Noise control
Sound components
ƒ reflected (reverberated) ρ
ƒ absorbed α
ƒ transmitted τ
Incident
sound
Transmission loss TL
TL = 10 Log(1/τ) = -10 Log τ
Transmitted
sound
Absorbed
sound
Reverberated
sound
Noise control
Mass law (Berger’s law)
ƒ theory: doubling of surface density ρS [kg/m2] → - 6 dB
i.e. TL ∝ 20 Log ρS
ƒ practice: - 5 dB
i.e. TL ∝ 17 Log ρS
Attenuation [dB] .
70
60
50
40
565 Hz Theor.
30
565 Hz Exp.
20
10
100
Surface density [kg/m²]
1000
Noise control
Mass law (Berger’s law)
Frequency law
ƒ doubling of frequency f [Hz] → - 6 dB
100
i.e. TL ∝ 20 Log f
1000
500
200
100
50
20
10
ρs [kg/m²]
90
Attenuation [dB]
80
70
60
50
40
30
20
10
TL ≈ 20 Log (0.08 f ρS)
0
100
1000
Frequency [Hz]
10000
Noise control
For low and high frequencies:
ƒ coincidence
Sound reduction index : dB
ƒ resonance
e
enc
d
i
c
n
Coi region
ce
nan
o
s
Re egion
r
100 Hz
Resonance Effect in a Panel
aw
ss l n
a
M gio
re
1000 Hz
10 kHz
Images by MIT OCW.
Coincidence Effect in a Panel
Noise control
Sound paths
1 - direct air transmission
2 - reverberation
3 - lateral transmission of airborne sound
4 - re-emission of impact sound
B
5 - transmission
"
5
Weakest path
4
5
5
1
1
2
A
2
3
1
Noise control
Sound paths
⎡ S' ⎛ ΔTL ⎞⎤
TL = TL 0 − 10 log⎢1+ ⎜⎜10 10 − 1⎟⎟⎥
⎢⎣ S ⎝
⎠⎥⎦
Weakest path
S'
TL'=TL0 -ΔTL
70
Loss of insulation [dB]
S
TL0
Δ TL [dB]
60
60
50
50
40
40
30
30
20
20
10
10
0
0.001
0.01
0.1
1 S'/S
Noise control
Planning phase
ƒ sensitivity to noise
ƒ noise sources
ƒ noise insulation requirements
Design phase
ƒ
ƒ
ƒ
ƒ
acoustic criteria in positioning and orientation
calm vs. noisy zones
construction elements
technical installations
→ e.g. cavities in walls, no connection between window layers
Noise control
Environmental noise
Noise control
35
Attenuation [dB] .
Environmental noise
ƒ Anti-noise barriers
­ of "infinite" length
θ
30
90°
25
30°
20
10°
5°
15
1°
10
0°
5
θ
h
0
0.1
1
10
h/ λ
100
Noise control
Environmental noise
ƒ Anti-noise barriers
­ of "infinite" length
d
25
25
20
20
15
15
10
10
5
5
0
0
0.1
1
10
100
L/d
1000
Attenuation if L infinite .
L
Attenuation [dB]
­ of finite length L
Noise control
Environmental noise
ƒ Anti-noise barriers
ƒ Acoustic urbanism
Pesay
Decibels
>70
65-70
60-65
55-60
<55
Noise control
Environmental noise
69 db
ƒ Anti-noise barriers
ƒ Acoustic urbanism
74 db
69 db
72 db
66 db
78 db
50 db
Noise control
Environmental noise
Noise source
Requisite noise barrier
Noisy factory
ƒ Anti-noise barriers
ƒ Acoustic urbanism
Activity or situation
A
C
B
Very loud radio
Threshold of audibility
Average workshop
Recording studio
Lorry passing at 5 m
Noisy restaurant or dance floor
Hospital ward, sleeping
75
Average light factory
Special discontinuous construction
300 mm concrete rendered
80
Office: typewriters
70
85
68 db(A)
Living room, loud radio
Quiet car passing at 5 m
75
Conversation
70
80
68 db(A)
85
Moderate radio
Average office
Average home
980
240 mm brick or 150 mm concrete
500
120 mm brick or 100 mm concrete
Double 3 mm glass, 100 mm space
140 mm hollow block
75 mm solid gypsum panel
250
Timber studs, 10 mm plasterboards
Timber floor plaster ceiling
Single 6 mm plate glass
Studying
730
Reading
150
100
50
25
120 mm lightweight concrete block
Single 3 mm glass
10
13 mm fibreboard
2.5
Houses
Flats
Hotels
Quiet office
Quiet restaurant
Badly fitting door
Quiet garden
75
80
85
Average office
70
68 db(A)
Subdued radio
Open door or window
0
Kg/m2
Image by MIT OCW.
Image by MIT OCW.
Noise control
Structure-borne noise
Noise control
Structure-borne noise
Noise control
Structure-borne noise
Noise control
Structure-borne noise
Noise control
Structure-borne noise
Noise control
Structure-borne noise
Floating floor
Flexible (soft) layer
Noise control
Sound source in room
Direct sound
Source
Reverberant sound: Sum of an infinite number of paths
S
90 dB
80
Image by MIT OCW.
Total sound level
Direct component
70
Reverberant component
60
0
2
4
6
8
10
12
14
16
18
20
22
24
Distance from source (m)
Image by MIT OCW.
Noise control
Sound source in room
ƒ Iabs = Iinc · αs
ƒ Pabs = I⊥ · A = I⊥ · αs · S
ƒ I⊥ = ¼ Istat
ƒ Lstat = 10 Log Istat/Io
= 10 Log (4P/(Io A))
Direct sound
Source
Reverberant sound: Sum of an infinite number of paths
90 dB
80
Total sound level
Direct component
70
Reverberant component
60
0
2
4
6
8
10
12
14
16
18
20
22
24
Distance from source (m)
Image by MIT OCW.
Noise control
Sound absorbers
ƒ Porous
1.00
0.75
Absorption coefficient
(a)
(b)
0.50
0.25
0
10
100
1k
10kHz
10
100
1k
10kHz
1.00
0.75
0.50
0.25
0
Image by MIT OCW.
Noise control
Sound absorbers
ƒ Porous
ƒ Membrane
1.00
Absorption coefficient
0.75
Two layers of
bitumenous felt
0.50
0.25
0
10
100
1k
10 kHz
1.00
0.75
10 mm plywood
0.50
0.25
0
10
100
1k
10 kHz
Image by MIT OCW.
Noise control
Sound absorbers
ƒ Porous
ƒ Membrane
Absorption coefficient
ƒ Cavity resonators
I
1.00
0.75
0.50
V
2r
0.25
0
10
100
1k
10 kHz
Image by MIT OCW.
Noise control
Sound absorbers
ƒ Porous
ƒ Membrane
ƒ Cavity resonators
Absorption coefficient
100%
80%
Porous
60%
Membrane
40%
Cavity
20%
0%
125
250
500
1 000
2 000
Frequency [Hz]
4 000
Noise control
Sound absorbers
ƒ Porous
ƒ Membrane
+
ƒ Cavity resonators
Absorption coefficient
ƒ Perforated panels
1.00
0.75
+
With porous
0.50
Without porous
0.25
0
10
100
1k
10 kHz
Image by MIT OCW.
Noise control
Absorbent baffles
(a)
(b)
Sound
partially
absorbed
Minimum 1 m
Ventilation duct
Bathroom
flat 1
Sound
transmitted
fully
Bathroom
flat 2
Absorber
(c)
Sixth floor
Ceiling
Absorbent
lining
no
ise
Absorbent
Fifth floor
Str
eet
Sound
almost
completely
absorbed
(d)
Sound
partially
absorbed
Section
Absorber
Plan
Image by MIT OCW.
Image by MIT OCW.
Noise Control
Reading assignment from Textbook:
ƒ “Introduction to Architectural Science” by Szokolay: § 3.3
Additional readings relevant to lecture topics:
ƒ "How Buildings Work" by Allen: p. 132 in Chap 14