ARCHITECTURAL ACOUSTICS

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

Monaural hearing causes

• Loss of Localization of sound or directional

discrimination

• Loss of sound perspective (Ability to distinguish

nearby sound)

• More susceptibility

• Increase in reverberation• Increase in reverberation