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Environmental Controls I/IG

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Environmental Controls I/IG Lecture 20 Acoustics Historical Overview Acoustical Design Acoustics Fundamentals – PowerPoint PPT presentation

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Title: Environmental Controls I/IG


1
Environmental Controls I/IG
  • Lecture 20
  • AcousticsHistorical Overview
  • Acoustical Design
  • Acoustics Fundamentals

2
Historic Overview
3
Historic Overview
  • Greek Theatre
  • Open air
  • Direct sound path
  • No sound reinforcement
  • Minimal reverberation

S p. 775, F.18.17a
4
Historic Overview
  • 1st Century AD
  • Vitruvius 10 Books of Architecture
  • Sound reinforcement
  • Reverberation

S p. 775, F.18.17b
5
Historic Overview
  • Late 1700s-early 1800s
  • Acoustics developed as part of physicsand
    applied mathematics
  • Broad outlines not specific details

6
Historic Overview
  • 1800s
  • 1856 Prof. Joseph Henry
  • Treatise on Acoustics Applied to Public
    Buildings
  • 1877 Lord Rayleigh
  • The Theory of Sound
  • 1895 Wallace Clement Sabine
  • Fogg Art Museum, 1895-1905

7
Historic Overview
  • Buildings
  • 1870 Der Grosse Saal der Gesellschaft der
    Musikfreunde, Vienna
  • 1879 Central Music Hall, Chicago
  • 1887 Chicago Auditorium, Chicago
  • 1888 Concertgebouw, Amsterdam
  • 1900 Boston Symphony Hall, Boston
  • 1900-1948 None of note
  • 1948 Royal Festival Hall, London
  • 1961 Lincoln Center, New York

8
Historic Overview
  • By the 1920s
  • Precise measurements became possible
  • Individual design and fabrication
  • 1920s
  • Radio, television, amplified sound/music, motion
    pictures fostered greater demand for
    analysis/design

9
Historic Overview
  • Today
  • Research to improve conditions for
  • Industrial noise
  • Hearing risks
  • Construction noise
  • Public health

10
Acoustical Design
11
Architects Role
  • Source Path Receiver
  • slight major design primarily interest
  • influence

12
Acoustical Design
  • Proper acoustical planning
  • eliminates many acoustical problems before they
    are built
  • Lee Irvine

13
Acoustical Design Relationships
  • Site
  • Location
  • Orientation
  • Planning
  • Internal Layout

14
Site
  • Match site to application
  • Match application to site

15
Site
  • Factory
  • Close to RR/Hwy
  • Seismic

16
Site
  • Rest Home
  • Traffic Noise
  • Outdoor Use
  • Contact/Isolation

17
Site
  • Concert Hall
  • Use building as isolator
  • Distance from noise

18
Location
  • Take advantage of distance/barriers

Distance
19
Location
  • Take advantage of distance/barriers

Natural or Man-made Berm
20
Location
  • Take advantage of distance/barriers

Acoustical Barriers
21
Location
  • Take advantage of distance/barriers

Building
22
Orientation
  • Orient Building for Acoustical Advantage

Playground
School
23
Orientation
  • Orient Building for Acoustical Advantage

Parking Lot
Factory
Office
Note Sound is 3-dimensional, check
overhead for flight paths
24
Planning
  • Consider Acoustical Sensitivity of Activities

Noisy Quiet
Barrier
25
Planning
  • Consider Acoustical Sensitivity of Activities

Critical Non-Critical Noise
26
Internal Layout
  • Each room has needs that can be met by room
    layout

I p.116 F.5-12
27
Basic Acoustic Goals
  1. Provide adequate isolation
  2. Provide appropriate acoustic environment
  3. Provide appropriate internal function
  4. Integrate 1-3 amongst themselves and into
    comprehensive architectural design

28
Acoustics Fundamentals
29
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

30
Noise
  • Any unwanted sound

31
Sound Propagation
  • Sound travels at different speeds through
    various media.
  • Media Speed (C)
  • Air 1,130 fps
  • Water 4,625 fps
  • Wood 10,825 fps
  • Steel 16,000 fps

32
Wavelength
  • Distance between similar points on a successive
    wave
  • Cf? or ?C/f
  • Cvelocity (fps)
  • ffrequency (hz)
  • ?wavelength (ft)
  • Lower frequency longer wavelength

?
33
Sound Magnitude
  • Sound Power (P)
  • Sound Intensity (I)

34
Sound Power
  • Energy radiating from a point source in space.
  • Expressed as watts

S p. 740, F.17.9
35
Sound Intensity
  • Sound power distributed over an area
  • IP/A
  • I sound (power) intensity, W/cm2
  • P acoustic power, watts
  • A area (cm2)

36
Intensity Level
  • Level of sound relative to a base reference

10 million million one
S p. 740, T.17.2
37
Intensity Level
  • Extreme range dictates the use of logarithms
  • IL10 log (I/I0)
  • IL intensity level (dB)
  • I intensity (W/cm2)
  • I0 base intensity (10-16 W/cm2, hearing
    threshold)
  • Log logarithm base 10

38
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

39
Intensity LevelThe Math
  • If IL160 dB and IL250dB,
  • what is the total sound intensity?
  • 1. Convert to intensity
  • IL110 log (I1/I0) IL210 log (I2/I0)
  • 6010 log(I1/10-16) 5010 log(I2/10-16)
  • 6.0 log(I1/10-16) 5.0 log(I2/10-16)
  • 106I1/10-16 105I2/10-16
  • I110-10 I210-11

40
Intensity LevelThe Math
  • If IL160 dB and IL250dB,
  • what is the total sound intensity?
  • 2. Add together
  • I1I21 x 10-10 1 x 10-11
  • ITOT11 x 10-11 W/cm2

41
Intensity LevelThe Math
  • If IL160 dB and IL250dB,
  • what is the total sound intensity?
  • 3. Convert back to intensity
  • ILTOT 10 Log (ITOT/I0)
  • ILTOT10 Log (11 x 10-11 )/10-16
  • ILTOT10 (Log 11 Log 105 )
  • ILTOT10 (1.04 5) 60.4 dB

42
Intensity Level
  • Add two 60 dB sources
  • ?dB0,
  • add 3 db to higher
  • IL60363 dB

S p. 743, F.17.11
43
Sound Pressure Level
  • Amount of sound in an enclosed space
  • SPL10 log (p2/p02)
  • SPL sound pressure level (dB)
  • p pressure (Pa or µbar)
  • p0 reference base pressure (20 µPa or
  • 2E-4 µbar)

44
Perceived Sound
  • Dominant frequencies affect sound perception

S p. 737, F.17.8
45
Sound MeterA Weighting
  • Sound meters that interpret human hearing use an
    A weighted scale
  • dB becomes dBA

46
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