NOISE CONTROL AND SOUND ABSORPTION IN BUILDINGS

7/25/2019 NOISE CONTROL AND SOUND ABSORPTION IN BUILDINGS

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NOISE CONTROL AND SOUND ABSORBTION SATHISH KUMAR T Page 1

ARCHITECTURAL ACOUSTICS

Unit 3

NOISE CONTROL AND SOUND ABSORPTION

Types of noises, transmission of noise, transmission loss, noise control and sound insulation, remedial

measures and legislation.

What is NOISE?

All sounds that are distracting annoying or harmful to everyday activities are regarded as

NOISE.

ANY SOUND JUDGED UNDESIRABLE BY THE RECIPIENT IS TERMED AS NOISE.

Whether or not the sound is undesirable depends on the

1. LOUDNESS

2. FREQUENCY

3. CONTINUITY

4. TIME OF OCCURRENCE

5. INFORMATION CONTENT

6. RECIPIENTS STATE OF MIND

7. RECIPIENTS TEMPERAMENT.

SOUND is a sensation of acoustic waves (disturbance/pressure fluctuations setup in a medium)

NOISE TYPES:

In a building, there are 2 types of noise.

1. EXTERNAL NOISE

VEHICULAR (Motor Cars, Buses, Two Wheelers, Air Traffic, Rail Traffic)

EXPOSED MECHANICAL EQUIPMENTS

EARTH MOVING, CONSTRUCTION EQUIPMENTS

STREET VENDORS

CHILDREN PLAYING (TOT LOTS) & PLAYGROUNDS

BLARING LOUDSPEAKERS.


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THE REDUCTION OF OUTDOOR NOISE WITH DISTANCE IS GOVERNED BY THE

INVERSE SQUARE LAW.

A drop of 6db will be noticeable every time the distance between the source and recipient is

doubled. (Provided there are no reflecting surfaces near the noise source).

TYPICAL NOISE LEVELS OF TRAFFIC

TYPE NOISE LEVEL (dB)

BOEING 707 (450M) 111

BOEING 737 (450M) 107

BOEING 747 (450M) 103

AIRBUS 4300 (450M) 101

CONCORDE (450M) 114

STEAM TRAIN (30M) 85

DIESEL (30M) 83

ELECTRIC (30M) 77

ELEVATED TRAIN 120

DIESEL TRUCK (15M) 80

PASSANGER CAR (6M) 70

HEAVY URBAN TRAFFIC 70

2. INTERNAL NOISE

LOUD CONVERSATION

RADIO / T.V / MUSIC SYSTEM

DOOR BANGING

STAIRCASE TRAFFIC

CHILDREN PLAYING

HOUSE HOLD APPLIANCES


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THE NOISE LEVEL AT ANY POINT IN THE INTERIOR IS MADE UP OF 2 PARTS.

SOUND RECEIVED DIRECTLY FROM SOURCE

REVERBERANT SOUND (after repeated reflections)

Direct sound is more near the source

Reverberant sound (reflected sound) is more away from the source.

ACCEPTABLE INDOOR NOISE LEVELS FOR VARIOUS BUILDINGS:

LOCATION NOISE LEVEL (dB)

AUDITORIA & CONCERT HALLS 20-25

RADIO &T.V STUDIOS 20-25

MUSIC ROOMS 25-30

HOSPITALS, CINEMA 35-40

APARTMENTS, HOTELS & HOMES 35-40

CONFERENCE ROOMS, SMALL OFFICES & LIBRARIES 35-40

COURT & CLASS ROOMS 40-45

LARGE PUBLIC OFFICES, BANKS, STORES 45-50

RESTURANTS 50-55

Noise may be classified as steady, non-steady or impulsive, depending upon the temporal

variations in sound pressure level.

STEADY NOISE is a noise with negligibly small fluctuations of sound pressure level within

the period of observation.

A noise is called NON-STEADY when its sound pressure levels shift significantly during the

period of observation. This type of noise can be divided into intermittent noise and fluctuating

noise.

FLUCTUATING NOISE is a noise for which the level changes continuously and to a great

extent during the period of observation.

TONAL NOISE may be either continuous or fluctuating and is characterized by one or two

single frequencies. This type of noise is much more annoying than broadband noise characterized

by energy at many different frequencies and of the same sound pressure level as the tonal noise.


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The chief sources of noise in building can be divided into 3 categories:

1. Sources associated with occupant activity and office equipments.

2. Sources associated with the operation of building services.

3. Sources of environmental sound from outside a building.

A source of noise may or may not be a source of vibration in a building.

Similar a source of vibration may or may not be a source of significant noise.

Eg: Door Slams, footfall, conversation, radios, etc.


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NOISE TYPES AND THEIR MEASUREMENT:

Noise characteristics classified according to the way they vary with time. Constant noise remains

within 5 dB for a long time.

Constant noise which starts and stops is called intermittent.

Fluctuating noise varies significantly but has a constant long term average (LAeq,T).

Impulse noise lasts for less than one second.

MASKING NOISE:

In many situation noises control problems can be solved by DROWNING (or masking)

unwanted noises by electrically created background noise. This artificial noise is often referred to

as ACOUSTICAL PERFUME OR ACOUSTICAL DEODARANT. This process suppresses

minor instruments which might interrupt the recipients privacy.

Example:-


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Noise from ventilating systems.

Uniform flow of traffic.

General office activities.

In designing landscaped offices, the provision of a relatively high but acceptable degree of

background noise is essential in order to mask undesirable noise like typewriters, office

machines, loud conversation, etc.

TRANSMISSION OF NOISE:

There are 2 paths of sound transmission between spaces:

1. Air borne Machine which excites air in the source room.

2. Structure borne Vibration from a machine to a structure.

Often the sound transmission is by both in varying quantities.

AIRBORNE & STRUCTURE BORNE SOUND

If the sound is transmitted through Air only, it is called AIRBORNE SOUND. (Example: -

Someone talking, A Singer, A Violin, etc.).

If the sound source not only radiates its energy through air, but also simultaneously sets into vibration of

solid parts of the building then it is called STRUCTURE BORNE SOUND (EX: - footsteps noises,

motors etc).


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AIRBORNE NOISE

Airborne noise originating in the source room can be transmitted to the receiving room in the

following ways.

1. along continuous air paths through openings, such as open windows, ventilating ducts, grilles,

shafts, crawl spaces, gaps and cracks around doors, pipes, conducts, electrical fixtures, built in

elements.

2. by means of forced vibrations setup on the boundaries of the source room (walls, floor, ceilings)

and transmit to the boundaries of the receiving room. actually, what the listener hears in the

receiving room is not a fraction of the original sound, but a reproduction of it.

STRUCTURE BORNE NOISE

Since they are readily transmitted with little attention and over great distances in a building

structure borne and vibration should be suppressed at the source or is close to the source as

possible.

This can be accomplished

1. By the use of adequately resilient flooring (carpet, rubber, tile) to reduce impact vibration

transmission into the floor.

2. By the use of flexible materials (mountings, anti vibration pads, floating floors) to prevent the

transmission of vibration and shock from various machines or exterior sources into the building.

SOUND TRANSMISSION BETWEEN ROOMS:

A sound source will develop a reverberation sound field in one room and its sound pressure level

will depend on the total absorption provided by the source room boundary wall.

Assuming the sound can travel only through the common separating wall, the transmitted sound

level will depend on:

1. Sound isolating properties of the wall Sound Transmission Loss.

2. Total surface area of the wall that radiates sound into the adjacent room.

3. Total absorption present in the receiving room.


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NOISE REDUCTION BETWEEN ROOMS:

The noise reduction NR between rooms is the arithmetical difference in sound levels Ls in

the rooms.

The reduction of sound between the rooms is given by

NR = L1 L2= TL + 10 log A2 / S

OR

NR = TL + 10 log A2 / S

L1 SPL in source room(dB)

L2 SPL in receiving room(dB)

TL Sound Transmission Loss

A2 Total Absorption in the receiving room in sabins.

S - Common wall surface area in Sq.Ft

Measurements of TL are made at several test frequencies (usually 16) between 125H z and

4000H z.


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NOISE CONTROL AND SOUND AB

The transmitted sound L2

sound level in the room.

The background sound le

It is a residual sound leve

The larger, the common

The absorbing material i

the receiving room.

Hence the material of the

The major loss sound ene

Light weight partitions /

Massive / Double constr

If the barrier size S coinc

SORBTION SATHISH KUMAR T

will be disturbing in the receiving room if it ex

vel is hence important for any sound isolation.

l present.

all is more sound is radiated.

the receiving room will reduce built up reflect

common wall is important.

rgy is provided by this wall / floor / ceiling, par

loor systems Sound Transmission Loss of 20

ction - Sound Transmission Loss of 40 60dB.

ides with the absorption in the receiving room

Page 9

ceeds the background

d sound radiated into

tition.

B.

2, NR = TL.


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SOUND TRANSMISSION LOSS:

Transmission loss is a measure of how much sound energy is reduced in transmission through

materials.

The more massive a material , the higher its TL.

THE TL CAN BE DETERMINED AS FOLLOWS

TL =L1 L2

Where TL = sound transmission loss(dB)

L1 = sound level in source room(dB)

L2 = sound level in receiving room(dB)

and

TL = 10 log 1/

Where TL = sound transmission loss(dB)

= sound transmission coefficient (no units)

is the ratio of the sound energy transmitted by a material to the incident sound energy.

A steady sound is generated in the source room at one side of the partition to be tested.

Sound levels are then measured at both sides of the partition (source room & receiving room).

The TL = Difference between the 2 values.

TRANSMISSION LOSS OF SINGLE LEAF PARTITIONS:

The TL of homogenous single leaf partition depends on the SURFACE WEIGHT of the partition

& also the FREQUENCY of sound transmitted.

To achieve an effective TL a partition should be impervious to airflow

Walls of porous concrete block will not yield a TL in proportion to the weight. However the TL

can be considerably increased by sealing its exposed surface with plaster, cement based paint

etc.

TRANSMISSION LOSS IN MULTIPLE PARTITIONS:

To achieve a significant improvement in the TL value of a single leaf partition requires doubling

or tripling its mass. Such as increase in the weight and thickness of an enclosure is obviously

different to achieve forFUNCTIONAL, SPATIAL, STRUCTURAL, AND ECONOMIC

REASONS.


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If a high degree of sound insulation is required, it is therefore advisable to use multiple

partitions built of 2 or 3 separate leaves.

Multiple partitions provided a higher TL than would be expected out of their weight, particularly

at the higher frequencies of the following precautions is observed:

1. The total weight has been established as a reasonable maximum.

2. The separation between the leaves has been consistently secured.

3. A maximum distance has been established between the leaves.

4. A continuous layer (or patches) of sound absorbing material have been mounted in the air space.

5. The leaves have been built of either different materials or different thicknesses of the same

material.

6. The leaves have been resiliently attached to the studs.

7. Noise leaks are completely avoided (particularly around perimeter edges).

8. The stiffness of the partition has been so established that it minimize the coincidence effect.

Sound insulation increases with ..

1. Increased weight

2. Wide spacing of studs

3. Studs (Ties) Eliminated

4. Staggered studs

5. Two levels of different weight

6. Resilient attachments

7. Max. separation between 2 leaves

8. Isolation blanket in Air space

9. Perimeter caulking


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COMPOSITE BARRIERS

If a door, window, or other opening is to be incorporated into a wall, the eventual overall sound

insulation of the resulting COMPOSITE PARTITION is determined primarily by its weakest

element.


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MATERIALS OF CONSTRUCTION:

1. Single Homogenous Wall:

The average TL increases with weight.

2 Plaster Wall 35dB

4 Plaster Wall 40dB

6 Plaster Wall 45dB

2. Double Walls:

If the 2 plaster wall is split into two 1 leaves separated by a 3 air gap, the average TL would

be 8dB . Large air spaces is required to achieve significant improvement.

Air space < 1.5 does not yield much improvement

Ideal separation is 12

Avoid rigid ties between the panels.

TL of

Construction

125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz 8000 Hz

12 painted

concrete block

wall with sand

filled cells

33 40 47 33 59 65 51

6 concrete block

+ 6 airspace + 6

concrete block

38 47 58 68 78 85 59

3. Absorption in Double Constructions:

Addition of sound absorbing materials within the cavity of the double wall construction Fibrous, glass,

mineral wool insulation materials can increase overall sound energy loss Provides a MUFFLER

LIKE effect to reduce sound transmission.

4. Composition Constructions:

Common walls are made up of more than one component

Doors, windows, Partition elements etc.


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SOUND TRANSMISSION CLASS STC:

STC is a single value (dB) calculated by matching the mid frequency bands TLs of a given

construction to a standard curve.

The STC of a construction is useful in determining the effectiveness of a partition in

reducing speech noise, similar to the NRCs application to absorption in the speech range.

Note that the actual reduction is 5-10dB less than the STC, so you must compensate for this ifyou have a specified isolation required. If a specification calls for a certain STC, then this is

already considered.


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TO DETERMINE THE STC OF A GIVEN SPECIMEN:

Measured TL values are plotted against frequency.

Compare with a reference contour.

Using a transparent overlay on which the STC contour is drawn, the STC is easily determined.

The STC contour is shifted vertically relative to the test data curve to as high a position as

possible.

When the STC contour is adjusted to the highest position that meets the below requirements, the

STC rating is read from the vertical scale of the test curve as the TL value.

The value corresponding to the intersection of the STC contour and the 500Hz ordinate.

CONDITIONS:

The maximum deviation of the test curve below the contour at any single test frequency shall notexceed 8dB.

The sum of the deviations at all 16 frequencies of the test curve below the contour shall not

exceed 32dB.


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EXAMPLE OF READINGS:

STC ratings reflect the significance of deficiencies such as the dip in construction Bs TL curve.

Bs STC 33 rating, indicated in the graph is governed by the 8dB deviation below the contour at

1000Hz. Although its total deviation is well under 32 dB.

Construction A has an STC 43 rating also shown in the graph.

Field Sound Transmission Class ( FSTC ) : a single STC value (dB) of a construction measured with

in-situ conditions; sometimes this is considered a more realistic estimate, but usually there is little

information on the specifics of the field condition itself, so it may be hard to reproduce.

NOISE CRITERIA CURVES:

The octave band spectra of background sound in buildings follow NC curve.

The NC curve is the most widely used means for specifying criteria and evaluating background

sound in buildings.

RECOMMENDED NOISE CRITERIA FOR ROOMS:

The noise criteria NC curves can be used as a method for specifying continuous background

noise levels to achieve sound isolation.


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NO TYPE OF SPACE & LISTENING

REQUIREMENTS

PREFERRED RANGE

OF NC

EQUIVALENT

DB LEVEL

1 Concert halls, opera houses, recording

studios

NC15 TO NC-20 25 - 30

2 Bedrooms, sleeping areas, hotels, residences NC20 TO NC-30 30 40

3 Auditoriums, theaters, churches, conference

rooms

NC20 TO NC- 30 30 40

4 Offices, classrooms, libraries NC30 TO NC35 40 45

5 Gyms, restaurants NC35 TO NC- 40 45 50

6 Labs, Engg.rooms, lobbies NC40 TO NC45 50 55

7 Kitchens, schools, garages NC45 TO NC-55 55 - 65

NC CURVE 63 125 250 500 1000 2000 4000 8000

NC 70 83 79 75 72 71 70 69 68

NC 40 64 57 50 45 41 39 38 37

NC 20 50 41 33 26 22 19 17 16

NC 15 47 36 29 22 17 14 12 11

EACH NC CURVES IS DEFINED BY ITS SPL FOR THE 8 OCTAVE BAND FREQUENCIES

SIX FACTORS THAT INFLUENCE SPEECH PRIVACY BETWEEN ENCLOSED ROOMS:

1. Background sound level in listeners space receiving room.

The background sound in a receiving room acts to mask unwanted speech sounds and renders them

less intelligible.

2. Strength of sound source vocal effort.

The louder the speech signals, the more intelligible it is in the receiving room.

3. Amount of sound absorption in receiving room.


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The less reverberant buildup of speech sound in the receiving room, the lower the speech signal

level, and the less the speech intelligibility.

4. Relative sizes of source and receiving rooms.

The larger the receiving room relative to the source room, the lower the speech in the receiving

room.

5. Sound transmission characteristics of intervening construction separating 2 spaces. The higherthe sound transmission loss TL of the wall, the lower speech signal in the receiving room.

6. Required speech privacy.

The higher the rating, the lower the speech signal must be relative to the background sound level in

order to ensure adequate masking of speech signals to minimize speech intelligibility.

FACTORS THAT INFLUENCE SPEECH PRIVACY IN OPEN PLAN SPACES:

The open office landscape has become increasing popular for large corporations. The basic

acoustical problem is really no different from the case of adjacent enclosed spaces.

Adequate privacy requirements are as follows:

Sufficient attenuation of the speech signal from the source to the listener location.

Speech effort and speaker.

Masking by the continuous background sound present.

The containment and buildup of reverberant sound is nor present in open plan spaces. Sound in

the open space continually falls off with distance at a rate dependent on the sound absorption of

the floor / ceiling surfaces.

Noise barriers reduce the sound at the receptor location if they break the direct path between the

source and receptor.

Speech Privacy required as in enclosed spaces.

Distance from source to listener.


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NOISE CONTROL:

In a building, there are 2 types of noise.

External noise and Internal noise.

EXTERNAL NOISE

Distance.

Avoiding zones of directional sound.

Screening.

Planning using noise sensitive parts of the building as barriers.

Positioning of openings away from the noise source.

Noise insulation building envelope.

INTERNAL NOISE

Reduction at source.

Enclosing and isolating the source use of absorbent screens.

Planning separating noisy spaces from quiet spaces.


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Reducing impact noises by covering surfaces with resilient materials.

Placing noisy equipment in the most massive part of building basement.

Reduce noise in space where it is generated by the use of absorbent materials.

Reduce airborne sound transmission by airtight and noise insulation construction.

Reduce structure borne transmission by discontinuity.

MEANS OF NOISE CONTROL:

1. DISTANCE AND SCREENING

Location of a building on a site as far from the noise source as possible. Every doubling of the

distance will reduce the noise level by 6dB, etc.

Example:- 65 dB noise: 59dB 10m, 53dB 20m, 47dB 40m.

Screening effort of walls, fences, plantation belts.

Any given barrier will be effective when it is as near the source as possible, or near the building

to be protected.

2. PLANNING

Separating areas which are not noise sensitive, where noise would not cause disturbance and

placing them on the side of the building near noise source.

Positioning and orienting major openings away from the source.

In a building, the weakest points for noise penetration are the openings.

Plan shape to provide screening from the sides.

Addition of special elements for protection wing walls, screens.

3. REDUCTION AT OR NEAR SOURCE

Machine vibration place the machinery on flexible mountings so the vibration is not

transmitted.

The resonant frequency of the mounting itself must be lower than the frequency of vibration to

be isolated.

Airborne sound emitted tackled near the source.

The source could be covered by an insulating enclosure box.

The box could be of massive construction with absorbent lining on the inside, to prevent the

buildup of reverberant noise level.


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Could be removable or have any transition between the full enclosure and a simple screen to

reduce noise emission.

4. REDUCTION WITHIN A SPACE

Direct noise placing a screen between the source and the listener

Reverberant noise use of absorbent materials on critical surfaces of the room.

Absorbent qualities of different materials vary with the frequency.

Porous higher frequencies.

Membrane low frequencies.

Resonant tuned to a very narrow band of any frequencies.

Perforated panel absorbers combination of resonant and porous medium frequency. Can be

tuned by variation of whole size, shape and placing and backing material and space.

The ceiling is the most critical surface as it causes multiple reflections of the sound.

Also as most absorbents are vulnerable to damage, the least exposed surface to mechanical

damage is the ceiling.

5. NOISE INSULATION

Depends on transmission coefficient and transmission loss TL.

For solid, homogeneous walls the insulating quality is a function of the mass.

The doubling of the wall mass increases the TL by 5dB.

STRUCTURE BORNE SOUND:

In structure borne sound, it is the effect of the solid coupling mechanism between the source and

hearer which is important.

The coupling between the source of vibration and the solid structure.

The type of vibration waves produced in the solid.

The coupling with the fluid at the hearing.

Coupling Loss Factor CLF the fraction of energy transmitted from one system to another in

one radian cycle and has the same meaning as the loss factor in mechanical systems.

NOISE CONTROL MEASURES:

A noise control program should involve the following:


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Preparation of a noise map after taking measurements in all areas.

The setting of target noise levels for all areas.

A description of all measures planned a cost analysis, and the attenuation expected.

The setting of priorities within a plan to achieve the agreed targets, stating start and finish times.

OUTDOOR BARRIERS FOR NOISE CONTROL

Better

Best


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NOISE REDUCTION FROM OUTDOOR THIN WALL BARRIERS

SELF PROTECTING BUILDING FORMS


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BALCONIES AND OVERHANGS

EARTH BERMS

ATTENUATION FROM VEGETATION


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ORIENTATION OF BUILDINGS


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ATTENUATION OF STRUCTURE BORNE SOUND:

Preventing transmission of vibration from machines and equipments to the load bearing structure

of the building using the following principles:

1. Vibration isolates machines with stiff or independent frames. Place the machine on a stablefoundation with an elastic separating layer rubber stocks or steel springs.

2. Place large heavy machines which cannot be effectively vibration isolated, on special machine

foundations which are completly separated from the building.

3. Vibration isolated machine panels mounted on the machine frame or coated with special

damping material to reduce vibration level transmitted to them.


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Severely vibrating machines requires separate foundations and isolating joints between floor

slabs to prevent the propagation of structure borne noise.

a) Before casting the floor, a thick strip of foamed plastic is placed in all the joints between the

floor and rest of structure.

b) After the floor is cast, the foam is pulled or burnt out, the joint inspected and cleaned. There

must be no bridging between the joints.

c) The joints is then filled with a flexible material synthetic rubber tube and sealed completely

with an elastic material of high density.

SOUND INSULATED ROOMS:

Automatic machines present with remote control of the process.

1. Build control and monitoring rooms with good sound insulating properties.

2. Well sealed door and window designs.

3. Provided ventilation openings with attenuators or acoustic louvers and ensure cables pipe cuts

are filled acoustic sealant.

GUIDELINES AND REMEDIAL MEASURES:

PLANNING THE BUILDING

The acoustically important details of the building load bearing structure and work areas should

be calculated and fixed early in the planning stage.

The need for noise control depends first on the way production plant is designed.

The structural design of the building depends on where the machinery is placed and the need for

insulation against air borne and structure borne sound.

1. The buildings load bearing structure, floors, and machine foundation should be chosen so that

sources can be effectively vibration isolated. Heavy equipments demand stiff and heavy

foundations, which must not be in direct contact with other parts of the structure.

2. Powerful noise sources should enclosed by structures which give adequate airborne sound

insulation. Doors, inspection windows and other building elements where there is a risk of sound

leakage required special attention.

3. Rooms where there are sound sources or where personnel are present should be provided with a

ceiling cladding which absorb the incident sound.

4. Office areas should be separated from building elements where vibrating material is installed by

a joint of elastic material.


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5. Walls, ceiling construction, windows, and doors should be chosen so as to achieve the required

sound insulation.

6. In open office plans, and large rooms where there are several office functions carried out in the

same room, there must be a ceiling with sound absorption, and soft carpeting on the floor. It is

important that there is sound absorption at low frequencies.

GUIDELINES AND REMEDIAL MEASURES:

NOISE REDUCTION MEASURES IN ROOMS

The shape and size of an industrial workshop is determined by the production processes and flow

of materials.

Guidelines for the layout of a new plant are as follows:

1. Workstations and machines should be so placed that the reduction of noise with distance can be

exploited a certain distance between noisy and quieter areas. Ensure a space is allowed

between screens and partitions.

2. Ensure that separate areas are available for particularly noisy machines basement.

3. Work which requires a quiet working environment or which does not itself produce noise should

be removed to a region with a low noise level work. Where possible mount absorbent ceilings in

such areas.

4. If noisy work is carried out close to a wall or any other reflective surface, it should be covered

with an absorbent material.

5. Workshop offices, rest rooms etc should be provided with sufficient sound insulation and

possibly mount on isolators, or separated from the rest of the building structure by flexible jointsto avoid vibration transmission.

6. Fixed installation ventilation equipment, cooling systems should be constructed with sound

attenuation in mind, and mounted so that sound from fans etc is prevented from spreading via

ducts, pipes and the building structure itself.

7. In open office plan and large rooms, work areas must sometimes be located bearing in mind that

noise occurs from certain processes while a relatively noise free environment is required for

others for conversation.


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ACOUSTICAL DEFECTS CAUSES AND REMEDIES

NO. DEFECT CAUSES ADVANCE IN DESIGN REMEDY FOR

EXISTING BUILDINGS

1. Excessive

reverberation

Excessive volume Keep volume limited to

100-150 cu.ft per seat. Use

of more absorbent

materials on distancesurfaces.

Increase seating or increase

interior surface by bold

decoration in relief. Use of

more absorbents.

2. Echoes Unsuitable shape

Distant reflecting

surfaces

Avoid curves.

Make distance surfaces

highly absorbent.

Alter shape.

Use absorbing materials on

offending surfaces. Make

distant surfaces highly

absorbent.

3. Interference Undiffused reflection

of sustained note

Design bold breaks in

walls and ceilings. Useresonating wall coverings.

Add bold decorative or

resonating covering or both.

4. Unsatisfactory

sound volume

Excessive volume

Leak of reflection

Excessive absorption

Provide hard reflecting

surfaces about the origin.

Adjust absorption to

obtain optimum

reverberation.

Provide just sufficient

absorbing surface.

Provided hard reflecting

surfaces

Adjust absorption to obtain

reverberation.

Replace part absorbent

surfaces by reflection

surfaces.

5. Distortion Use of selective

absorption

Screening at higher

frequencies

Uncontrolled

resonance

Use mixed absorbents to

obtain uniform

coefficients.

Avoid screening sound.

Select board absorbents

which resonate over a

wide range and fix on

battens at irregular

intervals.

6. resonance Flimsy partitions and

linings

Adopt rigid construction at

irregular spacing.

Stiffer partitions and linings.


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INSULATION AGAINST STRUCTURE BORNE NOISE:

Insulation against structure borne (or impact) noise can be achieved by the use of:

1. Soft floor finish (carpet, cork, vinyl, rubber, etc).

2. Floating floor.

3. Resilient (anti vibration) mounts.

4. Resiliently suspended solid ceiling.

The addition of a soft floor finish does not provide extra insulation against airborne noise but

merely reduces or eliminates impact noise such as footstep noise, at the source.

On the other hand, a floating floor or a resiliently suspended ceiling also improves the airborne

sound insulation in floor assemblies.


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MEASUREMENT OF STRUCTURE BORNE NOISE:

The measurement of structure borne noise is different from that of airborne noise. According to

the recommendation of the ISO, the insulation against impact noise. Provided by a given floor

must be determined by means of a standard tapping machine, which provides a series of

uniform impacts at a constant rate on the floor being tested by means of fine small hammers,

which fall freely at a specified rate on the floor.

The sound pressure level of the impact noise transmitted into the receiving room, beneath the

floor, are measured with a sound level meter in sixteen 1/3 octave bands with center

frequencies between 100 and 3150Hz.

The measured Impact Sound Pressure (ISP) levels are then compared to a standard IMPACT

NOISE REFERENCE CONTOUR.

Through there was objection for the tapping machine as a noise source in establishing sound

insulation ratings of floors, no better method is available.


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What is CROSS TALK?

Noise between adjacent spaces served by common ducts is known as crosstalk.

To reduce crosstalk, main duct runs should be located above corridors, with individual branches

extending to each space.

Return air transfer ducts to plenum spaces above ceilings should have duct liner installed, and

there should be an elbow in the duct

Internally lined return air transfer duct above ceiling (with one elbow) to control crosstalk.

What is DUCT LAGGING?

Duct lagging is usually specified as part of a design or as a retrofit to solve an existingbreakout

noise problem.

Duct lagging may include enclosing the duct in gypsum board or insulation wrapped in sheet

lead.

Duct lagging using a gypsum board enclosure (left) or lead-wrapped around insulation (right).

Documents

NOISE CONTROL AND SOUND ABSORPTION IN BUILDINGS