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Building Utilities III
(Acoustics and Lighting)
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ACOUSTICS
Introduction
Basic Principlesacousticsacoustics system
wave and propertiessound waves
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Quantity and units for acoustics
Sound Propagation
Reverberation
Acoustics design and analysis
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LIGHTING
Properties of Lighting
Quality of Light
Lighting System
Lighting Design
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Sound Properties
Speed = m/s = 344m/s
Intensity = watts/m2
Quality Level of energy
Structural component
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Sound Properties
Source = Energy = Sound energy
Path = disturbance = movement = wave
Wave = oscillation = elastic movement
Intensity = E (watts) = w = _w_
A (m2) m2 4r2
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1. = Wavelength= m Distance measured/wave cycle
2. V = Speed= m/s Air: v = 344 m/s
3. f = Frequency = Hertz Hz =125, 250, 500, 1000, 2000, 4000
4. a = Amplitude = phons/sound pressurlevel
w/m2
v = f; = v/f
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Intensity
I = w4d2 ;r = d
I = Intensity
w/m2 ; I = w
4d2
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IL = Intensity Level
Based on reference point
Threshold of hearing (Min IL and Max IL)
Minimum IL
BEL
Based on logarithm (10 = DECI + BEL)
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Threshold of hearing
IL = 10 log _I_Io
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Sound Propagation
Free Field sound waves continuously decay withoutreflections, as in fieldReverberant Field sound waves are blocked by structuralelements as in walls, ceiling, etc., and continuouslyreflecting back and forth
Ana echoic simulating free field condition as in arecording studio
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Sound Propagation
Sound Decay sound waves continuouslypropagate and intensity decreases as
distance from the source increases- The rate of decay is governed byinverse square law.
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Sound Propagation
Two modes:
1. Spherical 6db drop for each doubling
of distance2. Cylindrical 3db drop for each doubling
of distance
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Sound Absorption
Unit: Sabin
Unit area: ft2
Sabin in honor of Wallace Sabine
Sound absorption is expressed incoefficient (%) hence; sound absorption
coefficient
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Sound Absorption
In six frequency band:
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Sound Absorption
Construction materials technical data forsound absorption is expressed in these six
frequency
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Sound Absorption
Room Sound Absorption - the totalabsorption of exposed surfaces
Room Absorption - Sa = S1a1 + S2a2 +S3a3 + Snan
S = Surface area (ft2), a = absorption
coefficient
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Sound Absorption
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Reverberation
Persistent sound echoesEchoes sound reflections
Measured in 60 seconds interval t = v
SaWhere:
t = reverberation time in second0.05 = constant valueV = volume of enclosed space (ft3)Sa = room absorption (Sabin)
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Reverberation
Allowable reverberation time for oneroom, 1.0 sec (maximum allowable)
Sound should be intelligently audible
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Ray Diagram
Sound waves represented as vector
Vector graphical representation of sound
wavesAngle of incidence = AOI
Angle of reflection = AOR
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Ray Diagram
Angle ofincidence =
AOIAngle ofreflection =
AOR
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Transmission Loss
The property of a material to reducetransmission of sound decay
Transmission loss is due to soundreflection and absorption
Unit = Decibel (db)
Transmission coefficient the value usedfor computing the TL of a material; t =10-TL/10
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Transmission Loss
Average transmission loss = TLAVE
The computed average transmission loss
of a building component consists ofseveral construction materials
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Transmission Loss
TLAVE = 10log _____S______
S1t1 + S2t2 + Sntn
Where:
TLAVE= transmission loss average
S = total surface area (as in wall)
S1 = surface area of specificmaterial
t1 = transmission coefficient
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LIGHTING
Principles of Illumination
Illumination - defines as the intensity oflight per unit area
Quantity of Light - refers to the amount ofillumination of luminous flux per unit area
Quality of light - refers to the distributionof brightness in the lighting installation
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LIGHTING
Quality of light Brightness
Glare Color
Psychological effect
Contrast ratio
Diffuseness Aesthetics
Economics
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LIGHTING
Units: foot candle (fc) the amount oflight flux density
Expressed in lumens per sq. ft.Foot lambert the luminance of a surface
reflecting, transmitting or emitting onelumen of illumination per sq. ft.
Light flux density = fc
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LIGHTING
Factors that affects illumination:
1. Brightness
2. Contrast
3. Glare
4. Diffuseness
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