UNIT 1
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Transcript of UNIT 1
History of Acoustics:
• The greeks – Earliest
• The Earliest scientific contribution of importance to acoustic was made by Helmholtz (1826)
• W.C. Sabine put the science of acoustics on a firm & sure basics. => Phenomenon of Reverberation W.C. Sabine put the science of acoustics on a firm & sure basics. => Phenomenon of Reverberation Time (RT)
• Establishment of Acoustical society of America in 1929.
Acoustics is the science of sound which includes its
• Production
• Transmission
• Other Properties
Acoustics is
1. Generation, 1. Generation,
2. Transmission,
3. Reception – of Energy in the form of vibrational waves
in matter.
Behaviour of Sound:
OPEN - Simple
ENCLOSED - ComplicatedENCLOSED - Complicated
SEMI ENCLOSED - Combination
Acoustics – Two branches:
1. Physical Acoustics
� Speech & heaving
� Measurement of Sound
� Absorption of Sound
� Noise� Noise
� Sound Insulation
2. Architectural Acoustics
Aim of Acoustics:
• To appreciate & analyze the problems involved in the
propagation of sound in these enclosures.
• To suggest ways & means of producing optimum
conditions of heaving.
• To obtain both subjective & objective assessment of
the result achieved.the result achieved.
� To study defects
� To find means to eliminate
� To (find) remedy them.
The Contributing factors being:
• Growing population – hence noise levels.
• Gatherings in – Auditoriums, lecture halls, theatres,
concert halls, church/ religious buildings, Meeting
halls, Multipurpose halls, restaurants, etc.,,
• Locating various functional activities in/ of a project
judicially (eg – Music department & Gym in a school, judicially (eg – Music department & Gym in a school,
Equipment room & an auditorium.
• Open planning concept – leads to landscaping – Serve
better social purpose – Acoustical Implications.
• Thinner Structural Membrane – False ceiling
• Surface finishers.
• Quality of Sound – Absorption & reflecting qualities
of sound.
• Increasing trend of mechanization in buildings
(Heating, Ventilating, Air Conditioning, Type writers, (Heating, Ventilating, Air Conditioning, Type writers,
buzzer, Computers)
• Internal/ External Noise
• Vehicular traffic - Road, Air, Water.
• Industrial
SOUND:
Nature of sound:
• Physically, sound is rapid fluctuation of air pressure.
• Sound is caused by a vibrating body which moves
rapidly to & fro causing movement of the tiny
particles of air surrounding the vibrating source.
• Therefore sound required a medium for its • Therefore sound required a medium for its
propagation, the medium can be solid, liquid or gas.
• Human Ear drum is able to recognize the vibrations
within frequency ranges of 20-20000 vibrations per
second as the sensation of sound. 20Hz – 20000Hz.
Hertz (or) CPS (Cycles per Second)
Definition of sound:
• Physically : It is fluctuation in pressure, particle
displacement in an elastic medium like air.
• Physiologically : It is an auditory sensation/ sense
perception of the ear drum.
Classification of sound:Classification of sound:
• Ultrasonic: Disturbances of frequency too high to be
capable of exciting the sensation of hearing are
described as ultrasonic.
• Infrasonic: Disturbances of frequency too low to be
capable of exiting the sensation of hearing are
described as infrasonic.
Sound Waves: Sound waves exist as variations of
pressure in a medium such as air. They are created by the
vibration of an object, which causes the air surrounding
it to vibrate. The vibrating air then causes the human
eardrum to vibrate, which the brain interprets as sound.
Sound waves travel through air in much the same way as Sound waves travel through air in much the same way as
water waves travel through water. In fact, since water
waves are easy to see and understand, they are often
used as an analogy to illustrate how sound waves
behave.
• Frequency:The frequency of a sound wave refers to thenumber of vibrations per second, measured in units of hertz (Hz). Sound is found within a large frequency range; audible sound for young persons is between about 20Hz and 20,000Hz.
• Decibel (dB) :Sound levels are measured in units of decibels (dB). If sound is intensified by 10 dB, it decibels (dB). If sound is intensified by 10 dB, it seems to the ears approximately as if the sound intensity has doubled. A reduction by 10 dB makes it seem as if the Intensity has been reduced by half.
Sound Intensity
• Sound intensity is defined as the sound power per unit area. The usual context is the measurement of sound intensity in the air at a listener's location. The basic units are watts/m2listener's location. The basic units are watts/m2
or watts/cm2 . Many sound intensity measurements are made relative to a standard threshold of hearing intensity.The most common approach to sound intensity measurement is to use the decibel scale.
Sound has three basic characteristics:
1. Pitch
2. Intensity
3. Quality
• Each of these three characteristics is associated with • Each of these three characteristics is associated with one of the properties of the source or the type of waves which it produces.
• The pitch depends upon the frequency of the waves; the intensity depends upon the amplitude of the waves; and the quality depends upon the form of the waves.
• With the proper combination of these characteristics, the tone is pleasant to the ear. With the wrong combination, the sound quality turns into noise.
HUMAN EAR CHARACTERISTICS
Introduction:
Speech, Music, Noise are the three Categories into
which practically all important natural sound may be
grouped. NATURAL SOUND
• SPEECH
• MUSIC
• NOISE
Hearing is the Natural method for reception of Sound (Ultimate
Significant Termination).
For proper acoustical system – The Basic characteristics of speech
& Hearing.
Anatomy of the ear:
Human ear consists of 3 parts
• External ear
• Middle ear
• Inner ear
i. Pinna – Funnel Shaped receiver
ii. Auditory – Canal – Tapering tubeii. Auditory – Canal – Tapering tube
iii. Drum membrane – Ear drum – Tympanic
iv. membrane
Functions of external ear:
• Collects the sound wave
• Passes the sound waves to the ear Drum after
successive reflection on the inner wall of auditory tube.
• The ear drum sets in vibration.
The middle ear:The middle ear:
Is a cavity containing three small bones called OSSICLES:
• 1. Hammer (MALLUS),
• 2. Anvil (INCUS),
• 3. Stirrup (STAPES)
Functions of middle ear:
• The vibration at the ear drum sets the oscillate to
vibrate.
• These bones act as levers to transmit vibration from
the middle ear to inner ear.
• The last part of the stirrup is connected to the Oval
window or Fenestrate Oval is which forms the upper window or Fenestrate Oval is which forms the upper
part of the wall of the inner ear.
• On the lower part there is a Circular Window.
• There is a tube called Eustachian Tube which
connects the cavity of the middle ear to the throat.
This keeps the pressure of the middle ear equal to
that of the air in the mouth cavity.
Monaural and binaural hearing:
• In open air as well as in enclosures, the hearing is
direct and binaural (i.e., with both the ears)
• Binaural hearing helps to localize sound and obtain
a correct idea of the sound perspective.
• Binaural Hearing – Binocular vision.
IMPRESSION
DIRECTION
DEPTH
DISTANCE
• Monaural hearing causes loss of direction.
• A person can commonly / consciously – To suppress
sound coming from one Direction and to concentrate
on the desired sound from a given direction.
• Single ear is unable to do this and consequently the
noise and reverberation present in the room are
apparently increased.apparently increased.
• In Broadcasting studio,
The Micro phone
Radio
Loud speaker