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Noise Measurement. Training Module. Table of Contents. Physics of Sound (Hearing loss, terminology) OSHA (Regulations) Sound Level Meters Noise Dosimetry. Noise Measurement and Dosimetry Learning Objectives.

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Noise measurement

Noise Measurement


Table of contents
Table of Contents

  • Physics of Sound (Hearing loss, terminology)

  • OSHA (Regulations)

  • Sound Level Meters

  • Noise Dosimetry

Noise measurement and dosimetry learning objectives
Noise Measurement and Dosimetry Learning Objectives

  • Explain sound pressure level, frequency & respective units of measure

  • Describe level average, time weighted average & dose

  • Explanation of criterion, threshold & exchange rate

  • Proper placement & care of microphones and instrumentation

  • Explain hearing conservation regulations & OSHA requirements as it pertains to noise measurement

  • Hands on calibration, function & measurement with the noise dosimeter, sound level meter and octave band analyzers

Section i physics of sound
Section IPhysics ofSound


Why measure noise
Why Measure Noise?

I. Determine if the employee(s) are at risk for Noise Induced Hearing Loss (NIHL) & should be in a Hearing Conservation Program (HCP)

  • Differentiate between on-the-job & off-the-job noise exposure

  • Determine most effective hearing protection

  • Engineering Controls

  • Administrative Controls

  • Compliance with applicable Standards

Why measure noise1
Why Measure Noise?

  • Prolonged exposure to noise causes permanent and debilitating hearing loss

    • Mostly between 4 – 8 kHz

    • Lose ability to understand speech in many situations

    • Typically affects consonant reception

    • Individual losing hearing is often the last to know!

Why measure noise2
Why Measure Noise?

  • Long term health effects due to adrenaline release

  • More accidents in high noise environments

  • Measurable decrease in productivity

  • Measurable decrease in work accuracy

  • Increased fatigue

Noise induced hearing loss
Noise Induced Hearing Loss

  • Intensity + Duration

  • Damage occurs in the cochlea

  • Results in loss of comprehension, not loudness

  • Permanent

Definition of sound
Definition of Sound

Fig. I-3 Compression & Rarefaction of air molecules

What does sound look like
What does Sound look like?

Adapted from Acoustics Animations – Dr. Dan Russell – Kettering University Applied Physics

Compression rarefaction of air particles in a sine wave
Compression & Rarefaction ofAir Particles in a Sine Wave

Four characteristics of sound
Four Characteristics Of Sound

  • Frequency (measured in Hz)

  • Intensity (measured in dB)

  • Speed (measured in feet or meters/second)

  • Wavelength (measured in feet or meters)


  • Measured in Hertz (Hz)

  • kHz for 1000xHz

  • Relates to the pitch of the signal

  • Is a measure of the cycles completed in one second

Frequency pitch
Frequency – (Pitch)

Fig. I-4 1Hz and 10Hz Sine Waves

Typical frequency examples
Typical Frequency Examples

  • Lathe 50 to 1100 Hz

  • Compressed air 500 to 8000 Hz

  • Circular saw 300 to 12000 Hz

  • Cars 8 to 1100 Hz

  • Violin 300 to 9000 Hz

Frequency response weighting
Frequency Response & Weighting

  • The human ear is capable of responding to frequencies ranging

  • from 20 Hz to 20 kHz

  • The ear is less efficient at high and low frequencies

  • In the range from 500 Hz to 4 kHz a normal human ear is very


Frequency response weighting1
Frequency Response & Weighting

Fig. I-6 “A” and “C” Weighting Curves

S ound p ressure l evel

2 Sine Waves:

Same Frequency

Same Time Duration

Different Intensity

One is TWICE as loud as the other

Sound Pressure Level

Fig. I-7 Sine Waves with different sound pressures

Measured in decibels (dB)

Understanding d eci b els db

deciBels S P LdB SPL


Relates to measurements of the environment

deciBels H LdB HL


Relates to intensity of audiometric test tones

UnderstandingdeciBels (dB)

Doubling sound source

100 dB

100 dB


= 103 dB

Doubling Sound Source

  • Add 3 dB

  • 10 dB  perceived as “twice” as loud

Addition of decibels
Addition of Decibels

If the difference between two levels to be added is:

- 0 to 1 dB, then add 3 dB to the higher number

- 2 to 3 dB, then add 2 dB to the higher number

- 4 to 7 dB, then add 1 dB to the higher number

- 8 dB or more, then add 0 dB to the higher number

  • Decibels are logrithmic values

  • They can not be directly added or subtracted

Changing distance from source
Changing Distance From Source

  • Outside

    • Doubling distance

      • Decrease SPL 6 dB

  • Room

    • Very Near Source

      • Twice the distance decreases

        SPL by 6dB

    • Far from source

      • No change with change in distance

NOTE: These are general guidelines. Each case may vary.


Fig. I-11 Octave Bands

  • Focus on the frequency content of the overall noise signal

  • Important for noise control efforts

Occupational noise characteristics
Occupational Noise Characteristics

Fig. I-12 Mixture of Source Signals

  • In the real world of occupational noise the overall sound is a mixture of many simultaneous sources with a variety of frequencies and intensities.

Types or characteristics of sound measure all continuous variable and impact impulse sound
Types or Characteristics of Sound“Measure all continuous, variable and impact/impulse sound”

A fan is an example of

a continuous noise source

A forklift driver is an

example of a variable


An explosion or

gunshot are examples

of an impulsive noise

A hammer striking a nail

would create an impact

noise signal

Response time
Response Time

  • Slow 1 second rise and fall

  • Fast 0.125 second rise and fall

  • Impulse 35 millisecond rise 1.5 second fall

  • Peak 50 microsecond rise and fall

Noise measurement



Types of hearing protectors
Types of Hearing Protectors

  • Muffs

  • Plugs Foam formable Pre formed Custom

  • Others Plugs on a head band Noise cancellation

Hearing protection nrr
Hearing ProtectionNRR

Noise Reduction Rating

Nrr devaluation
NRR Devaluation

  • NRR- 7 dBAdjustedAttenuationthen divide this value by 2to determine if hearing protector’s are adequateto forego noise control

  • The OSHA method is described well on the OSHA Noise & Hearing Conservation e-Tool website

Niosh subject fit model
NIOSH subject fit Model

  • Muffs NRR less 25%

  • Formable Plugs NRR less 50%

  • All Other Plugs NRR less 70%

Graphic illistration

  • Assume you need 10 dB reduction

  • Assume NRR is 24 for all

  • De-rate muff by 25%

  • De-rate formable by 50%

  • De-rate anything else by 70%

Plugs muffs
Plugs + muffs


    • Earmuffs over earplugs provide a maximum of 5dB additional attenuation no matter what the muff rating.

Critical terminology
Critical Terminology

Criterion - If exposed to SPL on average for eight hours, it would result in a maximum allowable exposure. [90dB for 8 hrs]

Threshold – dB level below which, all SPL’s are assigned a value of zero. [80dB]

Exchange Rate - Results in a doubling or halving of the maximum allowable exposure.

Critical terminology1
Critical Terminology

Average Level (LAVG and Leq) - If present continuously, would generate the same amount of energy as the varying levels that are present in the environment measured in decibels.

Time Weighted Average (TWA) - A level average with an assumed fixed sample period of eight hours measured in decibels.

Dose - The allowable daily exposure value. A maximum allowable exposure is equal to 100% dose. [90dB x 8hrs = 100% Dose]

A basic concept
A Basic Concept…

  • TWA = Lavg @ exactly 8 hours

  • DOSE = Follows the same line!



8 hours

Exchange rates
Exchange Rates


    • 3dB exchange rate

    • When averaged, Leq (level equivalent)


    • 5dB exchange rate

    • When averaged, Lavg (level average)

Criterion and 5 db exchange rate
Criterion and 5 dB Exchange rate

  • 90dB x 8hrs = 90dB TWA = 100% Dose

  • 95dB x 8hrs = 95dB TWA = 200% Dose

  • 100dB x 8hrs = 100db TWA = 400% Dose

  • 100dB x 4hrs = 95dB TWA = 200% Dose

  • 100dB x 2hrs = 90dB TWA = 100% Dose

  • 100dB x 1hr = 85dB TWA = 50% Dose

Noise measurement

Section II



The occupational noise exposure standard
The Occupational Noise Exposure Standard

  • Derived from the Walsh-Healey Public Contracts Act.

  • 1971 adopted under the Occupational Safety and Health Act.

  • Permissible Exposure Level (PEL) of 90 dBA.

  • Noises with a higher level than 90 dBA can be sustained for periods of less than 8 hours.

  • Sounds with average levels less than 90 dBA can persist for periods of more than 8 hours.

Permissible noise exposure
Permissible Noise Exposure

Hours per Day Sound Level dBA slow response

8 90

6 92

4 95

2 100

1.5 102

1 105

0.5 110

0.25 or less 115

Hearing conservation amendment
Hearing Conservation Amendment

  • Published in the Federal Register on March 8, 1983.

  • The Hearing Conservation Amendment requires the employer to perform five key tasks:

    • Measure Noise

    • Audiometric Tests

    • Hearing Protectors

    • Education & Training

    • Record Keeping

Table g 16a abbreviated
Table G-16a (abbreviated)

A-Weighted Duration

Sound Level (Hours)

Measuring Threshold 80 32

H.C. Action Level (50% exp.) 85 16

8 Hour Criteria 90 8

95 4

100 2

105 1

110 0.5

115 0.25

120 0.125

125 0.063

Minimum Upper Range 130 0.031


Section II

Measuring method for osha surveys
Measuring Method for OSHA Surveys

Original Rule H.C.A.

Weighting/Response A/Slow A/Slow

Exchange (Doubling) Rate 5 dB 5dB

Criterion (LC=100%) 90dB 90dB

Threshold (Cut Off) 90dB 80dB

Limit 90dB/100% 85dB/50%

(PEL) Action Level


  • The focus of the Occupational Noise Exposure Standard and the Hearing Conservation Amendment, is to set minimum requirements to protect hearing for those workers in a noisy environment.

  • The Keys to Success

    • Positive attitude on the part of the management

    • Clear communication of the value of hearing

      • Hearing protection takes care of the problem of noise for the short term, but the key to real hearing protection is education and communication.

Noise measurement

Section IIISound Level Meters


Components of a sound level meter
Components of a Sound Level Meter

Fig. III-1 Block Diagram of a Typical Sound Level Meter

Microphone Amplifier Range Frequency Control Filter(s)







Classification of sound level meters
Classification of Sound Level Meters

  • Three types of SLM’s established by ANSI, and IEC Standards:

    • Class 0 Laboratory grade instrument

    • Class 1 Precision instrument

    • Class 2 General purpose instrument

Types of microphones
Types of Microphones

Random Direct Pressure

Incidence Incidence Microphone

Acoustical calibrators
Acoustical Calibrators


1) Loudspeaker

2) ON/OFF switch

3) Battery indicator

4) Microphone adapter




Soundpro se dl series
SoundPro SE/DL series

Understanding the KeyPad

Sound level meter placement keys
Sound Level Meter Placement Keys

  • Location, Location, Location

  • Reflection

  • Vibration

Noise measurement

Section IVNoise Dosimeters

Noise dosimeter components
Noise Dosimeter Components

Microphone Amplifier Range Frequency Fast/Slow

Control Filter(s)





Display Storage Calculator Clock Meter

Computer Printer

Environmental concerns
Environmental Concerns

  • Temperature

  • Humidity

  • Atmospheric Pressure

  • Wind

  • Radio Frequency Interference

  • Magnetic Interference

How to do a noise survey

Check Battery

Reset Unit

Check Set Up

Calibrate Unit

Inform Worker

Unit Placement

Microphone Placement

Leave It Alone


Check It


Remove Unit

Record or Download Data

How To Do A Noise Survey

Survey techniques
Survey Techniques

  • Individual Full Exposure Assessment

  • Representative Sampling

  • Task-Based Exposure Assessment Modeling


    IV. Area Mapping

Managing mobility and variability
Managing Mobility and Variability

  • 5 day , 40 hour evaluation

Infrequent exposures
Infrequent Exposures

  • The day OSHA inspects is reality

  • Use informative signs

  • Use HPD’s

Re monitoring

  • Change in process or procedure that affects inclusion and/or hearing protection effectiveness-production rates -material processed -production technique -machine placement

Survey pitfalls
Survey Pitfalls!!!

  • Microphone Placement

  • Employee

  • Project Assumption

  • Threshold Distortion

  • Wind

  • Battery & Calibration

What to record in addition to sound levels
What To Record In Addition To Sound Levels

  • Dates and Times

  • Model and Serial Numbers

  • Pre and Post Survey Calibration Levels

  • Workplace Descriptions

  • Task Descriptions

  • Environmental Factors

  • Instrument Settings

  • Unusual Conditions

Noisepro dosimeter key pad functions
NoisePro Dosimeter Key Pad Functions

The RUN/PAUSE button is pressed to Start and Stop integration and data logging.

The RUN/PAUSE button is pressed to Start and Stop integration and data logging.

The ON/OFF ESCAPE key has two functions. It is used to turn the instrument on and off. If also serves as an escape key in the instrument setups

The Enter key is used to accept values or actions in the Setup menu.

Proper mounting
Proper Mounting

Middle of Shoulder

Typically Belt


Noisepro exercise 2 noise measurement for osha compliance
NoisePro: Exercise 2 – Noise Measurement for OSHA Compliance

  • Pages 55 & 56 in Workbook

Measuring dose
Measuring Dose

  • Using the 5 dB exchange rate (doubling rate), we can conclude the following:

95 dB for 8 hours equals 200% dose

100 dB for 8 hours equals 400% dose

105 dB for 8 hours equals 800% dose

110 dB for 8 hours equals 1600% dose

Noisepro exercise 3 effects of exchange rate criterion
NoisePro: Exercise 3 – Effects of Exchange Rate & Criterion

  • Pages 55 & 56 in Workbook

Tim bailey
Tim Bailey

3M Detection Solutions

Phone: (800) 245-0779, ext. 152

Fax: (262) 567-4047

Customer Service: Heidi Tunak, ext. 106

Tech Support: Randy Sleggs, ext. 123

Mark Scherer, ext. 158

What we measure
What We Measure

Fig. I-13 RMS (Root-Mean-Square)

Crest factor
Crest Factor

Fig. I-14 Crest Factor - Impulse/Impact Noise