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CONTROL
OF

BACKGROUND /INTERFERING NOISE

CONTROL OF INTERFERING NOISE
The background noise levels in recording studios, listening rooms,
concert halls, and other acoustically sensitive spaces must be minimized
if these rooms are to be used in their intended way
...

The task of controlling interfering noise is perhaps the most challenging
problem in architectural building acoustics
...


APPROACHES TO NOISE CONTROL
There are five basic approaches to reducing noise in an acoustically
sensitive space:

• Locating the room in a quiet place
...

• Interposing an insulating barrier between the noise and the room
...

• Both airborne and structure borne noise must be considered
...

Locating an acoustically sensitive room away from outside interfering
sounds is an elegant solution,
It is useful to remember that doubling the distance from a noisy street
or other sound source reduces the level of airborne noise
approximately 6 dB
...


APPROACHES TO NOISE CONTROL

Continued
...

• Installing a carpet in a hall might solve a foot traffic noise problem,
• a rubber pad might reduce an equipment vibration problem
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APPROACHES TO NOISE CONTROL

Continued
...
An impinging noise level would be reduced by the transmission
loss of the wall
...

Example, a barrier may be built along a highway to shield nearby
residences from traffic noise
...

Noise can permeate a studio or other room when it is transmitted through
air pathways (airborne) or transmitted through solid structures (structure
borne)

APPROACHES TO NOISE CONTROL

AIRBORNE NOISE
If an airway exists, then sound will easily travel though the air
...

Sound can easily travel from room to room through a common
plenum or air-handling ducts
...

Air tightness is absolutely necessary to insulate against airborne
noises
...
Similarly, rubber gaskets
must be used around doors or other openings
...
In particular, TL can
be defined as difference between sound pressure level (SPL) on the
source side of the barrier, and the SPL on the receiver side:

TL = SPL source side − SPL receiver side

The difference between the outside noise level and inside noise level determines the transmission loss (TL)
of the wall
...


Porous absorbers are poor sound barriers as porous absorbers allow
airflow
...

The total amount of sound power that passes through a partition is
proportional to S x τ,
where S is its area and τ is the transmission coefficient
...

The more massive the wall, the more difficult it is for sound waves in air
to move it
...

If the thickness (and mass) is doubled to 8 in, the new TL is about 45 dB
...

Mass is extremely useful for sound insulation, but is not always the
best approach
...

This is because masses that are separated by an unbridged air cavity are
extremely effective isolators
...

This would be much more effective than simply doubling the surface weight of
one wall
...

For example, an 8-in concrete wall may have a TL of 50 dB, and a 16-in
concrete wall may have a TL of 55 dB
...

However, although ideal, completely unbridged cavities are unattainable ,the
combined TL will be much less than 80 dB

COMPOSITE PARTITIONS
The total sound power passing through a composite partition, for example,
a wall with a door and a window, is the sum of the sound powers
transmitted by each element at some specified frequency
...

A weak link in a composite partition is an issue of real concern
...
5% of the total area, is
introduced, the composite TL drops to 29 dB
...

For example: a hole measuring 1”x1” will transit as much sound as an entire 100sqft gypsum-board partition
...

However, as noted, they are of limited value in insulating against sound
when used as standalone absorbers or when placed on wall surfaces
...

This loss is about 1 dB (100 Hz) to 4 dB (3 kHz) per inch of thickness
for a dense, porous material (rock wool, density 5 lb/ft3) and less for
lighter materials
...


Porous absorbers are useful for reducing reflected or ambient sound in a
noise source room
...

The amount of sound transmitted through a barrier also depends on the
surface area of the barrier
...


COMPARISON OF WALL STRUCTURES

By adding gypsum-board partitions to both sides of a concrete-block wall,
STC can be increased to about 70
...
shows the very common 2×4 frame construction with 5/8-in gypsumboard covering
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PARTITION WALL CONST
...
WITH STUDS AND GYPSUM BOARD

STC:
STC 42 dB without glass fiber

STC 43 dB without glass fiber

STC 46 to 52 dB with glass fiber

STC 55 dB with 31/2" glass fiber
STC 58 dB with 9" glass fiber

PARTITION WALL CONST
...

After evaluating,
• wall A has STC of 56
• wall B has STC of 53
• wall C has STC of 48
• wall D has STC of 63

SOUND-INSULATING WINDOWS
A window with insufficient TL would be a
weak link that would seriously compromise
the acoustical isolation of the wall
...

practical solution to the
double window problem
for concrete-block walls
...
On the other hand, a double-pane window
designed for thermal insulation may have an STC value less than a single-pane
window
...

In the latter there are, in effect, two entirely separate frames-one fixed to
the inner and the other to the outer staggered- stud walls
...

•The transmission loss of a door is determined by its mass and
stiffness, and by the air-tightness of its seals
...

• Increasing the door weight (solid core) and taking reasonable
precautions on seals might gain another 5 or 10 dB,
•The door that matches a 50-dB TL requires great care in design,
construction, and maintenance
...

Fig
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• Heavy plywood (¾ in) is used for the door panels
...


Sound traveling between the door and jamb tends to
be absorbed by the absorbent door edge
...


A complete door plan is shown in Fig
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The magnetic material is barium ferrite in
a PVC (polyvinyl chloride) rod
...
The aluminum strip C
decreases sound leakage around the
periphery of the door
...

A decoupled “room-within-a-room” construction technique is often used
to minimize the problem of structure borne noise
...

A floating floor consists of an additional floor raised and decoupled from
the structural floor
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Example of a concrete floating floor const
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(B) Detail of floor perimeter
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Increase impact time
2
...
Minimize impact mass, increase mass
of impacted body
4
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TRANSMISSION REDUCTION
Use an absorption or reflection muffler

Acoustic screen

NOISE CONTROL PRINCIPLES

Thanks

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