatly reduce the noise from the source. The sound muffler is a container in the exhaust pipe that uses a clever set of baffles to stop the engine noise.

For some reason there are gasoline engines used that have no mufflers or a minimal muffler. Harley-Davidson motorcycles have been allowed to make extra noise, allowing the riders to get some sort of thrill. Gasoline leaf blowers also seldom are muffled. You will see the operator wearing ear protectors. Unfortunately, people in the surrounding area must suffer from the noise.

Some areas have anti-noise laws to help prevent excessive noise from gasoline engines. But this source of noise is still a problem.

Jet engines

In recent years, airliners have been produced with reduced-noise jet engines. This noise reduction at the source has been welcome by people living near airports.

Some airports require airlines to make efforts reduce their engine noise when taking off.

Noisy neighbors

Noise from dogs that bark all night, apartment neighbors who play their sound systems on high volume, and similar sources of noise by inconsiderate people can sometimes be reduced at the source by complaining to the police, apartment manager or other authority. It is no guarantee that the noise will stop though.

Sound absorbing materials

You can reduce the noise entering your house, apartment or room by using sound absorbing materials. This can also reduce internal noise from echoes off the walls.

Walls do a fairly good job of reflecting and absorbing much sound. Unfortunately, low frequency sounds such as bass tones readily travel through solid walls. Thus, you may not hear the neighbor's music, but you can hear a loud boom-boom-boom from the bass notes of the music.

(See Acoustics in Buildings for more information.)

Windows offer little filtering of outside sounds. Drapes over the windows can help a little.

Acoustical tiles on the walls and ceiling of a room can absorb much of the outside sounds, as well as eliminate echoes from sounds inside the room.

An interesting development has been Active Noise Cancellation. There are headsets available that cancel out most of the external sounds. Scientists are working on systems that will cancel sound coming through apartment walls. Such devices is still in the future, though.

(See Active Noise Cancellation for more information.)

Masking sounds

Although you can try to reduce external noise by various methods, you may never get a room quiet enough to be able to sleep or study in peace. One alternative is to create a random extra noise that will block the unpleasant sounds that may be irritating you.

One method is to use white noise, which is a random noise similar to static. There are white noise generators available to help mask unwanted noise.

White noise signal is a random mixture of sound frequencies and amplitudes

Another method is to use a CD that provides soothing sounds, such as water running, ocean waves, or nature scenes. These also can be purchased. They seem to be effective for people bothered by external noises.

Summary

The sound of noise can be very irritating to people. Acoustics devotes much of its studies to ways to reduce the noise from unwanted sounds. Methods include reducing the noise from the source, using sound absorbing acoustical materials and masking the sounds.

Answers to Readers' Questions

One person's music can be another's noise

Resources

The following resources provide information on this subject:

Websites

Sound Absorption - from the University of Western Australia

Silentium - Company provides products and solutions for the reduction of acoustic noise generated in electrical products

Physical Science Resources

Books

Top-rated books on Noise Reduction

Top-rated books on Acoustics

Products

Top-rated audio CDs on Relaxation Sounds

Soniscape Sound Masking CD

Miscellaneous

Mini-quiz to check your understanding

1. How can you reduce noise at its source?

2. What will prevent a room from being noisy?

3. What does masking of a sound do?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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Noise Reduction of Sound