The document discusses various methods for noise control, including noise barriers that absorb or reflect sound, and mufflers (or silencers) that reduce noise through absorption and reflection principles. It emphasizes the importance of barrier height, length, and material for effective noise reduction, as well as vibration isolation techniques using low impedance materials. Damping methods, such as viscous and hysteresis damping, are also outlined to help control vibration and noise in mechanical systems.

1. Rahul K Kamble

2. Noise barriers
Mufflers or silences
 Vibration isolation
Damping
Lagging

3. Barrier = obstacle
Noise barriers are
construction of
thick and high (> 2
m) covered with an
acoustic material
on the source side.

4. Noise barriers provides appreciable
protection from noise i.e. about 15 dB
(A)
Any solid material can acts as a barrier
Sound barriers can reflect or absorb
noise
Degree of sound reduction depends
upon physical form of barrier,
specifically on its height and length.

5. Buildings, earth embankment, stored
materials and other solids acts as barrier
Effectiveness is more when placed closer
to noise source or receiving point
No leak should be there
Length should be 10 times the height
For effectiveness barrier material should
have superficial mass of 7 kg/m2
, e.g.
brickwork, asbestos cement boards, fiber
board, wood wool slabs etc.

10. What is meant by silence ?
What are the means by which silence is
achieved?
Keep silence !!!
Silence = Silencer (the condition of no sound)
Where do you find silencers ?

11. It is a piece of pipe or duct treated or
shaped for reducing sound
At the same time it allows the flow of
gas

12. Two types of mufflers
Dissipative and reactive
Dissipative (absorptive) works on the
principle of absorption of noise. Use of
acoustic absorbing lining.

13. Reactive silencers works on the principle of
reflecting.
The performance is depends upon frequency
of sound
Dissipative silencers provides sound
attenuation over broad frequency range and
hence more popular
Reactive silencers are tuned to provide
maximum attenuation at specific frequencies
and woks in limited frequencies

16. Reduce the magnitude of vibration between
two sources attached to each other
Radiation and noise can be controlled by
impedance mismatch
Is a measure of the rate at which a unit mass
of material receives the acoustic energy.
Acoustic impedance of a material is given by
the product of density of the material and
velocity of sound in the material.

17. Material having low impedance is
inefficient sound transmitter or good
sound isolator.
Rubber between two blocks of steel can
provide a very good sound isolation.
Noisy machine should be floated on a soft
and low impedance mounting rather than
bolting it to the floor mounting.
Examples: springs, elastomers mounts,
flexible couplings to conduits, ducts and
pipes, gaskets on ducts.

19. A method to control vibration, shock
and noise.
The process involves converting
dissipating energy by heat
Damping can be applied to mechanical
systems by
Viscous, - Dry fiction, - Hysterisis
damping

21. Noise radiating surfaces are wrapped with
acoustic materials.
Applied to piping, values, vessels etc.
The porous material attenuates the sound
waves by reflecting them back into the
structure and by converting it into heat.
Fibre glass or mineral wool of 300 mm
thickness  attenuation of 60 dB (A) at
sound wave frequency of 1000 Hz.

22. e.g. of laggings: fibre, polyurethane foam, lead foil,
knee cement, PVC sheet

23. Thank you!!!