Lighting & Acoustics

7/23/2019 Lighting & Acoustics

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Lighting & Acoustics


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Objective of Course

To acquaint the students about light and sound theory and theirapplication to building design

Unit 1:

- Day lighting: Physical parameters of day lighting, Day light penetration, Day light factor

- Integrating day lighting with artificial, automatic control of artificial lighting in relation to

day lighting, calculation of requirements of artificial lighting in relation to available daylighting

- Types of lamps : Incandescent Lamp, Reflector Lamp, Blown bulb lamps, Tungsten HalogenLamp, Tubular fluorescent lamps, Mercury vapour lamps, Sodium Vapour Lamps, CompactFluorescent lamps

Unit 2:

- Vocabulary of artificial lighting: Lumens, Lux, M.F., R.I.R, Lighting level requirements forvarious areas

- Types of LuminariesDecorative commercial, Industrial, Outdoor, Working out room indexratio and coefficient of utilization

- Design of artificial lighting for various types of buildings

- External lighting : Lighting for various types of buildings


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Unit 3:

- Acoustical concepts: Wave theory, Sound power, Sound intensity, Decibels, Sound powerlevel, Sound intensity level, Sound pressure level, frequency bands concept of reflection,

absorption, transmission.- Absorption coefficient, NRC, Sound absorption materials, fibrous, membrane, resonators,perforated facing, application techniques.

- Noise control by absorption, Sound transmission, Transmission loss, Composite barriers,Noise reduction between rooms, Light construction.

Unit 4:

- Reverberation time (RT), Calculation of RT, Sample problems, RT and noise criteria forspaces for speech and music.

- Acoustical design of enclosed spaces for speech and music, reflection analysis, echoes,flutter echo, foci.

- Acoustical design consideration in interior design and sound amplification system.


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Introduction - Lighting

Building - acts as a barrier between the Internal andExternal environment

Internal environmentControlled

External environmentUndesirable conditions.

Building should be a selective barrier or filter, whichexcludes the unwanted influences whilst admits thosewhich are desirable.

One such desirable effect is Day light.

Most important communication channel for man withhis environment is Vision and without light thiscommunication is not possible.

Light is prerequisite for seeing


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Light

Natural Artificial

Source of Day light is Sun and Sky

Ultimate Source of Daylight is Sun

Large amount of thermal radiation are

received with light

In Bright Sunshine, Illumination isaround 100 Klux (1,00,000 Lux)

Light source is under designers control

Light source is independent of Location,

Climate


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Nature of Light Light is a narrow Wavelength band of electromagnetic radiations i.e. 380nm 780nm

These waves are vibrations of electric and magnetic fields that pass through space.

Each colour has its own particular wavelength and frequency.

A wavelength is the

distance between the

same locations on

adjacent waves

The frequency of a wave

is determined by the

number of complete

waves, or wavelengths,

that pass a given point

each secondElectromagnetic Spectrum


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Light travels along a straight path.

Velocity of light 3 X 108 m/s

When light from the sun passes through a prism, the light is split into the seven visiblecolours by refraction.

Refraction is caused by the change in speed experienced by a wave of light when it

changes medium.


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Transmission Reflectance (r)

Absorption (a)

Transmittance (t)

Transparent : These materials when exposed to light transmit large part of it.

Opaque: These materials when exposed to light block the passage of light.

Therefore behind an opaque object there is no light.

Translucent: These are materials which transmit part of incident light, break its

straight passage, scatter it in all directions, creating diffuse light.

In all cases, r + a + t = 1

In case of opaque objects, t=0, r + a = 1


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Photometric quantities/ Vocabulary of artificial lighting Intensity of Light (I) : Light flux emitted in a particular direction from a

given light source. {measured in units of Candela (cd) }

OR luminous intensityis a measure of the wavelength- weighted power emitted by a light source in a particular

direction per unit solid angle.

The SI unit of luminous intensity is the candela(cd)

Flux (or Flow) of Light (F)(): Light flux is the total quantity of lightemitted per second. {Measured in Lumens (Lm)}

It is the total perceived power emitted in all directions.

Illuminance (E): amount of flux falling on unit area i.e. Lm/m2

E = / Surface AreaIt is a measure of the intensity of the incident Light

Lux(= lm/m2)

Luminance (L): measure of brightness of a surface.

often used to characterize emission or reflection from surfaces

It is an indicator of how bright the surface will appear.L= I/ Surface area {measured in cd/ m2}


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Photometric quantities/ Vocabulary of artificial lighting

Candela Definition: The candela is the

luminous intensity, in a given direction, ofa source that emits monochromatic

radiation of frequency 540 1012hertz

and that has a radiant intensity in that

direction of 1683watt per steradian.

The steradian is the cone of light as it

emerges from the source, such that it

would light up one meter square of the

inside of a sphere with a one meter

radius.

The frequency chosen is in the visible

spectrum near green, corresponding to a

wavelength of about 555 nanometers.

The human eye is most sensitive to this

frequency, when adapted for bright

conditions.


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Conversions


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Lighting level requirements for various areas


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Illuminance


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Daylight Factor : In a building, at a certain point,

the ratio of the illumination to

the simultaneous out-door

illumination can be taken as

constant. This constant ratio,

expressed as a percentage, is

the daylight factor.

Day light factor concept is valid

only under conditions, when

there is no direct sunlight.

Day Light Factor Concept


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Consider a point inside abuilding {say P}

Light from sun reaches

P in following ways


Diffused or Skylight : Through a window or opening

Externally Reflected Light(ERC) : by ground or other buildings through same

window

Internally Reflected Light (IRC): From walls, ceiling or other internal surfaces.

Direct Sunlight: along a straight path from the sun


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DF = SC + ERC+ IRC

Where SC = Sky Component

ERC = Externally Reflected ComponentIRC = Internally Reflected Component

Day light factor concept is valid only under conditions, when there is no direct sunlight.

DF = E I / Eo X 100

Where E I = Illumination Indoor

(At the point taken)

Eo

= Illumination Outdoor

(from Unobstructed sky hemisphere)


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SC : The area of sky visible from the point considered and its average altitude angle (i.e.

Luminance of sky at that angle)

ERC: The area of external surfaces visible from the point considered and the reflectance of

these objects.

IRC: The size of the room and reflectance of these indoor surfaces.

DF = E I / Eo X 100

Where E I = Illumination Indoor

E o = Illumination Outdoor


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Concept of Utilization Factor

A source of I candela emits a total flux of 4I lumens

At a distance d this flux will be distributed over a

sphere of radius d i.e. 4d2

E = 4I/ 4d2

=I/ d2

This is known as Inverse square law and applicable

when the illuminated plane is normal to the direction

of light. i.e. angle of incidence, = 0

When the plane is tilted, the same flux is distributed

over a larger area, thus illumination is reduced.

This reduction is proportionate to the cosine of angle

of incidence.

E= EnX Cos

E= Illumination on a tilted plane

En = Illumination on normal plane


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Illumination of a surface from several sources will be

the simple sum of the component illuminations

E = E1+ E2+ E3+

But, the method above leads to very lengthy and cumbersome

calculation.

If the fittings are positioned in a regular array, much simpler method

can be followed, based on the concept of utilization factor.

UF = FR/ FI

Where FR= Total flux received on the working plane

FI = Total flux emitted by all the lamps.


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This UF depend on

- Geometrical proportions of the room.

- Mounting height of the lamp.

- Surface reflectance's

- type of fitting used.

Values of UF can be found in fitting catalogue . Generally

its value ranges from

For downward direct lighting 0.40.9

For diffusing fittings 0.20.5

For indirect lighting 0.050.2

Maintenance Factor: Allowance should be made for dirt on the fitting or

deterioration of the lamp.

The UF should be multiplied by maintenance factor (MF) (usually = 0.8)

f L


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Types of Lamps Incandescent Lamps:

An electric current passes through a

thin filament, heating it until itproduces light.

These are lamps in which current is

passed through a tungsten filament.

The enclosing glass bulb prevents the

oxygen in air from reaching the hot

filament, which otherwise would be

destroyed rapidly by oxidation.

These lamps have luminous efficacy

of 1016 Lm/ W

5% of Light and 95% Heat.

Low Installation cost Warm colour tone

Application: Interiors, Exteriors,

Night lamps, Decorative lighting in

chandelier, signboards, Torches etc.


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Types of Lamps

Reflector Lamps:

Reflector lamps are for directional

light. No more wastage of energy.

Lamps with Satin frosted front

finish and internal mirror reflector.

Satin frosted finish ensuresdiffused output and internal

reflector gives high intensity beam.


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Types of Lamps Halogen Lamps :

A halogen lamp is an incandescent

lamp in which a tungsten filament

is sealed into a compact

transparent envelope filled with an

inert gas and halogen

These last longer than Filament

bulb but are more costly. Produce white light than ordinary

tungsten.

Small and energy efficient.

Compact and easy to install and

maintain. Application: Car parks,

Construction areas, security

lighting, storage yards, Factory

Bays, Godowns, Monuments etc.


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Types of Lamps Fluorescent Lamps:

These tubular fluorescent lamps

are basically low pressure mercuryvapour lamps.

These have advantage of low

wattage consumption and higher

efficacy.

Use of these lamps are diverse and

almost universal.

These lamps give 40-70 lm/W

These lamps give 21% - light and

79% heat.

A fluorescent lamp tube is filled

with a gas containing low pressuremercury vapour and argon, xenon,

neon or krypton.

The inner surface of the bulb is

coated with a fluorescent (and

often slightly phosphorescent)

It is a gas discharge lamp that uses

electricity to excite mercury vapour.This exited mercury vapour then

produce ultraviolet light. The UV light is

absorbed by the bulb's fluorescent

coating, which re-radiates the energy at

longer wavelengths to emit visible light.


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Types of Lamps

High Intensity Discharge Lamps :

The high ceiling and heights in

Industrial interiors and outdoor

lighting applications necessitate

the use of high intensity light

sources.

These lamps have high lumen

output.

These include Mercury Vapour and

Sodium Vapour lamps.

A mercury-vapor lamp is a gas

discharge lamp which uses mercuryin an excited state to produce light.

A sodium vapor lamp is a gas

discharge lamp which uses sodium

in an excited state to produce light.


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Types of Lamps

High Intensity Discharge Lamps :

Application: typically used when

high levels of light over large areas

are required, large public areas,

movie theaters, football stadiums,

outdoor activity areas, roadways,

parking lots, floodlighting of

monuments, ports etc.


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Types of Lamps

Compact fluorescent lamp:

CFLs generally use less power

have a longer rated life

higher purchase price


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Three objectives of modern lighting design Task Lighting:

Designed specifically to direct light onto some task performed by a person or machine.

(e.g. focus on page while reading, type-writer, keyboard, rather than throwing shadows

or glare on to the screen)

Combine task lighting with background lighting to avoid eye strain.

Ensure that specific work areas are not in shadows.

Accent Lighting:

The basic purpose of an accent lighting is to produce a specific focus on a single object

or detail in a room.

Ambient Lighting:

This lighting fills the undefined areas of a room with a soft level of light.

This is to soften the contrast between the light source and surroundings areas.

Illumination should be uniform.

It helps to enhance the general ambience.


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Luminaires

Luminaire:

A body housing the light source which has been designed to produce a particular spatial

distribution of light by using reflector or diffuser surfaces. Certain light fittings

incorporate part or all or the auxiliary equipment necessary for correct functioning of

the light source.

Indoor Commercial Luminaire

Create an optimum ambience combined with high efficiency, good glare protection and

maximum comfort. Also perform other functions like creation of moods, add value by highlighting products.

Indoor Industrial Luminaire

High efficiency luminaires

Initial cost and maintenance expense.

Outdoor Lighting

Long life, economical in long run.

(include street lighting, floodlighting etc)


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Commercial Luminaires


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Indusrtial Luminaires


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Outdoor Lighting


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Factors to be considered while selecting light fixtures

Function:

A primary consideration about any fixture is to ensure that it directs the light where it is

needed.

Size:

Should be according to room area.

Design:

Personal taste, manufacturers offer variety of fixtures like spotlights, pendants, track

lights, wall, floor and ceiling fixtures.

Flexibility:

Movable or adjustable lamps offer more flexibility.

Cost:

Consider both purchase and operating cost in selecting light fixtures.

Maintenance:

To achieve optimum efficiency, all fixtures should be cleaned regularly.


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Light Fittings


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GLARE

Glare:

Glare is defined as a shine with a harsh, dazzling light.

One of the most important considerations in the placement of light fixtures is to study

the glare they produce.

Types of Glare:

Direct Glare:

A bare light source is the worst kind.

Deeply recessed light fixture will solve the problem.

The interior surface finish of the reflector can also affect the amount of glare.

Reflected Glare:

Light bounces from an object into our eyes from the same angle it hits it.

Angle should not be too steep. (safety range is about 3045 degree)

Veiling Glare:

If a light fixture is located directly over a flat, shiny surface, veiling glare can be a

problem.

GLARE


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Bright, concentrated light source above and forward of the task

surface present the ideal condition for veiling reflectance's.

GLARE

C l R diti / C l R d i i d / C l t d l t t


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Colour Rendition/ Colour Rendering index/ Correlated colour temperature

The interaction between an object and a light source is called colour rendition.

E.g. Colour of a blue vase under a blue light will be heightened as the colour of the light

intensifies the colour of vase.

Under red light same vase will appear dull (red absorbed and no blue light to reflect)

To solve this problem different light sources throw different amount of colours.

The colour rendering index (CRI) is a quantitative measure of the ability of a light source to

reproduce the colours of various objects faithfully in comparison with an ideal or naturallight source.

The colour rendering characteristic of a lamp describe how natural the surroundings appear

in its light.

Light sources with a high CRI are desirable in color-critical applications.

Technically, colour temperaturerefers to the temperature to which one would have to heat

a theoretical "black body" source to produce light of the same visual color.


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Colour temperature describes the

colour appearance of the light

source and the light emitted fromit.

Colour rendering describes how

well the light renders colours in

objects.


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Spectral Power Distribution :

the power per unit area per unit wavelength of an illumination

OR

more generally, the per-wavelength contribution to any radiometric quantity (radiant

energy, radiant flux, radiant intensity, radiance, irradiance, radiant exitance, or

radiosity).

SI units: watt meter3

is the radiant flux of the source

Ais the area over which the radiant flux is integrated

is the wavelength
http://en.wikipedia.org/wiki/Radiant_energyhttp://en.wikipedia.org/wiki/Radiant_energyhttp://en.wikipedia.org/wiki/Radiant_fluxhttp://en.wikipedia.org/wiki/Radiant_intensityhttp://en.wikipedia.org/wiki/Radiancehttp://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Radiant_exitancehttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Radiant_exitancehttp://en.wikipedia.org/wiki/Radiant_exitancehttp://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Radiancehttp://en.wikipedia.org/wiki/Radiant_intensityhttp://en.wikipedia.org/wiki/Radiant_fluxhttp://en.wikipedia.org/wiki/Radiant_energyhttp://en.wikipedia.org/wiki/Radiant_energy


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Soft, hard, Warm and Cool Colours


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Introduction - Acoustics

Acoustics is the branch of physics that deals with the production, control,

transmission, reception, and effects of sound.

The science of soundacousticscan be broadly divided into two major areas:a) The handling of wanted sound i.e. creation of most favorable conditions for

listening to a sound we want to hear. (room acoustics)

b) The handling of unwanted sound i.e. Noise

Hearing is most important communication channel (second to vision)

Noise is the term used for unwanted

sound, thus definition is subjective, one

mans sound is another mans noise.

Noise may also be defined as a disturbance

in an elastic medium which includes solid,

liquid and gasses.


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Areas

Rural Urban

low density of rural areas ensures

greater distance between source and

listener.

In village areas, one knows everyone

else, sound originates from knownsource.

Noise sources are Industries, factories,

aircrafts, radio etc.

High density townsDistances between

sources and listeners are much less.


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Nature of Sound Sound is sensation caused by vibrating medium acting on the ear, but term is usually

applied to vibration itself.

The medium conveying it to ear can be gas (air), liquid or solid.

In gases or liquids, vibrations are transmitted as a longitudinal wave motion.

In solids, vibrations are transmitted as lateral wave motion.

As density of air changes with temperature, velocity of sound also varies with air

temperature (for rough calculations340 m/s)

A wavelength is the

distance between the

same locations on

adjacent waves The frequency of a wave

is determined by the

number of complete

waves, or wavelengths,

that pass a given point

each second

Sound Waves


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Transverse wave

Longitudinal or compression wave (sound)

Sound consists of longitudinal or compression waves that move through air or

other materials. It does not travel in a vacuum. Sound has the characteristics of

wavelength, frequency, speed and amplitude. Sound waves are created by the

vibration of some object and are detected when they cause a detector to vibrate.

N t f S d Cl ifi ti f S d


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Nature of Sound - Classification of Sound

Depending upon the position of source, sound can be broadly divided into two classes :

Airborne sound

An airborne sound is one which is transmitted through air and travels direct to the ear

of the person.

This type of sound travels from one part of building to another or from outside of the

building to the inside through open doors, windows or other openings.

Impact sound/Structureborne sound

The sound which is first transmitted through structure is called impact sound.

The noise of footsteps, furniture movement, dropping of utensils.

Impact sounds are troublesome and are often very sharp.

Nature of Sound


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Speed of Sound Wave

In general, the speed of sound c is given by

where

C is a coefficient of stiffness (or the modulus of bulk elasticity for gas mediums)

is the density

Nature of Sound

Nature of Sound


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Nature of Sound Power and Intensity:

Poweris output of a source and it is measured as rate of energy flow (unitWatts)

Sound intensityis the strength of sound in a carrying medium (e.g. air) or in other

words, density of energy flow through unit area. (unitW/m2)

In case of a point source emitting sound uniformly in all directions

I = W/ 4d2

Where, I is intensity in W/m2

d is distance from sourceThis is known as Inverse Square Law.

Nature of Sound


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Sound Pressure

Sound pressure is the local pressure deviation from the ambient (average, or

equilibrium) pressure caused by a sound wave.

The SI unit for sound pressure is the pascal (symbol: Pa)

Sound Pressure Level

Where, P is sound pressure being measured

P0 is the reference sound pressure (usually = 20 Pa)

Sound Power Level

Where, W is power emitted

W0is the reference power (10-12 Watt)

Nature of Sound

i i i


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Ears Sensitivity The average person can hear

frequencies from 20 to 16000 Hz

(this range reduces with age) Standard threshold of audibility is

10 -12 W/m2 (1 picowatt per Sq. Mt.)

Threshold of pain is 1 W/m2

The ear has a built in defence

mechanism: its sensitivity decreases forhigher intensity sounds.

The logarithm of the ratio of the

measured sound intensity to the

intensity at the threshold gives the

sound level scale or decible (dB) scale.

N = 10 Log I /I0

Where I = the measured Intensity

I0= Reference Intensity (10-12 W/m2 )

E S i i i


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Ears Sensitivity Decibel (dB) is a unit for expressing

relative pressure or intensity of sounds

on a uniform scale from 0 for the leastperceptible sound to about 130 for the

average threshold of pain.

Because decibel measurement is based

on a logarithmic scale, the decibels of

two sound sources cannot be added

mathematically.

An equal loudness contour is a curve

that represents the sound pressure level

at which sounds of different frequencies

are judged by a group of listeners to be

equally loud.


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N i i E l d S


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Noise in Enclosed Space Sound incident on the surface of a solid

body is partly reflected, partly absorbed

and partly transmitted. Absorption coefficientall the sound

that is not reflected (i.e. includes the

part actually absorbed and transmitted)

Absorption coefficient is denoted by a

Absorption (A) = a X s

Where a = absorption coefficient

s = area of given surface

N i i E l d S


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Noise in Enclosed Space In an enclosed space, even from single

source, there will be a complex pattern

of interreflected sound (referred asreverberant sound)

At any point in room the total sound

received will consists of two parts:

-Direct Component

-The reverberant component

The magnitude of reverberant

component depends on the absorbent

qualities of room surfaces.

N i i E l d S


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Noise in Enclosed Space Reflective surfaces are useful when they

reinforce desirable sounds by directing

and distributing their paths in a room. The continued presence of reflected

sounds, can also cause problems of

echo, flutter or reverberation.

Echoes: when a reflecting surface is so

far away from the source that the sound

is reflected back as a distinct repetition

of the direct sound, the reflected sound

is called an echo.

Echoes are produced, when the timeinterval between the direct and the

reflected sound waves is about 1/15thof

a second.

Flutter: In smaller rooms, parallel

reflective surfaces can cause a rapidsuccession of echoes we call flutter.

N i i E l d S


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Noise in Enclosed Space Reverberation: when the sound waves

get reflected, a part of sound energy is

converted into heat energy by frictionand is absorbed by the walls.

Subsequently the reflected waves get

interreflected from one surface to

another until they gradually fade and

become inaudible.

This phenomenon of undue

prolongation of sound by successive

reflections from surrounding surfaces,

after the source has ceased is termed as

reverberation.

Reverberation: The persistence of asound within a space, caused by

multiple reflections of the sound after

its source has stopped.

While some music is enhanced by long

reverberation times, speech can

become muddled in such an acoustic

environment.

To ensure clarity of sound, it may benecessary to alter the shape and

orientation of a rooms surfaces or

adjust the ratio of reflective and

absorbent materials.

N i i E l d S


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Noise in Enclosed Space Reverberation Time: The reverberation

period is the time taken for the sound energy

to decay by 60 db, after the sound source hasstopped.

Formula for calculating reverberation time by

Prof. Sabine

t = 0.16 V / a1s1 + a2s2 + a3s3 + ..

Where t= time of reverberation

V = Volume of room in m3

a1, a2,a3..= Coefficient of absorptions1, s2, s3= area of absorbing surface

N i i E l d S


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Noise in Enclosed Space The time of reverberation plays a significant role in achieving

desired acoustical condition.

If the reverberation time is too long it results in overlapping of

speech, and if its too short, it produces the effect of deadness.

Reverberation time > 3 seconds (considered Bad)

3 sec > Reverberation time > 2 seconds (Fairly good)

2 sec > Reverberation time > 1/2 seconds (Very good)

The selection of correct time of reverberation is called optimum

time of reverberation.

Presence of audience in a room reduces the time ofreverberation. This is on account of the absorption provided by

the audience ( due to clothing worn by persons)

(Therefore theatre will have greater reverberation time when its empty )

N i i E l d S


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Noise in Enclosed Space

N i I l ti


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Noise InsulationNoise insulating qualities of an element can be expressed by:

Transmission coefficient (t): A decimal fraction, expressing the proportion of sound

energy (Intensity) transmitted.

Transmission Loss (TL) or Sound reduction index: The reduction effect of an element

expressed in dB.

e.g. A wall with TL = 30 dB will reduce noise of

9030 = 60dB

The relationship between the two quantities is reciprocal and logarithmic:

TL = 10 Log 1/t

or

t = antilog TL/10

Noise Control


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Noise ControlMeans of Noise Control:

Against External Noisethe following means of protection are available to the

designer: Distance

Avoiding zones of direction sound

Screening

Planning: Using non noise sensitive parts of the building as barriers

Noise insulating building envelope Against Internal Noise (generated within the building)the following means of

protection are available to the designer:

Reduction at Source

Enclosing and isolating the source, or use of absorbent screen

Planning: Separating noisy spaces from the quiet ones; placing indifferent areasin-between

Reduce impact noises by covering surfaces with resilient materials

Reduce noise in the space where it is generated by absorbent surfaces

Reduce airborne sound transmission by airtight and noise insulating construction

Reduce structureborne sound transmission by discontinuity

Noise ControlThe Screening effect of barriers


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g

Noise ControlThe Screening effect of barriers


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g

Reduction within a space


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Reduction within a space Noise in the space where source is located can be divided into two components

Direct and Reverberant Noise.

Direct Noise :

Can be reduced by placing a screen between the source and the listener.

The closer this screen is to the source, the better result will be (Optimum is full

enclosure)

Reverberant Noise :

Can be reduced by using absorbent materials on critical surfaces of the room.

Absorbent qualities of different materials vary with the frequency. Four basic type of

absorbents can be distinguished:

Sound


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Absorbents

Sound Absorbents


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Sound Absorbents


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Sound Absorbents Material having hard, rigid and non porous surface, provide the least absorption.

Flexible, soft , porous can vibrate and absorb more sound.

Classification of Absorbents:

Porous Absorbents:

When sound wave strike the surface of porous material, part of the wave get

reflected while part enters the pores and is thought to be dissipated into heat energy.

The efficiency depends upon thickness and porosity.

E.g. Slagwool, wood wool, faomed plastic, perforated fibreboards etc.

These are mainly selected to absorb sound having high frequency.

Resonant Absorbents:

The absorbent material is fixed on sound framing (usually Timber) with an air space

left between framing and the wall at the back.

Such arrangement works most efficient for absorbing low frequency sound waves.

The principle of sound absorption in this method is that sound waves cause vibrations

in the panel which act as a diaphragm. The absorption of sound takes place by virtue

of the dampening of vibration in the panel by means of the air space behind the

panel.

Sound Absorbents


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Sound AbsorbentsClassification of Absorbents:

Cavity Absorbents :

Cavity resonators essentially consists of a chamber with a narrow opening in which

absorption takes place by resonance of the air in the chamber which gives loss of

sound energy.

Such an arrangement is effective over a single selected frequency.

Application of cavity resonator is normally restricted to absorption from individual

machine or in similar cases.

Composite type of Absorbents :

They consists of perforated panels mounted on battens so as to leave a cavity

between panels and wall at the back.

The panels may be of metal, wood hardboard etc.

The area of holes in the panel should vary between 10 to 20% of total area of thepanel.

The effectiveness of this system can be increased by placing a porous material in the

cavity.

This type is commonly used, as it is easy to install, economical and accommodate

wide range of frequencies.

Multilayer Construction


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Multilayer Construction

Ventilators


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Resonance Data from Internet for reference


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_

A resonatoris a device or system that exhibits resonanceor resonant behavior, that

is, it naturally oscillatesat some frequencies, called its resonance frequencies, with

greater amplitudethan at others. The oscillations in a resonator can be eitherelectromagneticor mechanical (including acoustic). Resonators are used to either

generate waves of specific frequencies or to select specific frequencies from a signal.

Musical instruments use acousticresonators that produce sound waves of specific

tones.

A cavity resonator, usually used in reference to electromagnetic resonators, is one in

which waves exist in a hollow space inside the device. Acoustic cavity resonators, in

which sound is produced by air vibrating in a cavity with one opening, are known as

Helmholtz resonators.

In physics, resonanceis the tendency of a system to oscillateat larger amplitudeat

some frequenciesthan at others. These are known as the system's resonantfrequencies(or resonance frequencies). At these frequencies, even small periodic

driving forces can produce large amplitude vibrations, because the system stores

vibrational energy.

Acoustical Definitions
http://en.wikipedia.org/wiki/Resonancehttp://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Resonance_frequencyhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Acoustic_musichttp://en.wikipedia.org/wiki/Musical_acousticshttp://en.wikipedia.org/wiki/Helmholtz_resonancehttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Oscillatehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Periodic_functionhttp://en.wikipedia.org/wiki/Periodic_functionhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Oscillatehttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Helmholtz_resonancehttp://en.wikipedia.org/wiki/Musical_acousticshttp://en.wikipedia.org/wiki/Acoustic_musichttp://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Resonance_frequencyhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/wiki/Resonance


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Acoustical Definitions Noise Reduction Coefficient (NRC): NRC is a single-number rating representing and

overview of how much sound is absorbed by a material.

Example: gypsum board (drywall) on 2x4 studs has an NRC of 0.05.

Soft materials like acoustic foam, fibreglass, fabric, carpeting, etc. will have high

NRCs; harder materials like brick, tile and drywall will have lower NRCs.

A materials NRC is an average of its absorption coefficients at 250, 500, 1000 and

2000 Hz.

In general, the higher the number, the better the absorption.

NRC is useful for a general comparison of materials. However, for materials with very

similar NRCs, it is more important to compare absorption coefficients.

Sound Absorption Coefficient (a)

The actual absorption coefficients of a material are frequency dependent and

represent how well sound is absorbed in a particular octave or one-third octave band.

Example: drywall on 2x4 studs has an absorption coefficient at 125 Hz of 0.29.



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Acoustical Definitions Sound Transmission Class (STC):

STC is a single-number rating of how effective a material or partition is at isolating

sound.

Example: drywall has an STC of 28.

is a single-number rating representing and overview of how much sound is absorbed

by a material.

Hard materials like rubberized sound barriers, concrete, brick and drywall will

have high STCs. Softer materials like mineral fiber, acoustic foam and carpet will havemuch lower STCs. Virtually every material filters out some of the sound that travels

through it, but dense materials are much better at this than are porous or fibrous

materials. Like NRC, STC is useful to get an overview-type comparison of one material

or partition to another. However, to truly compare performance, the transmission loss

numbers should be reviewed.

Sound Transmission Loss (STL or TL)

The STL represents the amount of sound, in decibels (dB), that is isolated by a

material or partition in a particular octave or one-third octave frequency band.

Example: drywall has an STL at 125 Hz of 15 dB.



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Acoustical Definitions Decoupling:

STC This is the concept of detaching partitions from each other, or physically

detaching layers in a partition in order to improve sound isolation.

The most common methods of decoupling are:

Air gaps or air spaces between two partitions.

Using resilient channels between layers and structural framing members for walls

and ceilings.

Floating a floor using springs, rubber isolators or other decoupling layers.

Room Acoustics


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Room Acoustics Behaviour of sound in an Enclosed Space:

Various phenomena which may occur are -

1) Attenuation due to distance

2) Audience absorption of direct sound

3) Surface absorption of direct and reflected sound

4) Reflection from re- entrant angle

5) Dispersion at modelled surface

6) Edge diffraction

7) Sound Shadow

8) Primary Reflection

9) Panel resonance

10) Inter- reflection, standing waves andreverberation

11) Sound Transmission

Room Acoustics


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Room Acoustics Types of Auditorium:

Can be classified as follows

1) For Speech

2) For Music

3) Multipurpose


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Acoustics for Speech :

For Speech

1) Nature of Source of sound and its location is first to be considered.

2) Unamplified speech sound normally Range from about 30 dB (whispering)

to about 60 dB (Lecture voice) when measured at a distance of 3m.

3) Understanding depends upon the clear reception of a rapid sequence of

discreet sound, some are of which very short duration.

Power + Clarity = Intelligibility (able to be understood)

Power

Distance

From

Speaker

Directional

Relationship

to Speaker

Audience

absorption

of Direct

Sound

Reinforcement

by reflectors

Reinforceme

nt by Loud

Speakers

Sound

Shadows


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Clarity

DelayedReflection

Echoes

IntrusiveNoise Ambient Noise Duplicationof sound by

Loudspekers

Reverberation


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Distance from Speaker:

1) Its the extent to which the sound of human voice is accentuated by

distance alone.

2) It is important to discover the arrangement the arrangement which

minimizes the distance to rear rows of seats.

The measures which should be taken are therefore

a) Economy in seat spacing

b) Economy in Row spacing

c) Economy in Gangway width within the seating area

d) Economy in number of Gangways

e) Optimum shape of audience area

f) Introduction of a Gallery if necessary.


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S

Directional Relationship of

Speaker

Equal Intelligibility Contour

Speech intelligibility varies inaccordance with the directional

Relationship of speaker to

listener

ApproximatelyUpto 15 m = Relaxed Listening

15 to 20 m = Good Intelligibility

2025 m = Satisfactory

30 m = electronic amplification


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Open

StageTheatre

Box Set

Stage


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Restoration

Apron Stage

Theatre in

the Round

Documents

Lighting & Acoustics