basics, characteristics , factors affecting, sound impression and its characteristics , reverberation and sabine's formula time calculation

1. ACOUSTIC OF BUILDINGS
A. Rajalakshmi
Asst. Prof. Department of physics,
Bon Secours College

2. http://www.free-powerpoint-templates-design.com
Acoustic of Buildings

3. Outlines
Basic of Acoustics01
Characteristics Sound02
Building Acoustic03
Factors Building Acoustic04

4. Basic of
The invisible key to
Understanding of Nature
Acoustic

5. Sound
Impression
• Where we are beside can feel the sound .
Normally we distinguish between sound and
Noise
• Sound - Pleasant Impression as Sound
• Noise – More Chaotic and obtrusive as Noise

6. Bus stand Music Hall Forest
Sound Impression
Acoustic Deals with the production, propagation and detection of sound waves
• Infrasonic < 20 Hz (Inaudible)
• Audible 20 to 20,000Hz (Music and Noise)
• Ultrasonic > 20,000Hz (Inaudible)
1 Hz Equal to one vibration per second

7. Characteristics of sound
A scale which
measure the
sensation depends
on Frequency
Pitch Number of
vibrations of sound
producing object per
second
Frequency International
Telecommunications
Union (ITU) for
radar and radio
communications.
3MHz to 30 MHz
High frequency
Low frequency Transfer energy one
form another place
Transverse and
Longitudinal waves
Waves
International
Telecommunications
Union (ITU) for
radar and radio
communications.
30KHz to 300 MHz

8. Characteristics of sound
Intensity - Amount of sound energy
flowing per sec per unit area
I = Q /A watt/m2
Loudness degree of sensation varies
from one observer from other
Intensity or Loudnes
Distinguish b/w any two or more musical
sound having same pitch and frequency
Smallest frequency is called fundamental
and frequencies accompanying
fundamental are called overtones.
Quality or Timbre
Intensity or Loudness
Quality or Timbre
Weber- Fechner Law
Loudness is directly proportional to
the logarithm of intensity
L α log I
L = K log I
k is the constant

9. Three types are classified as
ACOUSTIC
Building
Acoustic

10. Acoustics for Music
Generally, it involves broad range of frequency
spectra (about 50 to 8,500 Hz, for an average
dynamic range of about 75 dBA). Orchestra,
Symphony hall etc.,
Acoustics for Multipurpose
Both Speech & Music Acoustics design of a
multipurpose space is quite challenging as the
design objectives and measures vary remarkably for
speech and music
Chruch Cinema Theatre etc.,
Building
Acoustics Acoustics for Speech
covers narrow range of frequency spectra in lower-mid
level (about 170 to 4,000 Hz, for an average dynamic
range of 42 dBA). Class room, Assembly etc.,

11. GoodAcoustic Building
Designs and constructions
Not uniform Intensity
Sound interfere reduce
the quality
Factors to be considered
• Reverberation time
• Loudness
• Focusing and interference
• Echoes and Echelon effect
• Resonance and
• Extraneous noise
Acoustic BuildingsFACTOR

12. Reverberation
persistence or prolongation of sound in
a hall even though the sound source is
stopped.
Reverberation
sound disappear quickly and become
inaudible.
Reverberation time Low
The time taken by the sound wave to
fall below the minimum audibility level
after the source is stopped
Reverberation Time
sound exist for a long period of time -
an overlapping of successive sounds -
can not hear the information clearly
Reverberation time to high
The reverberation time should be kept
at an optimum value
Good Auditability

13. Loudness and Echo
Measures the magnitude
of sensation produced in
the ear.
Loudness
Uniform distribution of
loudness must be
maintained throughout
the hall
Loudness
If the time interval
between the direct
sound and the reflected
sound is less than 1/15
of a second,.
Echo
Sound get scattered by
wall, instead of
reflection .
Echo
The reflected sound
reaches the audience
later than the direct
sound
Echo
Uniform distribution of
loudness must be
maintained throughout
the hall.
Loudness

14. Echelon Effect & Resonance
Echelon effect
New sound produced by repetitive echoes - regular
Reflecting surface like stair case may create this effect
Resonance
If window panels or any other wooden sections are not
covered properly, the original sound may vibrate with
the natural frequency of them.

15. Focusing and Interference Effect
Focus
Reflected sound by the ceiling and wall must be distributed evenly
throughout the hall rather it should not be focused at a particular area
of the hall..
Interference
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Reflect and distribute the sound evenly.
Focuses the sound in the
front portion only.
Maximum sound intensity occurs
Minimum sound intensity occurs

16. Noise
N O I S
S
Outside noise which
reaches the audience
through window, door
and ventilator
Air borne Noise
W
Noise reaches the
audience through the
structural defect of the
building.
Structure Borne
Noise produced inside
the hall like crying kids,
the sound generated by
type writers, fan, A/C,
Refrigerators, etc.,
Inside Noise
I
E
SA

17. Remedies
0201 Reverberation
• Reduced by installing sound absorbing
materials like
• Windows and openings
• Arranging full capacity of audience
• Completely covering the floor with carpets
• False ceilings
• Heavy curtains with folds decorating walls
Loudness and Echo
• Lowering the ceiling and placing
reflecting surfaces at necessary
places.
• Cover such regular reflecting
surfaces properly.
0403 Focusing & Interference
• Radius of curvature of concave
ceiling should be two times the
height of the building.
• cover the curved surfaces with
proper sound absorbing materials
• The usage of uniform painting
and absorbent it may be avoided
Resonance and Noise
• Vibrating materials should be mounted on
non-vibrating and sound absorbing
materials.
• Panels must be fitted properly.
• Eliminated through proper ventilation or
by Air-Conditioning
• Insulating materials
• Double walled doors, anti-vibration
mounts, carpets etc.,.
• covered with suitable sound absorbing
materials

18. Thank You