Basic Principles of Suspending Loudspeakers

8/2/2019 Basic Principles of Suspending Loudspeakers

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Basic Principles for Suspen ding Loudsp eaker Systems

Introduction:Contractors and sound installers hang loudspeakerequipment in public meeting places and performing artsfacilities as a matter of routine. This Technical Notedetails rigging practices appropriate for the soundindustry, and is intended to familiarize readers with theproper hardware and techniques for hanginginstallations. To insure a safe installation and to protectworkers on the job site, this work should be undertakenonly by persons with knowledge of the proper hardwareand safe rigging practices.This Technical Note contains data for rated capacity forvarious pieces of hardware, based upon manufacturersspecifications for products in new condition and freefrom defects, either apparent or hidden. All rated badvalues, unless otherwise noted, are for in-linepull-along the centerline of the item. It is theresponsibifii of the installer to inspect and determinethe actual condition of the equipment used, and toincorporate design factors appropriate to the local jobconditions. Where doubt exists as to the actual conditionor ratings of hardware, it should not be used.Load ratings shown herein are are based upon usualenvironmental conditbns. Further consideratbns mustbe given to item selection when unusual conditions areencountered. All products used for hanging purposesare subject to wear, misuse, overloading, corrosion,deformation, alteration and other usage factors which

may necessitate a reductiin in the products capackyrating or a reduction in its design factor. lt isrecommended that all products used for rigging and

hanging purposes be inspected piir to each use as abasis for determining if the product may continue to beused at its rated capacity, or removed from se&e.Welding of or to load supporting parts and structure canweaken the part or structure, and should be performedonly by persons with knowledge of metallurgy and theintended use of the materials being welded.The material presented in this Technical Note has beenassembled from recognized engineering data and isintended for informational purposes only. None of theenclosed information should be used without firstobtaining competent advice with respect to itsappfiibilii to a given circumstance. None of theinformation contained herein is intended as arepresentation or warranty on the part of JBL. Anyonemaking use of thii information assumes all liabifii arisingfrom such use.All information herein is based upon materials andpractices common to North America and may not directlyapply to other countries because of differing materialdimensions, specifications and/or local regulations.Users in other countries should consult with appropriateengineering and regulatory authorities for specificgu-


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Contents: Design Factor:IntroductionDesign FactorShock LoadingCenter of GravityRopes

Rope TerminologyKnot EfficiencyBendsBinding KnotsLoop KnotsHitchesWire RopeWire Rope ConnectionsSlingsLoad Angle Efficiency

1223333334456789991011131314151516

Design factor is a term used by the rigging industry todenote theoretical reserve capability. The rated capacity /of all lifting and hanging equipment b based upon thenominal strength of the equipment reduced by thedesign factor.

Design factor is a number representing the fraction ofequipment nominal strength chosen to be appropriatefor the particular application.RATED CAPACITY = NOMINAL STRENGTHDESIGN FACTORExample:Design factor = 5Rated capacity of equipment is only l/5 of its nominalstrength.

HardwareShacklesBoltsEye Bolts

Attachments ToThe Installation

.

LoudspeakersEnvironmentHangtng A SystemRules for Safe LiftingConclusionGlossary of Rigging Term sReferencesFigures:1 Rope Termincbgy 32 Tying Bowline 43 Tying Clove Hitch 44 Wire Rope Bend Efficiency 55 Wire Rope Clp installation 66 Load Angle Efficiency 87 Calculating Sling Tension 88 Screw Pin Anchor Shackle 99 Bolt Grading 1010 Eye Bott Fasteners 1011 Shoulder Eye Orientation 1112 Cabinet Reinforcement 1113 Miter-Fold Construction 1214 Attemate Miter-Fold Construction 1215 Typical Rigging Chain 14

Tables:1 Wre Rope Clip Data 62 Wire Rope sling Data 73 Screw Pin Shackb Data 94 SAE Grade 5 and Grade 8 Bolts 105 Forged Shoutder Eye Bolt Data 11

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Minimum design factors vary according to the application,and may be regulated from bcatbn-to-location. Nodesign factor discussed herein shoutd be assumed torepresent a recommendation on the part of JBL. Usersmust assume all responsibitii for the determination ofdesign factors suitable for local conditions.Shock Loading:When a bad is suddenly moved or stopped, its weightmay be magnifii many tknes the original value. This isknown as shock loading. Shock bading of liftingequipment shouid be avoided at all times.Shock bads will usually be instantaneous and may goundetected unless equipment is visibly damaged. Noequipment is desiined to compensate for poor riggingpractices or foolish planning, however. Every tool andpiece of equipment has limitations. Safe workingpractices demand that these limitations he known andfully understood, and that they never be intentionallyexceeded.A 900 pound budspeaker cfuster dropped four inchescod cause a shock bad of 4500 pounds if the riggingwere attached to rigid structures and of a material thatwoukf not stretch. However, because all rigging willstretch under shock bading, the exact shock bad on apiece of equipment isnt easily predicted. To protectpeople and property, all tools and equipment shoutd belimited to stresses that are several times smaller than theirminimum breaking strengths.Although shock bading of equipment and structure is >usuaity confined to iiing and instaliatbn, it should aisobe recognized that other forces (such as earthquakes)


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can impose shock loads upon structures many times thatof the static bad. It is therefore imperative that hardware

nd structures be capable of supporting several timesweight of the equipment b e in g h u n g .

Center of Gravity:The center of gravity of an object is the point at which theweight of the object acts as though it were concentrated.It is the point at which the object may be completelysupported or balanced by a single force.The center of gravity of a regularly shaped object may beestimated fairly accurately by determining its approximatecenter. Finding the center of gravity of irregularly-shapedobjects can be more difficult, but it is necessary,nevertheless. A bad will always hang from its attachmentpoint through the center of gravity. It is important tovisualize thii before making a Mt.All loads to be liied should be rigged above the centerof gravity in order to prevent tipping and possiblehazards to equipment and workers. The liiing forceshould afuvays be located above the center of gravity andexert a straight vertical pull to prevent swinging of thebad.1Ropes:Before diissing actual rigging hardware and systems,it is appropriate to examine ropes and their proper use.Ropes are used for many rigging functions. Althoughsynthetic ropes of great strength are available, mostcodes prohibit their permanent use in rigging for a varietyof good reasons. Nevertheless, ropes are necessary tolift approved cab& fixtures, tools and equipment intopositiin.In the interest of safety it is important that ground workersbe familiar with the proper use of rope and a few basicknots used in rigging.Rope Terminology (Figure 1):1. The Standing Part is the end of the rope which isinacttve.2. The End is the part of the rope that is free--typicallythe part in whll knots are tied.3. A Bight ls the central part of the rope between thestanding part and the working end.1. An Overhand Loop is formed by crossing the end over

the standing part.5. An Underhand Loop is made by crossing the end

under the standing part.6. Tightening. Once formed, a knot must be tightenedsbwty and with care. Failure to do so could result in atangle, or an untrustworthy knot.

Standing Part

Endp=

Bight

Overhand UnderhandLoop Loop

Figure 1. Rope Term inologyKnot Efficiency:Knot efficiency is the approximate strength of a rope witha knot as compared to the full strength of the rope. It isexpressed at a percentage of the ropes rated capacity,and refers to the stresses that the knot imposes uponthe rope. When a knot is tied in a good rope, failureunder stress is certain to occur at the knot. This isbecause bends result in uneven stresses upon thefibers, with the outsides of the bends taking a greatershare of the bad. lt follows that the tighter the knot, thegreater the percentage of the total bad that is carried onfewer fibers.Bends:Bends are used to join two pieces of rope, usuallytemporarily. Typical knot effiiiency is 56%. Bends offersome advantage over binding knots, as they resistuntying when slackened or jerked. The Sheet Bend is asimple knot to tie, consisting of an overhand loop on onepiece, with the second rope end fed up through the loopfrom behind, around the standing part of the first ropeand back down through the loop from the front.Binding Knots:Binding knots are also used to join two pieces of rope. Ingeneral, binding knots have a knot efficiency of 50%, butcan untie easily when a free end is jerked.In the square knot, the end and the standing part of eachline tie together through the btght of the other. In theuntrustworthy granny knot, the end and the standingpart are separated by the bight. The granny knot is 3


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particularly treacherous in that it will appear to besecure--only to slip under load. The thief knot isdeceptively similar to the square knot, but has the twoloose ends coming out of the opposite sides, instead offrom the same side as in the square knot. This knot isalmost certain to fail under bad.Loop Knots:Loop knots are used to hold objects where security is of

rigging, wont slip, yet is easily tied and untied. lt may betied in the hand or used as a hitch and tied around anobject, usually for lifting purposes (Figure 2).To tie: Make an overhand loop with the end toward you(Step 1). Pass the end up through the loop from behind(Step 2) then up behind and around the standingpart-then down through the loop again (Step 3). Drawup tight. The bowline has a knot efficiency of

paramount importance. The bowline, widely used inapproximately 60%..

Step 1

(standing part)

Form an overhandloop in the rope...(end)

Step

. .pass the end upthrough the loopfrom behind... I . .feed the endbehind and aroundthe standing part...

loop again...

Figure 2. Tying Bowline

Hitches:Hitches are used for temporary fastenings that untiereadily. They are generally tied directly around theobjectinstead of first being tied in the hand and thenplaced over the object. Hitches must be drawn up tight,as they have a tendency to slip if loose.

The clove hitch (Figure-3) consists of two underhandloops, which may be tied in the hand and slii over anobject at any point along the length of a rope. Knoteff&ncyis60%

Figure 3. Tying Clove Hitch.

. .plaoe the bpsover the object...

. .draw up tight

Form wo underhand kops...


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Wire Rope:Vast wire ropes are constructed from plow steel,nproved plow steel, or extra improved plow steel wire.

e wires are woven into strands, which are woven toform the wire rope. Typical wire rope may consist of sixstrands wound around a central core. The central coresupports the outer strands and helps to prevent the ropefrom crushing under stress. Wire rope core materials maybe fiber (abbreviated FC), independent wire rope(abbreviated IWRC), or wire strand (abbreviated WSC).Wire rope is classtfied by diameter, number of strands,number of wires making up each strand and core materialconstruction. Rope diameter is measured at its widestdimension. Wire rope is also classified according to thedirection the strands and wires are twisted. The distancealong the rope required for a strand to make one fullrevolution is one Lay.In RigIft Regular Lay c ons truc t ion ,Strands twist to theright, wires twist to the left.R&M Lang Lay construction finds both strands and wirestwisting to the right.Leff R8gidaf Lay ropes are constructed with strandstwisted left and wires twisted right.

Left Lang Layconfiiuration twists both strands andwires left.Regular lay ropes are less susceptable to crushing anddeformation because the wires lii nearly parallel to therope. Lang lay ropes twist the wires across the directionof the rope, and are therefore more flexible and resistant

to abrasion damage. If both ends of a lang lay rope arenot fixed, however, it will rotate severely when underload.Most sound and stage rigging requirements are easilyhandled by two wire ropes: 3/V and l/2 6 X 19 IWRCclassification. These ropes in improved plow steel have anominal strength of 13120 pounds and 23000 pounds,respectively. If we assume a design factor of 5, ratedcapacities become 2600 and 4600 pounds.Just as knotting a fiber rope reduces the nominalstrength of the rope, bending of a wire rope also resultsin a reduction in its nominal strength. The tighter theradius of the bend in the rope, the greater percentage ofthe bad is concentrated on fewer wires and strands. Thisresults in a reduction in the ropes nominal strength andrated capacity.Figure 4 shows the relationship between wire ropeeffiiiency and the ratio of bend radius to rope diameter.The chart is for 6 X 19 class wire ropes. Note that thechart is nearly asymptotic as the bend radius approachesthe rope diameter--such as might occur in wrapping abeam with a basket sling. Overloading of a cable underthese conditions could result in irreparable damage tothe wire rope, or a possible failure.Experienced riggers always pad beam edges withsofteners before wrapping the beam with a sling, andavoid sharp or jagged edges that could possibly injurethe wire rope or sling. Heavy burlap or thick polyester isusually used for this purpose.

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2 6 10 14 18 22 26 30Rat io f BendFtadiuso Wm Fbpe Diameter

Figure 4. Wire R ope B end Efficiency

34 38

5


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Wire Rope Connections:In the touring business, wire rope is em ployed or slings,usually in leng ths of 5,10,20,30 and 50 feet. Each endof the sling is terminated n a swa ged or zinccast eye,which yields a conn ection hat is at least as strong as thewire rop e itself. Thii type of connection is rated as 10 0%effii ient-the strength of the entire cable assembly sthat of the wire rope.Theseslings are alsoclean nappearance,won t tear flesh or do thing in the process ofhandling, and do not requ ire periodic re-toqueing.Custom ength slings are easily obtained for perm anentinstallations.Clips are used when eyes m ust be fabricated o wire ropein the field. Two types of dip are available or thispurpose: U-bolt or Crosby dips and J-bolt or fi igripclips. Only forged clips should be used. Correctly used,clips result in a co nnection efficiency of 80 ?! (e .g., if thewire rop e has a rated capadty o f 4600 tbs. and clips areused to fabricate an eye, the rated capacity of theassemb ly would b e 3680 lbs.).lt is important hat clips be properly nstalled. Failure o d oso coukf result in a reductiin of rated capadty. U-bo ltclips can be installed wrong . The dip saddle must beinstalled over the live end of the rope to prevent dam ageto the ba d-bearing com ponent. J-bolt dips cannot beinstalbd backwa rds.Always use the prope r size dii andthimbles or the wire rope (Figure 5).The proced ure or installing wire rop e clips is:1. Refer o Ta ble 1 for the num berof dips, dip spacingand tightening torque.

Diameters1

2. Determine he length of rope required o turn ha& forproper dip spacing and thimble size. Always use dthimbles.

Table 1. Wire Rope Clip Data3. Attach he clip u rthestrom the loop, a distance fromthe end of the rope equ al to the w idest part of the clip.Tighten securely.4. Ap ply the second dip as close to the thimble aspossible. Turn nuts on firmly, hut do not tighten.5. Add the rema ining dips betwee n the first two at thespacing ncremen ts rom Ta ble 1. Turn nuts on frmtly, hutdo not tighten.6. Apply a li iht stress on the rop e to equ alize he tensroi+on all clips, re-positionclips if required, hen tighten allnuts to the specified torque.

UseProper SueWire T ThimbleForAll ye SpliiAIICI SaddlesonLiveEndofRope Figure 5. Wire Rope Clip Installation

7. Load the cable and retighten all nuts to the spedfiedtorque setting. Do not over-tighten. This step isessen tial, as the w ire rop e will stretch stiihtty, redu cingits diameter when loaded.

necessary. Failure o make erminat*bns n accordancewith the ab ove instructbns, or failure to p erbdk&ycheck and m -torque as recommendedwill res ult in areduction in effbfency rating. This requiremen tmakesswage d or zinccast eyes an attractiveattemattve or8. Inspect periodically and retighten as necessary. permsneltinstalations..BM MW &@ nspec t periodiilly and retighten as

6


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2-Leg Bridle Hitchand Singlo Basket Hitch

Table 2. Wire Rope Sling Data

Slings:A sling s a b oped lineused o hoist,bwer or carrysome thing. lings n soundsystem igging re generallymade romwire ropeor polye ster iber,and are used ohitchbads to varbus par& in the chainof riggingcompo nents. able 2 showsseveralvariations f wireropeslings nd tabulates atedcapa&ies for eachconfigurationf hitchbasedupon6 x 19 classiiibn,Improved33w Steel, WR C at an assumed esiin factorof 5.Polyester r synthe tic iberslingsenjoyconsiderableor the rigging f portable oundand stagsequipment. hey offeradvantages n that hey are liiht in

weight, easy to handle,will notdamagedelicate ndunusually-shaped aterials nd, depending pon heindiial sling,are strongerha nwire rope.They alsoare better hanwire rope or working ight adiis bends.SpanSerY pmducb are typical of the rangeof syntheticfiberslingsavailable or thii prefer to themanufactureh ata forcapadtyrating n formation,s itcan vary romproduct o ptrduct.A noteof cautionregarding yn thetic lings: olyester abric s relativelypoo r n its ire rating6-comult local building codeauthorities before installing.


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Load Angie Efficiency:Loadangle s the angle.between he bad (horizontalsurface)and the sling.Figure6 illustratesheeffectsof bad angleeff ciincy usinga two-legsling o hangone JBL 4646bw frequency ystem.Thebad angleaffects he slingtension nversely.As thebad angle s reduced rom90 degrees o 0 degrees,the sling ension ncreasesfrom he slings hare of thebad to an infinite atue.

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80 45O 30Figure 6. Load Angle Efficiency

l o o

The sine of the bad angle s numericallyhe LoadAngleEffbiency, .g., a 30 degreeslinganglewill have a Load_ _ -___ _Angle Etticiency f 50% (Sine 30 = 0.5). A LoadAngleEffbiencyof 60% means hat he sting ensionwillbetwice that of the stings hareof the actualbad. The JBL4646 weighsapproximately 10 pou nds.Using woindependent lings,each will he tensioned o 55pounds. f we were to bridle he two sling egssuch hat

each leg were to forma 30 degreeanglewith hehorizontal urfaceof the cabinet,each leg wouldhe_ _tensioned o 110 pounds.As the angle between heslingand the horizontal urface s deminished,he slingtensionwill ncrease n inverseproportiono the sineofthe bad angle.It is importanto recounize hat the sling ension ffectsall of the ha&are thatcompriseshe slingassemhly, ncludinghe attachmen t oints.Thismay result n excessive oading f hardware,especially t the pointof attachmen to the d

1 2 5 0 bs.

Sling ensionsmay he directly alculatedro mphysicalmeasurementsFigure7) .A budspeakercluster o he liied w eighs1250pounds.Usinga two-legsling, he distance A)from he tii point o each anchorpoint s 46inches.The distance B) from he tii p oint o thehorizontal urface s 24 inches.The tensiononeach leg of the slingwill he A-[46]divided yB-(247 times /2 the bad (2 legs)= 1260pounds.This representsLoad AngleEfficiency f 50%. These cabulatbns shouldbeperformedor each bad to be lied in order opreventoverbadii of hardware r a reductionof dssiin factors.Bit the loudspea ker luster s being ifted roma singlepoint,guy lineswillhe required ostab&etheasserWyfrommtattng.

Flgun 7. Calculating Sling lenaion (aw text)g


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Hardware:There are as many diierent sources and qualii levels ofhardware as there are potential vendors for soundsystems, perhaps even more. lt should be noted,however, that the consequences of exercising poorjudgement in selecting hardware for rigging are notqualitative. In spite of thii fact, purchase decisions withrespect to hardware are often fast-minute items left toinstallers and technicians having liile or no knowledge ofsafe rigging practices.To the uninitiated, many similar hardware items appearidentical, yet may be orders of magnitude diierent interms of their load capacities. The highly competitivenature of the retail hardware and building-supplybusiness in the United States has generated a nearly

\ ;endless supply of fasteners of unknown (and suspect)quality and consistency.- Just as a chain is no strongerthan its weakest fink, it is a matter of the utmost prioritythat all hardware used in a rigging chain be of knownquality and strength. Thii is less a matter of expensethan one of good planning, as the use of bad-ratedhardware will make an insignifiint difference-in the totalcost of an installatbn.Almost without exception, bad ratings for hardware arefor axial loading only-a straight pull abng the axis of thefiiing. Failure to use a device in the manner in which it isintended to bs used can seriously weaken the part andrender an installation unsafe. ft ls the responsibifii ofdesigners and installers to make proper use of hardwareand hardware systems.

Shackles:Different types of shackbs are available for a variety ofapplications. The type most commonly used in soundsystem rlggii is the Screw Pin Anchor Shackle (Figure8). These parts are most often used to join SpanSets orslings to eye bolts or additional slings. Table 3 fists ratedcapacity information for Screw-Pin Anchor Shackles.Figure 8.

screwIAnchor Shackfe

I l - 1 1 4 l - 3 1 6 1 6 , 4 0 0Table 3. Screw Pin Shackle Data

Onlv b&rated fomed carbon-steel shac es should hil.used for nooing, The load rating will be stamped on thebody of the shackle.Screw Pin Shackles should be snugly finger tightenedonly. lf tools are required to seat the shackle pin it meansthat the threads are damaged, and the part should bediscarded.Shackles should always be loaded pin-to-end-never otheir sides.The pin end of the shackle should not be allowed tostraddle a moving rope, as friction could loosen the pin.Do not substitute bolts for shackle pins, as the pins areforged and considerably stronger than machine bolts.Always use packing washers to center narrow loads onthe pin. This will prevent the shackle from being pulled aan angle which will weaken and possibly damage thefiiing.Bolts:steef: comm ercial iron that contains u&on in anyamoun t up to about 1.7petcent as an essential albyingconstituent, is malleable when urn9er uitabbconditbns, and is d&inguished from cast iron by itsmaleabiMy and bwer cat&on content...resenWing steel-Websters Third New International DictionaryGiven thii rather broad definltiin of steel, there ls awide latitude for specific albys and the consequentialtensile strength and hardness that may be encounteredln.a steel bolt. When ungraded bolls are used in rlggingapplbaGins, unknown albys can result tn a fastener thatmay be unrefbble under stress.


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Fortunately, graded bolts are easily identified. Figure 9marks for SAE grade 5 and SAEists rated capacities for SAE

. SAE GradeUnknown

SAE SAEGrade 5 Grade 8

Figure 9. Bolt Grading

Area at Grade 5 Grade 0Thread Rated RatedDiameter Rcct capacity Capacity(inches) (sq. i nches ) w - ) V W

Table 4. SAE Grade 5 and Grade 8 Bolts

fasteners come in several varieties (Figure 10):

Lag-Screw Eye Formed Eye Bolt

Lag-Screw Eyes out threads into wood and rely uponthe strength of the wooden threads to carry the load.The uitimate strength of the bond depends upon thestrength of the material and total surface area threadedinto it. Wood or wood fiber makes untrustworthy threads

dand should m be used to support overh8ad loads.Formed Eye Bo/ts consist of steel rod bent into an eyewith a machine-sorew threaded shank. These productsare widely available at hardware counters anddo-it-yourself building material outlets. These productscome from a wide variety of domestic and offshoresouroes, are unmarked, and may be soft or brittle. Theeyes have a nasty habit of pulling straight or snappingwhere the ourvature of the formed eye meets the shankunder modest loads. Formed eye bolts must beconsidered untrustworthy and should not be used forrigging purposes.Note: Often eye bok are we&d closed to preventopening under bad. This pa&8 can damag e themetalb@al stfuctufe of an already suqpect fitting,CaUSinQ he b/t t0 bS8 resista/% t0 breakage UnderStf8SS and ~%?suttn an even more untrustwotthy part.Plain Pattern Forged Eye Bolts are designed for straightpulls only, and are trustworthy to support vertical loads.Note that plain pattern eye bolts should never be usedfor angle pulls. The rated capacities for plain pattern eyebolts will be the same as for shoulder bolts under vertical

dload.Fbrged Shoukler Eye Bolts are preferred for allappliins, especially those in which angle pulls arelikely to be encountered. Note that the rated wpaofty forshoulder eye bolts is reduced substantially for anglepulls. Note also the correct orientation of the bolt forangle pulls (Figure 11). Loading at angles greater than45 degrees from the vertical axis is not reoommend8d.Table 5 lii rated capacity information for forgedshoMereyeboRs.

Formed Eye Bolt Plain PatternWelded Closed Eye Bolt

ShouMerEye Bolt


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11 4 500 27 5 17 5 12 5.:.:j:;:.:.:.:....:_L,.:...:.,.:.,.:.,.:;;.:-:.~._:_:_._:_:_.: . .A _....A... : :: . ;._..... ..:.. .:::.,..;., :,........::..:.:/.:.:.,_::.:.~:.....:.::.:: ..:_ ..:.:;.:.:.:-:.:.:.~:-:~:~:~:::~:~:~:~~j::~~:~~:.;.:,..:._:...>>:_.:::. __,_, ,./... .~:_:_:_:_:_:_:.::..-:..:.:.~.:.:.:.~:-.:.::.i..:::::::::: :,.;::,:~~~~~.~~;:I:I:I:I;.l.,i ,,.,.,.~. :;:;..~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:3f0 1,200 660 420 30 0. .:.~,~.:::::::::::._.::::~.:.;:;:;:::~:,; .~.::~:::::::~:..~,-.:.::.j;j:: ..:.~,:j,:j_,::::~,~::-~.:..-/...i......~.~.~...~..~..~.~.~.~.~.~.~...~.:.:..~:~:~~.:.:.......::.:.:.: ..,.,--:..:: ._........_.::.::.:::::-:-:.:.:.:..~~..:. .. ._....,j.i,.,.,_::li{:::_:.:::.:.::,::.,,::.:::..._:_:_;:.:_~~~~~~~~~i~~~:~~~~~~~~~~~~~~~~~~~~~~:~.::.s/a 3,500 1,900 1,200 87 5. ._ _,._,......~.~.~___.::.:.-: ._.:_:_:_:_:_:_._:_:_;. .::. . : :... : :_ ,.,.......... . : :........ .. ._ i,...ii :~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:~.~

Table 5. Forged Shoulder Eye Bolt DataAttachments To Loudspeakers:Bolts, shackles, lipsand eye boltsall develop hegreateststrength long heiraxes-vertical orientationnhanging ppliitbns. It follows hat he safest ocationorhanging ttachment ointswill he at the topsof cabinetsto minim ize ngular tresses n hardwa re. hii requiresthat the cabinetbe strongenough o he safelyhungfrom ts top. Where multiple ncbsuresare needed, hiscan result n cabinetshanging romothercabinets. hiimake s he loudspeaker nclosure n integral a rtof thehanging ardware ystem.A five-to-one esign actor s generalty ssum ed orhanging ardware . t follows hat oudspeake r abinetsmL lst e capableof similar esign actors.Wfth heexception f the JBL ConcertSeries, ew budspeakersystems nd components re bad-ratedand suitable orhangingwithoutmodiibatbn.The secureattachment fhanging ardware s no assurancehat a cabinetwillno t. . .pullapartunder ts ownweight.An

. . .)Nalbenostraagarthanthe~nsmadefro m. . .3rd the IO- technrouew assemble t As ageneral ule,all woo dandwood-fiber oudspeakersystemsover 50 pounds equirestructural einforcemfor hangingnstallation. here are m anydifferentme thods f reinforcing abinets hat can provideacceptable afetymargins,wo of whichare shown nFttre 12.For plywoo d nclosures, anginghardware s shownbolted o steel reinforcem ent lates hat are securelyattached o the cabinet n a steel-wood-steelandwichn

cabinetSteel Comer Bracket

Sandwich Construction(Plywood Only)

Bolttocabinet6-8 inchspac@I,typical-4 sides

Cabinet

Steel GirdleConstruction

weld 4Placee) -Figure 12. Cabinet Reinforcement

confiiratbn. One comer s shown.All bad-bearingpanel ntetsectbns houldbe similarly einforced ithsteel plates.This reinforcement ethod s notsuitablfor wood iberor particle oardcabinets.Particlehoardand wood ibercabinets houldbeexternally einforced ithcontinuous teel strapor

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steel channel secured to the box so as toely surround the enclosure, capturing dadoed-in

back panels. This reinforcement method iss. lf the baffle board isnt

nto the side walls, the cabinet shouldnt beand an appropriate substitute found. Never relythe internal bond strenoth of oarticle board or

to carrv the weioht of a larae (over 5Q1 svstem,

systems are subject to the sameBecause they are small and

installers tend to make assumptionsprove unsafe in the long term. While

al failure of a small loudspeaker cabineta serious hazard, it can be avoided by

g conditions that could affect the choice of

Small loudspeaker systems often employassemblies, which usually attach to theVelcro or similar reusable fasteners. These

ues, while satisfactory for home use,be relii upon for overhead installation -in

places. Appropriate modiiitions are required.small loudspeaker systems employ miter-folded

board construction techniques (Figure 13). Aparticle board is grooved bngftudionally for

ng the baffle and back panel, milled transversely tomiter joints, then

by folding the sides around the back andel intersections before

is wrapped with elastic cordupon the integrity of the glue bonds at panel

and the internal bonding strength of thestructural integrity.

4 shows a variation of this constructionIn this example, the top, bottom, baffle and

and the completed sub-assemblyinto dadoed grooves in the side panels. Thii

Figure 13 . Miter-Fold Construction12

method of joinety enables the attachment of hanginghardware to the top, bottom or back (depending upontotal system weight), but the system should not besuspended from the sides.Many other variations in construction and joinery arepossible. lt is the responsibility of the installer to examinethe system and construction methods used to determinea safe attachment scheme for hanging hardware. In smallJBL systems that incorporate hanging hardware orattachments for hanging hardware, the locations

L

Figure 14. Alternate Miter-Fold Constructionprovided have been chosen on the basis of strength ofconstruction and the joinery methods used in the.enclosure. c

When particle board cabinets are to be suspended fromT-nuts and eye bolts, installers should be aware ofloading limits that attend this practice. New particle boardwill exhibit an internal bond strength of 80-70 psi (ASTMD-l 037). A 114-20 T-nut in 3/4 inch material will subtendapproximately 1.4 square inches of bonded surface,resulting in a nominal (breaking) strength of 85-98pounds. Using an assumed design factor of 5. themaximum axial bad on a single T-nut would become17-20 pounds. Reduce these factors by one-third forhalf-inch material. Thii is for particle board that is new orin new condition onfy. Clearfy, thii is M an acceptablesuspension method for large loudspeaker systems.

e w-typical temperature and humidiiyconditiins as encountered in a domestic residence oroffice environment. The resins used in the manufactureof most particle boards will not withstand prolongedexposure to moisture or high humidity. wide variations oftemperature will yield conditions of moisture saturationfollowed by evaporation, under which essential bondingagents will be leeched from the material. This processcan eventually result in a cabinet with lllle more strengththanamazker.


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The Installation Environment: Hanging A System:We have examined hardware systems and precautionarymeasures to ensure that the connections to the loud-speakers are made in a safe and secure manner. Whatremains is to properly hang the system in the installationenvironment.For new construction, the sound system contractorshould inform the architect of the planned hang pointsand the total weight to be concentrated on each point.The architectwill then be able to provide the necessaryload capacities and attachment fixtures as a part of thestructural plans and specifications. This informationshould be suoolied for each and event susoendedcomoonent. reaardless of size and weioht.The task becomes more difficult in existing buildings andstructures when adding sound facilities or remodelingexisting systems. Most projects are undertaken withoutthe professional services of an architect or structuralengineer. Under these circumstances, the soundsystem contractor is left to his own devices to render asafe installation.It is virtually impossible to predict the local conditions thata sound contractor may encounter in an installationenvironment. However, the following guidelines applyequally to any installation circumstance:

1. Never attach or suspend loads to/from a wall orceiling surface. Always make a secure attachmentto sfrucfufal members.

2. Be absolutely certain of the structural integrityof any member that is to be used to supportexternal loads-hidden structures can havehidden weaknesses.

3. Do Not rely upon nails or wooden threads tosupport overhead loads-nails, wood screws, lagscrews and lag screw eyes are untrustworthy.

4. Never assume anything. Owner or third-partysupplied suspension points may be inadequatefor the intended use.

5. Recognize your limitations. Seek help fromcompetent outside sources-architects, structuralengineers or rigging specialists+hen uncertainor in doubt.

6. Safety first. Public safety demands that thoseresponsible for placing equipment in potentiallyhazardous locations & so with full knowledge anduse of appropriate precautions and safetymeasures.

The first step in hanging a sound system is to obtainqualified advice about the load carring capacity of thebuilding or structure. The engineer or rigger will need tknow how much weight needs to hang where. If the loaisnt too heavy and youre not fussy, you may befortunate enough to be able to hang in straight drops.Figure 15 shows a portion of a such a hanging system.Although the example shown is a portable soundsystem, the principals involved are identical for fixedinstallations with the substitution of a one-leg sling forthe chain hoist. We will examine the rigging hardwaresystem, beginning at the top.The l-beam is shown wrapped with a SpanSet used as basket sling. The comers of the beam are padded withsofteners (burlap) to ease the tension of the outsidefibers of the sling. We have chosen a sling that is ofsufficient length to yield a 68 degree sling toad angle,which gives us a load angle efficiency of better than90%. Since our sling has a rated capacity of 7900pounds at an assumed 51 design factor, the sling willhave a rated capacity of 7900 pounds x 2 (basket sting90% (the load angle efficiency), or 14,200 pounds.An alternative sling is wire rope. Wire rope is preferred some venues and by certain riggers and fire marshallsdue to its ability to withstand greater heat than apolyester sling before failure in the event of fire. Whenusing wire rope around a beam, however, the bendradius often equals the diameter of the wire rope. Thisresults in a efficiency rating of 50%/L-the strength of thbasket (both legs) would be virtually the same as that osingle wire rope. Wire rooe beam-wraos need to bepadded carefullv,The two ends of the sling are then coupled with a l/2 x 19 wire rope sling assembly using a !Y8 screw-pinshackle having a working bad limit (rated capacity) of6500 pounds at an assumed 5:l design factor.Important: Carefully adjust shackles and slings toassure that the bad is carried by the end and the pin othe shackle. Do not allow the shackle to be turned so ato bad the sides, as the shackle will be weakenedconsiderably.The wire rope has a rated capacity of 4600 pounds at same 5:l design factor. This sling section may beomitted in venues with bw enough ceilings for the chahoists to bring the loudspeakers to trim.The chain hoist hook connects directly to the wire ropsling eye. Chain hoists come in a va riety of capacityratings and climbing speeds. Because we need to hanin many diierent locations, we have no desire to lii the

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Softeners (4 places)

Spat&P sling as basketforged, bad-rated shackle

chain hoiits into position each time by hand. RockyPaulson of Stage Rigging modified the CM hoiits tooperate upside-down and climb the chain. We choose abrace of Rockys 1 ton hoists. The rated capacity of thehoist is for Ming purposes and includes a generousdesign factor. The CM hoists also include a clutch whichwill slip if the hoist is overloaded. Both hoiit hooksshould he equipped with working safety latches, or besafety-wired (moused) closed to prevent the slings fromslipping out of the hook before commencing a lift.

1R6x1glVVRCwirerope sling a ssembly Below the chain hoist, the loudspeaker grid is carried bya two-leg SpanSet sling assembly to support the grid

front and back.

chain hoi hook (moused) Important: Do notuse a single sling to support a badcarried on two points-the sling could slip in the hook.Assuming a 45 degree bad angle for each sling leg, thebad angle effiiency is 70%. Each sling leg has a ratedcapacity of 5280 pounds, therefore the sling capacitybecomes 7390 pounds, or 3695 pounds per leg.

Chain Hoii

The sling attaches to forged carbon steel 3/4 shouldereye bolts using 5/8 shackles, described previously.Each eye bolt is limited to a rated capacity (tension) of1300 pounds at a 45 degree pull angle. This tension willbe realized when each eye bolt is loaded to 900 poundshecause of the 70% bad angle efficiency. Clearly, the d

chain hoii hook (moused) eye bolt ls the weakest link in this rigging chain.

forged, bad-rated shackles (2)forged, ye bolts (2)

loudspeaker fittingsrs (3)(3 )

Cur budspeaker grid design has been certified by alicensed structural engineer and welded by certifiedcraftsmen. Each loudspeaker hangs from three pointsusing l/2 shoulder eye bolts and bad-ratedcafabinders. The eye bolt6 are the weakerelement,having a rated capacity of 2200 pounds for a straight pull.We have chosen Concert Serbs laudspeaker systems,which incorporate three top attachment points, each ofwhiihasaratedcap&yof1OO0poundsatanassumed design factor of 5:l.

I : budspeakersystems: (typical)Figure 15. Typical Rigging Chain 2. Sling the material to be flied properly. Do not allow

Knowing the number and weights of the loudspeakersand the grid, the tension on each part of the two-leg slingcan he calculated. Assuming a total welght of 1250pounds, each leg of the sling must carry 625 pounds.Given the bad angle efficiency of 70?&, each sling,shackfe and eye bolt will be tensioned to 884pounds-well within the 1300 pound rated capacity ofthe eye bolts.Rule8 for Safe Lifting:

1. Do notoverload ny piece of equipment. /


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slings o be placedagainstsharpobjects r roughor CHOKER A shortsling hat orm sa slit noosearound cutting urfaces. object hat s to be movedor lined.3. AlwaysalignMing equipment ver he centerofgravity o enablea straight e rtical ift.Neverattacha hoistor liiing line o the bad at an angle.4. Alwaysuse property-installedad-ratedhardware ndfiiings. Do uble-check ll connections e fore ifting.5. Carefully nspect ll Ming equipm ent-everythingnthe rigging hain-before making Mt. Replaceany wornor defectiveequipment.6. Never ii or support verhead oads roman openhook.Alwaysuse safetyhooks, atchesor otherdevices

. .whenmaterial s beinghoistedoverhead.7. Use Tag .Lines o control ny bad whichmaybecomeunmanageable uring ifting.Conclusion:Safe soundsystem iggings the application f knownand simpleengineering rinciples bng witha healthydoseof comm on-sense nd know-hoi to a relativelyuncomplicatedet of problem s. here are no viableshortcutsn rigging quipment, oolsan dpotential ossesresulting rom propertydamageand personal njury ollowinghe failureofsecond-rate ardware r faulty igg ing rac tices an bestaggering. afe sog&y@ em rboino s no accident.Glossary of Rigging Terms:BACK -STAY Guy used o support boomor mast.Also,that sectionof a maincable, as on a suspen sion ridge,etc., leading rom he tower o the anchorage.BASKETHlTCH A U -shaped wo-leghitch ormed romasinglesling.BENDING STRESS Stress imposedon. he wires of astrandor ropeby a bending r curving ction.BIGHT Thebendofatine,mpeorcable.BREA KING STREN GTH The ultiiate bad at whiih atenslle ailure occurs n the device being ested. This issynonymbus ith actualstrength.CABLE A term m applbd to wire rope,wire strandand elect&al cond uctors.CENTE R OF GRA VITY The point hroughwhicha badwttt ang from any att&tment point.

CLEVIS See SHACKLECOM E ALONG Device or temporarily olding r pullinloadson rope,chainor wire rope.DEFLECTIONa) The sag of a rope n a span,usuallymeasured t centerspan.b) A ny deviationrom a straighline.DESIGN FACTOR The ratioof the nom inal trengthothe totalworking ad.EFFICIENCY Ratioof the norninal trength f a m odifiropaor wire rope o the nominal trength f anunmodifiedop eor wire mpe-usually expressed s apercentage.EYE BOLT A m achine olt ncorporating circularittinat the end for attachment urposes.EYE, OR EY E SPLICE A loop,withor without thimbformedat the end of a wire rope.FC (FiberCore) Cordor ropeof synthetic r vegetablefiberusedas the axialmem ber f a wire rope.FITTlNG A ny unctional ccessory ttached o a cable,ropeor sling.FLAG Markerplacedonaropesoastobcatethebadposition.GUY LINE A strand r ropeused orstabilizingrma intaining structure r tiiing bad in a fm edorpredetermined oisitlln.HlTCH A ropeknot ha t unties e adily hat s used ortemporary astening.IWRC IndependentWire RopeCore) A w ire ropeuseastheaxialcoreofalargerwiretope.KINK A deformatbnofawireropecausedbyabopbeingpulled ight. t constitutesrreparable am age oand an lndetenntnate ss of strengthn the rope.KNO T EFFICIENCY Ratioof nominal trength f aknotted ope o the nominal trength f a unmodiiidmpe-usually expressed s a percentage.LOADANGLE Anglebetween he bad (horizontalsurface) nd the sling.

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ANGLE EFFICIENCY The sine of the bad angleLoad Angle Efficiency, e.g., a 30 degree sling

will have a bad angle effiiiency of 59%. Theof the sling increases according to

of the sine of the bad angle.Wiring the throat of a hook to prevent a WSC (Wrre Strand Core) A wire strand used as the axial

out of the hook. mentxrofawiempe.The bad which a new rope, new wire

sling or fiiing may handle under given operatingassumed DESIGN FACTOR.

See DESIGN FACTORRefers to that portion of the

ominal strength of ropes, slings, chains and fiiings thatied either to move or sustain a bad. The term

, however; as it is valid only for newnd equipment in as-new condition. See

RATED CAPACITY.SHACKLE A U- or anchor-shaped fiiing with a pin.SHOCK LOADING A sudden movement or jerking of abad, such that the forces upon the hardware system aremagnified over those imposed by the static load.SLING An assembly that connects the bad to the liftingdevice.SOFTENERS Anything that is used to protect the bador cable, also rope and slings, from damage while makinga iii, or hanging from a beam. Also used to prevent a badfrom slipping.SPANSET Trade name for polyester slings widely usedin sound and lighting rigging work.STRESS The force or resbtance within any solid bodyagainst alteration of form; in the case of solid wire it woukfhe the bad on the rope divided by the cross-section areaof the wire.SWAGED FlTllNG Fitting into which wire rope can heinserted and then permanently attached by coldpressing @waging) the shank that encbses the rope.

THIMBLE Grooved metal fiiing to protect the eye, orfastening loop of a wire rope.WEDGE SOCKET Wire rope fiiing wherein the ropeend is secured by a wedge.

.

References:Committee of Wire Rope Producers, American Iron andSteel Institute Wire Rope Users Manual (Committee ofWire Rope Producers, 1000 16th Street, N.W.,Washington, D.C. 20036,1985).Crosby Application Instructions for Crosby Clips (TheCrosby Group, P.O. Box 3128, Tulsa, OK 74101,1985).Crosby General Catabg (The Crosby Group, P.O. Box3128, Tulsa, OK 74101,1986).Newberry, W. G., Handbook for Riggers, RevisedEdition, (Newbeny Investments, P.O. Box 2999, ,Calgary, Alberta, Canada, 1977).Paulson, Rocky, personal commrnicatbns with theauthor (Rocky Paulson, Stage Rigging, Inc., P.O.Box 95,San Carbs, CA 94070).Southern California Edison Occupational Safety andHealth Diiislln, Rigging Standards Manual (LosAngeles, CA 1982).SpanSet publication Safe Lifting (West Coast WireRope & Rigging Co., Inc., 597 85th Avenue, Oakland,CA 94621).Stage Rigging. Inc., Products and Services Catalog(Stage Riling, Inc., P.O.Box 95, San Carbs, CA94070).

JB LProfessional8500 Balboa Boulevard, EO. Box 2200Northridge, California 91329 U.S.A.nAnumml cornpvy

Documents

Basic Principles of Suspending Loudspeakers