accoustics

1. GUJARAT POWER ENGINEERING
& RESEARCH INSTITUTE
SUBJECT:- ACOUSTICS
prepared by:- VIRAJ SHAH

2. Acoustics
Acoustics is the interdisciplinary science that deals
with the study of all mechanical waves in gases,
liquids, and solids including vibration, sound,
ultrasound and infrasound. The word "acoustic" is
derived from the Greek word akoustikos, meaning
"of or for hearing, ready to hear". The scientific study
of the propagation, absorption, and reflection of
sound waves is called acoustics.

3. Acoustics Consultants May
Provide
Architectural Acoustics
Sound Isolation Testing
Impact Isolation Testing
Mechanical (HVAC) System Noise and Vibration
Environmental/Community Noise Assesment
Computer & Physical Acoustical Modeling
Field Testing
Industrial Noise Control
Sound Masking Systems Design

4. EXAMPLE OF ACOUSTICS

7. Sound, ultrasound,
infrasound
The entire spectrum can be divided into three sections: audio,
ultrasonic, and infrasonic.
Sound is a mechanical wave that is an oscillation of pressure
transmitted through a solid, liquid, or gas, composed of frequencies
within the range of hearing and of a level sufficiently strong to be
heard.
The audio range falls between 20 Hz and 20,000 Hz. The ultrasonic
range refers to the very high frequencies: 20,000 Hz and higher. This
range has shorter wavelengths which allows better resolution in
imaging technologies. Medical applications such as ultrasonography
and elastography rely on the ultrasonic frequency range.
On the other end of the spectrum, the lowest frequencies are known
as the infrasonic range. These frequencies can be used to study
geological phenomena such as earthquakes.

8. Physics of sound
The mechanical vibrations that can be interpreted as sound are able
to travel through all forms of matter: gases, liquids, solids, and
plasmas. The matter that supports the sound is called the medium.
Sound cannot travel through a vacuum. Sound is transmitted
through gases, plasma, and liquids as longitudinal waves, also
called compression waves. Through solids, however, it can be
transmitted as both longitudinal waves and transverse waves.
Longitudinal sound waves are waves of alternating pressure
deviations from the equilibrium pressure, causing local regions of
compression and rarefaction.
Matter in the medium is periodically displaced by a sound wave,
and thus oscillates.

9. Sound wave properties and
characteristics
A musical tone is a steady periodic sound. A simple tone,
or pure tone, has a sinusoidal waveform.
A compound tone is any musical tone that is not
sinusoidal, but is periodic, such that it can be described as
a sum of simple tones with harmonically related
frequencies.
A noise results from non-periodic vibrations (statistically
random vibration)

10. Decibel levels
0db -The softest sound a person can hear with
normal hearing
10 db - normal breathing
20 db -whispering at 5 feet
30 db -soft whisper
50 db -rainfall
60 db -normal conversation
110 db - shouting in ear
120 db -thunder

11. The human ear's response to sound level is roughly logarithmic
(based on powers of 10), and the dB scale reflects that fact.
An increase of 3dB doubles the sound intensity but a 10dB
increase is required before a sound is perceived to be twice as
loud.
Therefore a small increase in decibels represents a large
increase in intensity.
For example - 10dB is 10 times more intense than 1dB, while
20dB is 100 times more intense than 1dB.
The sound intensity multiplies by 10 with every 10dB increase.

12. Sound Waves:
amplitude & frequency
(cycles)

13. Reflection of sound
'Stradia': a sound simulation program

14. Radio signals
‘am’ means: amplitude modulation: the height of each wave
changes
‘fm’ means: frequency modulation: the length of each wave
changes

15. Sound Intensity

16. Subjective sound
perception
Musical Sounds may be generally
characterized by :-
PITCH
LOUDNESS
TIMBER

17. PITCH:-
This help in distinguishing between a note of high frequency
and low frequency sound of the same intensity produced by
the same instrument. A shrill sound is produced by a sound
of high frequency.

18. Loudness:-
It is a characteristic which is common to all sound, whether
classified as musical sound or noise.
It is depends on intensity and also on the sensitiveness of the
ear.
L ∞ log10 I
L= K log10 I
where K is constant.
This relation is seen that loudness is directly proportional to
logarithm of intensity and is known as WEBER FECHNER
LAW.

19. TIMBER:-
It is the quality of sound which enables us to distinguish
between two sounds having the same loudness and pitch. It
depends on presence of overtones.
It helps to distinguish between musical notes emitted by
different musical instruments and voices of different
persons even though the sounds have the same pitch and
loudness.

20. THANK
YOU