1. Technology in Architecture
Lecture 16
Historic Overview
Acoustical Design
Sound in Enclosed Spaces
Reverberation

2. Historic Overview Greek Theatre Open air Direct sound path
No sound reinforcement
Minimal reverberation
M: p. 1061, F.23.17a

3. Historic Overview 1st Century AD Vitruvius: “10 Books of Architecture”
Sound reinforcement
Reverberation
M: p. 1061, F.23.17b

4. Acoustical Design—Architect’s Role
Source Path Receiver
slight major design primarily interest
influence

5. Acoustical Design Relationships
Site
Location
Orientation
Planning
Internal Layout

6. Site
Factory:
Close to RR/Hwy
Seismic

7. Site
Rest Home:
Traffic Noise
Outdoor Use
Contact/Isolation

8. Location
Take advantage of distance/barriers
Distance

9. Location
Take advantage of distance/barriers
Acoustical Barriers

10. Orientation Orient Building for Acoustical Advantage
Playground
School
Note: Sound is 3-dimensional,
check overhead for
flight paths

11. Consider Acoustical Sensitivity of Activities
Planning
Consider Acoustical Sensitivity of Activities
Noisy Quiet
Barrier

12. Consider Acoustical Sensitivity of Activities
Planning
Consider Acoustical Sensitivity of Activities
Critical
Non-Critical
Noise

13. Internal Layout Each room has needs that can be met by room layout
SR-6: p.116 F.5-12

14. Acoustical Fundamentals—Sound
Mechanical vibration, physical wave or series of pressure vibrations in an elastic medium
Described in Hertz (cycles per second)
Range of hearing: 20-20,000 hz

15. Sound Power Energy radiating from a point source in space.
Expressed as watts
M: p1027, F.22.9

16. Sound power distributed over an area
Sound Intensity
Sound power distributed over an area
I=P/A
I: sound (power) intensity, W/cm2
P: acoustic power, watts
A: area (cm2)

17. Level of sound relative to a base reference
Intensity Level
Level of sound relative to a base reference
“10 million million: one”
M: p. 1026, T.22.3

18. Extreme range dictates the use of logarithms
Intensity Level
Extreme range dictates the use of logarithms
IL=10 log (I/I0)
IL: intensity level (dB)
I: intensity (W/cm2)
I0: base intensity (10-16 W/cm2, hearing threshold)
Log: logarithm base 10

19. Intensity Level Scale Change
Changes are measured in decibels
scale change subjective loudness
3 dB barely perceptible
6 dB perceptible
7 dB clearly perceptible
Note: round off to nearest whole number

20. Intensity Level—The Math
If IL1=60 dB and IL2=50dB,
what is the total sound intensity?
1. Convert to intensity
IL1=10 log (I1/I0) IL2=10 log (I2/I0)
60=10 log(I1/10-16) 50=10 log(I2/10-16)
6.0= log(I1/10-16) 5.0= log(I2/10-16)
106=I1/ =I2/10-16
I1= I2=10-11

21. Intensity Level—The Math
If IL1=60 dB and IL2=50dB,
what is the total sound intensity?
2. Add together
I1+I2=1 x x 10-11
ITOT=11 x W/cm2

22. Intensity Level—The Math
If IL1=60 dB and IL2=50dB,
what is the total sound intensity?
3. Convert back to intensity
ILTOT= 10 Log (ITOT/I0)
ILTOT=10 Log (11 x )/10-16
ILTOT=10 (Log 11 + Log 105 )
ILTOT=10 ( ) = dB

23. Intensity Level Add two 60 dB sources ΔdB=0, add 3 db to higher
IL=60+3=63 dB
M: p. 1029, F.22.11

24. Sound Pressure Level Amount of sound in an enclosed space
SPL=10 log (p2/p02)
SPL: sound pressure level (dB)
p: pressure (Pa or μbar)
p0: reference base pressure (20 μPa or
2E-4 μbar)

25. Perceived Sound Dominant frequencies affect sound perception
M: p. 1022, F.22.8

26. Sound Meter—”A” Weighting
Sound meters that interpret human hearing use an “A” weighted scale
dB becomes dBA

27. Sound In Enclosed Spaces—Sound Absorption
Amount of sound energy not reflected
M: p. 1047, , F.23.2

28. Sound Absorption Absorption coefficient α=Iα/Ii
Iα=sound power intensity absorbed (w/cm2)
Ii=sound power impinging on material (w/cm2)
1.0 is total absorption

29. Sound Absorption
Absorption coefficient
M: p. 1045, T.23.1

30. Sound Absorption Absorption A=Sα S=surface area (ft2 or m2)
A=total absorption (sabins)
S=surface area (ft2 or m2)
α=absorption coefficient
sabins (m2)= sabins (sf)

31. Sound Absorption Total Absorption Σα=S1α1 + S2α2 + S3α3 +…+Snαn or
ΣA=A1 + A2 + A3 +…+An

32. Sound Absorption Average Absorption αavg=ΣA/S αavg <0.2 “live”
αavg >0.4 “dead”
M: p. 1050, F.22.6

33. Reflection in enclosed spaces
Acoustical phenomena
M: p. 1063, F.23.20
M: p. 1064, F.23.21

34. Ray diagrams Trace the reflection paths to and from adjoining surfaces
angle of incidence = angle of reflection I R

35. Ray diagrams Trace the reflection paths to receiver
Reflected sound path ≤ Direct sound path+55
Note: check rear wall
and vertical paths
Note: SR-6=RR-7
SR-6: p.116, F.5-12

36. Reflection in enclosed spaces
Auditorium sound reinforcement
M: p. 1065, F.23.23

37. Reverberation Persistence of sound after source has ceased
M: p. 1047, F.23.2

38. Reverberation Time
Period of time required for a 60 db drop after sound source stops
TR= K x V/ΣA
TR: reverberation time (seconds)
K: 0.05 (English) (0.049 in SR-6) or 0.16 (metric)
V: volume (ft3 or m3)
ΣA: total room absorption, sabins (ft2 or m2)

39. Reverberation Time Application Volume M: p. 1058, F.23.13 ft3x1000
M: p. 1058, F.23.13

40. Reverberation Example
Compile data
Material Absorption Coefficient
Material Surface Area
SR-6: p.121

41. Reverberation Example
Compare to requirements and adjust
ft3x1000
M: p. 1058, F.23.13