Technology in Architecture
Lecture 17
Noise Reduction by Absorption
Sound Paths
Sound Isolation
Sound Privacy
Structure Borne Sound
Noise Reduction by Absorption
Increased absorption reduces ambient noise
S: p. 771, F.18.2
Noise Reduction
by Absorption
Reverberation
increases ambient
sound levels
S: p. 798 F.19.1
69 db
Sound Paths
Air-Borne Sound
Structure-Borne Sound
S: p. 806, F.19.10
Sound Transmission
Barriers reduce sound transmission to reduce
noise intrusion
S: p. 807, F.19.11
Air-Borne Sound
Transmission Loss (TL):
sound energy lost
through a construction
assembly
S: p. 813, F.19.17
Noise Reduction
Combined effect of TL and absorption
NR=TL-10 Log (S/AR)
NR: noise reduction (db)
TL: transmission loss (db)
S: area of barrier wall (ft2)
AR: total absorption of receiving room
(sabins, ft2)
Noise Reduction Example
What is the noise reduction at 500 hz
between two rooms separated by a 2x4 stud
wall with ½” gyp. bd. on each side.
Receiving room absorption: 450 sabins, ft2
Separation wall: 10’ x 20’
Noise Reduction Example
Find TL500
TL500=35 db
S: p. 813, F.19.17
Noise Reduction Example
Find NR500
NR500=TL500-10 Log (S/AR)
=35-10 Log (200/450)
=35-10 Log (0.444)
=35-10(-0.35)
=35+3.5=38.5 say 39db
Sound Transmission Class
Sound Transmission Class (STC): defines overall
transmission loss across center band frequencies
Barrier STC
Descriptor/
Ranking
Application
25
30
35
42-45
46-50
Poor/1
Fair/2
Very Good/4
Excellent/5
Total Privacy/6
Space divider
Room divider
Offices near quiet space
Party walls
Quiet next to noisy
from S: p. 828. T.19.6
Sound Transmission Class
STC can be compromised by:

Combination with lesser sound barriers

Gaps in construction
“An air path is a good sound path”
Sound Transmission Class
STC of a wall assembly
2x4 stud with gyp. Bd.
S: p.1712, Index K.1
Sound
Transmission
Class
Wall assembly
description
2x4 stud with gyp. bd.
S: p. 1716, Table K.3
Sound Transmission Class
Wall assembly
selection TL data
2x4 stud with
gyp. bd.
S: p. 1713, Index K.2
Sound Transmission Class
Floor assembly
follows same
process
S: p. 1724, Index L.1
Noise Criteria
Noise Criteria (NC): accepted noise level
for a given space.
Defined for center band frequencies
62.5 125 250 500 1000 2000 4000
Noise Criteria Curves
Accepted noise
level for a given
space.
S: p. 759, F.17.17
Noise Criteria
Noise Criteria for
various applications
S: p.831, T.19.8
Sound Privacy
Privacy is affected by initial sound source,
TL, NC and absorbtion
Room B
Room A
SPL
NC1
NC2
Privacy Maintained
TL
TL
Sectional View
Privacy Violated
Sound Privacy—Example 1
Room A: NC500=35
Room B: NC500=25
Room B
Room A
SPL=70
NC1=35
SPL=40
SPL=40
NC2=25
Privacy Maintained
TL=30
Sectional View
TL=30 Privacy Violated
Noise Criteria Curves
Privacy is affected by
background noise level
NC 35 @ 500 hz
Max SPL500=40 db
S: p. 759, F.17.17
Sound Privacy—Example 1
Room A: NC500=35, SPL500 ≤ 40 db
Room B: NC500=25, SPL500 ≤ 31 db
Initial check based on TL alone
Room B
Room A
SPL=70
NC1=35
SPL=40
SPL=40
NC2=25
Privacy Maintained
TL=30
Sectional View
TL=30 Privacy Violated
Sound Privacy—Example 1
Combine effect of TL and absorption for final
analysis
NR=TL-10 Log (S/AR)
NR: noise reduction (db)
TL: transmission loss (db)
S: area of barrier wall (ft2)
AR: total absorption of receiving room
(sabins, ft2)
Sound Privacy—Example 1
For each frequency:
If SPL-NR ≤ NCmax privacy achieved
If SPL-NR > NCmax privacy violated
Sound Privacy Enhancement
TL data can be enhanced by standard
enhancements
Wood stud wall (STC 35)





Add gyp bd to one side
+2 db
Add gyp bd to both sides
+4 db
Double thickness insulation +6 db
Staggered studs
+9 db
Double studs
+13 db
from S: p. 816, T.19.1
Sound Privacy Reduction
Privacy is
diminished by
flanking noise,
weaker STC
constructions
and/or gaps
S: p. 825, F.19.34
Sound Privacy
Privacy diminished by
weaker STC
constructions
S: p. 817, F.19.22
Sound Privacy—Example 1
A 100 ft2 wall
assembly has TL=50
[excellent]
What is the overall TL
if a 20 ft2 door with
TL=20 is part of the
wall?
S: p. 817, F.19.22
Sound Privacy—Example 1
S1= 100 ft2
S2= 20 ft2
S2/S1=20/100=20%
TL1-TL2=50-20=30 db
TL1-TLC=23
TLC=TL1-23=27 db
[fair-poor]
S: p. 817, F.19.22
Sound Privacy
Privacy diminished by
construction gaps
S: p. 817, F.19.23
Sound Privacy—Example 2
A 10x10 (100 ft2) wall
assembly has TL=35
[very good]
What is the overall TL
if a 1/16” gap exists
along each vertical
edge?
S: p. 817, F.19.23
Sound Privacy—Example 2
S1= 14400 in2
S2= 15 in2
S2/S1=15/14400=0.1%
TL1=35 db
TLC=29 db
[fair-poor]
S: p. 817, F.19.23
Sound Transmission Reduction
Impact Isolation
Structural isolation
Flexible connections
Spring mounts
Inertial dampening
S: p. 845, F.19.47
Sound Transmission
Reduction– Floors
Sound Transmission Class (STC)
Impact Isolation Class (IIC)
S: p.1726, Index L.3
Impact Isolation Class—
Enhancements
Construction Tectonics
S: p. 842, F.19.43
Impact Isolation Class—
Enhancements
Resilient Floor Finishes:






1/16” vinyl tile
1/8” linoleum or rubber tile
¼” cork tile
Low pile carpet on fiber pad
Low pile carpet on fiber pad
High pile carpet on foam pad
from S: p. 843
0 db
4 +/- 1 db
10 +/- 2 db
12 +/- 2 db
18 +/- 3 db
24 +/- 3 db
Mechanical Isolation
Moving parts (vibration
sources) eliminated by
mechanical isolation
S: p. 851, F.19.54