Dr. Marzuki Hj. IsmailDr. Marzuki Hj. Ismail

Semester I 2009/10 Semester I 2009/10

ENTECHENTECH

Sound is caused by pressure variation Noise – unwanted sound Noise – environmental pollutant

Health effects of noise

2 kinds of health effects of noise non-auditory effects and auditory effects

Non-auditory effects = Stress, Physiological and behavioural effects, and Safety concerns.

Auditory effects = Acoustic trauma, Tinnitus, THL(TTS), PHL(PTS)

PersekitaranPersekitaran Paras Leq* Paras Leq* maksimum maksimum

yang yang dibenarkan, dB dibenarkan, dB

(A)(A)

KesanKesan

Perindustrian/Perindustrian/PekerjaanPekerjaan

7575 Kerosakan Kerosakan pendengaran pada pendengaran pada

paras tinggiparas tinggi

Masyarakat/Masyarakat/Bandaran (siang)Bandaran (siang)

5555 Kerunsingan Kerunsingan bertambah pada bertambah pada

paras tinggiparas tinggi

Masyarakat/Masyarakat/Bandaran (malam)Bandaran (malam)

4545 Kesukaran untuk Kesukaran untuk tidur pada paras tidur pada paras

tinggitinggi

Domestik (siang)Domestik (siang) 4545 Kesukaran Kesukaran berkomunikasi pada berkomunikasi pada

paras tinggiparas tinggi

Domestik (malam)Domestik (malam) 3535 Kerap terjaga dari Kerap terjaga dari tidur pada paras tidur pada paras

tinggitinggi

Levels and DecibelLevels and Decibel

Low range = 0.00002 Pascal High range = > 200 Pascal

0

' logQ

QL

L’ = levels, belQ = measured quantityQo = reference quantityLog = log in base 10

0

log10Q

QL Decibel (dB)Decibel (dB)

Adding 2 sound and equivalent sound cannot be simply added or average arithmeticly

This is cause sound level are measure based on logarithm

There are 3 method to add sound pressure which is by using Formulate, Schedule or Chart

Combine Sound Level Pressure

FORMULATE This method based on Formulation:

10

1

10log10

iLni

iPL

Lp = Sound power level n = no of sound pressure level

SCHEDULESCHEDULE This method involve adding sound pressure This method involve adding sound pressure

based on Decibel Increment Schedule based on Decibel Increment Schedule (below)(below)

Different between 2 sound level need to be

added (dB)

Value need to be added to the highest value (dB)

0 – 1 3

2 – 4 2

4 – 7 1

7 – 10 0.5

Over 10 0

Solution is as below:

The more precise method is the Formulate method. Schedule (and Graph) method are used because it faster

The different can be ignored because as long as the calculation is correct, your answer can be accepted

The same can be used for 3 sound:

GRAPHGRAPH

This method is almost the same as the Schedule method in the way sound are added

In Schedule method, a schedule are used meanwhile for this method, a graph are you for the addition

The graph is as shown:

Eg:

What sound power level results from combining the following 3 levels: 68dB, 79 dB, and 75 dB?

Day-Night Sound Level - Day-Night Sound Level - LdnLdn is the A-weighted equivalent sound level for a is the A-weighted equivalent sound level for a 24 hour24 hour period period

with an additional with an additional 10 dB10 dB imposed on the equivalent sound imposed on the equivalent sound levels for night time hours of levels for night time hours of 10 p.m10 p.m. to . to 7 am7 am..

Day-Night Sound Level can be expressed asDay-Night Sound Level can be expressed as

where where Ldn = day-night sound level (dB)Ldn = day-night sound level (dB) Ld = daytime equivalent sound level (dB) Ld = daytime equivalent sound level (dB) Ln = nighttime equivalent sound level Ln = nighttime equivalent sound level

(dB)(dB)

Equivalent Sound Level – Equivalent Sound Level – LLeqeq

Quantifies the noise environment as a single Quantifies the noise environment as a single value of sound level for any desired duration. value of sound level for any desired duration.

Equivalent Sound Level - Equivalent Sound Level - LLeqeq - can be expressed - can be expressed asas

where where n = total no. of samples takenn = total no. of samples taken LLii = noise level in dBA of the ith = noise level in dBA of the ith

samplesample ttii= fraction of total sample time= fraction of total sample time

Eg: 1

A noise level of 90dBA exists for 5 min. and is followed by a reduced noise level of 60dBA for 50 min. What is the equivalent continuous equal energy level (Leq) for the 55 min period?

Eg: 2

Calculate equivalent continuous equal energy level (Leq) for a residential area in KT?

Time (h) Sound Level (dBA)

0000-0600 42

0600-0800 55

0800-1000 65

1000-2000 70

2000-2200 68

2200-0000 57

Good LuckGood Luck