Engineering Guide Noise Control

Home , Mechanical room, Noise control, Transmission Loss

SECTION M

Please refer to the Price Engineer’s HVAC Handbook for more information on Noise Control. ENGINEERING GUIDE - NOISE CONTROL source are present. This condition exists sound waves moving away fromthesound The soundfield where onlydirectlyradiated Free Field or supplyairflow. direction. airflow Also knownaspositive sound andairflowaremoving inthesame A condition that exists when airborne Flow Forward Air downstream ductpathasnoise. theinternal componentsandre-enters transmitted through thesilencer walls and excited intovibration,which isthen upstream sideofasilencerarereadily Is when the walls of the ductwork on the Flanking The unitofmeasurementisdB. changes with the absolute duct velocity. as theairflow. Silencerperformance traveling inthesameoroppositedirection varies dependingonwhetherthesoundis and velocity. The insertion lossofasilencer The insertion airflow direction loss at a given Loss Dynamic Insertion 10) ofthisratio. 10 timesthecommonlogarithm (tothebase amounts ofacousticsignalpowerequalto A unitforexpressingtheratiooftwo Decibel (dB) of frequencies. Noise withcomponentsover awiderange Broadband Noise space. enclosure orductworkintoanoccupied Noise thattravelsthroughthewall ofan Breakout Noise known asambientnoise. that isofinterestorbeingmeasured. Also Noise sourcesotherthanthenoisesource Background Noise of thehumanear. a closerelationshiptoloudnessjudgments prescribed frequencyresponsethatbears often abbreviateddBA,dB(a).Ithasa A weightingnetworkthatiswidelyused, A-Weighting known asbackground noise. no particular soundbeingdominant. Also of many soundsfrommany sources,with environmentin agiven andiscomprised An all-encompassing noise that is present Ambient Noise and plenum type walls. silencers absorptive The sound-absorbingmaterialusedinside Acoustic Media of sound. control, transmission,reception,andeffects The sciencethatisrelatedtotheproduction, Acoustics M-2 Terminology Engineering Guide Control Noise The sound power produced by air flowing The soundpowerproducedbyairflowing Generated Noise The lowestfrequencyinaharmonicseries. Fundamental Frequency to 1cyclepersecond. frequency is Hertz ( Hz), which corresponds a passing wave repeats itself. The unit of The numberoftimesinonesecondthat Frequency nearby surfacesarehighlyabsorbent. distance from reflecting surfaces, or when when asoundsourceislocatedlarge NC level. The singlenumber valueisknownasthe toeachsensitivity ofthe frequencybands. in the human because this system factors used bymanufacturestorate equipment of equipment. These values arecommonly frequency, being the NC rating for the piece highest pointontheNCcurve,regardless of at each ofthesefrequencybands,withthe Hz.Sound levelsareplotted 63 Hzto8000 bands withcenterfrequenciesranging from aspectrumofoctave of curvesthatcovers A weightedvalueobtainedfromaseries NC (NoiseCriteria) a singlemodule. A valuethatisusedtodefinethewidthof Module Factor velocity airflowandairbornecontaminates. protect themediafromerosionduetohigh media and the airstream of the silencer to A linerthatis appliedbetweenthefiberglass Media Protection See Sound IntensityLevel. Intensity Level See Sound Intensity. Intensity measurement isdecibels(dB). the sourceand the receiver. The unit of element is inserted into the path between when thesilencerorasound-attenuating sound intensity level measured at a receiver The decreaseinsoundpressurelevelor Loss (IL) Insertion them. resistance tosoundtransmitting through combination ofmaterialscreateahigher when aheaviermaterialorOccurs High Transmission Loss(HTL) the numberorcyclespersecond. The unitofmeasurementforfrequency, or (Hz) Hertz frequency. An integer multiple of the fundamental Harmonic measurement isdecibels(dB). direction (forward orreverse). The unitof velocityand through asilenceratgiven please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes,

inlet totheoutlet ofasystemcomponent. The difference instaticpressure fromthe Pressure Drop across thesilencer. insertion lossandincreasedpressuredrop free areatypicallyresultsinan increased of a silencer cross-section. A decrease in A code used to define the % of free area Pressure Attenuation (Pa) Code See Forward Air Flow. FlowPositive Air scale extendingfromlowtohigh. combination ofwaves, thatisplacedona by thefrequencyofasoundwave, ora sound quality that isA subjective determined Pitch power densitydecreasesby3dBperoctave. wide. When comparedwithwhitenoise,the power inbandsthatareproportionally is flatinlogarithmic scale,andhasequal A soundwithafrequencyspectrumthat Pink Noise meter (N/m tooneNewtonpersquare that isequivalent A metricunitofmeasurementforpressure Pascal (Pa) separated byanoctave. A segmentofthefrequencyspectrum Octave Band of astandardpiano. the keyboard frequency ratio of2. There are 8 octaves on The intervalbetweentwosoundshavinga Octave and roundingtothenearestmultipleof0.05. Hz and 2000 coefficients at 250, 500, 1000 averaging thematerial’s soundabsorption a single value. This value is calculated by performance ofamaterial,expressedas A measure of the acoustical absorption NRC (NoiseReductionCoefficient) The unitofmeasurementisdecibels(dB). points along the path of sound propagation. sound pressurelevelbetweenany two A valuethatrepresentsthedifference in NR (NoiseReduction) of greaterthanusualvolume. Any unwanted soundormeaningless sound Noise See Reverse Air Flow. Flow Negative Air of phase. pressure andtheparticle velocityareout of thesoundsource.Inthisfield influenced by the radiation characteristics the source where the sound pressure is The sound field immediately surrounding Near Field

2 ). © Copyright P rice Industries Limited2014.

©Copyright Price Industries Limited2014. one airpathlocated betweentwoacoustic A portion ofthesilencerthat consistsof Silencer Module a largersilencerbank. with othercomponentsinthefield tocreate more baffles andmayornotbecoupled A factoryassemblythatcontains oneor Silencer Component and typicallymatch theductdimensions. overall dimensions of the complete silencer, components. The bankdimensionsarethe can contain oneor multiple silencer A complete silencer assembly that Silencer Bank resonant chambers. of perforatedmetalandacousticmediaor A silencer component that is comprised Silencer Baffle understood. with theabilityofspeech tobeheardand Hzoctavebands. 4000 This ratingdeals Hz,and Hz,2000 Hz,1000 (dB) inthe500 The arithmeticaverageofsoundlevels SIL (Speech Interference Level) material. by one square foot of a perfect absorptive absorption inrelationtothe A unitofmeasurementforacoustic Sabin negative airflow. direction. Also knownas return airflowor and airflowaremoving intheopposite A conditionthatexistswhenairbornesound Flow Reverse Air radiated andreflectedsound waves. The soundfieldthatconsistsofbothdirectly Reverberant Field See Reverse Air Flow. Flow Return Air RC level. with asinglenumbervalueindicatedasthe provide a rating of an occupied indoor space sound formasking. The curvesareusedto maintaining acertain levelofbackground systems, as it provides guidance for created toestablishdesigngoalsforHVAC Hz. 4000 This ratingsystemwas specifically center frequenciesrangingfrom16 Hzto that cover aspectrumofoctavebandswith A value obtained from a series of curves RC (RoomCriteria) instant oftime. magnitude isnotspecifiedforany given An oscillationwhoseinstantaneous Random Noise function ofthetime. the soundpressureisasimplesinusoidal A single frequency sound. A sound for which Pure Tone Terminology Engineering Guide Control Noise

power (e.g.84dBre10 decibels in respect to the reference sound unit used to express sound power level is reference power (typically 10 soundpowertoa of theratioagiven is tentimesthelogarithm (tothebase10) equation indicates that sound power level to a reference pressure (typically 20 x 10 10) sound of the pressure ratio of a given is twentytimesthelogarithm (tothebase equation indicatesthatsoundpressurelevel where typicallyPref =20x10-6 Pascal. This Algebraically definedasLP=20log(P/Pref) 10 sound intensityinreferenceto of agiven by takingtentimesthecommonlogarithm The ratio of sound intensity, which is obtained Sound IntensityLevel Sound Pressure Level (L is typicallyPascals (Pa). pointinspace. a given The unitofmeasure and theaverageorbarometricpressureat actual pressure produced by a sound wave The instantaneousdifference betweenthe Sound Pressure re 10 give anestimateofthesound insulation give A single figure rating system designed to Sound Transmission Class(STC) x 10 x reference soundpressure(e.g. 87 dBre20 pressure levelisdecibelsinrespect tothe Pascal). The unitusedtoexpresssound position(W/m energy atagiven The amount and direction of flowacoustic Sound Intensity oscillation describedabove. (B) bytheAn auditorysensation evoked alterations. or thesuperpositionofsuch propagated in anelasticorpartially elasticmedium, particle displacement, particle velocity, etc. (A) An oscillation in pressure, stress, Sound listener’s thresholdofhearing. that hasanintensity40dBabove the Hz sound equal to the loudness of a 1000 loudness foranaveragelistenerthatis unit of measurementA subjective for Sone modules withinonecomponent. baffles. A silencercanhavemultiple where typically Wref = 10 Algebraically definedas LW=10log(W/Wref) Sound Power Level the watt (W). per unittime. The unitofmeasurementis The totalsoundenergyradiatedbyasource Sound Power please visitwww F -12 or moreinformation onadditionalimperial andmetricsizes, -6 W/m -12 Pascal). W/m 2 . The unitofmeasurementisdB 2 .priceindustries.com orcontactyourlocal Price representative. . -12 watts). P ) -12 -12 watts. This watts). The 2 ).

-6 -6

Static Pressure (P etc. windows, doors, properties walls, offloors, ceilings, Total Pressure (P also be defined as the difference between on asystem,regardless ofairflow. Thiscan The pressureexerted equallyinalldirections This canalsobedefinedasP which actsonlyinthedirectionoffluidflow. The pressureexerted byamoving fluid Pressure (P defined asthealgebraicsumofStatic and thestaticpressure. This canalsobe The combinedeffect ofvelocitypressure = P given bandwidth. given band andatany centerfrequency havinga linear scale.Ithasequalpowerin any linear A soundwithaflatfrequency spectrum in White Noise by oneperiod. points of a sound wave which are separated The linear distance between two successive Wavelength Velocity Pressure (P elastic medium. A periodicmotionordisplacementinasolid Vibration are expressedwithaunitofdecibels(dB). wall, partition, or ductwork. These values passage throughanobstructionsuch asa A reductionofsoundlevelsasaresult Transmission Loss(TL) (P Total Pressure (P the fundamentalfrequency. harmonics atmultiples(2x,3x,4x,etc.)of a singlefrequencyandtypicallycontains An intense sound that is concentrated at Tone installed inthesystem. was testedandhowtheproductisactually the difference betweenhowtheproduct for apieceofequipment. This iscausedby A deviation from the cataloged performance System Effect See Forward Air Flow. Flow Supply Air the cross-sectionalareaofductwork. velocity pressurecausedbyanincreasein incorrelationoccurs withadecreasein An increase in system static pressure that Static Regain inlet tothedischarge ofaductelement. The difference instaticpressurefromthe Static Pressure Loss v ), expressedasP s +P v . s ) and Velocity Pressure (P t ) andthe Velocity Pressure t ) s =P s ) v ) t -P v . v =P M-3 t -P s . v ), P t

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL M-4 Fundamental Concepts Engineering Guide Control Noise Eq.1 Eq.1 Decibel levelisdefinedas: corresponding dBlevelsofcommonnoises. Sound Pressure Level chart (right)tosee a moremanageablerange.Refer tothe because it reduces the scale of values to describe sound pressure levels in acoustics large. The decibel (dB) scale is used to be detected by the humanear is extremely The rangeofpressurefluctuationsthatcan tobe. loud somethingisperceived these fluctuationsisproportional tohow atmospheric pressure. The amplitudeof fluctuation above andbelowtheambient Sound ispropagated asapressure Sound Pressure Levels into1/3octavebands. can besub-divided For moredetailedanalysis,octavebands Hz. Hz,and8000 Hz,4000 Hz,2000 Hz, 1000 HVAC noiseare63Hz,125 Hz,250500 The eightcommonlyusedoctavebandsfor band isidentifiedbythecenterfrequency. analysis moremanageable.Each octave measurementand octave bandstomake down intofrequency range is broken Hz. is about20Hzto20000 This large The audiblefrequencyrangeforhumans at 250Hz. middle Conapianorepresentspuretone per secondofanoscillation.For example, Frequency tothenumberofcycles refers Frequency guide. panels arediscussedinthisengineering Control Products such and assilencers as noise. The proper application of Noise is unwanted orannoying,werefertoit be desired in certain situations, when it is not necessarily a problem and may even undesirable sound. While soundingeneral Noise isdefinedasany unwanted or What isNoise? in airanddetectedbyaperson’s ears. commonly thoughtofasbeingtransmitted (solid, liquidorgas). Sound ismost disturbance or wave in an elastic medium Sound is a propagating vibrational What isSound? where:

p p L ref oot meansquarevalue of P

eference quantitydefined ound pressurelevel = = S =

R 20uPa as thethreshold ofhearing, Pa acoustic pressurefluctuation, R

Subjective andObjective Sound Changes

Just Perceptibly Louder Louder Twice asLoud Much Louder Subjective Change

please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Sound Pressure Levels Comparision of Wavelengths for Different Frequencies THRESHOLD OF HEARING OF THRESHOLD 0 20

02 04 06 70 60 50 40 30 20 10 Forest

0 ,0 0002000200002,0,0 200,000,000 20,000,000 2,000,000 200,000 20,000 2,000 200 Library

Wavelength

µPa Level dB Level Ofﬁce 3 dB 5 dB 10 dB More than10 dB Objective Change

09 0 1 2 130 120 110 100 90 80 Heavy Truck Heavy

rice Industries Limited2014. Jet Take-Off Jet

14 0 PAIN OF THRESHOLD

Eq.2 sound sources. Sound power is defined as: allow forfaircomparisonsbetweendifferent sound levelsduetotheenvironment and levels to facilitate calculation of expected Equipment isratedintermsofsoundpower the operatingconditionsofequipment. of theenvironment andonlydepends on by asource.Sound powerisindependent measure oftheacousticalenergyemitted The sound power level of a source is a Sound Power Levels w ©Copyright Price Industries Limited2014. the walls, windows,furnishings,etc. sound energyabsorbedandtransferred by the measurementpointandamount of as well asthedistance from the source to the soundpowergeneratedbysource, measured intheroomwillbeafunctionof energy orpowerlevel. The soundpressure source hasacertain amountofsound walls, windows, etc. Similarly, a sound by thewalls, andheattransferthroughthe the distance from the heater, heat absorbed on thepowerratingofheater, butalsoon measured intheroomwillnotonlydepend surroundings. However, thetemperature is apowerratingthatindependentofthe watts. The amountofheatenergyproduced specific amountof heat energy, measuredin electric roomheater. The heateremitsa sound powerandpressureisan A goodanalogyforthedistinctionbetween environment. or intensity measurements in a controlled levels are calculated from sound pressure cannot bemeasureddirectly. Sound power determining soundpowerlevelswhich There are several general techniques for absorption characteristics. laboratory environment withknownsound using soundpressurelevelsmeasuredina directly. Values are typically calculated Sound powerlevelscannotbemeasured Watts w L where: Fundamental Concepts Engineering Guide Control Noise Watts W = ref = = Acoustic energyradiatedbysource, Sound powerlevel Reference powerdefinedas 10

-12 -12

Emergency • Compressors, • Room • Air • VAV • Rooftop • Fans • Various HVAC Sound Sources please visitwww F or moreinformation onadditionalimperial andmetricsizes, Heat Source

Flow

Systems

Air

Mounted Generated

.priceindustries.com orcontactyourlocal Price representative. Devices

Generators

Chillers,

Air (GRDs)

Noise

Handling

and

Air -Cooled

Units

Condensers Sound Source M-5

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL M-6 following sections. orpackless,reactive are discussedinthe filmlined,and ordissipative, absorptive paths. including The main types of silencers, a systemtoreducenoisefrom duct-borne means ofincorporatingnoisecontrol into areaneffective andeconomical Silencers occupant intheadjacentroom. isthehuman and acompressor;thereceiver is anairhandlerthatcontainsbothafan receiver. Inthisexample,thesoundsource and vibrationfromthesourceto possible transmissionpathsforthesound The Sound Paths diagram(right)illustrates pathwillnotbeeffective. to thefirst become dominant and any further treatment once onepathistreated,anothermay and evaluatedappropriately. Additionally, so possible paths must be acknowledged multiple paths,bothairborneandstructural, to notethatnoisetypicallytravelsthrough transmitted to beidentified.Itisimportant This willallowthepathbywhich thenoiseis can be determined. relation to the receiver Once thesourcesareknown,positionin Path components, andmechanical equipment. are fans,elementgeneratedflownoise, VAV Common soundsourcesinanHVAC system manufacturer supplieddataisnotavailable. should onlybeusedasalastresort where Estimatesmanufacturers. of power levels can be compared and evaluated between recognized standardensuresthattheresults per ASHRAE 130. Testing accordingtoa according to AHRI 260, terminalunits per or320, AMCA 300 Air Handlingunits equipment. Fans arecommonlytested to arecognized standardapplicabletothat from tested performance according derived supplier. The soundpowerlevelsshouldbe obtain sourcesoundpowerlevelsfromthe Wherever possible, itisimportant to Sound Sources loud occupationalexposure. at thereceiver, withhearingprotectionfor options. The lastresort istypicallytreatment barriers, absorption,lagging,orother next best option and can include silencers, Treatment optionsalongthepathare noise problemsbeforetheyevenbegin. of quieterequipmentcaneliminatemany to treatthenoiseatsource.Selection The mostdesirableandeffective optionis reducing thenoiseateach component. There are different options available for hearingthenoise. noise, andareceiver creating thenoise,apathtransmitting the downintoasource problem canbebroken – Receiverconcept.Everynoisecontrol components. This is theSource –Path break each problemintoitsfundamental approachA key tonoisecontrolis Approach toNoiseControl Engineering Guide Control Noise or designsoundcriteriaisthe intended main consideration for specifying a target contributions fromallpath types. The concept,andcombinespath-receiver is thefinalcomponentto source- of the sound pressure level at the receiver noise problemcanbeselected. Calculation effective andeconomical solution to the are consideredacceptablesothatthemost anddeterminingwhatsoundlevels receiver identified, itisamatter ofassessingthe After thesource andpathhavebeen Receiver please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Sound Paths Source, Path, Receiver occupied space. occupied space. the walls oftheductworkorpassesthrough supply/returnductworkintothe Path C – receiver. Path B – through thefloor. Path A –

Duct-borne path,wherenoisefromtheequipmentradiates through Airborne path,wherenoisefromtheequipmentradiatesdirectlyto S tructure-borne path, where the vibration of the air handler passes

value specifiedataproperty line. ordinance in terms of overall A-weighted sound criteria are typically specified by local ASHRAE Applications Handbook.Outdoor criteria foranindooroccupiedspaceisthe referenced source for typical design use ofthespace. The mostcommonly © Copyright P rice Industries Limited2014.

©Copyright Price Industries Limited2014. Engineering Guide Control Noise moisture intheairstreammaybeofconcern. laboratories, cleanrooms, andhospitalswhere contaminantsand the perforatedmetal. Typical filmlinedsilencerapplicationsinclude effects, athinacousticstandoff linerisplacedbetweenthefilmand absorbing capabilitiesoftheacousticmedia. To minimize these that theadditionoffilmlinerwillnegativelyaffect thesound present intheairstreamofsomesystems.Itisimportant tonote the mediafromairbornecontaminantsandmoisturethatmaybe polymer filmlinerwrappedaroundtheacousticmediatoprotect However, silencers. standard absorptive have a thin these silencers workonthesameprincipleas silencers Film linedabsorptive Lined Absorptive Film general HVAC supply, returnandexhaust. ventilation,fanplenums,and handling units,generatorsilencers, applications includerectangular, elbow, andcircularductwork,air on the acoustic performance of the silencer. Typical absorptive the glassfibermediaforprotectionagainst erosionwithnoeffect fiberglass clothcanbeplacedbetweentheperforatedmetaland will experiencehighgap velocitieswheninstalled,asheetof sound levels at the discharge of the silencer. For that silencers thereby reducingtheamountofacousticenergyanddecreasing convertsenergy andtheglassfibers theacousticenergyintoheat, consists ofstrandsglassfiber. Thefrictionbetweentheacoustic media,whichacoustic energyinteractswiththeabsorptive typically free areatobeacousticallytransparent.Onceinsidethebaffle, the being erodedbytheairathighvelocities,buthasalargeenough liner. This perforatedmetallinerprotectstheacousticmediafrom thebafflesenters throughtheholesininternalperforatedmetal noise inside the duct passes through the silencer, the acoustic energy utilize sound-absorbing media toattenuate sound levels. As the which Acoustic silencers, silencers, arealsoknownasdissipative Absorptive Silencer Types and Applications and Silencer Types Film Lined Absorptive Film Absorptive

please visitwww F or moreinformation onadditionalimperial andmetricsizes, .priceindustries.com orcontactyourlocal Price representative. that frequency. size andshapeoftheinternalchambers thataretunedtoremove silencer peaksinthemidfrequencyranges. This peakisduetothe insertion losscurveacrossthefrequencyranges,whilepackless silencer provides a standard fairly absorptive predictable broad utilizes tuned resonating chambers instead ofacoustic media. The unique performancecharacteristics ofthepackless silencer, which the perforatedmetalandfilmliner. Thegraphalsoshowsthe at thehigherfrequenciesbyplacinganacousticstandoff between silencer,effectiveness oftheabsorptive butcanbegreatlyimproved addition ofafilmlinersuch asMylarsignificantlydecreasesthe best overall performanceacrossthefullrangeoffrequencies. The silencerhasthe The graphshowsthatthestandardabsorptive The graphbelowisacomparisonofthedifferent silencertypes. Effect of Acoustic Media laboratories, cleanrooms,hospitals,orelectronicsmanufacturing. it is necessarytosterilize theentire duct system. This mayinclude typically specifiedwhenglassfibermediaisnotacceptableor attenuation over broadbandfrequencies.Packless are silencers narrow bandoffrequencies,itismoredifficult toachieve significant discharge ofthesilencer. aretunedtoa Sincethesesilencers resonator concept,which resultsindecreasedsoundlevelsatthe the acousticenergydissipatesinamannersimilartoHelmholtz the perforatedmetalliner. As soundpassesthroughthesilencer, using multipleresonantchambers ofvaryingsize locatedbehind and perforatedsheetmetal. Attenuation ofsoundisachieved by materialandareconstructedsolelyofsolid contain noabsorptive Packless sometimesreferred silencers, silencers, toasreactive Packless Packless Comparison of5ft LongSilencerPerformance

M-7

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL M-8 model line. a size thatisnot availableinthestandard thatrequire andsilencers shaped silencers, designs includetransitionalsilencers, T orZ the required performance. Typical custom custom silencercanbedesigned toprovide the silencerisdirectlycoupled toafan, to asystemwithlimitedspaceorwhen noise controlproductsmustbeapplied requirements of the application. When develop auniquesilencerthatmeetsthe situation. Inthesecasesitisnecessaryto always beadaptedtoworkinevery A standardsilencerconfigurationcannot Custom static pressureregain. silencer deceleratestheairtomaximize the loss over thefanhub. A discharge axialfan is properly sized tohelpreduce the pressure the fan. The axialfansilencer’s centerpod performance at the inlet and discharge of at thesourceandimprove aerodynamic engineered toprovide noiseattenuation coupled toanaxialfan. are These silencers aredesignedtobeclose Axial fansilencers Axial Fan attenuation andpressuredrop. sizes which allowforvaryingrangesof areavailable inawiderangeof silencers pressure dropsandsystemeffects. Circular to-round transitionsthatcauseundesirable system. They eliminatetheneedforsquare- when roundductworkisutilized inthe areanexcellentsolution Circular silencers Circular the useoftransitions. configured tosuitmostductsizes without in pressuredroponthesystem,andcanbe withasmallincrease rectangular silencers perform atorabove thelevels of silencers lengths ofductworkarenotavailable.Elbow excellent choice forsystems wherestraight andan butare extremelyversatile silencers, performance characteristics ofrectangular havemanyElbow silencers ofthesame Elbow fpm. 0-2500 can beapplied to systems ranging from drop andalargeselectionofmediatypes range ofdesignswithlowtohighpressure into any HVAC systemwithease. A wide of options that allow them to be integrated system. They areavailablewithanumber lowest pressuredropontheairdistribution choice forthehighestsoundattenuation and them the first low cost make and relative ductwork. Their straightforward design for silencingnoisetransmitted through Rectangular arethe standard silencers Rectangular Applications and Silencer Types Engineering Guide Control Noise please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Custom Axial Fan Circular Elbow Rectangular

©Copyright Price Industries Limited2014. or industrialnoisesource. oranycompressors otherunwanted HVAC turbines tosmallerunitsforpumps,motors, applications ranging from large units for gas and inlet and exhaust plenums; with barrier systems, custom enclosures, requirements. Typical applicationsinclude and sizes tomeetspecificnoisereduction enclosures areavailableinmany shapes equipment, Price acousticpanelsand Used Acoustic Panels andEnclosures drop. aerodynamic tohelpminimize thepressure flow. are designedtobe Acousticlouvers protect themediafromerosionbyair sound energy and a perforated metal to useacoustic mediatoabsorbthe louvers the necessarysoundattenuation. Acoustic to flowthroughanopeningwhileproviding canbeusedforallowingair Acoustic louvers Acoustic Louvers to attenuate returnairnoise. transmission between adjacent spaces or standard transfergrillestoreducesound They are great for applications in place of staggered inaframethatisonly4in.thick. baffles filledwithacousticmediathatare utilize Thin line return dissipaters multiple Thin LineReturnDissipater acoustic airtransferproblems. that can be used to solve many different manufactured in a varietyof configurations are into adjacentrooms.Cross-talksilencers commonly usedtopreventspeech intrusion transferring unwanted noise. They are the necessaryattenuation toprevent air to adjacent areas while providing areusedtotransfer Cross-talk silencers Cross-Talk part ofthewall construction. aretypicallynotductedand silencers the acousticintegrityofwall. These one area to another without compromising allow air to moveAir transfer silencers from Products Air Transfer Applications and Silencer Types Engineering Guide Control Noise

for

controlling

excessi

noise

from

please visitwww F or moreinformation onadditionalimperial andmetricsizes, and Enclosures Acoustic Panels Acoustic Louvers Thin LineReturnDissipater Cross-Talk .priceindustries.com orcontactyourlocal Price representative.

M-9

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL of Price acoustical productsconformto All componentsusedintheconstruction Construction Standards silencers. characteristicsthe absorptive offilmlined liner, the acoustic standoff greatly increases between theperforatedlinerand thefilm performance oftheunit.Byproviding agap in order to improvewith film liners the Acoustic standoff isrequiredinsilencers Acoustic Standoff insertion loss levels. suchliners asMylarwillcausedecreased acoustic performanceofthemedia,while a fiberglass cloth liner will not affect the be found in the air. It should be noted that moisture orothercontaminantsthatmay or Tedlar canbeusedtoprotectagainst air flow. suchPolymer filmliners as Mylar erosion inapplicationswithhighvelocity protect theinternalacousticmediafrom fiberglassclothareusedto like Liners installed dependingontheapplication. Various silencer liner materials can be Liner customer’s preference. andthethe applicationparameters, including localandinternationalstandards, material maybe based onrequirements through thesilencer. The selectionofthis energy fromthesoundwaves astheypass is theinternalfibrousmaterialthatabsorbs the acoustic media silencers In absorptive Acoustic Media media. sound energy to penetrate the acoustic but isacousticallytransparent,allowing protection totheinternalacousticmedia, the silencerisspeciallydesignedtoprovide The perforatedmaterialontheinteriorof Perforated Liner stainless steelandaluminum. available casingmaterialsare304and316 M-10 development rating of50. spread classification of25andasmoke ASTM a coating from hot-dippedgalvanized steelwitha Standard silencercasingsare manufactured resistance totheelementsorothersources. thesilencermorerobusttoprovide make space. A heaviergauge materialwillalso of thesilencerandenterintooccupied of noisethatcanbreakoutthroughthewalls of thesilencer, which reducestheamount improve thetransmissionlossproperties A heaviergauge casingisoften usedto in thickness from24gauge to10 gauge. fabricated fromvariousmaterialsandrange of solidsheetmetal. This shellcanbe The outer shell of the silencer is constructed Casing Silencer Construction Engineering Guide Control Noise

zinc

E84,

coating weight

UL723,

of of

and

G-90 .90

NFP

oz/f

(G-90 A255 t 2 ). Additional

designates

for

flame

please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Perforated Liner

©Copyright Price Industries Limited2014. dimensions. program shouldbereferencedfor available datasheetsorsilencerselection individual dimensional constraints, therefore the Varying silencermodelsmayhavedifferent modules. which are made up of one or multiple may consistofoneormultiplecomponents, the silencer is installed. The silencer bank equal totheductwidthandheightinwhich dimensions ofthesilencer, andaretypically The silencerbankdimensionsaretheoverall Silencer Bank silencer bank. uptheare assembledon-sitetomake performance required. These components one ormoremodules,dependingonthe components. A componentmayconsistof manufactured inseveralpieces,called needtobeconstraints, largesilencers Due torawmaterialsize andshipping Silencer Component dimensions. requirements, availablespace,andduct depend on a combination of performance geometry, and length of the silencer will all width. The module width dimension, baffle baffles andoneair gap, andcanvaryin A silencer module consists oftwo half Silencer Module bank dimensions. variables are the module, component, and configuration ofthesilencer. Thesethree consist of three variables that represent the available. Rectangular andelbowsilencers to have multiple silencer configurations performance requirements,itisnecessary Due to construction constraints and insertion lossrequirements. only to the length necessary to meet the cost effective solutionistobuildsilencers pressure drop and additional cost. The most must beweighedagainst theincreased will provide greaterinsertion loss,butthis and thespaceavailable. A longersilencer determined byperformance requirements The length of the silencer is typically and generatednoisetoincrease. air flow that may cause the pressure drop discharge ofthesilencerwillcreateturbulent performance. Transitions attheinletand effect ofthetransitionsonsilencer elimination ofcostlytransitionsandthe dimensions to the ductwork are the The mainbenefits ofmatching thesilencer typically specifiedtomatch theductwork. Silencer widthandheightdimensionsare and downstreamofthesilencer. and dimensionsoftheductworkupstream available space,performancerequirements, The dimensionsofasilencerdependonthe Silencer DimensionalConsiderations Engineering Guide Control Noise

Multiple Module,ComponentSilencer Multiple Module,SingleComponentSilencer Effects of Transitions on Air Flow please visitwww F Air Flow Pattern whenSilencerMatches Ductwork or moreinformation onadditionalimperial andmetricsizes, .priceindustries.com orcontactyourlocal Price representative.

M-11

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL center lineoftheentireelbowassembly. while thebankcenterlineisgeometric center lineofeach component, individual line. The performance center line is the line willbedifferent fromthebankcenter silencer is nested, the performance center for thesilencerinletsandoutlets. When a anevenductconnection are usedtomake in size and performance. Duct extensions multiple componentswhich areidentical nested whenthebankwidthismadeupof The elbowsilencerconfigurationwillbe Nested Elbow will perform. model numberrepresentshowthesilencer the performance center line length as the length. The modelnumberwillalways show line lengthisequaltothebankcenter configuration, theperformancecenter un-nested configuration. For thiselbow bank width,theelbowsilencerwillbean When thecomponentwidthisequalto Un-Nested Elbow Silencer DimensionalConsiderations Engineering Guide Control Noise M-12 Performance CenterLine=Bank–Component Width Bank Nested Elbow Configuration Component Width) (or Bank Width Bank Un-Nested Elbow Configuration please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes,

(Geometric) (Geometric)

Center

Line

Leg

P A erformance

Leg

–

Bank

Center

Width

Line

L eg rice Industries Limited2014.

L eg

–

©Copyright Price Industries Limited2014. * and Prefabricated Silencers. ources Air FlowPerformance ofDuctLinerMaterials and ASTM E477Measuring Acoustical and Precision Method forReverberation Rooms Noise Determination of Sound Power Levels of to current of versions ANSI S12.51 for acousticalproducttestingaccording The Price Sound LabisNVLAP accredited nor isthedataitselfverifiedinany way. laboratory is neither certified by NVLAP standard, but the data produced bythe the laboratoryiscapableoftestingtothis for ASTM E477(orany otherteststandard), means that when a laboratory isaccredited does notimplyproductcertification. This trade publications provided that this use reports, stationery, andinbusiness and usetheNVLAPtermsymbolon A laboratorymay cite its accredited status solely afindingoflaboratorycompetence. performance ortest/calibrationdata;itis guarantee orcertification oflaboratory NVLAP accreditationdoesnotimplyany items; andtestcalibrationreports. sampling; handling of test and calibration equipment; measurementtraceability; environment; testandcalibrationmethods; accommodationsystems, and personnel, technical requirements pertaining to quality in accordancewithNVLAPmanagementand laboratory hasdemonstratedthatitoperates 17025.a NVLAPaccreditationsignifiesthat encompass therequirementsofISO/IEC Procedures Regulations (CFR, 15, PartTitle 285)andNVLAP accordance Accreditation criteria are established in to carry outspecificcalibrationsortests. technical qualifications and competence laboratories basedonevaluationoftheir accreditation topublicandprivate This organization provides third-party of Standards and Technology (NIST). administrated by the National Institute Accreditation Program (NVLAP*)is The National Voluntary Laboratory AccreditationLab standards developmentprocess. party toparticipate whowouldlike inthe of these groups are open to any interested ASHRAE, ANSI, SAE, ISO, Many andothers. profit groupssuch as ASTM International, administered byindependent,not-for- procedure. These documentsaretypically and interestedinthespecificmeasurement formed bypeoplewhoarefamiliarwith and typically written by a committee consensus based documents developed measurement orprocedure. These are and requirementsforperformingaspecific Test standardsarepublishedprocedures Testing NoiseControl Products Engineering Guide Control Noise

organizations. approved byeach ofthe respective organizations hasbeenreviewed and All information per

and with

General Using

the

.S.

S R taining tothese ound equirements,

Code

P of ressure

F ederal

and

serving theindustry andthepublicsince markets. AMCA International hasbeen industrial, commercial and residential and otherairsystemcomponents forthe measurement stations,acousticattenuators, aircurtains, dampers, airflow fans, louvers, equipment -primarily, butnotlimitedto: world’s of related air system manufacturers not-for-profit internationalassociationofthe Association (AMCA)International, Inc.isa marks. The Air Movement andControl of theassociation’s familyofcertification tested andcertified by AHRIcanapply one had theirproductperformanceclaims whohavecomponents. Manufacturers heating andcoolingequipment performance certification programsfor commercial refrigeration(HVACR) industry’s the heating,ventilation,airconditioningand Refrigeration Institute(AHRI)administers results. Air-Conditioning, Heating,and in accordancewithindependentthird-party tested toverifythatcatalogdataispublished products are often randomly selected and manufacturer performancedata.Sample independent third-party verificationof for thelab.Product certification involves the internalprocessesanddocumentation being compared. A labcertification looksat and labcertification isthescopeofwhat The distinctionbetweendatacertification widely adoptedwithintheHVAC industry. Performance datacertification hasbeen Product Certification please visitwww F or moreinformation onadditionalimperial andmetricsizes, .priceindustries.com orcontactyourlocal Price representative.

product tocarry the AMCA seal. test methodandprocedureforlicensinga 13. The AMCA publication1011-03 detailsthe obtained inaccordancewith ASTM E477- pressure dropasafunctionofairflows losses, airflowgeneratednoise,and whichsilencers looksatdynamicinsertion (CRP) forprefabricatedacousticalduct has developed a certified rating program system components. AMCA International evaluation, andtroubleshootingofair with an interestinselection,others and engineers, manuals fordesigners, standards, references,andapplication International publishesanddistributes movement andaircontroldevices. AMCA and art ofengineeringasitrelatestoair authority inthedevelopmentofscience 1917,

and

considered

the

world’ M-13 s

leading

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL that meettherequirementsoutlinedin ASTM filtering equipmentandasoundanalyzer room (3)usingarotatingboommicrophone, inthereverberation measurements aretaken With thesilencerandductworkinplace, voice coil. measuring thevoltage attheloudspeaker test, andismonitoredelectronicallyby maintained within ± ½ dB throughout the Hz. 10 000 The test signal in each band is with center frequencies rangingfrom 50 to M-14 reflection. factor thataccountsfortheeffects ofend the two measurements with a correction of thesilencerisdifference between place. The generatednoise performance then measuredagain withthesilencerin ductwork, andlaboratorysurroundings, establish thesystemnoise,includingfans, with an empty piece of duct to are taken turned off. The soundlevelmeasurements single source sound chamber, which is setup isused,withtheexceptionof To obtain generatednoisedata,thesame flow. and reverse test isalsorununderconditionsofforward will change basedonairflowdirection,the and sincetheperformanceofsilencer at variousairflowrates,includingnoflow, severaltimes The measurementsaretaken is theinsertion lossofthetestedsilencer. difference between thetwomeasurements construction in place of the silencer.like The then again withanunlinedpieceofduct with thesilencerinstalledinductand are obtained by taking sound measurements test noise thathasaseriesof ductwork. produceapink These speakers room by pathsother than through the chance ofsoundentering thereverberation chamber andductsystem tominimize the arestructurallyisolatedfromthe speakers areactinginphase. ensure allspeakers The that are electronically coupled to speakers NRC. Insidethisenclosurearemultipleloud sound-absorbing material that exceeds 0.25 a heavygauge enclosurethatislinedwith The single source chamber (2) consists of no lessthan10 ductdiameters. equivalent and downstreamofthesilencerdischarge ductdiameters, a minimumof5equivalent straight runwithnotransitionsorelbowsfor upstream ofthesilencerentrancemustbea a reverberationroom(3). The ductwork that joins a single source chamber (2) and installed in a straight length of ductwork of version ASTM E477. A silencer(1)is and requirementsspecifiedbythelatest obtained according to the procedures Duct silencerperformancedatais Method Silencer Test Testing NoiseControl Products Engineering Guide Control Noise

method

E90.

The

inser 1 /3 octave bands /3 octavebands tion

loss

values

environment. environment areverberanttest versus for thelouverbeinginstalledinafreefield reported as a noisereductiontoaccount transmission loss. The performanceis often tested penetration. aretypically Acoustical louvers pressuredrop,andwaterfor airleakage, rated by AMCA accordingto AMCA 500L aretypicallytestedand Acoustic louvers wall. the overall transmission loss of the installed transfer openingdetermining the effect on larger assembly, withthepercentageof areinstalledaspartThese silencers ofa as noisereductionortransmissionloss. data for these products is typically reported for airtransfersilencers. The performance There iscurrently notestmethodestablished Method SilencerTestAir Transfer please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Silencer Test Setup per ASTM E477

according 3

A STM

E90

for

sound

1 a coefficient of 1. where allacousticenergyisdissipated, has reflected intospace. Aperfectabsorber, mean thatmostoftheacoustic energyis by asurface.Smallabsorption coefficients a measureofthesoundenergyreflected using ASTM C423. Acoustic absorptionis acoustic absorptionofpanelsismeasured absorption, andthespecimenarea. The room sound pressurelevels,thereceiving specimen iscalculatedusingthemeasured measured. The transmissionlossofthe roomsarein thesourceandreceiving room, andtheresultingsoundpressures creates adiffuse soundfieldinthesource path isthetestspecimen. A soundsource the onlysignificantsoundtransmission with the rooms being isolated such that artitions between twoadjacentreverberationrooms, partitions. The testspecimenisinstalled sound transmissionlossofbuilding is alaboratorymeasurementofairborne Building of Airborne Sound Transmission Loss of Test Method for Laboratory Measurement tested loss andabsorption. Transmission lossis Acoustic panelsaretestedfortransmission Acoustic Panel Test Method

according

P © Copyright P

and to

A 2

Elements. STM rice Industries Limited2014.

E90

A Standard STM

E90

Testing NoiseControl Products ©Copyright Price Industries Limited2014. acquisition system andNIST traceable Utilizing ft 6,500 In thePrice Air DistributionLaboratories, innovation andperformance. our commitmenttonoisecontrolproduct state-of-the-art test equipment solidifies class research anddevelopmentfacilitywith include noisecontrolproducts,thisworld- the capabilitiesofPrice Laboratoriesto noise control product lines. By furthering for testinganddevelopmentofthePrice toincludethenewPrice Sound in 2007 Lab Our laboratorywas expandedandupgraded in-housetestfacility.units usinganextensive diffusers, andterminal grilles, registers, accurate, reliable performance data for For over Price 30 years, has been generating Price Sound Lab of theteststandard. tested accordingtothemostcurrent version should always beperformedwithdata performance dataandacousticcalculations manufacturer. Comparisonsofsilencer 999, was left tothediscretionofindividual to defining howtotestelbowsilencers. Prior band. The othersignificant change was a realisticnumberfortheentireoctave spectrum ofthesoundsourceandprovides of calculation is unaffected by the frequency the 1/3rdoctaveperformance. This method loss basedonthelogarithmic averageof and on)calculatetheoctavebandinsertion Current band thanwouldberealized inpractice. insertion octave lossvalueforanindividual old teststandardcouldprovide ahigher 1/3rd octavebandvalue.Results fromthe insertion losscanbebiasedtothehighest source. Ifthesoundspectrumisnotflat, sound spectrumgeneratedbythe 1996 duct. Insertion losscalculatedaccording 996 pressure levelsfortheemptyandsilenced the difference between octave band sound up 999 insertion loss. Versions oftheteststandard significant changes tothecalculationof The Relevance of Test Standard Version Engineering Guide Control Noise for testing of supply and return applications. 4 in. w.g. in both directions, which allows cfmat capable ofproducingupto30,000 variable speed axial fan. This fan system is is suppliedbyadedicatedbi-directional, Air flowtothereverberantsound chamber standards, downto50Hz. accordance with ASTM and ANSI test and industrialnoisecontrolproductsin designed specificallyfortestingcommercial ft³ reverberant Sound Chamber a 21,000 Sound Lab. The Price Sound Labincludes the testing anddevelopment ofthePrice

1 and

2 the ver ofspacehasbeendedicatedto

ver

calculated a earlier

sions test

sion network

method

of ver

A the

inser STM sions ed

test for

tion

graphical E477

elbow

standard assume

loss

introduced

silencer based

a (1 data

999 flat

on s

standard. custom products to theappropriate testing perform in-housetestingonawide array of Price leading facilityalsogives the abilityto latest AMCA teststandards. This industry- designed andconstructedutilizing the The entirenoisecontroltestfacility was accuracy ofsoundmeasurement available. Multi-Channel Analyzers ensurethehighest level of precision, while Bruel and Kjaer conditions aremonitoredwiththehighest and thetestparameters flow meters, please visitwww F Insertion Loss Insertion Price Sound Laboratory or moreinformation onadditionalimperial andmetricsizes, .priceindustries.com orcontactyourlocal Price representative.

accurately. our laboratoryis conductingmeasurements third-party testingweareable toverifythat our noisecontrolproductline. Through this continue toseekindependent testingfor and catalog testing, we sought andwill why throughout ourproductdevelopment designed andperformingcorrectly. That is catalog dataandfinishedproducts are excellent way to verifythatthepublished verification ofcertified testdataisan At Price webelievethatthird-party Independent Testing M-15

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL level. attenuated levelstopredict the finalsound noise valuesare logarithmically addedto 10 dBoftheattenuated levels,generated When thegeneratednoisevalues arewithin attenuated sound levels exiting the silencer. sound levelifthevalueis10 dBbelowthe band does not contribute to the overall octave note thatgeneratednoiseinagiven must beappliedtothedata.Itisimportant to proportional tothecross-sectionalarea a correction factor thatislogarithmically and whenthisareaincreasesordecreases, based onastandardcross-sectionalarea, Hz. ranging from63Hzto8000 This datais each oftheoctavebandcenterfrequencies for generatednoiselevelsareprovided at value will indicate better performance. Data of soundproducedbythesilencer, alower Since thesevaluesrepresenttheamount velocity and direction (forward or reverse). when airflowsthroughasilenceratgiven Generated Generated Noise achieve highinsertion lossvalues. this isnotalways possiblewhentryingto a silencerbelow0.35in.w.g. (87Pa), but thepressuredropof It isdesirabletokeep a). system operateinefficiently orineffectively. the entire in a highpressure drop can make (249 from 0.01 in.w.g. (3Pa) upto1.00 in.w.g. silencer, pressuredroptypicallyranges always beconsidered. With acommercial an HVAC system,thepressuredropshould the silencer. When addingany componentto location isaminimumof10 from diameters upstream andthedownstream diameters location isaminimumof5equivalent pressure ofthesilencer. The upstream The pressure drop is the differential static Pressure Drop duct velocitiesinforwardflow. andreverse Hz and atvarying ranging from 63Hzto8000 octave bandcenterfrequenciestypically receiver. The dataisprovided ateach ofthe into the path between the source and the be expectedwhenasilencerisinserted decrease in sound pressure levels that can is theinsertion loss.Insertion lossisthe The foremostparameterinsilencerselection Loss Dynamic Insertion determine theperformanceofasilencer. mustbeknowntoproperly parameters performance of a silencer. Both of these flow throughtheductwilldirectlyaffect the The directionandfacevelocityoftheair Air Flow Direction& Velocity considered. needtobeperformance parameters products foranHVAC system,thefollowing or noise control When selecting silencers Performance Performance Engineering Guide Control Noise M-16

n poor oise

silencer

i s

t he

s ound

selection

p ower

resulting

c reated

please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, Generated NoiseCorrections(Basedona4ft Generated Noise Pressure Drop Loss Dynamic Insertion Silencer FaceArea(ft dB AdditionorReduction Face Velocity Face Velocity +1000 (+5.08) -1000 (-5.08) +500 (+2.54) +1000 (+5.08) -500 (-2.54) -1000 (-5.08) +500 (+2.54) fpm (m/s) -500 (-2.54) fpm (m/s) 0 (0.00) Length in.(mm) 108 (2744) 60 (1524) 84 (2134) 36 (914)

63 Hz 63 Hz 63 63 61 63 6 7 7 7 8 2 Dynamic InsertionLoss(dB)MeasuredatOctaveBandCenterFrequencies ) Generated Noise(dB)MeasuredatOctaveBandCenterFrequencies 125 Hz 125 Hz 10 10 11 12 12 0.5 -9 53 52 50 56 0.16 (40) 0.16 (40) 0.18 (45) 0.17 (42) 500 fpm Pressure Drop(in.w.g. [Pa])ataSpecificFace Velocity 1 -6 250 Hz 250 Hz 47 42 37 51 23 24 26 28 29

2 -3 500 Hz 500 Hz 48 45 32 46 36 37 38 39 40 4 0 0.61 (152) 0.66 (164) 1000 fpm 0.7 (174) 0.7 (174) 1000 Hz 1000 Hz 2 53 46 33 46 silencer) 38 39 40 41 42 8 +3 2000 Hz 2000 Hz 16 +6 © Copyright P 59 43 31 51 28 29 30 31 32 32 +9 4000 Hz 4000 Hz rice Industries Limited2014. 57 33 28 49 16 16 16 16 16 1.48 (368) 1.57 (391) 1.57 (391) 1500 fpm 1.4 (348) 64 +12 8000 Hz 8000 Hz 47 29 31 42 14 14 14 14 14 128 +15

©Copyright Price Industries Limited2014. direction offlow, shouldalways beused. corrects the insertion lossvaluesforthe the exactairvelocitytobeenteredand software Price like All-In-One, which allows critical noise control applications, selection decision fortheselectionofasilencer. For can beimportant inmakingthebest factors The directionofairflowandvelocity high frequencies. frequencies andincreasedperformanceat is decreasedacousticperformanceatlow direction ofsoundpropagation theresult applications. When the air is flowing in the The oppositeistrueofforward flow from theacousticmedia. toward the center of the passageandaway silencer passagetendstofocusthesound decreases as the velocity profile in the high frequencies,however, theattenuation frequency insertion loss performance. At passages. This resultsinimproved low a longerperiodoftimetotravelthesilencer decreases slightly,causing thesoundtotake sound wave theeffective speedofsound air flowsintheoppositedirectionof flow conditions, when theIn reverse application. include areturnairsystemoranexhaust the noise. Examples of these conditions the silencerinoppositedirectionof indicate that the air is flowing through flowornegative(-) The termsreverse supply airsystemorontheoutletofafan. is traveling. These conditionsoccurina silencer inthesamedirectionsound indicate thattheairisflowingthrough The termsforward(+)flow floworpositive loss. velocity itisknownasdynamicinsertion include theeffects ofairflowdirectionand will provide. When insertion lossvalues insertion loss performance that asilencer sound istravelingwillhaveanaffect onthe a silencer inreference to the direction The direction and velocity of air flow through Effect ofFlow onSilencer Attenuation PerformanceFactors Affecting Engineering Guide Control Noise

Inside Air Handler Inside Air Exhaust Applications Standard Ductwork Reverse Flow Forward Flow please visitwww F or moreinformation onadditionalimperial andmetricsizes, .priceindustries.com orcontactyourlocal Price representative.

M-17

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL M-18 corresponding systemeffect correction factor. increase fromthecatalogedsilencerperformance. To obtaintheinstalledpressuredrop,multiplycatalogeddropby of one of these seven elements, the actual pressure drop will duct diameters When a silencer is installed within 3 to 4 equivalent Below arecommoninletconditionsthatasilencermaybeinstalleddownstreamof, alongwiththeircorresponding correction factors. Silencer InletConditions DuctDiameter=SquareRootEquivalent [(4xDuct Width xDuctHeight)/π] 0.35 in.w.g., withthecorrection appliedtoensurethatasilencerperformsasintended. factors of the silencer inlet or outlet. 4 duct diameters The ASHRAE Handbook recommends the pressure drop across a silencer not exceed provides correction that can be applied factors to the pressure drop of a silencer for various duct elements at a distance within 3 to however, onbothsidesofthesilencershouldbeadesigngoal. aminimumof3to4ductdiameters The ASHRAE Applications Handbook silencer andnolessthan10 downstreamofthesilencer. ductdiameters Inactualapplicationstheseconditionsareoften notpossible; Standard E-477, to which upstream of the are tested, states that there shall be straight duct of no less than 5 duct diameters silencers an elementwillhaveonperformancedependsthetypeofanditsdistancetoinletoroutletsilencer. The ASTM located tooclosetothesilencerinletordischarge. The effect oftheseelementsonasilencer isknownas “system effect.” The effect that Elements inaductsystem,such aselbows,tees,andtransitions,canhaveanegativeeffect ontheperformanceofasilenceriftheyare Installed Pressure Drop, System Effect PerformanceFactors Affecting Engineering Guide Control Noise cataloged performance data. result inamoderatedeviation from applied. This typeof installationwill pressure dropfactorof downstreamofafan, diameters When asilencerisinstalled3to 4duct performance data. result inaslightdeviationfromcataloged factor of with turningvanes,apressuredrop downstreamofaradiuselbow diameters When asilencerisinstalled3to4duct cataloged data. performance thatisverysimilarto This type of installation will result in ductwork upstream of the silencer. ofstraight have 3to4ductdiameters The desiredinstallationforasilencerwill 1. StraightUnobstructedDuct 4. RadiusElbow with Turning Vanes 7. Fan Discharge 1.05 shouldbeapplied. This will 1.3 shouldbe cataloged performancedata. will result in a moderate deviation from drop factorof without turningvanes,alargerpressure downstreamofaradiuselbow diameters When asilencerisinstalled3to4duct performance data. result inaslightdeviationfromcataloged be applied. This typeofinstallationwill pressure dropfactorof withsmoothinlet,aintake/plenum downstream ofdiameters a free air When asilencerisinstalled3to4duct Vanes 5. RadiusElbow withNo Turning 2. Free Air/Plenum withSmoothInlet please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, 1.1 should beapplied. This 1.05 should

cataloged performancedata. result inamoderatedeviationfrom be applied. This typeofinstallationwill pressure dropfactorof with asharpinlet, intake/plenum downstream ofdiameters a free air When asilencerisinstalled3to4duct data. deviation from cataloged performance of installation will result in a moderate factor of elbow, anevenlargerpressuredrop downstreamofamitereddiameters When asilencerisinstalled3to4duct 3. Free Air/Plenum withSharpInlet 6. MiterElbow 1.3 shouldbeapplied. This type © Copyright P 1.1 to1.3 should rice Industries Limited2014.

©Copyright Price Industries Limited2014. Installed pressure drop=0.21x1.3 x1.4 =0.38in.w.g. Therefore: Outlet correction factorforanabruptdoubling ofductarea=1.4 Inlet correction factorforamiterelbow=1.3 Pressure dropof therectangularSilencer=0.21in.w.g. Installed Pressure Drop=CatalogedPressure DropxInletPressure DropFactor xOutletPressure DropFactor multiply thepressuredropbycorresponding correction factors. fpm. shows apressuredropof0.21in.w.g. at2000 To determinetheinstalledpressuredropofsilencerincludingsystemeffect, downstream. Fromdoubling of the duct area 2 duct diameters the catalog or software selection program, a rectangular silencer model upstreamandanabrupt Determine theactualpressuredropforarectangularsilencer installed withamiteredelbow4ductdiameters Example corresponding systemeffect correction factor. increase fromthecatalogedsilencerperformance. To obtaintheinstalledpressuredrop,multiplycatalogeddropby When a silencer is installed ofwithin one duct of3 todiameters these 4 equivalent seven elements, the actual pressure drop will Below arecommonoutletconditionsthatasilencermaybeinstalledupstreamof, alongwiththeircorresponding corrections factors. Silencer OutletConditions PerformanceFactors Affecting Engineering Guide Control Noise cataloged performancedata. result inamoderatedeviationfrom applied. This typeofinstallationwill drop factorof upstreamofafan,pressure diameters When asilencerisinstalled3to4duct performance data. result inalargedeviationfromcataloged factor of with turningvanes,apressuredrop upstream ofaradiuselbow diameters When asilencerisinstalled3to4duct cataloged data. performance thatisverysimilarto This type of installation will result in ductwork downstreamofthesilencer. ofstraight have 3to4ductdiameters The desiredinstallationforasilencerwill 11. RadiusElbow with Turning Vanes 14. Fan Inlet 8. StraightUnobstructedDuct 1.5 should beapplied. This will 1.2 to1.4

shouldbe cataloged performancedata. This will result in a large deviation from drop factorof without turningvanes,alargerpressure upstream ofaradiuselbow diameters When asilencerisinstalled3to4duct from catalogedperformancedata. of installation will cause a large deviation factor of area of the duct work, a pressure drop that abruptlydoublesthecrosssectional upstream ofaducttransition diameters When asilencerisinstalled3to4duct Vanes 12. RadiusElbow withNo Turning Doubles AreaAbruptly Duct 9. please visitwww F or moreinformation onadditionalimperial andmetricsizes, 1.4 .priceindustries.com orcontactyourlocal Price representative. shouldbeapplied. This type 1.9 shouldbeapplied.

performance data. in alargedeviationfromcataloged 2.0 shouldbeapplied. This willresult an even larger pressure drop factor of upstream ofamiteredelbow, diameters When asilencerisinstalled3to4duct factor of expansion/plenum, apressuredrop upstreamofanabrupt duct diameters When asilencerisinstalled3to4 data. deviation from cataloged performance type of installation will result in alarge 10. Abrupt Expansion/Plenum 10. Abrupt 13. MiterElbow 2.0 should beapplied. This M-19

ENGINEERING GUIDE - NOISE CONTROL ENGINEERING GUIDE - NOISE CONTROL M-20 can beusedwith centrifugal fans aswell. types offaninlet anddischarge that silencers the discharge silencer. There are several other fan byproviding staticregain attheoutlet of but canalsoimprove theperformanceof designs not only greatlyreducefannoise, that is “off theshelf.” These customsilencer the fanitself, ratherthanutilizingasilencer silencer designthatcorresponds directlyto In theseinstances,itisimportant tocreatea fan noisedirectlybeforeorafter anaxialfan. In somecasestherewillbeaneedtosilence 5. CloseCoupledtoFan office spaces. manufacturing plantfromenteringadjacent meeting rooms,or to preventthenoiseofa speech transferbetweenadjacentoffices or spaces. Itisoften necessarytoeliminate with pressuredifferentials betweentwo sound transfer inductwork that isdealing areusedtoreduce Instead, thesilencers typical supplyorreturnairductingsystem. applications wheretheyarenotpart ofa may also be used inDuct silencers 4. Speech /Equipment Noise control valves,orexhaustfans. terminal units,fanpoweredboxes, dampers, far fromthemechanical room,such as attenuated noisegeneratedbyductelements This canbeduetospaceconstraintsor required closertotheoccupiedspace. Sometimes noise control products are DuctTerminations 3. the building. occupied spaceofeach floorin respective dealt withbeforethenoisemoves intothe riser branches, thenoiseconcern canstillbe downstream. are placed in When silencers the needtoattenuate thenoisefurther at thesourceofnoise,which creates It isoften notpracticaltoinstallsilencers 2. RiserBranches the building. noise from propagating through therest of eliminate both airborne and structure borne the noiseatsourcecanalsohelpto sound attenuation downstream. Attenuating reducing oreliminatingtheneedforfurther used toattenuate noiserightatthesource, of airhandlingequipmentaretypically placedattheinletand/ordischargeSilencers 1. Inlet/Discharge of Air Handler noise levelsintheoccupiedspaces. to the occupied spaces, and the required location ofthemechanical roomwithrespect by thetypeofequipmentbeingused, systems. The choice of location is determined silencer locationsthatareusedinHVAC achieved. Listedbelowaresometypical location thedesiredresultswillnotbe system. If the silencer is installed in a poor areanimportantSilencers part ofanHVAC Silencer Location Location inSystem Engineering Guide Control Noise please visitwww.priceindustries.com orcontact yourlocalPrice representative. For moreinformation on additionalimperialand metricsizes, 5. CloseCoupledtoFan h /Equipment Noise 4. 3. 2. 1.

Speec Inlet/Disc Duct TerminationsDuct Branches Riser harge of Air Handler

©Copyright Price Industries Limited2014. is fullyattenuated. from breakingoutofthesilencerbeforeit material mayberequiredtopreventnoise mechanical roomwall, butaheaviergauge the silencer should again be located at the located outsidetheroom.Inthissituation is notavailable,thesilencermayneedtobe adequate spaceinsidethemechanical room just before the mechanical room wall. If the silencerisinsidemechanical room, When thisisthecase,bestlocationfor located atthewall ofthemechanical room. spaces. However, aretypically firedampers concerns of breakout noisein occupied the mechanical room, which eliminates the sound createdbytheequipmentas it leaves wall. This locationremoves theunwanted silencer isstraddlingthemechanical room mechanical room, the ideal location for the by fans and other equipment located in a When removing airbornesound created Mechanical Room be aconcern. noise breakout through the duct walls will through theductsystemtoanareawhere the sound before it has a chance to travel This willallowthesilencertoattenuate as closepossibletothenoisesource. HVAC system the silencer should be located When tryingtolimitbreakoutnoiseinan a CL1silencer. casing of a HTL2 silencer as compared to therefore lessnoisewillbreakoutofthe the highesttransmissionlossperformance, construction classes. The HTL2casinghas of different rectangularsilencercasing the rightshowstransmissionlossvalues in thewalls. The transmissionlosstableto casing, and the amount of acoustic media the gauge ofmaterialusedtoconstructthe including theshapeandsize ofthesilencer, able to break out of the silencer casing, contribute to the amount of sound that is is calledbreakoutnoise.Many thingswill walls oftheductworkandsilencercasing Sound thatisallowedtopassthroughthe Breakout Noise Location inSystem Engineering Guide Control Noise

please visitwww F or moreinformation onadditionalimperial andmetricsizes, Transmission Loss Class HTL1 HTL2 CL1 CL2 Construction .priceindustries.com orcontactyourlocal Price representative. Gauge 22 18 16 10 63 Hz 25 27 28 31 125 Hz 26 28 29 33 Transmission Loss(RectangularSilencers) 250 Hz 28 30 31 34

500 Hz 30 32 33 36 1K Hz 33 35 36 38 2K Hz 37 38 39 42 4K Hz 40 41 42 45 M-21 8K Hz 40 41 42 45

ENGINEERING GUIDE - NOISE CONTROL