Technology in ArchitectureTechnology in ArchitectureTechnology in ArchitectureTechnology in Architecture

Lecture 16Historic OverviewAcoustical Design

Sound in Enclosed SpacesReverberation

Lecture 16Historic OverviewAcoustical Design

Sound in Enclosed SpacesReverberation

Historic OverviewHistoric Overview

Greek Theatre Open air Direct sound path No sound reinforcement Minimal reverberation

S: p. 785, F.18.17a

Historic OverviewHistoric Overview

1st Century ADVitruvius: “10 Books of Architecture”

Sound reinforcementReverberation

S: p. 785, F.18.17b

Acoustical Design—Architect’s Acoustical Design—Architect’s RoleRole

Source Path Receiver

slight major design primarily interestinfluence

Acoustical Design Acoustical Design RelationshipsRelationships

SiteLocation

OrientationPlanning

Internal Layout

SiteSite

Factory: Close to RR/Hwy Seismic

SiteSite

Rest Home: Traffic Noise Outdoor Use Contact/Isolation

LocationLocation

Take advantage of distance/barriers

Distance

LocationLocation

Take advantage of distance/barriers

Acoustical Barriers

OrientationOrientation

Orient Building for Acoustical Advantage

Playground School

Note: Sound is 3-dimensional, check overhead for flight paths

PlanningPlanning

Consider Acoustical Sensitivity of Activities

Noisy Quiet

Barrier

PlanningPlanning

Consider Acoustical Sensitivity of Activities

Critical

Non-Critical

Noise

Internal LayoutInternal Layout

Each room has needs that can be met by room layout

I: p.116 F.5-12

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

Acoustical Fundamentals—Acoustical Fundamentals—SoundSound

Sound PowerSound Power

Energy radiating from a point source in space.

Expressed as watts

S: p. 750, F.17.9

Sound IntensitySound Intensity

Sound power distributed over an area

I=P/A

I: sound (power) intensity, W/cm2

P: acoustic power, wattsA: area (cm2)

Intensity LevelIntensity Level

Level of sound relative to a base reference

S: p. 750, T.17.2

“10 million million: one”

Intensity LevelIntensity 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 Intensity Level Scale ChangeChange

Changes are measured in decibels

scale change subjective loudness3 dB barely perceptible6 dB perceptible7 dB clearly perceptible

Note: round off to nearest whole number

Intensity Level—The MathIntensity Level—The MathIf 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=I1/10-16 105=I2/10-16

I1=10-10 I2=10-11

Intensity Level—The MathIntensity Level—The MathIf 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 MathIntensity Level—The MathIf 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 LevelIntensity Level

Add two 60 dB sources

ΔdB=0,

add 3 db to higher

IL=60+3=63 dB

S: p. 753, F.17.11

Sound Pressure LevelSound 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)

PerceivePerceived Soundd Sound

Dominant frequencies affect sound perception

S: p. 747, F.17.8

Sound Meter—”A” Sound Meter—”A” WeightingWeighting

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

S: p. 771, , F.18.2

Sound AbsorptionAbsorption 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 AbsorptionAbsorption coefficient

S: p. 769, T.18.1

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”

S: p. 774, F.18.6

Reflection in enclosed Reflection in enclosed spacesspaces

Acoustical phenomena

S: p. 787, F.18.20

S: p. 788, F.18.21

Ray diagramsRay diagrams

Trace the reflection paths to and from adjoining surfaces

angle of incidence = angle of reflection

I R

Ray diagramsRay 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 inReflection inenclosed spacesenclosed spaces

Auditorium sound reinforcement

S: p. 789, F.18.23

ReverberationReverberation

Persistence of sound after source has ceased

S: p. 771, F.18.2

Reverberation TimeReverberation 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 TimeReverberation Time

ApplicationVolume

S: p. 782, F.18.13

ft3x1000 3.5 35.0 350

Reverberation ExampleReverberation Example

Compile data Material Absorption

Coefficient Material Surface Area

SR-6: p.121

Reverberation ExampleReverberation Example

Compare to requirements and adjust

S: p. 782, F.27.13

ft3x1000 3.5 35.0 350