Technology in Architecture
Lecture 16
Historic Overview
Acoustical Design
Sound in Enclosed Spaces
Reverberation
Historic Overview
Greek Theatre
 Open air
 Direct sound path
 No sound reinforcement
 Minimal reverberation
M: p. 1061, F.23.17a
Historic Overview
1st Century AD
Vitruvius: “10 Books of Architecture”
Sound reinforcement
Reverberation
M: p. 1061, F.23.17b
Acoustical Design—Architect’s Role
Source
slight
Path
major design
influence
Receiver
primarily interest
Acoustical Design Relationships
Site
Location
Orientation
Planning
Internal Layout
Site
Factory:
 Close to RR/Hwy
 Seismic
Site
Rest Home:
 Traffic Noise
 Outdoor Use
 Contact/Isolation
Location
Take advantage of distance/barriers
Distance
Location
Take advantage of distance/barriers
Acoustical Barriers
Orientation
Orient Building for Acoustical Advantage
Playground
Note: Sound is 3-dimensional,
check overhead for
flight paths
School
Planning
Consider Acoustical Sensitivity of Activities
Noisy
Quiet
Barrier
Planning
Consider Acoustical Sensitivity of Activities
Critical
Non-Critical
Noise
Internal Layout
Each room has needs
that can be met by
room layout
SR-6: p.116 F.5-12
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
Sound Power
Energy radiating from a point source in
space.
Expressed as watts
M: p1027, F.22.9
Sound Intensity
Sound power distributed over an area
I=P/A
I: sound (power) intensity, W/cm2
P: acoustic power, watts
A: area (cm2)
Intensity Level
Level of sound relative to a base reference
“10 million million: one”
M: p. 1026, T.22.3
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
Intensity Level Scale Change
Changes are measured in decibels
scale change
3 dB
6 dB
7 dB
subjective loudness
barely perceptible
perceptible
clearly perceptible
Note: round off to nearest whole number
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)
60=10 log(I1/10-16)
6.0= log(I1/10-16)
IL2=10 log (I2/I0)
50=10 log(I2/10-16)
5.0= log(I2/10-16)
106=I1/10-16
I1=10-10
105=I2/10-16
I2=10-11
Intensity Level—The Math
If IL1=60 dB and IL2=50dB,
what is the total sound intensity?
2. Add together
I1+I2=1 x 10-10 + 1 x 10-11
ITOT=11 x 10-11 W/cm2
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 10-11 )/10-16
ILTOT=10 (Log 11 + Log 105 )
ILTOT=10 (1.04 +5) = 60.4 dB
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
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)
Perceived
Sound
Dominant
frequencies
affect sound
perception
M: p. 1022, F.22.8
Sound Meter—”A” Weighting
Sound meters that interpret human
hearing use an “A” weighted scale
dB becomes dBA
Sound In Enclosed Spaces—Sound Absorption
Amount of sound energy not reflected
M: p. 1047, , F.23.2
Sound Absorption
Absorption coefficient
α=Iα/Ii
α=absorption coefficient
Iα=sound power intensity absorbed (w/cm2)
Ii=sound power impinging on material (w/cm2)
1.0 is total absorption
Sound Absorption
Absorption coefficient
M: p. 1045,
T.23.1
Sound Absorption
Absorption
A=Sα
A=total absorption (sabins)
S=surface area (ft2 or m2)
α=absorption coefficient
sabins (m2)= 10.76 sabins (sf)
Sound Absorption
Total Absorption
Σα=S1α1 + S2α2 + S3α3 +…+Snαn
or
ΣA=A1 + A2 + A3 +…+An
Sound Absorption
Average
Absorption
αavg=ΣA/S
αavg <0.2 “live”
αavg >0.4 “dead”
M: p. 1050, F.22.6
Reflection in enclosed spaces
Acoustical
phenomena
M: p. 1063, F.23.20
M: p. 1064, F.23.21
Ray diagrams
Trace the reflection paths to and from
adjoining surfaces
angle of incidence = angle of reflection
I
R
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
Reflection in
enclosed spaces
Auditorium sound
reinforcement
M: p. 1065, F.23.23
Reverberation
Persistence of sound after source has ceased
M: p. 1047, F.23.2
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)
Reverberation Time
Application
Volume
M: p. 1058, F.23.13
3.5
ft3x1000
35.0
350
Reverberation Example
Compile data


Material Absorption
Coefficient
Material Surface Area
SR-6: p.121
Reverberation Example
Compare to
requirements
and adjust
M: p. 1058, F.23.13
3.5
ft3x1000
35.0
350