Sound insulation: Light weight floor and wall structures'

1
Sound insulation Light weight floor and wall
structures.
2
In practice for airborne sound insulation
1 Direct transmission
1
2,3 och 4 Flanking transmission
2
4
3
3
In practice for impact sound transmission
1 Direct transmission
2 Flanking transmission
1
2
4
Building acoustic measures

• Transmission loss R (dB)
• Impact sound level Ln (dB)

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Building acoustic definitions

• High R means high sound insulation
• Low Ln means high impact sound insulation

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Sound insulation with no flanking transmission

• Light weight partition walls and floors
• Concrete partition walls and floors, for
  comparison

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Transmission loss RSingle frame wooden wall
160 mm
d
fcx
fcy
f0
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Phenomena at frequency 80 Hz

• Resonance between surface layer mass and cavity
  compliance in the wall.
• f0 50v 1/d (1/m1 1/m2)
• d cavity depth
• m1 mass per unit area, surface 1
• m2 mass per unit area, surface 2

9
Phenomena at frequencies 250 Hz and 3150 Hz

• Critical frequency.
• fcx c2/(2p)v mx / Bx)
• 
  z
• fcy c2/(2p)v my / By)
  y
• 
  x
• fcx critical frequency parallel to the beams
• fcy critical frequency perpendicular to the beams
  

10
Impact sound transmission Ln Wooden floor
structures
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Phenomena at 150 Hz

• Critical frequency.
• fc c2/(2p)v m / B)
  

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Impact sound transmission Comparison between
concrete floor and light weight floor structures
- - - - - Wood
Concrete
13
Flanking transmission

• Important to design mechanically weak
• Develop walls and floors structure that gives low
  direct sound transmission.

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Examples
A
B
Interrupted layer
Interrupted plate

• Ceilings
• Schools
• Offices
• Public buildings

• Ground plate

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A
R (dB)
10 dB
Interrupted layer
Continuous layer
Frequency (Hz)
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B
R (dB)
Interrupted plate
20 dB
Continues plate
fc
Frequency (Hz)
f0
150 Hz 250 Hz
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Rule of thumb

• Indices measured without flanking transmission
  4 dB In situ results.

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Rule of thumbin field

• Rw Ln,W 110 dB

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Rule of thumbs

• Increased mass/ unit area
  increased sound insulation
• Increase density
• Increase surface thickness

• Increase cavity deepth increased sound
  insulation

• Increase mineral wool increased sound
  insulation

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Increased mass/ unit area
R (dB)
2M (kg/m)
M (kg/m)
12 dB
Slope approx. 12 dB/octave
.
Frequency (Hz)
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Increased cavity depth
f0 50v 1/d (1/m1 1/m2)
R (dB)
Only variation of cavity depth
Frequency (Hz)
f0
fc
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Increased absorbing material thickness
R (dB)
100
30
10
6 dB
Frequency (Hz)