1. By:
Sepideh Abolghasem
Shabnam Alaghehband
Mina Khorram
May 2006

2. Noise Reduction Benefits Noise Reduction Methods Some Examples
Outline
Introduction to Noise
Noise Effects
Noise Reduction Benefits
Noise Reduction Methods
Some Examples

3. Noise is an unwanted sound. Its intensity is measured in decibels (dB)
Introduction to Noise
Sound versus Noise
Noise is an unwanted sound.
Its intensity is measured in decibels (dB)
The decibel scale is logarithmic.
Human can hear sounds between Hz

4. Typical Noises Corresponding to dBA Values
Source Noise Level
Normal threshold of hearing
Whisper
Quiet park
Normal conversation
Noisy office
Noisy factory
Dog bark
Car horn
Jackhammer
Jet takeoff

5. Factors that can affect how hazardous noise is:
Intensity
Time duration
Time distribution
Frequency
Sound Pressure Level (dBA) 83 85 87 90 92 95 97
100
102
105
108
110
Reference duration (hours)
21.1 16
12.1 8
6.1 4 3 2
1.5 1
.66 .5

6. What problems can noise cause?

7. Hearing Loss Risk of damage starts at 85 dB or higher
Longer exposure time increase your risk
Excessive noise damages the hair cells in the cochlea
Noise makes your ears ring all the time

8. Effective Noise Level(db)
Recommended Maximum Duration(hr)
Effective Noise Level(db)

11. Percentage of hearing loss due to intensity and duration of exposure :
Intensity(dB)
After 10 years work(8 hours a day)
After 35 years work(8 hours a day) 80 0% 85 3% 9% 90
10%
20% 95
17%
32%
100
29%
44%
105
42%
51%

12. 2. Annoyance and Distraction
Noise from office or production equipment can reduce the effectiveness of communication and make it difficult for people to concentrate in some tasks.
A handful of research studies confirm that noise has a negative effect on a child's ability to learn.

13. Preferred Noise Criterion (PNC) Curves
The Preferred Noise Criterion (PNC) curves provide guidelines for ambient sound pressure levels.
The higher the frequency of the noise, the lower its intensity must be to bring it to the appropriate PNC curve for hearing or communication.

14. Pressure Level(dB)
Frequencies (Hz)

16. Evaluation Of Pump Noise In a Forman’s Office

17. 3. Interference with Communication
Speech interference by noise is common around machinery and business equipment.
The most common method for rating the speech interference effects of noise is called the Preferred Speech Interference Level (PSIL).

18. Curves are drawn to estimate the distance at which intelligible communication can be made at different levels of PSIL.

19. The ability to hear and converse effectively on the telephone is also important and can be predicted by PSIL measurement.
The following guideline for calls between telephone exchanges should be used :
PSIL
Telephone Use
60 dB or less
60 to 75 dB
Above 75 dB
Satisfactory
Difficult
Impossible

20. 4. Performance Effects Of Noise
The following general observation apply to situation where noise may affect performance:
Paced tasks
Information transfer
Noise features

21. 5. Physiological effects :
The hazardous effects of noise does not limit to hearing loss but also includes the other parts of your body.
The exposure to noise has an effect that results in having more adrenaline in blood and causes stress.
Disturbing sleep.
Extreme exhaustation. ….

22. 6. Increased risk of accidents
Noise need not be excessively loud to cause problem in the workplace. Noise can interact risks to workers by :
Increasing the risk of accidents by masking warning signals;
Being a casual factor in work-related stress.

23. Music
In some factories background music has been used to improve the environment.
Do not provide music if the background noise level is more than 70 dB.
It can be use for repetitive tasks.
In offices the white noise served to mask some of the speech sound from neighboring areas.
White noise levels of 48 dB can be effective, but levels above 52 dB may be distracting and annoying.

24. Evacuation Alarms
Evacuation alarms notify people in a work area of a situation requiring them to leave the building.
It should precede any sounds around.
It should have a minimum duration of 10 s.
Alarms should be repeated until the building is evacuated.
Also for people with hearing loss we should consider visual alarms.

25. Noise Reduction Benefits
Workplace noise is a major occupational health problem resulting in thousands of disability claims per year.
Potential benefits of workplace noise reduction:
improved safety and productivity
reduced hearing loss
better communication
warning sounds heard more reliably

26. Noise Reduction Methods
Noise reduction methods can be applied at the noise source, in the path of noise transmission. Methods of reduction involve the following techniques:
Reducing the level or altering spectrum of the generated noise.
Using barriers to reduce noise transmission through air or structures.
Absorbing incident or reflected noise.

27. Engineering Controls Then: Protect your ears
Keep doors shut (reduces noise by dB).
Take care of mufflers and other controls.
Damping.
Then: Protect your ears
Find comfortable hearing protection (ear plug, canal cab, ear muff)
Learn to wear them correctly.
Don’t go into noise without it!

30. Acoustical Noise Reduction Blankets
Advantages
can be installed with plant personnel
can be removed and reused numerous times
is a closed insulation system
is custom-fit to existing conditions
is vibration resistant
Applications
any load manufacturing process
gear box casings
steam and gas turbine housings
compressor housings
pressure reducing valves
liquid chillers

31. Noise Control In Child Development Center

33. Wall system at the kiwi Grille

34. Quieting a computer server room
Nowadays, every company has to have a computer server room. These rooms are host to lots of computers and servers that all require
fans to keep their systems cooled. All of these fans running at one time create excessive ambient noise.

35. The End!