noise 2 what is sound? hertz (hz) – frequency a high or low pitch decibels (db) – the loudness...
TRANSCRIPT
![Page 1: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/1.jpg)
NOISE
![Page 2: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/2.jpg)
2
What is Sound?
• Hertz (Hz)– Frequency a high or
low pitch
• Decibels (dB)– The loudness of the
sound
![Page 3: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/3.jpg)
NOISEDefinitions• Low Frequency Sounds
– Easily travel around corners and through openings• High Frequency Sounds
– Does not turn corners well, and it can be reflected– Are more attenuated by distance traveled in air than low frequencies– Are more annoying
• Pure Tone, a one-frequency sound• Broadband noise, most industrial noise is a mixture of frequencies
known as broadband noise• White Noise, when frequencies are equally distributed throughout the
audible range, sounds like rain• Impulse Sound, when duration of sound is < 1 s
![Page 4: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/4.jpg)
الصناعية االنشطة نتيجة الصناعية الضوضاء االنشطة نتيجة الضوضاء
معينة نقطة فى الزمن و الضغط بين العالقةالصوت مستوى من
![Page 5: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/5.jpg)
الصوتية الموجات من مختلفة اشكال
صوت مستوىمتوسط
صوت مستوىمتوسط
صوت مستوىعالى
عالى صوت مستوى
لفترة صوتصغيرة
لفترة صوتكبيرة
![Page 6: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/6.jpg)
6
Frequency
• Humans can typically hear between 20 - 20,000 Hz
• You can hear different frequencies better than others
![Page 7: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/7.jpg)
7
Decibels
• The quietest sound most humans can detect is 0 dB
• Some humans can even hear sounds as quiet as -5 dB
![Page 8: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/8.jpg)
Decibels• Decibels measure level of sound pressure.• Sound pressure and sound power are
analogous to temperature and heat.• Mean minimum level of hearing for the
unimpaired-hearing population is 4 dB.
![Page 9: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/9.jpg)
Examples of Noise Levels(Table 23.1)
DECIBEL LEVEL, dBA
EXAMPLE
30 Quiet library, soft whisper
40 Living room, refrigerator, bedroom away from traffic
50 Light traffic, normal conversation, quiet office
60 Air conditioner at 20 ft, sewing machine
70 Vacuum cleaner, hair dryer, noisy restaurant
80 Average city traffic, garbage disposal, alarm clock at 2 ft
90 Subway, motorcycle, truck traffic, lawn mower
100 Garbage truck, chain saw, pneumatic drill
120 Rock Concert in front of speakers, thunderclap
140 Gunshot blast, jet plane
180 Rocket launching pad
![Page 10: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/10.jpg)
Noise of leisure activities (Table 23.2)
MEAN, dBA ACTIVITY
90 Woodcutting, rough terrain driving
92 Motorcycling
94 Farming
95 Powerboating
96 Powered lawn equipment
98 Woodworking
99 Discotheques
101 Stock car races
110 Concerts (rock), hunting/target shooting
121 Drag races
![Page 11: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/11.jpg)
11
The Loudness of Common Sounds0 dB Threshold of Hearing
30 dB Soft Whisper
40 dB Quiet Office
60 dB Conversational Speech
80 dB Very noisy restaurant
90 dB Subway
110 dB Woodworking
120 dB Hydraulic press
140 dB Threshold of Pain – Jet plane
180 dB Rocket
![Page 12: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/12.jpg)
![Page 13: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/13.jpg)
Sound level, dBA Permissible time, T(hours) 80 32
85 16 90 8 95 4 100 2 105 1 110 0.5 115 0.25 120 0.125 125 0.063 130 0.031
![Page 14: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/14.jpg)
البشرية لالذان مخطط
![Page 15: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/15.jpg)
Anatomy of the Ear
Cochlea
Ear Drum
Ear Bones
Semi-Circular Canals
![Page 16: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/16.jpg)
16
How do we Hear?
• The outer ear collects the sound waves
• The waves hit the eardrum, and cause it to vibrate
• The vibrations are sent through the ear bones to the cochlea
![Page 17: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/17.jpg)
17
Inside the Cochlea (snail shell)
• Delicate hair cells vibrate to different frequencies• Hair cells detect the vibration, and send a signal
to the brain• Loud sounds destroy the hair cells, and they stop
functioning FOREVER!
![Page 18: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/18.jpg)
18
The Ear does something else too!• The Semi-circular canals
– Three tubes laying perpendicular to one another
– Filled with fluid and tiny hair cells– When your head is tilted, the fluid moves the
hair cells, and they send a signal to your brain
• Responsible for balance
![Page 19: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/19.jpg)
Hearing LossOverview
• Conductive Hearing Loss– Occurs in the outer and middle ear– From wax, punctured eardrum, corrosion of the bones,
etc.– It can be often cured with medical or surgical treatment.
• Nerve Loss– Occurs in the inner ear– Caused by age, viruses, drugs, and noise.– Rarely curable- منها الشفاء يمكن ما .-ونادرا
![Page 20: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/20.jpg)
Hearing Measurement
• Audiograms– Most common– Tests the hearing threshold for different frequencies– Gives the total loss in the outer, middle, and inner ear– Refined tests can give the specific loss of each part of the
ear
• Audiograms should be performed annually.
![Page 21: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/21.jpg)
Hearing Loss
• TTS – Temporary Threshold Shift– Measured 2 minutes after exposure– Repeated exposure can produced PTS or NIPTS
• PTS – Permanent Threshold Shift
• NIPTS – Noise-Induced PTS
![Page 22: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/22.jpg)
Occupational Hearing Loss• Not all hearing loss is occupational
– A series of audiograms over the years will help establish the causes.
• First occurs in the inner hair cells (3000 – 6000 kHz)
• Workers under occupational noises over 85 dB, set their car stereos ~9 dB higher after work than before work. (Evidence of TTS)
![Page 23: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/23.jpg)
SLM 2260 Brüel &Kjaer instrument
![Page 24: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/24.jpg)
مستوياتضغط عند لالنسان السمع مدى
المختلفة الصوت
![Page 25: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/25.jpg)
25
How to measure noise• Decibels are measured on a logarithmic
scale• Every time you add 5 dB, you double the
sound. 80 dB 85 dB
An addition or reduction of 5dB causes either an addition or reduction of 100% in noise according to OSHA.
![Page 26: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/26.jpg)
26
Example• In the field, we determined the loudness of
two compressors right next to each other• How loud is this area?
– Do we add?– Do we add and take the average?
89 dB 87 dB?
![Page 27: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/27.jpg)
27
• Neither, because it is a log scale• We use the following chart
• 82 dB + 83 dB = 86 dB• 87 dB + 89 dB = 91 dB
Difference in dB values
Add to Higher Value
0 or 1 dB 2 or 3 dB 4 or 10 dB 10 or more dB
3 dB 2 dB 1 dB 0 dB
![Page 28: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/28.jpg)
دراسة حالة
Machine C82db
![Page 29: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/29.jpg)
Difference between 2 decibel level to be added (db)
Amount to be added to larger level to obtain decibel sum (db)
0 3
1 2.6
2 2.1
3 1.8
4 1.4
5 1.2
6 1.0
7 0.8
8 0.6
9 0.5
Scale for combined decibel
![Page 30: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/30.jpg)
Difference between 2 decibel level to be added (db)
Amount to be added to larger level to obtain decibel sum (db)
10 0.4
11 0.3
12 0.2
Scale for combined decibel
( الضوضاء ( مستوى الموجة سعة حساب اسلوب
المعدة بين الفرق صفر =(A , B ) يحسبيضاف الجدول ديسبل 3ومن
للمعدتين = الموجة سعة ديسبل 89=3+86مجموع
المعدتين بين الفرق المعدة (A,B)يحسب ديسبل C = 89-82=7 و
بضاف الجدول من ديسبل0.8و
![Page 31: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/31.jpg)
للمعدات الموجة سعة 89+ 8 =(A,B,C) مجموع ديسبل 89.8و=
المعدات بين المعدة (A,B,C)الفرق 89.8 -12= 12= ( D) وديسبل
يضاف الجدول ديسبل 0.2من
للمعدات الضوضاء سعة =89.8+0.2=(A,B,C,D) مجموعديسبل90
العامل فى تؤثر التى الضوضاء مستوى محصلةيكون المعدات هذه به محاط مكان فى يعمل الذى
ديسبل90 .
![Page 32: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/32.jpg)
![Page 33: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/33.jpg)
![Page 34: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/34.jpg)
حالة حالة دراسة دراسة
![Page 35: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/35.jpg)
![Page 36: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/36.jpg)
36
How does the Safety Person determine noise levels
• Sound level meter– Determine the
loudness (dB) of noise at any given moment
• Personal Dosimeters– Worn by employees– Measures the average
loudness in an 8 hour work shift “8hr. TWA” (Time Weighted Average)
– Can also measure noise dose
![Page 37: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/37.jpg)
37
What does BLS say?• At 85 dB (8hr. TWA) (50%
Dose)– Train employees– Make hearing protection
available– Sample for noise levels– Do hearing tests– Notify employees of
results
• At 90 dB or more(100% Dose)– We must keep levels at
or below 90 dB– Or require hearing
protection that will lower noise levels to to 90 dB
![Page 38: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/38.jpg)
38
Hearing Tests
• Determine a baseline audiogram• Hearing test every year to determine if you have
experienced a hearing loss (Standard Threshold Shift)
• Standard Threshold Shift - A loss of 10 dB or more at 2000, 3000, or 4000 Hz.
![Page 39: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/39.jpg)
39
Hearing Loss
• Impact - One loud bang• Cumulative - Years of a noisy environment• Tinnitus - Ringing in the ears• Presbycusis - Hearing loss due to aging
![Page 40: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/40.jpg)
Hearing
• Hearing loss increases when exposed to over 67 dBA.
![Page 41: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/41.jpg)
Hearing
– US occupational standard is 90 dB for 8 hours of exposure per day.
![Page 42: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/42.jpg)
42
Hearing Protection
• NRR - Noise reduction rating– Ear Plug - 25 NRR– Ear Plug - 29 NRR– Ear Plug - 30 NRR
• DO NOT Subtract the NRR from the noise level– WRONG (109 dB - 25 NRR = 84 dB)
• You must use the “Safety Factor.” explained on separate slide
![Page 43: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/43.jpg)
43
Safety Factor
• OSHA says the hearing protection is designed to reduce the noise by the NRR, but that is unlikely to happen due to :– Leaks in the seal– Vibration– Improper insertion
![Page 44: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/44.jpg)
سدادات اإلذن وقاءاإلذن
![Page 45: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/45.jpg)
Frequency Foam plug Fiberglass down High performanc muff Popular muff125 31 10 14 10250 34 12 23 15500 39 17 32 23
1000 38 19 37 312000 35 26 35 353150 42 33 38 424000 44 34 39 396300 46 37 39 378000 47 35 38 35
EARPLUG EARMUFF
من اإلذن واقيات بين المقارنةلإلذن الحقيقي الوهن حيث
المختلفة الترددات عند
![Page 46: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/46.jpg)
46
Example of NRR Protection
• The noise from an average chainsaw is 110 dB• You are wearing the foam plugs with an NRR of 25
• Do you have enough protection to place you below 90 dB level?
![Page 47: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/47.jpg)
47
• (NRR 25 - 7) = 18
• 18 / 2 = 9
• - 9 =
• YOU ARE ABOVE OSHA LIMITS OF 90 dB
101110 dB
![Page 48: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/48.jpg)
48
Final Thoughts
• Hearing is important• In time, noise levels at 85 dB can
permanently damage your hearing• Wear your hearing protection both at work
and at home• Choose hearing protection with a proper
NRR, and wear it properly
![Page 49: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/49.jpg)
Effects of Noise
(in work stations)
![Page 50: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/50.jpg)
Comfort and Annoyance• Noise increases fatigue.
• Noise requires more concentration.
• Annoyance has increased over the years.
• Noise reduction is required regardless of high cost or low benefits
![Page 51: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/51.jpg)
Comfort and Annoyance
• Community reaction to industrial noise is highly variable.
• Variability of noise increases annoyance.
![Page 52: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/52.jpg)
Performance
• No firm evidence of lower productivity at high noise level (100dBA) unless max. mental capacity used.
• Assumption: speech communication is not an important part of the job.
![Page 53: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/53.jpg)
PerformanceSpeech Interferance Levels (SIL)
Note: Levels above 60 dB, masking spreads over a wider range
![Page 54: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/54.jpg)
Noise Reduction
![Page 55: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/55.jpg)
Noise Reduction
• Reduce signal/noise ratio by increasing noise (masking signal)
• In offices, coworkers’ conversations are the main source of noise.
• Reducing noise on hearing:A) Plan ahead C) Modify sound wave
B) Modify existing D) Use personal protection
noise source
![Page 56: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/56.jpg)
A. Plan Ahead
I. Substitute Less Noisy Processesi. Reduce the use of impact toolsii. Replace internal combustion with electric enginesiii. Replace gear transmission with belt transmission
II. Purchase Less Noisy EquipmentIII. Use Quieter Materials and Construction
i. Reduce Impactii. Reduce Vibrationiii. Reduce Turbulence iv. Reduce Transmission
![Page 57: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/57.jpg)
A. Plan Ahead
Good: Bevel gears Poor: Spur gears Better: V-belt Transmission
Drumheads with holes:Perforated guards have less vibration
![Page 58: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/58.jpg)
A. Plan Ahead
Pipe isolation reduces noise produced by vibration
![Page 59: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/59.jpg)
A. Plan Ahead
Poor Better
2. Avoid abrupt directional changes
1. Increase distance for turbulence to die
3. Avoid abrupt volume changes
![Page 60: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/60.jpg)
A. Plan Ahead
• A. Plan AheadIV. Separate People and Noisy Equipment
i. Locate noisy equipment in an isolated room.ii. Penetrations (ducts and pipes) should be sealed airtight.
iii. Inverse square law: Each doubling in distance from source reduces 6 dB in noise.
iv. High frequency sounds have high magnification ratio (Q) therefore avoid locations at higher Q.– corner Q= 8– Junction of walls Q= 4– Wall Q= 2
![Page 61: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/61.jpg)
B. Modify the Noise Source
• Start with the loudest noise
I. Reduce the Driving Force
II. Change the direction of noise
III. Minimize Velocity and Turbulence of Air
![Page 62: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/62.jpg)
B. Modify the Noise Source
YES NO
Exert force over a longer time
Reduce sharp edges
![Page 63: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/63.jpg)
C. Modify the Sound Wave
• Confining and absorbing of sound waves are expensive and reduce dB very little
• Use if no ahead planning nor source modification were possible. I. Confine
i. Problems:• Long wavelength • Requires total or near to total enclosure
![Page 64: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/64.jpg)
C. Modify the Sound WaveI. Confine (cnt.)
ii. Goal: Confine and absorb before transmission of sound occurs
– Sound absorbing materials also transmit, yielding little attenuation
– Hard materials transmit little but also absorb little
– Transmission is less for over 1000 Hz
– Absorb inside, prevent transmission on the outside www.owenscorning.com/around/sound/whatis.asp
![Page 65: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/65.jpg)
C. Modify the Sound WaveDouble-wall construction gives good transmission losses (TL)
![Page 66: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/66.jpg)
C. Modify the Sound Wave
II. Absorb– Once the sound is out, using absorbent panels is
not cost effective
– Remember logarithmic properties
– In most rooms 5 dB is the maximum reduction possible
![Page 67: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/67.jpg)
D. Use Personal Protection
I. Time – In the U.S. there is a 5 dBA
trade off for each doubling of time (3 dBA in Europe).
– Reduce exposure by making noise intermittent
– Consider job rotation
dBAdBA Time Time (hrs.)(hrs.)
9090 88
9595 44
100100 22
105105 11
110110 ½½
>115>115 Not Not PermittedPermitted
![Page 68: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/68.jpg)
D. Use Personal Protection
II. Equipmenti. Hearing Protector Devices (HPD)
• Give greater attenuation of higher frequency noise
• Noise Reduction Rating (NRR) summarizes attenuation regardless of frequency
• Earmuffs tend to give better protection than earplugs
![Page 69: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/69.jpg)
D. Use Personal Protection
III. Earmuffs Advantages:
– Once size fits all– Easy to supervise
Disadvantages:– They are hot, heavy– Glasses reduce their seal– Apply pressure to head
![Page 70: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/70.jpg)
D. Use personal ProtectionIV. Earplugs
Advantages:- Better accepted if fitted properly- Allows hearing better in noise- Light, compact and do not affect appearance
Disadvantages:- Need to be individually fitted- Harder to supervise - Easy to lose
![Page 71: NOISE 2 What is Sound? Hertz (Hz) – Frequency a high or low pitch Decibels (dB) – The loudness of the sound](https://reader036.vdocuments.us/reader036/viewer/2022062516/56649e4b5503460f94b3fda3/html5/thumbnails/71.jpg)
D. Use Personal Protection
V. Recommendations- Use a cord on earplugs - Be sure to have spears- In very high noises use earmuffs
over earplugs “Goal is ears alive at 65! ”