noise control for industry & commerce

7/28/2019 Noise Control for Industry & Commerce

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GALLOWAY

ACOUSTICS Noise Control forIndustry and Commerce

S I L E N C E R S


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STANDARD CONSTRUCTION SPECIFICATION 3

Galloway Acoustics standard rectangular and cylindrical plastic silencers are generally manufactured from pre-galvanised sheet steel

in accordance with DW144 (or the latest HVCA ductwork standard at that time) and as per the construction specification shown below.Other material options include: -

Stainless Steel to 304/316 (or any other Galloway approved grade). Generally stainless steel silencers are manufactured tothe same casing thicknesses as their pre-galvanised sheet counterparts, unless otherwise advised.

Plastic Poly-propolene and UPVC/GRP generally in accordance with DW155 and as Galloway Acoustics data sheets,PGB 2-5 Sheet 1 and 2, available upon request.

Plastic Silencer

Galloway Acoustics Rectangular Silencer Constructional Specification

These would be constructed with pre-galvanised sheet steel casings with mastic filled Grooved Seam longitudinal joints, and wouldbe generally manufactured with casing thicknesses in accordance with DW144.

The material to be used is Prime galvanised mild steel to BS EN 10142 1991 DX51D+Z Z275 quality, lock forming and workingup quality, normal spangle finish (N), Coating type C.

Flanges would be knock on type Ductmate and would generally be fabricated from pre-galvanised sheet as follows: -

Ductmate 25 and 35 are standard, however where specifically requested Ductmate 20 and 30mm can be substituted and again sizedin accordance with DW144 and the chart above.

Due to the splitter casings being riveted to the main attenuator case creating an inherently stiff component, intermediate stiffeners areonly used on attenuator lengths over 1800mm as required.

Where RSA flanges are specifically requested or the width or height of the silencer exceed DW144 classifications the flanges would

be in accordance with Galloway Acoustics drawing 01-SK6 1 of 2.Arranged within the casing would be attenuating splitter sections manufactured from a minimum of 0.8mm sheet steel, fixed to thecasing with rivets at 250mm centres (one row for sideliners and two rows for splitters).

DW144 End Flanges DW144 Class C End FlangesClass A/B

W or H (mm) W or H (mm)

Ductmate 25/20 Up to 800 Ductmate 25/20 Up to 600Ductmate 35/3, 30/3 801 to 1250 Ductmate 35/3, 30/3 601 to 1000

Ductmate 35/4, 30/4 1251 to 1600 Ductmate 35/4, 30/4 1001 to 1250

Ductmate 45 1601 to 3000 Ductmate 45 1251 to 2500

Stainless Steel Silencer


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4 STANDARD CONSTRUCTION SPECIFICATION

All GALLOWAYattenuators would have aerodynamically shaped

bullnose fairings to the front and back of the splitters, 0.7mmexpanded metal facing to the acoustic infill and polythene sheetblocked ends, which must be removed prior to installation of theunit.

This type of construction has been tested in accordance withHVCA specification DW144 and at a pressure of 1000N/M_,a leakage of class B was obtained.

The acoustic media used is ATTENUFILL, which is manufacturedby the Galloway Group. This is a mineral fibre slab with aminimum installed compression rating of 5.0%. The material isinert, non combustible, non hygroscopic, vermin proof, rot proof,will not support bacterial growth and sound absorbent to BS3638 1963 absorption coefficient with a minimum density of45kg/m3 and faced with a glass fibre tissue.

Where M has been added to the code the acoustic infill wovenglass fibre mesh facing will be replaced with a HermeticallySealed Melinex membrane bag retained behind expanded metalfacing. Where advised the silencer hygiene will match the TMspecification relevant to the site.

Differential Pressures up to 2000pa as above but manufacturedto obtain Class C leakage DW144 positive pressure (pleaseadvise if this is a requirement).

Splitter Bend Type VB/HB - These shall be constructed as above.

Horizontal Splitters - Attenuators with code suffix (H) will beconstructed with horizontal splitters.

Matching Flanges - Available for all Galloway Silencers areavailable as standard at extra cost.

Galloway Acoustics Cylindrical Silencer ConstructionalSpecification

Dependent upon quantity and specification, cylindrical attenuatorswill be constructed from pre-galvanised sheet steel either as an

overlapped longitudinal seam or spiral wound with all casingsand leakage being to a minimum of DW144.

End flanges would be internal and manufactured from lock-formed

rolled steel. In all cases the flanges have nut inserts to our standarddrilling dimensions. These can be altered as required to ensurecompatibility with other components on site.

The acoustic media used is ATTENUFILL specification as describedunder rectangular silencers.

All podded Galloway Cylindrical silencers have flat entry andexit with 0.7mm expanded metal facing to the acoustic infill andpolythene blocked ends, which must be removed prior to installationof the unit. The acoustic media is further protected by the use ofexpanded pre-galvanised sheet steel as standard.

Melinex membrane specification as described under rectangular

silencers.When units are manufactured in sectional lengths these areconnected together using SPIRALMATE manufactured by Ductmate(Europe) Limited.

GALLOWAYcylindrical attenuators are suitable as standard forinternal duct pressures up to 1000N/M_, DW144 class A/B.As a non standard they can be manufactured suitable for internalduct pressures up to 2000 N/M_, DW144 Class C at an extracharge (please advise when required).

CA/CPA SPGThe addition of SPG on the code denotes theuse of spigot connections in preference to the internal flanges

and nut inserts.

CA/CPA SPG SFor quick installation and release applicationthe code S after SPG denotes the use of SPIRALMATE connectionsfor which compatible mating flanges will be supplied.

CAXT 1 & 2 SILENCERS The units are manufactured as abovewith spigot connections each end to fit into most standard ISOduct systems. Their main purpose is to provide high levels ofcross talk privacy between adjacent rooms served by a commonductwork system, whilst producing a negligible additional pressureloss on that system.

Matching Flanges As with rectangular, available at additionalcost.


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Optional Features

Facings: Whilst not specifically covered under DW144,Galloway Acoustics strongly recommends that all duct mountedsilencers and acoustic splitters provided on modern day ventilationprojects should have their acoustic media protected not only bya glass fibre tissue but also expanded or perforated metalprotection. Galloway Acoustics provide this feature as standard.The photograph below shows what can happen if it is not.

Other facings available are Melinex hermetically sealed bagsand full glass cloth wrap.

Full glass cloth wrap is used for clean applications that requirethe mid and high frequency performance that Melinex bagged

units lose.

Fire Rated/HTC

The Galloway Group, of which Galloway Acoustics are a part,are licensees for the fire protection of ductwork using FenlandFire Spray (FF) treatment methods.

This being the case the Galloway Acoustics range of silencerscan be manufactured from the above certified alternativeconstructional methods to meet any specific requirement relatingto BS476 Part 4 (Fire) and BS5588 Part A (Smoke).

For systems requiring the use of only a high temperature casingfor non certified applications, our HTC option is available. Pleasenote this is not a certified fire rated construction.

OPTIONAL FEATURES 5

Fire Rated Silencer In Factory

Large Cylindrical Silencers

Damaged silencer seam - This is not an option

Fire Rated Silencer


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6 OPTIONAL FEATURES

Bends All Galloway rectangular silencers can be manufacturedas either vertical (VB), horizontal (HB) or T-section (TB) bends.

Multi Section (MSL, MSW, MSH) and Flat Pack (FP)Options are available where lack of lifting mechanisms and pooraccess on site require large silencers to be broken down intosmaller component parts. Multi section silencers are split on thelength, width, height or a multiple of all three to provide handablesectional sizes.Flat pack silencers are generally broken down into individualcasing and splitter sections. Both options are for site assemblyby others. Please advise when issuing your enquiry/pricing

request whether these options are required.Ductwork TerminationsAll Galloway silencers can be manufactured with a range ofoptional complementary ductwork components as an integral partof the silencer, e.g.: - Inlet and Outlet plenums for silencers being situated close to

an obstruction such as a louvre, filter, damper etc.

Square to Rounds, straight through and stepped spigots wherespace is limited.

Transformation sections and in the case of cylindrical silencers,Spiralmate quick fix and release connection flanges to facilitateeasy installation and removal to and from the ductwork system.

PaintingThe complete range of standard silencers can be painted to ahigh standard using Polyester Powder Paint to both the internaland external metal surfaces for both chlorination protection and

aesthetic appearance requirements.Special features such as lifting lugs for cranage, special flangeconnections, fully welded units for high pressure applications,dual skin silencers to reduce noise breakout into critical areasand drop in roof silencers for roof curb mounted fans etc. can allbe provided by Galloway Acoustics.

For further assistance on all the options availableplease contact Galloway Acoustics Technical SalesDepartment who will be happy to assist you withyour enquiry.

Square to Round

Flat Pack Assembled

Bend Silencer


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STANDARD CODINGS 7

RECTANGULAR SILENCERS

A Silencer Configuration Type followed by referencenumber

ASL Adjust Sideliners

EOA Even Out Airways

H Horizontal Splitters

C Class C Construction

HTC High Temperature Casing

M Melinex, hermetically sealed bag with silencer.

Hygiene to match TM specification relevant to theproject

GLW Glass Cloth Wrap to all faces of acoustic media

VB Vertical Bend

HB Horizontal Bend

TB T Section Bend

MSL Multi Section Construction in Length

MSW Multi Section Construction in Width

MSW Multi Section Construction in Height

SF Self Flange

FP Flat Pack

DF Standard Ductmate

IF Internal Ductmate Flange

GF RSA Flanges to suit specification, hot dippedgalvanised after manufacture

IGF Internal RSA Flange to suit specification, hot dippedgalvanised after manufacture

SPG Spigot Connections (straight through, i.e. silencerduct size)

SPGS Stepped Spigot Connections

SPGC Capped end with Cylindrical Spigot, i.e. SPGC150 150 dia spigot end

PLI Inlet Plenum, i.e. PLI300 = 300mm long

PLO Outlet Plenum, i.e.. PLO300 = 300mm long

PP Polyester Powder Coated to BS/RAL colour

SPF Other Paint finishes to be specified

PC Polypropylene Construction

UPVC/GRP

UPVC/GRP construction

ST/ST Stainless Steel Construction

FF Fenland Fire Spray

DS Double Skin Construction

DIS Drop in Silencer refer to drawing for details

NS Non standard construction refer to drawing fordetails

CYLINDRICAL SILENCER CODINGS

CA Cylindrical silencer without concentric pod

CPA Cylindrical silencer with concentric podSPG Cylindrical CA/CPA unit with spigot connections in

lieu of nut inserts

S Spiralmate connections

FLG Circular silencer with external angle flange. Drillingsto be advised

CAXT1 Spigotted cylindrical crosstalk silencer 50mm lining.

CAXT2 Spigotted cylindrical silencer 100mm lining

C DW144 Class C Construction

M Melinex hermetically sealed bag with silencer hygieneto match TM specification relevant to project

GLW Glass Cloth Wrap to all faces of acoustic media

PLI Inlet Plenum i.e. PLI300 = 300mm long

PLO Outlet Plenum i.e. PLO300 = 300mm longPP Polyester Powder Painted to required BS/RAL colour

SPF Other paint finishes to be specified

PC Polypropylene construction

UPVC/GRP

UPVC/GRP construction

ST/ST Stainless Steel construction

FF Fenland Fire Spray

DS Double Skin Construction

NS Non standard. Refer to drawings and schedule and

includes all multi-secion variables


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8 ACOUSTIC DESIGN

Acoustic Design

Having read the introduction to this catalogue you will know that our standard silencers have been tested on the UKASaccredited test rig shown below.

With regard to the results obtained the items that were measured to both standards were: -

1 Static Insertion Loss (Not dynamic. Please note that BS 4718 1971 does not define or require the testing of dynamicinsertion loss. ISO 7235 1996 defines dynamic insertion loss but does not class testing of this as compulsory. Bothstandards require static insertion loss to be measured for the standard to be met.) With regards to IOS 7235 thisstandard requires the static insertion loss data to be presented in the form of 1/3 octaves. This being the case GallowayAcoustics have accurate information on silencer performance figures at these frequencies, essential for the treatmentof applications including tonal noise problems.

2 Inlet and outlet flow generated noise.

3 Silencer pressure loss due to airflow.Regenerated airnoise and pressure losses are kept to a minimum by the use of aerodynamic bullnoses to both the inletand outlet of the rectangular silencers. This also negates the requirement of airflow directional arrows and eliminates therisk of the silencer being installed in the wrong direction.

UKAS Accredited test rig to BS 4718 and ISO 7235 at Salford University used for the testingof our silencers. This test rig was designed, manufactured and installed by Galloway Acoustics.


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ACOUSTIC DESIGN 9

Acoustic Design

However, what is not apparent from the above is the breadth and depth of the data available from these tests. To explain,Galloway Acoustics currently has 55 different silencer configurations, A1 to A55, in its range, with a melinex equivalent,A1M TO A55M for each type, i.e.: - 110 data sheets. In addition the cylindrical silencer range has 8 different datasheets covering both standard internally flanged and spigotted silencer types.

In both cases, rectangular or cylindrical, these configurations can be adopted for the use of in-duct crosstalk. However,and to our knowledge we are unique in this feature, we also have 5 types of crosstalk silencers that have been designedspecifically for non-ducted applications. That is the actual Sound Reduction Index (to BS EN ISO 140-3 1995) of theunits has been measured and not the static insertion loss (which is based on a ducted scenario in the case of BS47181971 and ISO 7235 1996). This allows accurate assessment of the performance of a crosstalk silencer when installedas an air transfer unit, for instance in a wall above and between two false/suspended-ceiling voids or as an air transferthrough a wall or door i.e. a true crosstalk application.

The above information is exactly the reason you will not find any performance figures shown in this catalogue. There arefar too many to publish. These are thus produced as data sheets available through issue by Galloway Acoustics staff,project dependent. Alternatively a CD or our members area website showing the full range of standard silencers to datealong with all other products and a selection programme is available for use by designers. Should you not wish to indulgein the rigours of carrying out acoustic selections (after all if done properly it is a time consuming task), Galloway Acousticsstaff are on hand to provide you with this service.

Any products ordered as a result of this assistance are covered by our Professional Indemnity Insurance in addition toour standard Product Liability.

Silencer Selection

The following sections explain what information is required to carryout an acoustic calculation and hence then select a

silencer. The starting point has always got to be what are the design requirements. For instance what is the applicationand what are the acceptable noise levels for such an environment. NR (Noise Rating) and NC (Noise Criteria) levelsare sound curves that can be used, as a guide to estimate how loud a certain noise will appear to the human ear. Thesecurves are a guideline and not an exact science. Different people may well have varying degrees of tolerance from onetype of noise to another. Always it is sensible to engage in discussion with the client (end user) to establish what theirrequirements are likely to be.

Overleaf are graphical and tabulated NR and NC graphs/figures. Generally the NR scale is used throughout Europewhile the NC is used in the USA and throughout large areas of the rest of the world.

Page 11 shows guides for the selection of NR/NC levels for different applications and should be treated as the maximumoverall level as a direct result of all the different noise levels. In the case of a mechanical design this means with all plantrunning.

With regards to an external or atmospheric specification the NR or NC guide poses little use. The main source of referencefor this would BS4142 1997 Rating Industrial Noise Affecting Mixed Residential Sites and Industrial Areas. This standardgives clear recommendations/guidelines on the potential effect of increasing the existing background noise level by varyingdegrees for a development on an existing or new site. However the final decision will rest with the Planning Departmentand Environmental Health Officer who may decree that no increase in background level is acceptable especially forcritical sites adjoining residential areas.

Invariably an acoustic survey will be required to establish the existing background noise level.

This should be carried out during the worst case scenario i.e. at the time of day that is deemed to be the 'quietest' whenthe plant in question will be operating. Hence for equipment operating 24 hours, or with potential to do so, this wouldbe during the night.

Galloway Acoustics can provide comprehensive testing and subsequent recommendations for all background applications.


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10 ACOUSTIC DESIGN

063 125 250 500 1000 2000 4000 8000

20

30

40

50

60

70

80

90

OctaveBandSo

undPressureLevel(dB)

NR60

NR40

NR25

NR30

NR35

NR55

NR50

NR45

NR65

NR15

NR20

10

Frequency (Hz)

063 125 250 500 1000 2000 4000 8000

20

30

40

50

60

70

80

90

OctaveBandSo

undPressureLevel(dB)

NR60

NR40

NR25

NR30

NR35

NR55

NR50

NR45

NR65

NR15

NR20

10

Frequency (Hz)

Freq (Hz) 63 125 250 500 1k 2k 4k 8k

NR65 80 75 71 68 66 64 63 62

NR60 77 71 67 63 61 59 58 57

NR55 74 67 62 58 56 54 53 52NR50 71 64 58 54 51 49 48 47

NR45 67 60 54 49 46 44 43 42

NR40 64 57 50 45 41 39 38 37

NR35 60 52 45 40 36 34 33 32

NR30 57 48 41 35 31 29 28 27

NR25 54 44 37 31 27 24 22 21

Freq (Hz) 63 125 250 500 1k 2k 4k 8k

NR65 87 78 72 68 65 62 61 59

NR60 83 74 68 63 60 57 55 54

NR55 79 70 63 58 55 52 50 49NR50 75 65 59 53 50 47 45 43

NR45 71 61 54 48 45 42 40 38

NR40 67 57 49 44 40 37 35 33

NR35 63 52 45 39 35 32 30 28

NR30 59 48 40 34 30 27 25 23

NR25 55 44 35 29 25 22 20 17


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ACOUSTIC DESIGN 11

Fan SWL Estimated Data

Spectrum Corrections

Fan Type 63 125 250 500 1k 2k 4k 8k

Forward CurvedCentrifugal

-2 -7 -12 -17 -22 -27 -32 -37

Backward CurvedCentrifugal

-7 -8 -7 -12 -17 -22 -27 -32

Axial Flow -5 -5 -6 -7 -8 -10 -13 -15

50

60

70

80

90

100

110

120

130

140

0.1 0.2 0.3 0.4 0.6 0.8 1.0 2.0 3.0 4.0 8.0 10.0 30.0 40.0

Volume Flow (m3/s)

ReferenceSoundPowerLevel(dBre.

10

-12W

)

10000N/m2

6000N/m2

4000N/m2

3000N/m2

2000N/m2

1500N/m2

1000N/m2

600N/m2400N/m2

300N/m2200N/m2

150N/m2100N/m2

60N/m2

40N/m2

30N/m2

20N/m2

15N/m2

10N/m2

Having established the specification and on selection ofthe plant (which could be an Air Handling Unit, extractfan, chiller or any other specific type of equipment thatmay involve the silenced passage of airflow) for the purposeit is proposed, the inherent sound qualities of the equipmentwill be required. In the case of a silencer selection for afan for instance, this will be the Induct Sound Power Level(SWL). The equipment manufacturer would normally providethis information.

If the design is preliminary and the accurate SWL unknown,

an estimate of the fan SWL can be achieved by utilisinga formula known as the Berenek Fan SWL Estimated Data.For ease of use, a simplified version of this is shown

opposite. By cross-referencing the air volume against thefan pressure the reference SWL can be found. Correctionfor different fan types and frequencies are given.

The Sound Power level of the equipment is the starting pointof any acoustic calculation, while the specified noise is theend giving the required acoustic performance or in thecase of the silencer the static insertion loss. The middlesection is the information required that changes from oneapplication to another. This is demonstrated by way of

the sample silencer calculation sheet on the opposite page.Further discussion with reference to this calculation sheetand information required is shown on page 14.

RECOMMENDED NR AND NC CRITERIA FOR VARIOUS APPLICATIONS

NR/NCIndex

Studio and AuditoriaSound Broadcasting (Drama)_________________________________15Sound Broadcasting (General), TV (General) ____________________20Recording Studio __________________________________________20TV (Audience Studio) _______________________________________25Concert Hall, Theatre _____________________________________20-25Lecture Theatre/Cinema ___________________________________25-30

HospitalsAudiometric Room ________________________________________20-25Operating Theatre/Single Bed Ward _________________________30Multi Bed Ward/Waiting Room______________________________35Corridor/Laboratory ______________________________________35-40

Wash Room/Toilet/Kitchen ________________________________35-40Staff Room/Recreation Room _______________________________30-40

HotelsBedrooms: Standard Room Day _____35

Standard Room Night _____30Luxury Room Day _____30

Luxury Room Night _____25Ballroom/Banquet Room___________________________________30-35Corridor/Lobby __________________________________________35-40Kitchen/Laundry__________________________________________40-45

Restaurants/Shops/StoresRestaurant/Department Store (upper floor)_____________________35-40Night Club/Public House/Cafeteria/Canteen_________________40-45Retail Store (main floor) ____________________________________40-45

NR/NCIndex

OfficesBoardroom/Large Conference Room 25-30Small Conference Room/Executive Office 30-35Reception Room 30-35Open Plan (Burolandschaft) Office 35Drawing Office/Computer Suite 35-45

Public BuildingsCourt Room 25-30Assembly Hall 25-35Library/Bank/Museum 30-35Washroom/Toilet 35-45Swimming Pool/Sports Arena 40-50

Ecclesiastical and Academic BuildingsChurch 25-30Classroom/Lecture Theatre 25-35Laboratory/Workshop 35-40Corridor/Gymnasium 35-45

IndustrialWarehouse/Garage 45-50Workshop (Light Engineering) 45-55Workshop (Heavy Engineering) 50-65

Private DwellingsBedroom 25Living Room 30


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12 ACOUSTIC DESIGN

GALLOWAY ACOUSTICSLow Mill Lane, Ravensthorpe

Dewsbury, West Yorkshire. WF13 3LN

Tel: 01924 498 818 Fax: 01924 498 414

EN:

Room / Area Served:

63 125 250 500 1k 2k 4k 8k

Spectrum 100 95 90 85 80 75 70 65

Type

1 2 1 1 0 0 0 0 0

4 0 10 20 30 30 30 30 30

4 0 0 2 4 6 6 6 6

2 0 0 0 0 0 0 0 0

2 1 1 1 2 2 2 2 2

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

OWN

DATA

400 mm X 400 mm Grille location: 2 1=Free Space, 2=Flush, 3=Jn. of 2 surfaces, 4=Corner

End Reflection Loss: m2 9 5 2 0 0 0 0 0

Sound Power Leaving: 88 78 64 49 41 36 31 26

No. of Noise sources in Room: 3 3 3 3 3 3 3 3

Sound Power to Room: 5 m3/S 100 % 0 0 0 0 0 0 0 0

15 m X 10 m X 2.4 m 360 m3 -12 -12 -12 -12 -12 -12 -12 -12

Reverberation Time: Secs. 5 4 3 3 3 3 3 3

Reververant S.P.L. : 84 73 59 43 35 30 25 20

Sound Power to Outlet: 0.32 m3/S 6.4 % -12 -12 -12 -12 -12 -12 -12 -12

Distance to Listener: Metres -11 -11 -11 -11 -11 -11 -11 -11

Directivity Factor: m2 4 5 6 7 8 9 9 9

Direct SPL: 69 60 47 33 26 22 17 12

Resultant SPL: 84 73 59 44 36 31 26 21

NR / NC Level Required: NR35 63 52 45 39 35 32 30 28

Attenuation Required: 21 21 14 5 1 0 0 0

-26 -16 -9 -3 0 1 1 -1

A-Weighted Equivalent: 58 57 50 41 36 32 27 20

Resultant dBA Level (without additional attenuation): 61 dBA

1 2 3 87 78 72 68 65 62 61 59

Selection: 83 74 68 63 60 57 55 54

Type: 79 70 63 58 55 52 50 49

Length: 75 65 59 53 50 47 45 43

Width: 71 61 54 48 45 42 40 38

Height: 67 57 49 44 40 37 35 33

Air Volume: 63 52 45 39 35 32 30 28

Pressure Loss: 59 48 40 34 30 27 25 23

Price: 55 44 35 29 25 22 20 17

Completed By: Date:M DECIBEL XXX

SWL

#N/A

NR65

3

3

???Project:

Fan Details:

CATALOGUE EXAMPLE

??????

1200

0.16

300

2

10

10

2

dBA Correction:

0.16

2

R o o m S i z e:

D

U

C

T

AT

T

E

N

U

A

T

I

O

N

#N/A

#N/A

NR25

NR60

NR55

NR50

NR40

NR35

NR30

NR45

Grille size:

N / m2

5

ATTENUATOR INSERTION LOSS

m3/ s

Fan Duty:

DimensionMtrs/No. offDescription

1

CIRC DUCT

CIRC DUCT

#N/A

ATTENUATOR FLOW GENERATED NOISE(estimated)

#N/A

RECT DUCT

RADIUS BEND

RADIUS BEND

1200

600

450

ENGINEERS

CALCULATION

SHEET

(ROOMSIDE)


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SILENCER SELECTION 13

To carryout an accurate acoustic assessment of a ductwork

run for the selection of a silencer, the following informationwill be required:

1 Ductwork Losses This is assessed from ductworklayout drawings provided by the design team. Howeversite co-ordination can often result in some ductwork runsbeing altered. Ductwork losses should always be checkedwith the mechanical contractor prior to final scheduleselection of the silencers.

2 Grille Size and Location Required to assess endreflection. The End Reflection - the energy loss andsubsequent attenuation of sound change in cross sectionfrom one area to another and directivity without theneed for detailed drawings, air volumes, and approximatepressure and fan type.

3 Number of Noise Sources in a Room Forinstance one extract and one supply grille would be twonoise sources. This would add 10(Log2) to the overallsound pressure, i.e. 3dB. Hence if one calculatedNR30 independently for each noise source, withouttaking into account the two noise sources within thecalculation, the overall result could be NR30 + 3dB, anexcess. The greater the number of noise sources theworse the potential problem.

4 Sound Power to Room Sound is measured indecibels, a logarithmic scale, and this changesin proportion to the amount of air entering a roomfrom the total being handled by the fan.

5 Room Size (Volume) In reality it is reallythe room volume that one requires. Howevermost rooms tend to be a standard Length x Widthx Height, hence Room Size.

6 Reverberation Time (RT) The reverberationtime can dramatically change overall soundpressure measured in a room from the same soundsource. The lower the reverberation time the

lower the contribution to the overall sound level,and vice versa with a higher RT. However as itis affected by the amount of total absorption ina room (the greater number of soft furnishings,i.e. chairs, curtains, carpets etc., the greater theabsorption and the lower the reverberation timeand hence overall sound level in the room, froma given noise source), it is often difficult to assessat design stage. Opposite is a basic guide fordifferent applications where the RT is unknown.

7 Sound Power to Outlet This is effectivelythe outlet for the sound power, which in the case

of an induct silencer is often an air inlet or outletgrill, diffuser, stub duct or other termination, suchas an atmospheric louvre. The principle withrespect to energy loss/attenuation is the sameas 4) above.

8 Distance to Listener The distance from the sound

source (for instance the grille) to the receiver, the humanear. Generally for a ceiling mounted grille with astandard room height of 2.8m this is usually calculatedas 1.0m (average human height is 1.8m). In the caseof an atmospheric calculation this will change from siteto site and will be dependent upon the proximity of othernoise sensitive areas on the site, i.e. office or bedroomwindows and/or the site legal boundary, i.e. industriallocation or close to residential properties.

The above is a basic guide only with regards to the minimumof information required to carryout an induct silencer selection.Galloway Acoustics staff are on hand to carryout anyselections required and advise on what other data may beneeded for more complicated applications including potentialductborne noise breakout into noise sensitive areas.

If the scheme being considered is provisional and the abovedata is not available, Galloway Acoustics have developeda quick budget selection programme that will, without theneed for detailed drawings, select a silencer based uponthe application, air volume, approximate fan type andstatic pressure, and the specification required (NR/NC).Please Note this system is a guide only andnot a substitute for accurate calculations.

TYPICAL REVERBERATION TIMES

Application Reverberation Time (seconds)At 500 Hz

a Department Stores/Restaurants 0.4 - 0.5

b Homes, Hotel Rooms, OfficesLibraries and Class Rooms 0.8 - 1.2

c Multi-purpose Halls, SchoolsAssembly Rooms, Large Canteens 1.4 1.6

d Art Galleries, Public BuildingsHospital Wards, Operating Theatres 1.6 2.2Banks, Building Lobbies

e Large Churches, GymnasiumFactories, Swimming Pools 2.5 4.5

The figures given in the table above apply only at mid frequency typically500 Hz and the following adjustments should be made for values at otherfrequencies. This correction is not applicable to large music rooms and studios.

Value at required frequency = Tabulated value x factor below

Hz 63 125 250 500 1000 2000 40001.5 1.3 1.1 1.0 1.0 1.0 1.0


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14 STANDARD DRAWINGS

Rectangular


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STANDARD DRAWINGS 15

Rectangular & Cylindrical Standard Units


16/20


Rectangular Construction Notes and Flange Connection Details


17/20

Cylindrical Connection Notes and Flange Details

STANDARD DRAWINGS 17


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Crosstalk Silencers



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Installation and Other Products

Normally Galloway Acoustics silencers areprovided on a supply only basis, to be installedby the ductwork contractor. However, whererequired, a professional and skilled installationservice is offered by Galloway Acoustics. Thisis backed by a comprehensive Public andEmployers Liability Insurance and working

practices compliant with all relevant and currentCOSHH and Health at Work Safety Standards.Specific method statements are provided foreach project undertaken by Galloway Acoustics.

All contracts both supply only and those involvingan element of installation are project managedby an experienced engineer who will co-ordinatethe design for approval, manufacture, despatchand on site installation programme.

Upon completion of silencer deliveries, O andM guidelines can be provided upon request.

Other Products

In addition to silencers, Galloway Acoustics fullrange of products and services comprises:ACOUSTIC AND NON ACOUSTIC

LOUVRES

SPECIALISED ACOUSTIC DUCTINGCOMPONENTS

METAL ACOUSTIC AND FIRE RATEDDOORSETS

ACOUSTIC ENCLOSURES AND SCREENS

ACOUSTIC MATERIALS

VIBRATION ISOLATORS

INERTIA BASES

FLOATING FLOORS

INSTALLATION SERVICES

ACOUSTIC CONSULTANCY

CUSTOM DESIGNED PRODUCTS


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noise control for industry & commerce

Documents