Transcript Slide 1

Technology in Architecture
Lecture 18
Noise Reduction by Absorption
Sound Paths
Sound Isolation
Noise Reduction by Absorption
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
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 Isolation
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
Room Criteria
Room Criteria (RC(x)): accepted noise
level for a given space.
Defined for NC frequencies plus extremely
low frequencies
(~16 and 31.5 hz)
Beginning to replace NC curves in practice
Room Criteria Curves
Room Criteria
accepted noise
level for a given
space.
S: p. 761, F.17.18