By Khairul Akmal Bin Shamsuddin

Terminology Frequency and amplitude define pure tone in physics.

Pitch and loudness are the counterparts.

Noise is defined as sound at such amplitude to cause annoyance or to interfere with communication.

Measurement of Sound Amplitude of sound is evaluated by measuring the

Sound Pressure Level (SPL)

The unit is Decibel (dB)

Decibel is dimensionless unit related to logarithm of ratio of measure sound level to a reference level.

CalculationsLp = 20 log10 (p/pr) dB

Lp = sound pressure level, dB

p = sound pressure, N/m2

pr = reference sound pressure level (0.00002 N/m2)

p also known as Pressure Amplitude, N/m2

Range of Human Hearing

Self Study1. The ear

2. The outer ear

3. The middle ear

4. The Inner ear

5. Sensitivity to ear

6. Noise-induced pathology of the ear

7. Frequency analysis

8. Several sound sources

9. Measuring noise exposure

Measurement of Sound Sound level meters provide different measures of

sound intensity.

Dosimeters

Safe Exposure Levels OSHA specified 90 dB(A) as the maximum

permissible exposure to continuous noise for an 8-hour shift

Noise Surveys Useful method in evaluating distribution of noise in a

working area.

Approaches are area sampling and personal sampling.

Information for Noise Measurement1. Description of space which the measurements were

made.

2. A description of the source itself.

3. Calibration weighting network and response mode of the sound level meter.

4. Background noise level

5. Number and location or personnel

6. Position of microphone

Information for Noise Measurement7. Extent of fluctuation of noise levels.

8. A weighted measurements at operator’s ear level.

9. Time spent at machine by operator each day.

10. Results of any previous audiometric testing of workers.

11. Previous attempts at noise control.

12. Whether ear protection is available.

Some Basic Steps in Management of Industrial Noise Exposure1. Short term measure

1. Issue earplugs or earmuffs

2. Medium term measures

3. Long term measures

Medium term measures

1. Reposition noisy machines

2. Soundproof noisy machines

3. Demarcate noisy areas with warning signs.

4. Rotate workers between noisy and quiet jobs.

Long term measures Institute a comprehensive nois-reduction

program

1. Soundproof machines

2. Replace with less noisy machines

3. Change the process

4. Build acoustic refuges

5. Conduct audiometric testing

6. Implement rules and procedures for wearing ear protection

7. Implement audiometric testing program.

Ear Protection

EarmuffEarplug

Characteristic of Effective Ear Protectors1. Impervious to air

2. Adaptable to shape of user’s head or external auditory canal.

3. Remain firmly in place without causing pressure ischemia.

Design of Acoustic Environment1. Reverberation

1. Like echo. Cause by reflection of noise.

2. Can be minimize by in applying sound absorbing materials in the room.

2. Building Design and the Auditory Environment

1. Old building wall is thick so that it can absorb the noise and also can put outdoor noise outside.

Effects of Noise Below 85 dB (A)Noise Level dB(A) Effect

80 Conversation if difficult

75 Telephone conversation is difficult

70 Upper level for normal conversation

65 Upper acceptance level when people expect a noisy environment

60 Acceptable level for a daytime living conditions

55 Upper acceptable level when people expect quiet

50 Acceptable level for people who expect quiet.

40 Very acceptable for concentration

<30 Low-level intermittent sounds become disturbing.

Industrial Noise Control Several approaches identified

1. Eliminate the threat to hearing by redesigning the machine or using a less noisy machine.

2. Remove personnel from noisy environment

3. Issue earplug to workers or build acoustic refuge.

Some Characteristics of Reverberation in Rooms1. Reverberation time in a room does not depend on

the position of source or the listener.

2. Excessive reverberation is major cause of blurring acoustic signals such as speech.

3. Room shape has little effect on reverberation time.

Some Characteristics of Reverberation in Rooms4. Intensity of reverberant field depends on factors

1. Sound level of the source

2. Volume of enclosed space

3. Amount of sound-absorbing material in a room.

Noise problems and solutions1. Fans

1. Fans or blowers are noisier when running at high. Use larger fan running at a lower speed.

2. Muffling

1. Pneumatic tools produce noise due to exhaustion of compressed air to atmosphere. Pipe away the noise.

Noise problems and solutions3. Part Ejection

1. Pneumatic ejectors are noisy. Mechanical ejectors are quieter.

4. Pneumatic Tools1. Hydraulic or electric equivalents are quieter.

5. Impact Tools

1. Large electric solenoids are source of impact noise. Put resilient bumpers fitted to the point of impact.

Noise problems and solutions6. Hydraulic reticulation

1. Cativation can increase noise. Reduce by decreasing fluid flow velocity.

7. Vibration

1. Reduce vibration by regular maintenance and replace worn parts.

Noise Insulation If the machine cannot be redesigned, then isolate it.

Or make a wall to cover the machine.

Self Study Noise and Communication

Auditory warnings and cues

Voice warnings

Representational warnings and displays

Auditory environment outdoors

Effects of noise on task performance.

Noise and satisfaction

Vibration