1. Technology in Architecture
Lecture 17
Noise Reduction by Absorption
Sound Paths
Sound Isolation
Sound Privacy
Structure Borne Sound

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

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

4. Sound Paths
Air-Borne Sound
Structure-Borne Sound
M: p. 806, F.19.10

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

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

7. Noise Reduction Combined effect of TL and absorption
NR=TL-10 Log (S/AR)
NR: noise reduction (db)
TL: transmission loss (db)
M: area of barrier wall (ft2)
AR: total absorption of receiving room (sabins, ft2)

8. 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’

9. Noise Reduction Example
Find TL500
TL500=35 db
M: p. 813, F.19.17

10. 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

11. 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 M: p T.19.6

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

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

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

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

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

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

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

19. Noise Criteria Noise Criteria for various applications
M: p.831, T.19.8

20. Sound Privacy
Privacy is affected by initial sound source, TL, NC and absorbtion
Room A
Room B
SPL
NC1
NC2
Privacy Maintained TL TL
Privacy Violated
Sectional View

21. Sound Privacy—Example 1
Room A: NC500=35
Room B: NC500=25
Room A
Room B
SPL=70
NC1=35
SPL=40
SPL=40
NC2=25
Privacy Maintained
TL=30
TL=30
Privacy Violated
Sectional View

22. Noise Criteria Curves Privacy is affected by background noise level
NC 500 hz
Max SPL500=40 db
M: p. 759, F.17.17

23. 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 A
Room B
SPL=70
NC1=35
SPL=40
SPL=40
NC2=25
Privacy Maintained
TL=30
TL=30
Privacy Violated
Sectional View

24. 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)
M: area of barrier wall (ft2)
AR: total absorption of receiving room (sabins, ft2)

25. Sound Privacy—Example 1
For each frequency:
If SPL-NR ≤ NCmax privacy achieved
If SPL-NR > NCmax privacy violated

26. 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 M: p. 816, T.19.1

27. Sound Privacy Reduction
Privacy is diminished by flanking noise, weaker STC constructions and/or gaps
M: p. 825, F.19.34

28. Sound Privacy Privacy diminished by weaker STC constructions
M: p. 817, F.19.22

29. 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?
M: p. 817, F.19.22

30. 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]
M: p. 817, F.19.22

31. Sound Privacy Privacy diminished by construction gaps
M: p. 817, F.19.23

32. 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?
M: p. 817, F.19.23

33. Sound Privacy—Example 2
S1= in2
S2= 15 in2
S2/S1=15/14400=0.1%
TL1=35 db
TLC=29 db
[fair-poor]
M: p. 817, F.19.23

34. Sound Paths
Structure-Borne Sound
M: p. 806, F.19.10

35. Sound Transmission Reduction
Impact Isolation
Structural isolation
Flexible connections
Spring mounts
Inertial dampening
M: p. 845, F.19.47

36. Sound Transmission Reduction– Floors
Sound Transmission Class (STC)
Impact Isolation Class (IIC)
M: p.1726, Index L.3

37. Impact Isolation Class—Enhancements
Construction Tectonics
M: p. 842, F.19.43

39. Impact Isolation Class—Enhancements
Resilient Floor Finishes:
1/16” vinyl tile 0 db
1/8” linoleum or rubber tile 4 +/- 1 db
¼” cork tile 10 +/- 2 db
Low pile carpet on fiber pad 12 +/- 2 db
Low pile carpet on fiber pad 18 +/- 3 db
High pile carpet on foam pad 24 +/- 3 db
from M: p. 843

40. Mechanical Isolation
Moving parts (vibration sources) eliminated by mechanical isolation
M: p. 851, F.19.54