Instrumentation and Measurement Presentation

1. Sound & Acoustic
G R O U P 5
A I M A N D A N I E L B I N M O H D R A I S I D D E D M 9 4 6 2 6
A F R I E N A S H A Q I R A B I N T I S A R I F F D M 9 4 3 4 9
M O H D I R F A N B I N M O H D D Z A H I E R D M 9 4 0 4 1
A Q M A L H A K I M B I N A B D U L L A H D M 8 7 4 1 4

2. Introduction
In terms of physics, sound is categorized as a
vibration that typically broadcasts as an audible
wave of pressure, through a transmission medium
such as a gas, liquid or solid. Sound pressure or
acoustic pressure is the local pressure deviation
from the ambient (average or equilibrium)
atmospheric pressure, caused by a sound wave. In
air, sound pressure can be measured using a
microphone, and in water with a hydrophone. The
SI unit of sound pressure is pascal ( Pa ).

3. In human physiology and psychology, sound is the reaction of
such waves and their perception by the brain. Normal human
beings can receive sound waves with frequencies between about
20 Hz and 20 kHz. Sound above 20 kHz is ultrasound and below
20 Hz is infrasound. Plus, pressure wave can reach as high as 50
kHz which is beyond human capability.

4. Sound waves can travel at 340 m/s if there is no
resistance presence such as temperature and
pressure
Sound waves are absolutely vital in today's
industries. Some of the applications are for
developments of quieter vehicles, quieter air-
conditioning and even silencer for various
industries that always leads to noise pollution.
Moreover, maintenance personnel may measure
sound to identify trouble prone machines.

5. SPL IS ACTUALLY A RATIO OF THE
ABSOLUTE, SOUND PRESSURE AND A
REFERENCE LEVEL (USUALLY THE
THRESHOLD OF HEARING, OR THE LOWEST
INTENSITY SOUND THAT CAN BE HEARD BY
MOST PEOPLE).
SOUND PRESSURE LEVEL
The unit of pressure is usually expressed as
1 dyn / cm2 = 1 ubar = 1.45 x 10^-5 psi

6. Sound pressure level can also be measured using decibels (dB). The reason
why is because of the wide range of intensities human beings can hear. The
sensitivity of ears and eyes are considered logarithmic. Therefore, to compare
different sound intensities the following formula should be applied.
Sound dB = 10 log 10(I1 / I2)
I1 and I2 are the sound intensities
at 2 different locations and are
scalar units.
The formula below is used to to
compare different pressure level
Sound dB = 20 log10 (p1/p2)
Same like sound, p1 and p2 are
at 2 different locations..

7. C O N F L I C T
T Y P I C A L F I G U R E S F O R S O U N D P R E S S U R E L E V E L