Environmental Controls I/IG Lecture 20 Acoustics—Historical Overview Acoustical Design Acoustics Fundamentals

Historic Overview

Historic Overview Greek Theatre Open air Direct sound path No sound reinforcement Minimal reverberation S: p. 775, F.18.17a

Historic Overview 1st Century AD Vitruvius: “10 Books of Architecture” Sound reinforcement Reverberation S: p. 775, F.18.17b

Historic Overview Late 1700s-early 1800s Acoustics developed as part of physics and applied mathematics Broad outlines not specific details

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

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

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

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

Acoustical Design

Architect’s Role Source Path Receiver slight major design primarily interest influence

Acoustical Design “Proper acoustical planning eliminates many acoustical problems before they are built” Lee Irvine

Acoustical Design Relationships Site Location Orientation Planning Internal Layout

Site Match site to application Match application to site

Site Factory: Close to RR/Hwy Seismic

Site Rest Home: Traffic Noise Outdoor Use Contact/Isolation

Site Concert Hall: Use building as isolator Distance from noise

Location Take advantage of distance/barriers Distance

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

Location Take advantage of distance/barriers Acoustical Barriers

Location Take advantage of distance/barriers Building

Orientation Orient Building for Acoustical Advantage Playground School

Orientation Orient Building for Acoustical Advantage Parking Lot Factory Office Note: Sound is 3-dimensional, check overhead for flight paths

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

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

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

Basic Acoustic Goals Provide adequate isolation Provide appropriate acoustic environment Provide appropriate internal function Integrate 1-3 amongst themselves and into comprehensive architectural design

Acoustics 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

Noise Any unwanted sound

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

Wavelength 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 λ

Sound Magnitude Sound Power (P) Sound Intensity (I)

Sound Power Energy radiating from a point source in space. Expressed as watts S: p. 740, F.17.9

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)

Level of sound relative to a base reference Intensity Level Level of sound relative to a base reference “10 million million: one” S: p. 740, T.17.2

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

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

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=I1/10-16 105=I2/10-16 I1=10-10 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 S: p. 743, F.17.11

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 S: p. 737, F.17.8

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