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Lecture 16Acoustics—Historical Overview

Acoustical DesignAcoustics Fundamentals

Lecture 16Acoustics—Historical Overview

Acoustical DesignAcoustics Fundamentals

Historic OverviewHistoric OverviewHistoric OverviewHistoric Overview

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

Today

Research to improve conditions for Industrial noise Hearing risks Construction noise Public health

Historic OverviewHistoric Overview

Acoustical DesignAcoustical DesignAcoustical DesignAcoustical Design

Architect’s RoleArchitect’s Role

Source Path Receiver

slight major design primarily interestinfluence

Acoustical DesignAcoustical Design

“Proper acoustical planning eliminates many acoustical problems

before they are built”

Lee Irvine

Acoustical Design Acoustical Design RelationshipsRelationships

SiteLocation

OrientationPlanning

Internal Layout

SiteSite

Match site to applicationMatch application to site

SiteSite

Factory: Close to RR/Hwy Seismic

SiteSite

Rest Home: Traffic Noise Outdoor Use Contact/Isolation

SiteSite

Concert Hall: Use building as isolator Distance from noise

LocationLocation

Take advantage of distance/barriers

Distance

LocationLocation

Take advantage of distance/barriers

Natural or Man-made Berm

LocationLocation

Take advantage of distance/barriers

Acoustical Barriers

LocationLocation

Take advantage of distance/barriers

Building

OrientationOrientation

Orient Building for Acoustical Advantage

Playground School

OrientationOrientation

Orient Building for Acoustical Advantage

Parking Lot Factory

Office

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

Basic Acoustic GoalsBasic Acoustic Goals

1. Provide adequate isolation2. Provide appropriate acoustic

environment3. Provide appropriate internal function4. Integrate 1-3 amongst themselves and

into comprehensive architectural design

Acoustics FundamentalsAcoustics FundamentalsAcoustics FundamentalsAcoustics Fundamentals

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

SoundSound

Any unwanted sound

NoiseNoise

Sound travels at different speeds through various media.

Media Speed (C)

Air: 1,130 fpsWater: 4,625 fpsWood: 10,825 fpsSteel: 16,000 fps

Sound PropagationSound Propagation

Distance between similar points on a successive wave

C=fλ or λ=C/f

C=velocity (fps)f=frequency (hz)λ=wavelength (ft)

Lower frequency: longer wavelength

WavelengthWavelength

λ

Sound Power (P)Sound Intensity (I)

Sound MagnitudeSound Magnitude

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