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Theinclusionofanyinformationofanycompanyorproductorreferenceto

brandnamesofanyparticularproductinthisbookletdoesnotinanyway

implyrecommendationorendorsementbytheGovernmentofHongKong

SpecialAdministrativeRegion(theGovernment).Theinclusionorreference

isfordemonstrationpurposeonlyandthenoninclusionofanyproductor

companyhereinshallnotbeconstruedasdisapprovaloftheproductor

companybytheGovernment.Thedataregardinganyproducthereinhave

beencertifiedtobeaccuratebyrelevantmanufacturersortheirauthorized

agentsorrepresentatives.However,nowarrantyorguaranteewhatsoeverisorshallbeconstruedasbeinggivenbytheGovernmentinrespectofany

productreferredtoherein.Readersareadvisedtoseekindependentexperts

ortechnicaladviceregardingtheoperation,use,installation,maintenanceor

otherwiseofanyproductreferredtoherein.

CONTENTS

Page No.

1. INTRODUCTION...............................................................................7

2. QUICKREFERENCEGUIDE...........................................................8

3. PLANNINGAGAINSTNOISEPROBLEMS...................................9

3.1 PositioningofEquipment.............................................................9

3.2 SelectionofQuietEquipment....................................................10

3.3 ScheduledMaintenance..............................................................10

4. PROBLEMSANDPRACTICALREMEDIES

ONPUMPINGSYSTEMNOISE....................................................11

4.1 AirborneNoisefromRingingPipes.........................................11

4.2 StructureborneNoisefromPipes..............................................13

4.3 AirborneNoisefromPumpsets.................................................15

4.4 StructureborneNoisefromPumpsets.......................................19

4.5 ImportantNote...........................................................................21

5. RECOMMENDEDPRACTICALREMEDIESFOR DIFFERENTEXCEEDANCELEVELS..........................................22

6. GLOSSARYOFACOUSTICTERMINOLOGY.............................23

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2.QUICKREFERENCEGUIDE

Thefollowingquickreferenceguideallowsthereadertogodirectlytothe

relevantsectionorappendixconcerningaparticularproblem.

Table 1 : Quick Reference Guide

SourceofNoiseProblem Remedies RelevantSection

RelevantAppendix

Pumpsets Barrier 4.3 VI Partialenclosure 4.3 V

Completeenclosure 4.3 IV

Replacementofbearing 3.2&4.3 -

Inertiablock 4.4 VII

Vibrationisolator 4.4 VIII

Flexibleconnector 4.4 -

Pipes Largeradiusbendpipe 4.1 -

Compositelagging 4.1 -

Lowwaterflowvelocities 4.1 -

Rigidmountings

aroundthebend

4.1 -

Vibrationisolator 4.2 VIII

Compressiblematerial 4.2 -

Pressurereducingvalve 4.2 -

8

3.PLANNINGAGAINSTNOISEPROBLEMS

3.1 PositioningofEquipment

Theinstallationpositionofapumpsetisofcriticalimportancein

determiningthenoiselevelattheaffectednoisesensitivereceivers(e.g.

residentialbuildingsorschools).Wherepracticable,theequipmentshould

beplacedinaplantroomwiththickwallsoratamuchgreaterdistance

fromthereceiverorbehindsomelargeenoughobstruction(e.g.abuilding

orabarrier)suchthatthelineofsightbetweenthereceiverandthe

equipmentisblocked.Ifnoisyequipmenthastobeplacednearareceiver

duetospatialorotherconstraints(e.g.thepumpsetislocatedinsidearesidentialpremiseswithnoisesensitivereceiversaboveorbelow),

sufficientnoisecontrolmeasuresshouldbeconsidered.Figure1showsa

pumpingsystemofanewdevelopment,whichhasbeenplacedinapump

roomequippedwithadequatenoisecontrolmeasuresinthedesignstage

topreventnoiseproblems.

(Pumps are located below residential units)

Figure 1 : Inertia Block, Spring, Isolation Pad and Flexible Connector

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3.2 SelectionofQuietEquipment

Onaverage,quieterequipmentmaygenerallybemoreexpensive.

However,itisalmostalwaysmoreeconomicalinthelongruntobuy

quieterequipmentthantoreducenoisebymodificationafterpurchase

(e.g.silenttypepumps).Mostequipmenthasarangeofreadilyavailable

noisecontroldevicesthatareabletodealwiththenoiseproblems.Itis

advisablethatnoiselevelsspecificationisincludedwhenorderingnew

equipment.Thisallowstheequipmentsupplierstoselectappropriate

equipmentandoptionalnoisecontroldevicesto suit theacoustic

requirements.

3.3 ScheduledMaintenance

Inordertopreventincreasingnoiseproducedbyexistingequipment,itis

necessarytoputinplacearegularlyscheduledequipmentmaintenance

programmesothatequipmentisproperlyoperatedandservicedinorder

tomaintaincontrolledlevelofnoiseandvibration.Maintenancemay

includelubricatingmovingparts,tighteningloosenparts,replacingworn

outcomponentsorinspectingequipmentalignment,etc.Vibration

measurementsatvariousfrequenciesmayhelptodetectcausesofexcessivevibrationornoiseofamachine.Aguidetovibrationidentificationis

giveninAppendixXII.

4.PROBLEMSANDPRACTICALREMEDIESON

PUMPINGSYSTEMNOISE

4.1 Air-borneNoisefromRingingPipes

(A)Problems

Waterflowsinapipecausingvibrationatthepipewallandgenerating

broadbandnoisewhichmaycausenoisedisturbancetonearbyresidents

(seeFig.2).Whenthewaterflowchangesdirectionsuddenlybecauseof

obstaclesinthepipesuchassharpbendsorvalves,aloudnoiseisgenerated

whichbecomeslouderwithincreasingwaterflowrateandpipesize.

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(B) PracticalRemedies

Usepipeswithlargerradiusbends(seeFig.3)soastominimizevibration

ofpipewalls.

Userigidmountingsaroundthebendwithsuitablevibrationisolators(seeFig.3)tominimizepipevibration.

Applypipelaggingtodampthepiperingingnoise(seeFig.3).

Usealargerpipeoradjustwaterflowvelocitiestobelow2m/secto

minimizepipevibration.

( NOISE REDUCTION UP TO 10dB(A))

4.2 Structure-borneNoisefromPipes

(A)Problems

Vibrationfromthewaterflowinpipesmaybetransmittedfromthepipe

runstotheinteriorofthebuildingthroughbuildingstructurewherethepipesaremounted.Itbecomesmoreseverewhenthepipesareindirect

contactwithlargeplanessuchaswallsorslabs(seeFig.4).Thevibration

transmittedmayactivatethebuildingstructuretogeneratenoisewhich

causesnoisedisturbancetoresidentsinsidethebuilding.

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Usevibrationisolatorsforattachingpipestowalls,ceilingsorfloors

(seeFig.5),therebyisolatingthemfromthebuildingstructure.

Isolatepipeswheretheypenetratetheslabsandwallsbycompressible

materials,suchasrubbersleeveorglassfibrepacking(seeFig.5),

therebyisolatingthemfromthebuildingstructure.

Installpressurereducingvalvestoregulatewaterpressureandhence

thewaterflow,therebyreducingvibrationofpipes.


4.3 Air-borneNoisefromPumpsets

(A)Problems

Themajornoisesourceofapumpisusuallythebearingnoiseasaresult

ofbearingwornout.However,thenoisecontributedbythepumpitselfissmallrelativetothatgeneratedfromitsassociatedmotor.Themajor

noisesourceofamotorisusuallytheairmovementinducedbythecooling

fan,whichmaycausenoisedisturbancetonearbyresidents(seeFig.6).

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Replacewornoutbearingsoastoreducethenoise.

Erectabarrierbetweenthepumpsetandnearbyresidentialbuildings

(seeFig.7)soastoblockthenoisepropagationpath(seeApp.VI).

Fabricateapartialenclosuretocontainandabsorbthenoiseenergy

radiatedbythesource(seeApp.V).


(B) PracticalRemedies(Contd)

Fabricateacompleteenclosurewithsilencersatoutletandinletofthe

enclosure(seeFig.8)soastocontainandabsorbthenoiseenergyradiatedbythesource(seeApp.IV).


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(B) PracticalRemedies(Contd)

Locatethepumpsetinsideaplantroom(seeFig.9)withsilencersatair

inletandoutlet,andasoundproofdoor(seeApp.XI).


4.4 Structure-borneNoisefromPumpsets

(A)Problems

Vibrationfromanoperatingpumpsetmaybetransmittedtotheinterior

ofthebuildingthroughbuildingstructurewhenthepumpsetisdirectlymountedonasupportingstructurewithoutproperisolation(seeFig.10).

Thevibrationtransmittedmayactivatethebuildingstructuretogenerate

noisewhichcausesnoisedisturbancetoresidentsinsidethebuilding.

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Provideaninertiablocktosupportthepumpset(seeFig.11)soasto

addrigidityandstabilitytothepumpingsystem,andprovidevibration isolators(seeFig.11)tosupporttheinertiablock,therebyisolatingit

fromthebuildingstructure(seeApp.VIIandVIII).

Provideflexibleconnectorsbetweenthepumpandassociatedpipework,

therebypreventingthevibrationofthepumpsetbeingtransmittedto

thepipework(seeFig.11).


4.5 ImportantNote

Theaboveonlysuggestssolutionsforaparticularnoiseproblem.Inreal

life,thenoisemaybecausedbymorethanonesource.Inthosecases,

severalremediesmayberequiredsimultaneouslytosolvetheproblem.

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5.RECOMMENDEDPRACTICALREMEDIES

FORDIFFERENTEXCEEDANCELEVELS

Thefollowingrecommendedpracticalremediesfordifferentnoiseexceedance

levelsareforreferencepurposeonly.Noguaranteeisgiventotheperformance

oftheapplicationoftherecommendedremedies.Thereaderisadvisedto

seekprofessionaladvicefromindependentexpertsincaseofdoubtsor

complicatedproblems.

Table 2 : Recommended Practical Remedies

CauseofProblem NoiseExceedanceLevel(dB(A))

RecommendedPracticalRemedies

BearingNoise 15 Quieterpumporpumprelocation

WhiningPumpNoise 20 Completeenclosureandsilencers

Structureborne

noisefromPumps 20 Pumprelocation

Ringingpipenoise

10 Partialenclosure

Structureborne

noisefromPipes 20 Pipingsystemrelocation

6.GLOSSARYOFACOUSTICTERMINOLOGY

AWeightedDecibel(dB(A)) The Aweighted decibel is a unit for

measuringnoisetakingintoaccounttheway

humanearrespondstosound.

AirborneNoise N oise a rrives a t a point o f i nterest b y

propagationthroughair.

Frequency Thenumberofrepetitivevariationsofsound

pressureperunitoftimewhichisusuallystated

inHertz(Hz).

Noise Noise is any soundwhich at the timeof

receptionisunwantedordisturbing.

SoundPowerLevel Ameasure,indecibels,ofthetotalacoustic

powerradiatedbyagivensoundsource.Itis

independentofanyreferencedistanceorother

extraneousfactors.

SoundPressureLevel Ameasure,indecibels,ofthesoundpressure

ataparticularpoint.Itisdependentupon

distancefromthesourceandmanyother

extraneousfactors.

StructureborneNoise Noisearr ives at a point of interest bypropagationthroughasolidstructure.

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AppendixII(Contd)

Step 3 - Distance Attenuation

Theplandistanceorwhereappropriate,theslantdistancebetween

individualnoisesourceandthemostaffectedNSRshallbe

determinedandthecorrespondingdistanceattenuationshallbe

obtainedfromTable5.Thesevaluesshallbesubtractedfromthe

individualsoundpowerlevelsforeachnoisesourcetogivethe

individualsoundpressurelevelsforeachnoisesourceattheNSR.

Step 4 - Summation of Noise Levels

Allindividualsoundpressurelevelsforeachnoisesourceatthe

NSRshallbeaddedlogarithmicallyinaccordancewithTable6togiveasummednoiselevel.

Step 5 - Correction for Acoustic Reflections

In case the NSR is a building, a positive correction of3dB(A)

shallbeappliedtothenoiselevelobtainedinstep4.

Pleasenotethatacorrectionof3dB(A)or6dB(A)fortonality,impulsivenessorintermittencymayberequiredtoapplytothenoiselevelobtainedinstep5.

Fordetails,pleaserefertotheTechnicalMemorandumfortheAssessmentof

NoisefromPlacesotherthanDomesticPremises,PublicPlacesorConstruction

Sites.

AppendixII(Contd)

Table 5 : Distance Attenuation at Given Distances

Distance(m) Attenuation(dB(A)) Distance(m) Attenuation(dB(A))

1 8 30to33 38

2 14 34to37 39

3 18 38to41 40

4 20 42to47 41

5 22 48to52 42

6 24 53to59 43

7 25 60to66 44

8 26 67to74 45

9 27 75to83 46

10 28 84to93 47

11 29 94to105 48

12 30 106to118 49

13 30 119to132 50

14 31 133to148 51

15to16 32 149to166 52

17to18 33 167to187 53

19to21 34 188to210 54

22to23 35 211to235 5524to26 36 236to264 56

27to29 37 265to300 57

Fordistancesgreaterthan300m,calculationofdistanceattenuationshouldbebasedonstan-

dardacousticalprinciplesandpractices.

Table 6 : Summation of Noise Levels

DifferenceindB(A)Between

TwoNoiseLevelsBeingSummed

AmountindB(A)toAdd

totheHigherNoiseLevel

0to0.5 3.0

1.0to1.5 2.5

2.0to3.0 2.0

3.5to4.5 1.5

5.0to7.0 1.0

7.5to12.0 0.5

morethan12.0 0

NoiselevelsshouldbesummedinapairwisefashionwhenTable6isusedandthefinaltotal

roundedtothenearestwholedB(A),withvaluesof0.5ormorebeingroundedupwards.

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AppendixII(Contd)

Example:

Twopumpsets(AandB)havingsoundpowerlevelsof100dB(A)and105dB

(A)respectivelyareinstalledoutdoors.Themostaffectednoisesensitive

receiverisidentifiedtobearesidentialflatwhichisat20mand25maway

fromAandB,respectively.Thesoundpressurelevelattheresidentialflat

contributedbythetwoequipmentisestimatedbelow.

NSR(step1)

NoiseSources

SWL(dB(A))

(step2)

Distance(m)

DistanceAttenuation

(dB(A))(step3)

NoiseLevel(dB(A))

Residential

Flat

PumpA 100 20 34 66

PumpB 105 25 36 69

SummedNoiseLevel(dB(A)) (step4) 71

CorrectionforAcousticReflection(dB(A)) (step5) 3

NoiseLevelatNSR(dB(A)) 74

ANL(seeTable3) 60

NoiseExceedance 14

RecommendedPracticalRemedies(seeTable2insection5):

partialenclosures

AppendixIII

TYPICALSOUNDPOWERLEVELSOFPUMPSETS

Thefollowingsoundpowerlevelsforvariousratingofpumpsetsaregivenin

Tables7aand7bforreferencepurposeonly.Wherepracticable,thesoundpowerleveloftheconcernedpumpsetshouldbereferredtotherespective

manufacturers.

Table 7a : Typical Sound Power Levels of Pumpsets at 3600 rpm

HorsepowerofPumpset(hp) SoundPowerLevel(dB(A))

5to10 100

11to20 103

21to30 105

31to50 107

51to100 109

Table 7b : Typical Sound Power Levels of Pumpsets at 1800 rpm

HorsepowerofPumpset(hp) SoundPowerLevel(dB(A))

5to10 92

11to20 92

21to30 94

31to50 97

51to100 100

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AppendixIV

COMPLETEENCLOSURES

Whenanoisereductionof20dB(A)ormoreisrequired,itisgenerallynecessary

touseacompleteenclosureifthenoiseproblemisaresultofairbornenoisetransmission.Theenclosureshouldbeinternallylinedwith50mmthicksound

absorbingmaterial(e.g.fibreglass).Avarietyofmaterialscanbeutilizedfor

fabricatinganenclosure.Thesoundtransmissionlossforenclosuresusing

differentmaterialsaregiveninTable8.Ventilationofenclosuresshouldnot

beoverlookedasmostequipment,suchasmotors,requiresanadequateair

supplyeithertopreventoverheatingortoenablethemtofunctionefficiently.

Asilencedventilationsystemincorporatingsilencersattheairintakesanddischargeopeningsshouldbeemployed(seeFigure8).

Table 8 : Sound Insulation Materials for Enclosures

Material Thickness

(mm)

SurfaceDensity

(kg/m2)

SoundTransmissionLoss

(dB)125Hz 500Hz 2,000Hz

PlasteredBrickWall 125 240 36 40 54

CompressedStrawboard 56 25 22 27 35

AcousticPanel(Sandwichtypesteel

sheetwithfibreglass)50 27 19 31 44

Chipboard 19 11 17 25 26

PlasterBoard 9 7 15 24 32

Plywood 6 3.5 9 16 27

AppendixV

PARTIALENCLOSURES

Partialenclosuresarestructureserectedaroundasourceofnoise,butnot

fullyenclosingthesourceandleavingspacefornaturalventilation,whichwillbeeffectiveonlywhenthereisnolineofsightbetweenthenoisesource

andthereceiver.Theuseofpartialenclosureshasadvantagesovercomplete

enclosuresintermsofcost,accessibility,andventilation,butdesignand

constructionshouldbedonecarefully.Ideally,areductionofupto20dB(A)

canbeachieved.

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AppendixVI

BARRIERS

Tobeeffective,anacousticbarrierneedstobeplacedascloseaspossible

eithertothenoisesourceorthereceivingposition.Thereshouldbenogaporjointinthebarrierthroughwhichnoisewillleak.Thesurfacedensityofthe

barriermustbeatleast10kg/m 2.Ideally,thelengthofthebarriershouldbeat

least5timesitsheight.Lineofsightbetweenthesourceandthereceivermust

becutoffcompletely.

Areductionofnoiselevelofbetween5dB(A)to10dB(A)cangenerallybe

resulted.Noisereductionwillbegreaterifthebarrierislinedwithsoundabsorbingmaterialatthesurfaceofthebarrierfacingthenoisesourceoris

extendedashighaspossibleabovethelineofsight.

AppendixVII

INERTIABLOCKS

Aheavyandrigidinertiablockisoftenusedasthebaseforequipmentin

ordertoreducemotion,lowerthecentreofgravity,minimizetheeffectofunequalweightdistributionofthesupportequipment,andstabilizetheentire

vibrationisolationsystem.Generallyaninertiablockshouldbeatleast15cm

thickandverystiffandrigidtoavoidsignificantflexureinanydirection.

Table9showsarecommendedweightofinertiablockforvariousratingof

pumpsets.

However,whenthemassofthesupportedequipmentisenormous,theremaybenoneedforadditionalmassintheformofinertiablocks;arigidframeto

support(e.g.ReinforcedConcreteBeam)theentireassemblymaybesufficient.

Table 9 : Guide for Inertia Block Selection

Equipment Power Speed(rpm)

WeightRatio(1)at

Min Area(2) Normal Area(3) Critical Area(4)

Pumpset

1800 2.5 1.52.5 23

20100hp

450900 23 23 34

9001800 1.52.5 23 23

>1800 1.52.5 1.52.5 23

>100hp450900 23 34 349001800 23 23 23

>1800 1.52.5 23 23

Note

1.WeightRatio:Weightofinertiablockoverweightofequipmentmountedoninertiablock.

2.MinimumArea:Basementorongradeslablocation.

3.NormalArea:Upperfloorlocationbutnotaboveoradjacentsensitiveareas.

4.CriticalArea:Upperfloorlocationaboveoradjacentsensitiveareas.

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AppendixVIII

VIBRATIONISOLATORS

Motordrivenequipmentvibratesduringoperation.Themethodofreducing

vibrationtransmissiontoothersensitiveareasistoseparatetheequipmentfromthesupportingstructurebyvibrationisolators.Generally,therearetwo

typesofvibrationisolators,metalspringsandisolationpads,thatarewidely

usedforvibrationisolation.

i) Metal Springs

Springsareparticularlyapplicablewhereheavyequipmentistobeisolatedor

wheretherequiredstaticdeflectionsexceed12.5mm.Staticdeflectionofaspringisavaluespecifiedbythesuppliers.Selectionofappropriatespringsis

importantasthismayresultinpoorisolationefficiencyorevenamplification

ofvibration,especiallyinthecasethatthevibrationfrequencyisextremely

low.

Themostimportantfeatureofspringmountsistoprovidegoodisolationdue

toitsabilityofwithstandingrelativelylargestaticdeflection.Metalsprings

howeverhavethedisadvantagethatatveryhighfrequenciesvibrationcantravelalongthespringintotheadheredstructure.Thisisnormallyovercome

byincorporatinganeoprenepadinthespringassemblysothatthereisno

metaltometalcontact.Mostcommerciallyavailablespringscontainsucha

padasastandardfeature.Figure14showssomecommonspringmountings.

Table10providestheminimumstaticdeflectionrequiredforachieving

particularisolationefficiencyatdifferentequipmentspeeds.

AppendixVIII(Contd)

Table 10 : Minimum Static Deflection for Various Speeds of Machines

MachineSpeed(rpm)

MinimumStaticDeflectionat

VariousIsolationEfficiency(mm)1% 5% 10% 15%

3600 14.0 1.5 1.0 0.5

2400 30.5 3.5 2.0 1.5

1800 56.0 6.0 3.0 2.0

1600 71.5 7.5 4.0 3.0

1400 91.5 10.0 5.5 4.0

1200 124.5 13.5 7.0 5.0

1100 150.0 15.5 8.5 6.0

1000 180.5 19.0 10.0 7.0

900 223.0 23.5 12.5 9.0

800 282.0 30.5 15.5 11.0

700 - 38.5 20.5 14.0

600 - 53.5 28.0 19.5

550 - 63.5 33.0 23.0

400 - 117.0 61.0 43.5

350 - 155.0 81.5 56.0

300 - 211.0 109.5 76.5

250 - - 157.5 109.5

Note

1.Theabovestaticdeflectionsareobtainedbytheoreticalcalculations,whichareforreference

only.Commercialproductswithstaticdeflectionsgreaterthanabout100mmmaynotbe

availableinthemarket.

2.Thereaderisalsorecommendedtoconsultindependentexpertsforinstallationinvolving

vibrationisolatorswithhighstaticdeflections.

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AppendixVIII(Contd)

ii) Isolation Pads

Isolationpadscanbemadeofrubber,neoprene,glassfibreorcombinationof

them.Theyarerelativelycheap,easyforinstallationandreplacement,and

havetheadvantageofgoodhighfrequenciesisolation.However,attention

shouldbegiventothelifeoftheisolationpadsassomeofthemcanbedamaged

byoverloadorlowtemperature.Figure15showssomecommonisolation

pads.

(Courtesy of Builders Federal (HK) Limited)

Figure 14 : Metal Springs

(Courtesy of CEMAC (HK) Limited)

Figure 15 : Isolation Pads

AppendixIX

SILENCERS

Silencersarecommerciallyavailabledevicesthatallowthepassageofair

whilerestrictingthepassageofsoundgeneratedfromairdistributionequipment.Theysubdividetheairflowintoseveralpassageseachlinedwith

perforatedsheetbackedbymineralwoolorglassfibre.Asilencerusuallyhas

acrosssectiongreaterthantheductinwhichitisinstalledsuchthatnoise

inducedbyhighairflowvelocitypassingthroughthesilencercanbeavoided.

Silencersareavailableforcircularorrectangularducts,asshowninFigure

16,andarefabricatedinmodularformincrosssection,andinlengthsof0.6,

0.9,1.2and1.5m,etc.Theyaregenerallyspecifiedbytheinsertionlossin

decibels(dB)ineachoctaveband,sothatthedegreeofmatchwiththesound

powerdistributionofthenoisesourceoverthefrequenciesmaybejudged.

Theotherimportantparameterassociatedwithsilencersistheresistanceto

airflow.Theuseofsilencerwillinevitablyincreasetheloadofthefananditis

essentialforengineerstoconsiderboththeacousticandairflowperformances

duringthedesignstage.

Circular Silencer Rectangular Silencer

(Courtesy of NAP Acoustic (Far East) Limited) (Courtesy of Industrial Acoustic Company)

Figure 16 : Silencers

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Appendix X

ACOUSTIC LOUVRES

Similar to silencers, acoustic louvres are also commercially available devices

that allow the passage of air while restricting the passage of sound generatedfrom noisy spaces. They act much the same as ordinary louvres but consist of

hollow acoustic vanes instead of flat sheet vanes. The acoustic vanes, with the

underside (the side facing the noise source) formed from perforated sheet, are

filled with sound absorptive material. A typical construction of an acoustic

louvre is shown in Figure 17. The acoustic performance of an acoustic louvre

is specified by the transmission loss in decibels (dB) in each octave band.

This enables a direct comparison to be made between the performance of the

louvre and a solid wall/structure which it probably replaces. Since an acoustic

louvre is a very short attenuator, it is appropriate only where the length of

space is restricted and the noise reduction requirement is low. Acoustic louvres

are frequently installed in the facades of buildings where they are architecturally

acceptable and provide a requisite amount of noise attenuation to prevent

creating unacceptably high noise levels outside.

Appendix XI

SOUNDPROOF DOORS

The sound insulation provided by a door depends not only on the type of door

but also on installation details (e.g. the gaskets around the perimeter). Generally,rubber or plastic compression seals, which are set around the door edges,

provide the best result of insulation when closing the door. The degree of

sound insulation of a door is usually specified by sound transmission class

(STC). Table 11 gives typical STC values of some conventional types of doors.

However, if doors are required to have STC values greater than 30, it is

recommended that packaged soundproof door units are to be employed. They

are usually supplied with them fixed in a frame together with suitable seals. A

variety of soundproof doors is available in the market, offering average STC

values up to 45 which is equivalent to a 112mm brick wall.

Table 11 : Sound Transmission Class of Doors

Type of Door(45mm Thick)

Surface Density(kg/m2)

Sound TransmissionClass

Hollow-core wood 7 20

Solid-core wood 17 26

Steel-faced door 16 26

Fiberglass-reinforced plastic door 12 24

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AppendixXII

VIBRATIONIDENTIFICATIONGUIDE

Thecausesofexcessivevibrationornoiseofamachinecanbedetectedby

vibrationmeasurementsatvariousfrequencies.AvibrationidentificationguideisgiveninTable12.

Table 12 : Vibration Identification Guide

CauseofExcessiveVibration

FrequencyRelativetoMachineSpeed(rpm)

Unbalance 1xrpm

Defectivesleevebearing 10to100xrpm

Misalignmentofcouplingorbearing 2xrpm,sometime1or3xrpm

Bentshaft 1or2xrpm

Mechanicallooseness 1or2xrpm

Defectivebelt 1or2xbeltrpm

40 41

AppendixXIII

EXAMPLESOF PRACTICALNOISECONTROLMEASURES

Successfulnoisecontrolmeasuresandthecorrespondingnoisereductionsare

showninFigure18forreference.

Installation of Mountings with Rubber for Isolation

(Noise Reduction: 5dB(A))

Installation of Isolation Pads Installation of Spring Hangers

(Noise Reduction: 16dB(A)) (Noise Reduction: 8dB(A))

Figure 18 : Examples of Noise Control Measures

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AppendixXIV

REFERENCE:

1. AnnArborScience(1980),Reference Data for Acoustic Noise Control.

2. AtkinsResearchandDevelopment(1977),The Control of Noise in

Ventilation Systems - A Designers' Guide.

3. Bruel&Kjaer(1986),Noise Control Principles and Practice.

4. CyrilM.Harris(1991),3rdEdition,Handbook of Acoustical Measurements

and Noise Control.

5. DavidAHarris(1991),Noise Control Manual - Guidelines for Problems-Solving in the Industrial/Commercial Acoustical Environment.

6. FederationofHongKongIndustries(1989),Handbook on Industrial Noise.

7. JohnRobertsandDianeFairhall(1993),Noise Control in the Built

Environment.

8. L.L.Faulkner(1976),Handbook of Industrial Noise Control.

9. LewisH.Bell(1982),Industrial Noise Control Fundamentals and

Applications.

10.LyleF.Yerges(1978),2ndEdition,Sound, Noise & Vibration Control.

11.MarkE.Schaffer(1991),A Practical Guide to Noise and Vibration Control

for HVAC Systems.

12.PaulN.Cheremisinoff(1978),Industrial Noise Control Handbook.

13.SoundResearchLaboratoriesLtd(1991),3rdEdition,Noise Control in

Industry.

14.TradeandTechnicalPressLtd(1983),5thEdition,Handbook of Noise

and Vibration Control.

42

AppendixXV

OTHERRELEVANTNOISECONTROLMATERIALS

Description PlacewheretheHardCopyisObtainable

WebSiteAddress

NoiseControlOrdinance,

Cap.400

ForsaleatGovernment

PublicationsCentres

http://www.justice.gov.hk/

blis.nsf/curengord?

OpenView&Start=

400&Count=25&

Expand=400

AConciseGuidetothe

NoiseControlOrdinance

EnvironmentalProtection

Department'sOffices

(RefertoAppendixXVI)

http://www.info.gov.hk/

epd/E/epdinhk/noise/

index.htmTechnicalMemorandum

fortheAssessmentof

NoisefromPlacesother

thanDomesticPremises,

PublicPlacesor

ConstructionSites


Department'sOffices




index.htm

GoodPracticeson

VentilationSystemNoise

Control


Department'sOffices




index.htmGoodPracticeson

PumpingSystemNoise

Control


Department'sOffices


http://www/info/gov.hk/


index.htm

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Appendix XVI

ADDRESSES AND TELEPHONE NUMBERS OFENVIRONMENTAL PROTECTION DEPARTMENTS OFFICES

District Covered(Following DistrictCouncil Boundary)

AddressEnquiry

TelephoneNo.

Kwun Tong,

Wong Tai Sin,Sai Kung,

Yau Tsim Mong &

Kowloon City

Regional Office (East)

5/F., Nan Fung Commercial Centre,19 Lam Lok Street, Kowloon Bay, Kowloon.

2755 5518

Hong Kong Island &

Islands

Regional Office (South)

2/F., Chinachem Exchange Square,

1 Hoi Wan Street, Quarry Bay, Hong Kong.

2516 1718

Tuen Mun,

Tsuen Wan,

Kwai Tsing &

Sham Shui Po

Regional Office (West)

8/F., Tsuen Wan Government Offices,

38 Sai Lau Kok Road, Tsuen Wan, New Territories.

2417 6116

Yuen Long,

Sha Tin,

Tai Po &

North

Regional Office (North)

10/F., Sha Tin Government Offices,

1 Sheung Wo Che Road, Sha Tin, New Territories.

2158 5757

Revenue Tower Office

33/F., Revenue Tower,

5 Gloucester Road, Wan Chai, Hong Kong.

2824 3773

Branch Office

28/F., Southorn Centre,

130 Hennessy Road, Wan Chai, Hong Kong.

2573 7746

Branch Office

8/F., Cheung Sha Wan Government Offices,

303 Cheung Sha Wan Road, Kowloon.

2402 5200

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