BU III Presentation

7/27/2019 BU III Presentation

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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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