2. INTRODUCTION:
Acoustics:
Physics dealing with generation, propagation and
applications of sound
Architecture of Acoustics:
Physics dealing with construction of buildings with :
intention to provide good audible sound .
History:
Prof. Wallace C. Sabine from Harvard
University performed the
systematic study about acoustical defects
and presented Sabine's theory of
reverberation to minimize acoustical
defects and proposed precautions
regarding the same.
3. SOUNDWAVES:
o Any vibrating body will displace the air layers nearby and initiate
mechanical wave which propagates in the medium through
alternate compression and rarefactions, sets the ear drum
vibrating and causes the sensation of hearing.
4. • PROPERTIES:
• Mechanical wave which propagates in the medium via
• alternate compression and rarefactions
• Propagation of sound needs an elastic medium
• Sound waves are longitudinal in nature
• Creates Pressure variation region during propagation
• Can be classified on the basis of frequency as Infrasonic
• waves (less than 16 Hz), Audio waves (16 to 20 KHz) and
• Ultrasonic waves (greater than 20 KHz)
• Velocity of sound wave depend upon nature and temperature
• of the propagating medium
5. Noise: creates Unpleasant Sensation
Musical Noise: Pleasant Sensation
Pitch: Subjective sensation related with frequency
of sound
Timber: Subjective sensation related with quality of
sound
Intensity of Sound: Energy transported by sound
wave per unit area per unit time
Intensity Level: Logarithmic ratio of intensity produced by the
source to the reference intensity
6. Threshold of Audibility: When I = I0, it’s intensity level
becomes 0 dB. This is called threshold of audibility.
Echo: An echo is defect produced due to reflection of sound.
When sound is reflected from reflecting surface which is either 17
or meter away or there is 100 ms gap between original sound and
reflected sound we can distinct between them. Such a reflection
of sound is known as echo.
Reverberation: A sound produced in a volume is reflected
multiple times from the various surfaces. As a result sound
persists in the volume for sometime of gradually decreasing
intensity even the source stop emitting the sound. This
persistence of the sound in a room due to multiple reflections,
even when the source stops, is known as reverberation.
7. Reverberation time: It is defined as the time during which the
sound energy falls from its steady state value to 10-6 times after
the source is cut off.
Coefficient of absorption: It is a ratio of sound energy
absorbed by its surface to that of total sound energy incident on
the surface.
Sabine or Open Window Unit (OWU): 1 m2 Sabine is the
amount of sound absorbed by one square meter area of fully
open window.
8. EYRING’S EQUATION:
Sabine’s formula works for large enclosures.
However, it leads to paradox for highly absorptive
surfaces. For instance when a = 1, all sound energy
incident on the surface is absorbed and T = 0. Such
room is called dead room in acoustical terms.
Sabine’s formula does not leads to T = 0 when a =
1. Actually, experiments shows that Sabine’s
formula is valid only for a 7 0.2.
Eyring proposed modification in the equation as
Following.
9. • DEFECT
• Excessive reverberation
• Echoes
• Sound foci
• Dead spots
• Insufficient Loudness
• Noise
• Effect
• Bad quality of sound
• Superposition of sound
• Non-uniform distribution
of sound
• Sound of large intensity
is focused at focal point
ACOUSTICAL DEFECTS AND EFFECTS:
