Document kmN8MOBMKgx78nK9Dmw5JxGmD

LIA24381 -a.,..,;^= - -^r^-<-imii~'il iii I. Mut St Shiirs iV II II mMil Pin 1 and Engineering and Purchasing Personnel LEAD INDUSTRIES ASSOCIATION at MADISON AVINUI NEW YORK 17. N. Y. 4 J'/</!jU+4* ( October Zk, I960 SUBJECT: IMPROVES 30UHP BARRIERS EMPLOYIHO LEAD To Members of the head Industrie* Association: The attached engineering report has Just been published by the Lead Industries Association and explains In detail how to calculate the effec tiveness of a partition or sound barrier. It Is based on a study Bade for our Expanded Research Program by one of the country's leading acoustical engineering firms, Bolt Beranek and Kevnan, as a result of earlier recommendations made to ua In th* report of Skidmore, Owinga It Merrill, architects and engineers, cc expanding; the use of lead In building construction. It deals with office pertltlcns, wHr*ry enclosures, and other sound-containing structures. Among other things. It deconstrates that If a vail or partition is to be built of one Daterial, such as brick, wood, lead, etc., the lightest vail that can be built to ceet a sound barrier requirement Is lesd. In addition to shoving the sound transmission characteristics of a number of conventional vail constructions and lead, the report Includes calculation methods applicable to most simple partitions. We believe that the data included vill enable design engineers, architects and others concerned vith the control of sound to determine how the use of lead cay help them solve their problems. The report Is being circulated imediately to soma 15,000 architects, building contractors, design engineers, and manufacturers of building equipment and components. Additional copies are available to members In quantities up to 25 ftre* of charge and In larger quantities at our cost of 10 cents per copy. Very truly yours, RLZ:JRH Alt. ' Secretary I .J |ll|l>W^.W!irtfy^UW?yt,|!r ..in .. -L-' fW M '.^jy .).lL^.i:.J.Wi|,. |i .-it. LIA2A382 ~rr i' < ;; V :.--- V ~aWBggg 6 `,N i j; ...-w . -' iv- ; i ,* 1 k- o Inducing an anglnaarlng report by Balt, Boranak and Nswmon, acoustical consultants, on tho affacfivonass and applications of tbl mataHal In buildings and mochanlcal oqulpmont. ' p u n n n jin n in u^ ! Iw w uwj i. 1 A.I.A. NO. 39 LEAD INDUSTRIES ASSOCIATION 292 MADISON AVENUE, NEW YORK 17, NEW YORK '49m . myippWBIHi;V. gJBWBjWIPBy!^^ IS 1685.01 r* -----LIA2A383 the need for a better sound barrier tcbl of contents page Improved Mvnd barrfet employing koC 3 what tho dota thaw S how food can bo vtod at an acoustical matorial 4 onglnooring and dotlga calculations f typical example t load laminate example II Hi*w valuable is silence? Though (here arc few instances where tc can get a firm dollar-and-ccnts answer to this question. there is no doubt that the noisy riant or office, btd room ot home rus a nuisance saluc. Often that "nuisance" produces fa* tiguc .'nd irritation leading to errors. People prefer a quiet place to lice and wi*rv. And. he and large, people do a better 106 when they hate a quiet place to w<*k. Vh what t4hce can operate in to* day's business u!J *";,b*Tt tvne* writers and ttltjheis? What hmes arc wittucu radios. TV and revord players? The plant that has no sources of disturbing m*isc is rare indeed. Hciausc we tanme Jo without the equipment which causes noise, <*ir homes and olticcs, kbsh and fac* tories rmiNt.be designed to minimize its dfut and j n we surround nursclscs with more muhanical aids, the noise reduction problem htcnts more im portant. Two noise reduction problems are imohed. The first is the presto* tkm or minimizing of sound reflection -the use ot drapes w acoustical tiles arc examples. The v\ond, reduction of wcind transmission, has felted on mas* sice iorwriktum and "wiltd'' walls to confine sources id noise. As a roult of studies made for the l-cad Industries Asvxtaiion by* the amustkal usisuhing firm of Bolt, Bcranek and Newman sunc surprising fails about reducing sound transmis* \i* ha\e come to light. They* hate f<*und that it is quite possible to build walls and partitions which Iot4 'masuse" to uund, yet actually weigh tea and ouupy less space than contention* ally constnutcd walls. It is hoped that the report on the following paces will sersc as an aid tn arihitcsts and design engineers in pusduiing building and mechanical equip ment wih Niter iharaiteristHS f*r re ducing s>wmd transmissHm and will encourage them to inscstigatc fully (lie usefulness of lead in soiling problems if this kind. LIA 24 38 4 0 IMPROVED Sound Barriers Employing Lead what block* tound? The list of new materials and ar chitectural products to block sound his grown and is growing longer. It in cludes sufficing rrulcTiils, acoustical tile md plastics, movable partitions and door types. TlvCfC are special building techniques, too, for laminat ing materials, for panels, doors, walls, and ceilings. It is important to discern between materials that stop sound tranuniswon and those which simply present sound reflection A room finished in acoustic tile, for example, seems less noisy be cause sounds originating in it are not reflected bisk to a listener in the room A mu*)* conversation next door. however, can penetrate the tile. And rnnses from the tiled room leak out to ad joining rooms. To blexk this **rt of leakage" the partition or sound barrier muvt e have two key prt*ptflies: weight The greater ihe tij;hl tper squjrc tH<) the greater the iso lation. or tranvmivvu-n loss given by the panitistfv material. limpness - - ITk jo>u>tKal efficiency of any material as a sound isolator de pends i*< only on its weight hut on its ' betiding stiffness ' If a partition is stiff enough it can actually lose mu.h of the advantage it gains by be ing heavy. Tins happens because the stiffness of a partition increases much more rapidly than its weight as its thkkrx is increased. A general rule is: lead approaches the ideal Lead is an obvious choice in the search for a heavy, limp material for construction of partitions. Having a density two or three times that of common huiiJmg materials (and 10 to n times that of wood) it is also a limp" material in the aciHisiicil sense. This csxnbination of properties, approaching the idea! for acoustical harriers, leads to the surprising con clusion that if two equally effective sound harrier partitions arc built, one of lead and one of any *xhcr common construction, the lead barrier will al most invariably be the lighter. Table I compares thickness and cost /of lead alone versus common partition materials. TMU I Type a Weight Fortition Weight of Fortition loti* tqviv.lM* Ih/s^fi ft/l*fl Ffyweod 2JJ IV 4f Sheet StteT 3.0 13 I7S SoMHoHw 11 m 41 Matencl Cos! equiv. Wad S/s^tt 0.31 17S1 .JJ' 0.14 0.S7 1.12 (MerWeefc n Hester m studs 12 Hotter ea dovbhstvds U lock 104 Si 41 OS' 1 44 7$ i* 0.411 ?2S 111 1.4 tss1 U7 IS* 71 130 4.S0 Thkkntu iadm 1/4 1/14 I 4 4-4 mha 1/71 1/M 1/1* 1/M 1/1 $-1 3/14 1 1/4 MOHS. 1) os rmploH " nwvobk portirton, tor iumpk. 7} rsfimeftd kjr total reeled rests kr hr# to frf metrnd tests. f**rv wm I'H) 1^,1 111* HI IB IJ IIIIHHHII im in n ^ WEIGHT BLOCKS SOUND sjttypiM - i-- ,u. Pfyifim-Jt  W0 ii'.i'-'l--W' W*'--*1'. LIA2A385 saving* with lighter partition* LIMP WEIGHT SAVES SPACE The advantage of Km Height to the structural enpneer is of more sig nificance thin might at first he obvi ous For example, while a cinder- hhxk partition weighs 22 lb s<p ft., 51/* lb. ft- f lead will accom plish the umc acoustical isolation task. Thus, there is a saving of lfl ^ lb for escry sa|. ft. of partition erected or lt>5 Jb for every linear fo< if the ceiling height in the room it 10 ft. This added weight w ill he reflected in incrcuvcd floor slab thickness required for support of the partitions ana also in supporting beams, columns and so cm all the wiy down to the footings. Another area for general consid eration m *)nli weight ma)' lie more important than any other factor ii where, for one reason or another, an acoustical harrier has to he moved pcfksjujllv. Siwind isolating diwirs or loldtng partitions arc examples. Surfacing: TACKABLE RENTABLE MALLEABLE laving* with thinner partition* A review of the Table shows that i<hcr materials take up to thirty times as much thickness as Ic j J to aicom pitch cvjual speech privacy The actual sawn,: represented by decreased parti lion thickness must he based on the mcrviwd useful area within a build ng By replacing a brick wall with m lead sheets (avowing a 2 in thickness lor a structural framing syv (cm for (Ik lead) a 6 in. strip of use lul floe* space can he sjeed. Based on an average building <ct today of ap pruximately $15 per Sep ft , this 6 in strip represents a sac mgs of appfoxi nutetv AO per linear fo< ol parti- looking at lrd a* a L.-Ming material % ('sing Kad for sound harrier par titions nuy, at first, seem unorthodox. Of course radio and television studios, as well as other facilities where critical sound conditions prewit, have long used lead as an imcgnl part of woJU, doors, and partitions. Aside from novelty, is there anything to recom mend or condemn lead as a sound harrier in buildings? Let's look at cost. The most ex pensive lead partition considered in Table I cost $4.50 per square foct, or $45 per running foot in a room with a ten foot ceiling. Of this, about $7.50 worth of usable space is returned per foot and an unknown saving is made because a lighter building structure o required. It would appear, though, that lead cannot economically rcpLcc interior twocoune brick walls at about $10 per running foot for in terior partitions unless building space or weight is at a high premium. Considering cinJcrblock, sheet steel, or even comcntionil stud-andplaster walls, on the same bauv it can he seen that the costs of a lead parti 0tion wall arc competitive. Indeed, lead has uuite an advantage over cvni'en tiooil metal partitions. Aside from considerations of cost, lead has many assets is i building material. It is (askable- it can he nailed, stapled, or, in light weights, cvc-n consented in place. It is printable lead sheet as supplied is rcaJy tor painting without any further surface preparation, and it forms a durable beHid With all conventional paints Lead is fuepnof. It is malleable folJ it or bend it met any regular surface. It tin even be "JrcswJ over complex surfaces. Finally, lead is easily cut and worked. A uw, shears, or even a knife can be used in titling lead. < 0 FIREPROOF WPP PWPilW P!P ,'^IWWUIIJ ^ A - -*- ~r- *MW L IA 24386 W! > What the data show i * When the transmissmt l*ss of a 1i ij partition plotted ipaimt the ttujuuu). (f igure l) it tin he seen that the loss increases ith frequency up t" the pennt %herc the transmission |nw reaches about to tit decibel*. S>nHhj| ahosc this frequency A dip in the tnnvnis'h'fl l*'" curse occur*. At hi.chcr frequencies. the loss in- ifCJxs it h h c rapidly. At fre qucruics the transmrswon !**> i* sei by the weight of the lead Ibc dir is set N the stiffness of the k-aJ. (Thr less stiffness the partition has the higher the frequency of the dip. thus the hi chef the mcrall transmission loss ) ' In Fipgfe J. hclJ measurements f. r j painted cindcrblock all are corn- pared with ihc calculated effect f a partition **f lead 0 0"*' in thick As a imal comparison, t ipurc i 'horns the TV* c*l h serai cnntmto soltj pariii*i<ts. These curse* hase Ken plotted against the product of frequency and tK *urfaic of the partition Figure \ \ho* clearly the uniquely hi^h demit) to-stiffnc** ratns of lead, especially hro ctvn- pared *ith a cellular nutina) such as pl)<<d wer1 1W J LIA24387 How lead can be used as an acoustical barrier lead "wallpapw" Many existing problems of noise transmission coulJ he remedied if the weight of (he wall ccnild be signifi cantly increased without increasing it* stiffness significantly. Since (he weight of many typical partiticini could he doubled by the jdJtiion of a laser <*f IcaJ as thin as 1 * in. on cash side, few modifications have to he made in the OHistniction to significantly incrciv the acoustical isolation prosidcd. Leaded cloth similar to leaded vinyls already in production might also be used in a wallpaper-like fashion. door linings There may he considerable appli cative in improving the avCMistic isola tion properties of door*. Approxi mately *jfl in. thuk lead sheets with a decorative mood veneer laminated to one face of the sheet and a pressure sensitive adhesive laminated to the opp-'itc favc van eavily he abided to in k or h>*(h fates of doofi where high acoustic isolation thnugh (he demurs is required- suih as in broadcast studios, music school*, and d<<tor*' crfth.es Thus, for example, mhtn a doctor tAcs over an old building mnh typical lightweight pane! doors, the*< doors tan he < inerted into door* of higher aoHistu isolation and nvsJtrn Hush m.-d jppcarancc by simply cement ing lead sheet anj trimming the edges. machinery endoturet Lead laminated to fairly thin sheets of materials such as aluminum can he formed into machinery enclo sures for ntHsy pieces of equipment. Such a constructive) has the advantage of higher transmissnii loss and coo sidcrahle Jamping while the externr material provides a hard, clean, work mg surface. A leaded fal>nc and pressure-sen sitive adhesive or simply thin lead fotl with pressure sensitive adhesive has tonviderahlc applicant*) N*h in the fabrication ol new inathmery etnlosurcs and in improving tlse acoustical properties of existing enclosures. Lor example, in the manufacture of mull window room air conditioners after the individual elements of the case have been formed and attached to <*se another, ilsc use of such a lead tape serves three functions: First, it in creases the weight of the enclosure and thus improves its transmission loss. hevonJ, it provides some vibration damping for the enclosure. And finally, because it will lap over joints m the enclosure, it seals it airtight. A similar application could be en visioned immediately in the field of oil cooled transformers for elcclntal substations within buildings. Additional ipplicjtions for such a pressure-sensitive lead tape might be found in the field of plastic phono graph and radio enclosures as well av in commercial nsctal Loudspeaker en closures for installation in the ceilings of buildings. ^uai mgfi tran$rr.isii9(t lost lead structure As the title suggests, this is a very general type of proposal Av an example of a structure of this type one might <(*i*idcf a Vlayer lam.nation as follows: vinyl film. \n" lead sheet. of relatively low density Fiberglass of other resilient hoard, lead and a final c<ut of vinyl. Theoretically, such a ecjustructicai w AilJ fuve the transmission love shown If the very high transmission levees, particularly at low frequencies. indicated by theory were realized in practice. such a far,cl would have con siderable application, particularly in special arras such as jet engine test cells, dynamometer cells, special audiomcim facibtK-v and other types of rcseanh lab*, load backad ocouttk tiU One of the major problems now facing the manufacturers of standard acoustical tile is that the low weight and porosity of nwr*t cflcitive *ourd al>sorning tr.iterials permits the transmiwion of sound. Modern building techniques and Cconcmics requite that nx>y partitions be erected up against the hottiwr. surface of the aowistn tile in such a manner that they do me extend from live acoustic tile ceiling up to the structural slab above. As a result, more and more difficulty is experienced with sound transmission through the acoustic tile over the top of the partition and down into the next space. Several of the manufacturers have begun adding layers of opaque paint or paper or even sheet metal to the hack surfaces of acoustic tile Others have nullified the ingredients from which the tiles arc made to render the hack surface more airtight, providing higher transmission lens. The arplkalioa of 'cry thin lead foil to the tuck *h >.--,.1-. 1 tile will prove acoustnally effective and should pennit the tile manufactu.cr to wll all of hiv various decora tive patterned tiles with or without the required transmissive) loss without modifying his production run :n a serious w ay a specific panel material By carefully selecting the maxi mum stiffness compatible with the re quirement fc* transmission !<ss. a laminated lead partition can be acous tically tailored to s<4ve many s|xiifc priblcms !sxh a partition, which might have considerable application in the field ;*f rrv-vable office partitions wvnld be constructed of a thick lead sheet hon-led between two l/j** lasers of p!\wJ and w-<uIJ have the following advantages: a Trinvnuvsion loss tailored to solve speech privacy pnJdcrm between c-thces having the background noise levels typual for quiet. air conditM-oed trftKcs. b Sufficient structural rigidity to be supported in lull height panels he tween mull metal posts $* or a* on center. c. Attractive appearance whether finished in natural wood, paint or erfher coatings. d. Field cutihihty without special equipment. e. <h *J surfacc to receive thumb tacks, wrews, small nails and which may he readily re finished, using standard cquqxnent f. Fxirrmc thinness compared to 0vonvetitntful obstruction resulting in low shipping costs, cjvy storage and eventual space saving m the erected fvmtKb. -6 - "1 1 IntM'Mpn LIA24388 1 Engineering and design calculations * Figures l, V. and f* arc valu able comparisons of the effect of sheet lead with three conventional mall con stmetions. In desipnio^ partitions 'o reJuce sound transmmirvn. however, the starting point mill he the sound reduction required and not the ma terial of construction In other word* me mill sec horn* much *f each type of partition material ii needed to achieve a satisfactory sound rcdikiues. As the first step in doinp this, me must know mha sound levels are pernm*? Ic. tig 7 has been established bjr studies of tests in typical o Mk c s and thus senes is i to what transmission loss is needed for quiet environments. It can be seen that scry quiet others require a very hiph transmission loss partition Horn* can the tranunissun tens <*f a simple partition be fmnd? It is p\trntd by iIk familiar factors of wcipht and stiffness. In the case of any parti tion material v.hcre a simple structure is u>cd (cp Steel, lead. . plywood- but not plaster on md of mire lath with 'tuJs). the transmission loss mill increase from low to hiyh frequencies o at a rate f about < decibels per oc tave. In ther mordv when the frequervy of the sewmd doubles, the m tensity will be roughly half as preat for v<md passing lhru^h the panel This ft ilh ictise increase in transmission loss is solely a function <*f the surfjvc weight of the partition At yew frequent. it will drp off in to the plateau " And the frequency at which the plateau stilts is a fur*.ti*i <-t the stiffik ss of the material. Atnc the pliteau. the rise in transmission loss with frequency mill loercisc to aWvt lo db octave This increased rate of roc with frequency lasts, u m ally. <4ily until the curve comes mithin about db of a project**) ( the lowfrequency p*ftmn. Ir*n this point on, it remains parallel to and about ' db below the projection of tlw lorn frequency curve. Refer aprin to Ftp. J (pipe All of the curves shown ate (vised on a surface meipht of I pound per square foe4 of surface The point al which each plateau begins iv trialed to the stiffness of ihc material in (his weight l if plywood, quite stiff in this weight relative lo the other materials, Q shows a plateau hrpmninp at 19 dh. Aluminum, nearly three times as thick as steel in the same weight, is much slirfer ami thus starts itv plateau at .*9 2 inches of selid sand plaster !; lM - Cj*vts cc mama wi. : | , *n o uo w*u : 1/U ittii ef sheet lead f *i \f i ,i I: * ffcj-.C V * Gyptum lath plat 1/2 inch af land plotter on roch tidi oI itt tnni stud I /I inch of shrrt trod Staggrtrd itud gypsum lath plot 1/2 inch of tand platlar on iloggactd win tnm itudi I/I inch * th*flood nnj-niMPUC'1 _y mwwqI LIA24389 Jb. mhilc ucel Mart* at h i l.in;pc%( 0} ail. kad shorn* a plateau Marline '<* Jb 11k midth i4 <ih plateau 1* aim* ihatxti-rWH <4 the psen mi tc-nal. Thus it < an be seen that there 1* nu>h thi *urxc* hasc m prx-ral: i!k \ base the un* (i db stavr slojx- below the plateau this ha*c !*e vine general vhijt m tl*c plateau fipion. but Jirfif ,11 p-n? o( i-finl atiofdir.p to ;fv stiffness of the mattnal and :n pl-ittau mi.bh they Hi'c tlc virnc central \hj|H- iS'n c the plateau. Mart m.C m:ih 4 to lb *xtjsc rac mhuh riiiims info 4 ( db <\ta\c nsr a* the (unr ap prtvuhe* mithm > db 4 the projesti-ri <4 ihc low frr'pKrvT slope Appartnt!), then, the mholc iunt fot any material can be defined rf *nl' trv-m the hxation and mtdth 4 the plateau And to help l*ate the plateau me knom that C4vh .*rutenii nit 4 charavtrfistk transmission k*s m db, Mependinc **1 it* stiffness, * mhKh (he plateau Wart*. Ml <4 (hi* informal**! 1* cvneriliacd :n Ftp S. The 'nly problem reiruinmp n to liikl the fre*juciv\ at mhnh the plitciu Man* or to jxit it ar**!** may -to (tod the height of intercept <( the U-m Ircsjucrvy p*t-n f the i*jn*at vmc kn> mn frtnK__ .. do this, ;viy on the formula t u * ~ t ! v +19 r *) wrt -- ILm, n fbr froMmM Wu la * t <00 Qi V !S# artvol wfotc wtift* ! tM portifitt per invert fo* (19 n a awmehcal (MKtoot) ' O TYPICAL EXAMPLE Finding the transmission loss of % in. fir plywood I j fr-rn the fir*4 column 4 the table in 11 H. hnd a demit* 4 ) tb wj It fof I inh thkl hr pKmt<J Then. 31* US ft/u H. 7| I md thv iranurti*\on loss <4 (hi* panel at w*o tp This 1* pure!* a furwlH*! il surface met^ht auordmj* to the twmula iu , - m*w + 19* - Mhf 1 m it - 70(00517) 19 nM - 1070 F 19 Wf 70* >j PiM the point: 400 cyilc* pet and 7< db irinsfm*vt*i !*** 11 Thn*n.*h thi* pewnt. I>j.htl> .Jram the line rtprixntm^* 4 o db jxf reta*c live m trariunivsHO I*as i An <ta*e ' an c*a,t Joubbnj; 4 the fre vjumo. thine at to it ij'* the k%* mould be .'t, Jb. at Itam , p-v it m<-uld be- i7 db. tit ) ') Riftf to the Kiitkl i4umrt <4 thi (aide tn lit! K to Imd'that the transmission los* height for the >nscl i4 the plattau fof hr pl\m1 1% |U db Mark thi* punt (appro*mutt I) U-O <ps. 10 db) on the lm frts|VK<m) ur\< yu have dfjmn ft) From (olunm three 4 the table, take 4 plateau midth lof hr |4\ mood <( ' 4mta\cv Mark the* <4f on the W lb loci Thu nut be J<nc ^raphnalU (three disisi*<i* ev^ual one *lac) The plateiu mill trhl at aNuC :> p* ") ASne the end *4 the plateau (7700 ipv 1*>db) the hss tufse m-ill siirt t* rtsc at Id db (tate and n this parihular use mill Ixjjn to dn^s s4f to (t db * * t as c wenemhete hcyirid the finp 4 hearing (l'.th>0 to TO.ono <p). Skrth in the plateau tune Ihe masm>um and minimum mill !c abut * ' tn t db ahosc and KU-m th 1 nxan piatwu k'<l *4 l' db ' Hs tKcnparini* 9*c pl4 for 4 m tir pl)masj part it* *i. just drama ww? mrcjm 0 nnytwmmK? LIA24390 ~Vt t iw i rmi >i 7AANSM.$S<0 LOSS C l* I LlS ^0 UO M6 K9 L i :u 30 i io novfNcr crocs re* scco*<o svflfAcr *t i * s q f t 9  IW i^m mj*'*' *- LIA2 43 9 1 lO lO C l'/E l' o ^<UPH 'F io -- 1.1 IWW.IMH.I^ ip -.U1I,'I'J IHJ.I <*ti'nw npiw^y^^pwn mnmmrnmqwjwrtwf?*--*-- - LIA2A392 jfg,, t , , - jji L & l m . (Fig. 9), to the permissible wamd Ic'd Jala of Fig. 7, you can >ce that 3 such a panil ion will ru< he satisfac- lor)-. It will help to reduce the s*iunds with frequencies above 2000 cps- high frequency clicks and hisses--but permits too much sound to pass in the normal soke frequency tinge (200* 2(Kxi rps) and is relatively transparent to hums, rings, bumps and whines of office <>r production machinery. Using a thicker partition of plywood would tend to shift the whole curve to the left (into a lower frequency ra.ige) without raising it. It can be calculated that to shift the curse far enough to (he left to gisc satisfactory transmis sion loss to meet the "moderately noisy office * standard, the plywood partition would fuse to be something like 3 to 4 inches thick! Quite obviously ait these con struction materials except lead are in adequate for sound transmission loss in problem situations. Is it possible to improse the sound transmission loss <f a partition by using a laminate of some desired partition material with lead** Indeed it is. In some cases the lamination of lead will produce a dra matic increase of transmission loss: in others the increase is small or mar- TABIE N Approximate thickr.es> of single, simple partrtiom to meet permissible transmission loss requirement Material FV plywood $und plot** Gto* Owns* conereto Aluminum Steel Itod Thickness required m inches Moderately noisy offic* 3.67 .20 -IJ .14 .13 .045 .030 QvM cffico 6.67 .'.45 4.70 4.S3 57 70 .135 L vr quirt offleo 13.33 If 93 133 113 73 -54 The stepped line through the table indicates the br4 between those partition materials which arw limp enough so that their weight is efficiently used (below the tine) and those which ore so stiff that port of the effectiveness of thee weight is lost (obove the line). ______________ __ ______________________ TYPICAL EXAMPLE Finding the effect of laminating lead to plywood As an example of the tutt of in* cfti< that can be expected, consider ihc effect <*f cementing *|# in, of leaJ to a yt in. pl)W<md panel. The two familiar factors of surface weight and stiffness will come into play in tw-o ways. First, the new surface weight w ill be higher than that of hr plywood atone, so the transmission loss in the hrw frequency portion of the curse wtfl he higher. Sccctnd, the new- coroNna!t(>n of surface weight and stiff ness will produce a plateau height uuncwhcre between those of plywood and lead. | To find tho now low fro* qvaixy froiumlulofl lot* follow the pnecdure n page II. 1) m. pfywcxd will fuse a surface weight of 3 lb su ft if I in. thick, thus 1 12' lb sq ft in in. thickness. The sheet lead laminated to it will, fnxn the listed density of '9 lb sq ft pet in . have a surface weight of--- jt x i/h - Mw| fhtsa. m |d - UTS J4I Tn h/tfk 2) The transmission lost at kXJ cps. then, (if the partitnei had no stiffness) wiwild he - TU*-WU,4*+ H* -m + if mm* -- II -- 3) Pie* the -100 cps trammmma lost of 32.6 db i) Draw* the low frequency slope (6 db per octase) Now at this point wr must depart from the original procedure because the new plateau hcicHt will be deter mined by the sfiffnc* and weight characteristics of the Lunina*. 'a) First, from the ^ in Fig. 10. we c an find t*sc <f the change in partition Xilr,H. To use this data, we base to <1crminc the ratio of thkkncsHs b.iwcvn the plywmd base and the wh 4c laminated partition: fUpmi tow thick*** ___ 4 total fhkkiwo J/| + l/U " f m F^g'UlUiij mmmrrr-zr j* w.uijiwuMiiJff1 s: r A * AnJ me will also hive to determine the ratio of moduli of elasticity for the two material* of the laminate. The moduli arc given in Fig K mfvhn hr Im4 S X 10* ^ moArttn t< pfvwJ j~x ij* Vk'ith these two figures me can enter Fig. lo. At d.J on ttie ratio ot moduli vale and * (ju< bclom the 7* parameter) the ordinate is - \ db This it a Joe reave in the plateau height of the transmission lost curve due to the stiffening effect ot the lead *b) Second, using Fie. II. me mili find the contribution of m eight to the shift in the patcau height. Herr, in addition to the thickness ratio used in step 'a, me mill need the Jensity earn* for the materials. From the table m Fig. 8, me hive- - tvrfoti wrifhf ftr lack fm iq It torhoJ St , H trf wAfht p* Mb ftrpfjrwted I Tittering Fig. II at a density rat:o of 20 me Imd, for a thickness- ratio parameter of an tm reave in the plateau height of the transmission loss cune of 16 db. This increase is due to the surface mcight increase brought j Kh it bv laminitmi* the lead to **'* plywood. V) The net effect of the lamination on the plateau height is there fore Ah mm 4 to stifffwi| mmst Aw to oddd wrijtat Nffinemu -3A HA ISA Gening back to the table in Fig. M me* find that the base material, hr ply* mined, had a plateau height of lo dn Adding 11 db to the- gises us the nem plateau height of \2 db The fre quency a* the beginning of the plateau mill be about $*U epi ts) The prcscss of accurately de termining the new plateau width i* complex and need not he carried out. Actually, (he result of laminating two materials mith differing plateau midihs mill produce a nem plateau mtdrh mhich is seme* here intermediate be tmeen the tmo original values. Since the effect of small change* in plateau midth u insignificant m the whole transmission loss curse, it is good practice to take the larger ut the pla tcau widths for the two starting nu (trials. The actual performance *4 k*- laminate mil! .ilmavs be slightly better thai* J..\ Thus, me can (Ac. from the table in Fig. 8. the plateau midth of 2.? given for tar plywood Mari the )2 db level 2.7 octaves above the start of the plateau found at '70 cps The plateau mill end. then, at about 2400 cps. 7) Above the end of the plateau drjm- the 10 db utavr rise mhich, again mill begin to drip off to a 6 db octave rise somewhere above the normal hearing range. 8) Sketch in the plateau curve as before. If me compare b*h this curve (Fig. 12) and the curve for unlaminated in. plywood to the transmis sion loci criteria curve* of Fig. 7, 8 can be wen immediately that adding (he shell lead has made the plywood partition acceptable for moderately noisy offices and. nds|. clowr to the cune for quiet iifhces than to the former. u n -ii * (nun -- 12 - tkii -m pirtMrt M to*4 H* I* U ( A W'"AU <