1. Technology in Architecture
Lecture 18
Noise Reduction by Absorption
Sound Paths
Sound Isolation

2. Noise Reduction by Absorption

3. Noise Reduction by Absorption
Increased absorption reduces ambient noise
S: p. 771, F.18.2

4. Noise Reduction by Absorption
69 db
Reverberation increases ambient sound levels
S: p. 798 F.19.1

5. Sound Paths

6. Sound Paths
Air-Borne Sound
Structure-Borne Sound
S: p. 806, F.19.10

7. Sound Transmission
Barriers reduce sound transmission to reduce noise intrusion
S: p. 807, F.19.11

8. Air-Borne Sound
Transmission Loss (TL): sound energy lost through a construction assembly
S: p. 813, F.19.17

9. 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)

10. 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’

11. Noise Reduction Example
Find TL500
TL500=35 db
S: p. 813, F.19.17

12. Noise Reduction Example
Find NR500
NR500=TL Log (S/AR)
=35-10 Log (200/450)
=35-10 Log (0.444)
=35-10(-0.35)
=35+3.5= say 39db

13. Sound Isolation

14. Sound Transmission Class
Sound Transmission Class (STC): defines overall transmission loss across center band frequencies
Barrier STC Descriptor/ Application
Ranking
25 Poor/1 Space divider
30 Fair/2 Room divider
35 Very Good/4 Offices near quiet space
42-45 Excellent/5 Party walls
46-50 Total Privacy/6 Quiet next to noisy
from S: p T.19.6

15. Sound Transmission Class
STC can be compromised by:
Combination with lesser sound barriers
Gaps in construction
“An air path is a good sound path”

16. Sound Transmission Class
STC of a wall assembly
2x4 stud with gyp. Bd.
S: p.1712, Index K.1

17. Sound Transmission Class
Wall assembly description
2x4 stud with gyp. bd.
S: p. 1716, Table K.3

18. Sound Transmission Class
Wall assembly selection TL data
2x4 stud with gyp. bd.
S: p. 1713, Index K.2

19. Sound Transmission Class
Floor assembly follows same process
S: p. 1724, Index L.1

20. Noise Criteria
Noise Criteria (NC): accepted noise level for a given space.
Defined for center band frequencies

21. Noise Criteria Curves Accepted noise level for a given space.
S: p. 759, F.17.17

22. Noise Criteria Noise Criteria for various applications
S: p.831, T.19.8

23. 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

24. Room Criteria Curves
Room Criteria accepted noise level for a given space.
S: p. 761, F.17.18