sound barrier a material should consist of the capacity, and (4) … · 2013. 11. 6. · documsnt...

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ED 031905 EF 003 340

Practical Application of Sheet Lead for Sound Barriers.Lead Industries Association, New York, N.Y.Report No -AIA -39; CSI -DIV -13Pub Date May. 65Note-12p.Available from-Lead Industries Association. 292 Madison Avenue, New York, New York 10017

EDRS Price MF -S025 HC 10.70Descriptors -*Acoustical Environment. *Acoustic Insulation, *Acoustics, Building Design. *Building Materials.

Construction (Process)Identifiers -*Sound Barriers

Techniques for improving sound barriers through the use of lead sheeting aredescribed. To achieve an ideal sound barrier a material should consist of thefollowing properties--(1) high density. (2) freedom from stiffness. (3) good damping

capacity, and (4) integrity as a non-permeable membrane. Lead combines thesedesired properties to a greater extent than any other common building material. Theproper use of lead in combination with other materials can compensate for theirdeficiencies and improve the acoustical performance of the composite barrier. Three

ways in which barriers are rated for their effectiveness are discussed and compared.Practical tips for designing better sound barriers as well as pitfalls to be avoided

are listed. Design and construction information for installing practical lead walls ispresented and guidelines are recommended. (TO

I

PRACTICAL APPLICATION

OF SHEET LEAD

FOR SOUND BARRIER:)

LEAD IS AN EXCELLENT BARRIER MATERIAL for reducing the

transmission of air-borne sound.

LEAD IS TECHNICALLY SOUND because it combines high den-

sity, natural limpness, good damping capacity, and is non-

porous.

LEAD IS A WORKABLE MATERIAL since it is easily formed and

fitted, requires no special tools, and can be readily adhered

or fastened to other materials.

LEAD IS ACOUSTICALLY GOOD because pound for pound it is

a better sound barrier than any other conventional building

material.

LEAD IS ECONOMICAL because it is reasonable in cost, takes

less space, often saves weight, is easy to install, and isU S DEPARTMENT OF HEALTH, EDUCATION & WELFARE

salvageable. OFFICE OF EDUCATION

THIS DOCUMENT HAS BEEN REPRODUCED EXACTLY AS RECEIVED FROM THE

PERSON OR ORGANIZATION ORIGINATING IT POWTS OF VIEW OR OPINIONS

STATED DO NOT NECESSARILY REPRESENT OFFICIAL OFFICE OF EDUCATION

POSITION OR POLICY

LEAD INDUSTRIES ASSOCIATION292 Madison Ave. New York, N. Y. 10017

ook Ahead with Lead

Practical Sound Barriers

Employing Lead

THE NATURE OF SOUNDThe sounds we hear are the re-

sult of air pressure waves impingingupon our ultra sensitive ears. The fre-quency (pitch) of audible pressurewaves ranges from 20-20,000 cyclesper second. The intensity of these pres-sure waves in terms of their physicalenergy varies over a fantastic rangeand accordingly, it is expressed loga-rithmically in units known as decibels.

Sound can be pleasant, acceptable,tolerable, objectionable or injurious.Noise is unwanted sound and in to-day's society the control of noise is fastbecoming a problem of major propor-tions. Unsuppressed noise can causepetty annoyance, loss of privacy, low-ered working efficiency, higher acci-dent rates and physical impairment ofhearing.

The information presented here isconcerned with air-borne noise ratherthan impact or structure-borne noise.Air-borne noise includes familiarsources such as the crying baby, TV& HiFi sets, loud conversation, officemachines, motors, pumps, manufac-turing operations, etc. It does not in-clude noise from objects dropped orfoot traffic on bare floors above, waterhammer in pipes, vibration fromheavy machinery or the rumble of asubway train, all of which are trans-mitted primarily through the groundor the structure involved.

The pressure waves in air-bornesound radiate in all directions fromtheir source much like ripples in apool radiate from a dropped pebble.These pressure waves will readily pen-etrate a porous barrier. They will alsoset a rigid barrier into unnoticed vi-bration which, in turn, generates new

air-borne sound of lower intensity onthe opposite side of the barrier. Thisis how sound "passes through" a wall.

WHAT CONSTITUTESA GOOD SOUND BARRIER

A good sound barrier wall is onewhich will reduce offending noisefrom adjacent areas to the level of thebackground noise normally presentand accepted in the desired quiet areaor to some slightly higher level whichis still deemed acceptable to the occu-pant of the quiet area and which willprovide speech privacy or freedomfrom annoyance or distraction. Forexample, an 80 db (decibel) noiseimpinging on a 30 db wall will gen-erate a 50 db noise on the other side.If the normal and accepted level ofbackground noise in the quiet area is50 db, no annoyance will be experi-mced. If, however, the normal back-ground noise level is 40 db, it willnow increase to 50 db indicating thatthe barrier is inadequate.

The physical properties of a ma-terial or a composite wall that goto make up an ideal sound barrierare high density, freedom from stiff-ness, good damping capacity and in-tegrity as a non-permeable membrane.Lead combines these desired proper-ties to a greater extent than any othercommon building material. Theproper use of lead in combination withother materials will compensate fortheir deficiencies and will improve theacoustical performance of the com-posite barrier.

HOW A BARRIER IS RATEDT-) select or design a barrier one

must have a measure of its effective-

- 2

ness. This is known as its Transmis-sion Loss (TL) and represents thereduction in the level of air-bornesound transmitted by a given barrieras determined under controlled condi-tions. The TL is expressed in decibelsas a single figure which, in turn, repre-sents the arithmetic average of nineseparate TL measurements taken atspecified frequency ranges between125-4000 cycles per second. This por-tion of the sound spectrum encom-passes the frequencies most commonlyencountered and most critical in effectupon speech intelligibility.

Transmission Loss is a fixedproperty of a barrier but varies withthe frequency of the sound. The TLof all materials and barriers increaseswith frequency but at some point inthe curve a plateau or dip will occurwith most materials where the barrierdevelops traveling waves (like micro-scopic versions of the waves in ashaken rug) in sympathy with the dis-turbing sound waves.

When this "coincidence" occurs,the amplitude of vibration in the bar-rier increases and more sound is trans-mitted. Thus, in appraising the ca-pacity of a barrier one should considerboth the stated TL figure and the fre-quency plotting of the separate valuesthat make up the figure.

Lead, by virtue of its limpnessand density, does not exhibit this co-incidence dip in the frequency rangewith which we are concerned. Thus,when properly combined with othermaterials, it will improve or dominatetheir inherent weak spots and improvethe acoustical performance of the com-posite barrier.

Three Ways Barriers Are Rated70

60

50

In

040

0

ELC' 30

20

10

0

Ø.4ce*.

50 100 200 400 800 1600 3200Frequency in cycles per second

SOUND TRANSMISSION CLASS (STC)

A standard STC "profile" can be lo-cated just under the performance curveso that the center section of the profileis just tangent to the curve. The twoouter portions of the profile may aver-age one db higher than the test curve.When this is done the high end of theprofile is at the STC for the barrier.Note that the solid curve has a betterSTC than the dashed, even though itsaverage performance is not as high.

70

so

50

In

400InIn

E30

20

10

0

6400 12,800

STC 40Solid curve

STC 30Dashed curve

70

60

50

040

F 30

20

10

0

average35 dbSolid curve

Dashed curve40 dbaverage

NINE-FREQUENCY AVERAGE

The average of the TL at nine speci-fied frequencies (125, 170, 250, 350,500, 700, 1000, 2000, and 4000 cyclesper second) is the most usual ratingfor sound barriers. Note that the solidcurve averages 35 db and the dashedcurve averages 40 db on this basis.

--r-

oue

al II pow wow ems

4.44

104

410"

de

#

/,

50 100 200 400 800 1600 ,

<-

_ . ,I

50 100 200 400 800 1600 3200 6400 12,800Frequency in cycles per second

3

Frequency in cyclts per second

N 64

PRIVACY ANALYZERA standard "dot field" for one of sev-eral types of environment is adjustedover the test curve until exactly tendots exceed the curve. The index ofthe dot field template then shows theprivacy analyzer rating. In this case(same solid curve as above), the rat-ing with an "N" dot field is 64.

A more recently accepted meansof expressing the sound attenuationcapacity of a barrier is known as theSound Transmission Class (STC) num-ber. This method has gained accept-ance because it gives a more reliablesingle figure measure of barrierswhich have sharp dips in TL at cer-tain frequencies.

There is a further improvedmethod which expresses the adequacyof a barrier in the form of a specificSpeech Privacy Index. It narrows thefield of attention to the 200-4000 cpsrange, takes into account the type ofbackground conditions and rates thebarrier according to its capacity toshut out all but that portion of thesound which will be unintelligible onthe receiving side. In ranking tests ofvarious materials or panels for barrier

performance, an arithmetic average ofthe noise reduction in the speech rarlgefrom 200-4000 cps also provides a use-ful single figure rating.

The required index for a barrier inany given situation will depend uponthe amount of background noise pres-ent, the degree of quiet desired, theamount of absorptive material presentand the character and intensity of theoffending noise.

For example in a typical privateoffice without air conditioning andwhere reasonable quiet is desired, thepartition barrier or wall should prefer-ably have a minimum STC rating of45 db. Recently revised F.H.A. mini-mum Standard Requirements fo:Apartment House construction call forparty walls with higher STC ratings.See table, below.

FEDERAL HOUSING AUTHORITY "TABLE 4-6"

Location of

Sound transmission ratings for Partitions

SOUND TRANSMISSION CLASS (STC)(1)

Land-use intensity less than 6.0 Land-use intensity 6.0 or highernoise 2 h h( ow background no ) ( ) ( ig background noise) (3)

Partition Room adjacent to partition Room adjacent to partitionBedroom (4) Other Bedroom (4) Other

Living unit toliving unit (5)

Class 50 Class 45 Class 45 Class 40

Living unit tocorridor (6)


Living unit topublic space(average noise) (7)


Living unit topublic space andservice areas(high noise) (8)


Bedrooms to otherrooms within sameliving unit (9)

Class 45 NA Class 40 NA

NOTES:

(1) Sound Transmission Class as determined by ASTM E90-61T.(2) See M301 for Land-use intensity.(3) Living units in buildings having year-round air-conditioning and in living units

above the 'ighth floor, use column for Land-use intensity less than 6.0.(4) Where bedrooms are separated from corridor or from adjacent living units with

closets or storage walls, the effect of such noise attenuation may be consideredin partition sound transmission.

(5) In high-rental apartments where an extreme tenant sensitivity is expected, anincrease of 5 db over the values shown is recommended.

(6) These values assume floors in corridors are carpeted; otherwise increase 5 db.See M505.6 for corridor doors.

(7) Public space of average noise includes lobbies, laundries, storage rooms, stair-ways, etc.

(8) Areas of high noise include boiler rooms, mechanical equipment rooms, elevatorshafts, incinerator shafts, garages and most commercial uses.

(9) Acoustic separation of bedrooms within living units is desirable, but not re-quired.

Lead( d Vinyl

Leaded vinyl sheet is a compositematerial comprising two vinyl sheetswith a filler of lead powder embeddedin vinyl. It is available in weightsfrom 1/2 to 3 lbs. per sq. ft., up to 1/8"in thickness and is completely limp inthe acoustical sense.

Where sheet lead and conven-tional constructions are ruled out, flex-ible leaded vinyl sheet has oftenanswered. Its performance as a free-hanging septum is given by the curvesin plate 5, page 7 and in the table

PITFALLS To111=11111=WO

The installed barrier when tested in

place will frequently fall short of its TL

or STC rating. This can be due to faulty

installation in failing to eliminate sound

leaks in seams, doors, and perimeter joints.

In many cases this lowered performance

stems from the existence of numerous

flanking paths through which the soundwaves can circumvent the barrier wall.

Common flanking paths include windows,

back b back electrical fixtures, medicine

cabinets, convector panels, cracks or leaky

wall joints, door louvres, heating ducts, an

open plenum above a hung ceiling, low TL

doors in a high TL wall etc. Failure to ap-

ply relatively simple corrective measures to

these common defects can seriously jeop-

wdize the performance of an otherwise

good barrier.

Even hairline cracks can spoil a good

barrier's effectiveness. As the example

shows, if leaks constitute 1/10 of 1 percent of the area, a barrier with a potentialTL of 38 db can only deliver 29 db.

-AVVIIMM110111.01010141a

Barrier

under section 5, page 8.While it is an expensive material,

relative to sheet lead and other build-ing materials, its use is often the leastexpensive way of solving a problemand not infrequently the only prac-tical solution. One great convenienceto the architect or designer is the widevariety of colors, embossed textures, orprinted surface patterns available. Ithas a durable surface and can lend ahandsome finish to the treated or cov-ered area.

Be Avoided

90

70

50

40(IL)

real!,

20

04ci

10In

w 7

z 54

3

2

1

0101011110 ROMM.1....'.

COVERAGE-

1 .....----100%

9919%

, ..01"---9%Fr 98%

98%

90%

80%400

rAaro_ _76%_O60%

50%pit

0 10 20 30 40Barrier transmission I s db

50 60

PRACTICAL TIPS

For Better Sound BarriersAcoustical theory shows the importance of mass,limpness, and internal damping. Field experienceshows the vital importance of freedom from leaks.The practical tips listed here are based on experi-ence and translate these theoretical factors intohow-to-do-it information.

The importance of MASSA heavy wall is normally a more effective barrier than a' light wall.The weight of lead in a composite skin should equal and preferably exceedthat of the other material in ordar to offset the coincidence.

The penalties of STIFFNESSAs a wall is made stiffer, the likelihood of problems with a coincidence dipincreases.The presence of studs fastened directly to surface skins increases the stiffnessof a wall and increases transmission of sound.Resilient mounting of surface skins is helpful.Thin skins are preferable to thick.Thin sheet lead applied to thin panel skins can solve coincidence problemsand reduce drumming noise.Viscoelastic adhesives are better than rigid varieties for laminating leadedpanels.Intermittent attachment or free hanging lead sheet can be beneficial.Stiff components of a composite panel are best located near the center orneutral plane.Leaded panel skins in double walls are frequently a more effective barrierthan stiffer, heavier and thicker conventional wall board or plaster skins.

What to do about LEAKSAir leaks in walls thru convectors, back to back electrical fixtures, wireraceways and the like should be plugged with fibrous material and a septumwhere required.Wall or panel joints must be tight. Gasketing or calking is most effective.Never underestimate the importance of small air leaks.A thin lead membrane sealed at the edges is impermeable to air.Plenum barriers are essential over partitions which stop at a hung acousti-cal ceiling. Free hanging thin lead sheet is a most effective barrier andsimple to install.Lightweight low-cost acoustical tile can acquire barrier capacity by an over-lay of thin lead sheet.Gaskets are a must around door openings.Hollow core doors should be avoided. The same is true of louvres.If in doubt about potential leaks, gasket, calk, or tape during construction.

Other considerationsA double wall is far more effective than a single one, even when the totalweight is no greater.Increasing the air space between skins will improve results particularly inconjunction with a filler or fiber glass, mineral wool or other fibrous material.Inadequate existing walls can be substantially improved by adding a sup-plemental wall comprising a thin overlay of absorptive material and a

leaded decorative surface skin.

CurveNo.

Frame or Core

2 x 4

Wood Studs

2 x 4

Wood Studs

Tabulation of Practical SouDtSCRIPTION

One Face

-x1 /2" gypsum board 1/2" gypsum board 51/2 J 22 26 31

1 17 22 27

A ix1/2" gypsum board 1/2" gypsum board 111/2 28 35 36

plus 3 lb lead plus 3 lb lead

STEEL STUD

1%" %" gypsum lath %" gypsum lath

Steel Studs plus 1/2" plaster plus 1/2" plaster

1w,

Steel Studs

amr---7-%" gypsum lath 3/8" gypsum lath

plus 1/2" plaster plus 1/2" plaster

plus 3 lb lead

1%" %" gypsum lath %" gypsum lath

Steel Studs plus 1/2" plaster plus 1/2" plaster


70

60

50

01,g 400c0

E 30c43

it

20

131/4 27 32 37

161/4 35 38 43

191/4 36 40 45

WOOD STUD

CURVE2x4 WS

3 lb lead

181/2" gypsum

both sidesbd ,

I\

v

Shaded areavalues in

2x4 WSboth

CURVE 1Aencloses

four separate

-1/2" gypsumsides, no

swm,m

extremetests )

bd ,lead

\.i'

70

60

50

1,2 400c0v.

i 30c43

H

20

Nom .Transmission loss at stated frequency Average

Wt. TLOther Face (psf) 125 170 250 350 500 700 1000 2000 4000 (db) STC Remarks

WOOD STUD WALLS

T(maximum and minimum values)

37 38 40 44 46 43 35 40 Riverbank

32 35 37 41 43 39

45 43 47 51 56 61 44 47 Riverbank

WALLS

41 43 44 46 39 47 39 41 Catalog data

46 45 47 47 49 58 45 43 Riverbank

47 47 47 49 53 61 47 47 Riverbank

STEELWs

STUD WALLS' steel studs

1

3

CURVEsamelb lead

2Cas 2A plus

both sides

same4

CURVE 2Das 2A plus

lb lead both sides

/f /i fi /

URVsamC e

3 lb le

E 2as 2A plus

I

ad both sides

15 /s'lath,

CURVEsteel studs,

1/2 plaster

2A*3/8" gypsumboth sides

1

*Curve 2A only rrcm catalog data

-0.0

lg 400c0FA

. 30(V3

it

10 10

0 060 125 250 500 1000 2000 4000 8000 60 125 250 500 1000 2000 4000 8000

Frequency in cycles per second Frequency in cycles per second

d Barrier Walls Using Sheet LeadCurve

NoFrame or Core

DESCRIPTIONOne Face Other Face

Nom . AverageWt. Transmission loss at stated frequency

TL(psf) 125 170 250 350 500 700 1000 2000 4000 (db) STC Remarks

7.1%" 3/4" gypsum lath 3/4" gypsum lath 211/4 39 40 44 48 48 48 50 55 60 48 50 RiverbankSteel Studs plus 1 /2" plaster plus 1 /2" plaster


4" lightweight paint

cement block

paint

CINDERBLOCK

4" lightweight none

cement block

6.

4 lb lead on

1/4" ply'on

1 x 2 fui.ring

40 38 40 38 40 45 48 55 56 45 44

41 43 46 44 47 54 56 63 67 51 49

Riverbank test. Much

lower TL is typical for

installed walls because

of leaks.

Riverbank

PERIMETER FRAMED PARTITIONS AND MACHINERY ENCLOSURES

Wood perimeter. %" plywood none

frame

K WALLS

VE 38t concrete block

on t/4" plywood1%" (1x2)

CURVE 3A4" lightweight cement block

painted one side

250 500 1000 2000 4000 8000Frequency in cycles per second

50

40

O

520

E

It40

30

0

11/4 18 18 16 21 21 24 25 27 22 21 24 Riverbank

I. PERIMETERPARTITIONS

MACHINERY

I

FRAMED

ENCLOSURESAND

CURVE 4Bsame as 4A plus 3 lb lead

CURVE 4Awood perimeter frame

Vs' ply one side

A --------7--,.....- .....

CURVE 4D"same

_7.__,.1"-"../as 4C plus 3 lb lead...,,,,.........

/ .. ...."......I.%'.I'/ CURVE 4C

steel framega steel sheet

,00.0I18

/N....I-----1

60 125 250 500 1000 2000 4000 8000Frequency in cycles per second

70

60

50

g 40

2

2 30

20

10

060 125

FREELEADED

I

HANGINGVINYL SHEET

CURVE 54 3 lb ft2

/--

CURVE 5B 1 5 lb ft2

//

__.........- 0 ....../

Ic......./

.0"

v/CURVE

CURVE 5C

5D - .5-

.75 lb

lb ft2

ft2

250 500 1000 2000 4000 8000Frequency in cycles per second

CurveNo.

Tabulation of Practical SoundBarrier Walls Using Sheet Lead

Frame or Core

DESCRIPTIONOneOne Face

(continued)

Nom. Average

Wt.Transmission loss at stated frequency TL

Other Faces (psf) 125 170 250 350 500 700 1000 2000 4000 (db) STC Remarks

PERIMETER FRAMED PARTITIONS AND MACHINERY ENCLOSURES

tiWood perimeter 3/4" plywood none 41/4

frame plus 3 lb lead

Steel angleand channel

1

1frame

Steel angleand channelframe

18 gauge steel none

r18 gauge steel none

plus 3 lb lead

Free-hanging leaded virvl sheet

Free-hanging leaded vinyl sheet



2

5

LEADED

3.0

1.5

.75

.50

Hollow core existing existing 2

wood (withgasketing)

Hollow core 2 lb lead existing 4.3

wood (with plus 1/2" plywood

gasketing)

Hollow core 2 lb lead plus 2 lb lead plus 6.6

wood (with 1/e" plywood 1/8" plywood

gasketing)

Solid wood existing existing

core door

33 33 34 35 37 38 41 44 45 37 40 Riverbank

26 25 27 2., 30 32 35 38 41 31 33 Riverbank

33 32 34 35 38 39 41 44 46 38 40 Riverbank

VINYL SHEET

26 26 28 28 30 32 35 41 45 32 34 Riverbank

22 22 23 23 25 29 30 35 42 28 28 Riverbank

16 16 17 16 18 21 24 30 35 22 22 Riverbank

13 13 14 13 15 18 21 26 32 18 18 Riverbank

DOORS

14 12 12 15 12 19 24 27 28 18 16 Tested at Goodfriend-Ostergaard Associates

23 20 21 27 23 28 29 31 32 25 26 Tested at GoodfriendOstergaard Associates



8

Design and Constructionof Practical Leaded Walls

Better leaded walls are being de-veloped and built every day. Thelimits of performance for new com-binations of materials and methods ofconstruction have surely not yet beenreached. Therefore, this section offersno last word on good design and con-struction. It is intended, rather, tosuggest to the designer and buildersome guide lines for improving theperformance of sound barriers.

Preparing sheet lead foruse. Because it is a soft, limp material,lead is usually shipped in rolls. It iseasily flattened by unrolling it on anyclean, smooth surface. Where necessary,kinks or wrinkles may be removed byuse of a roller or dressing with a paddedblock or small sandbag.

If the lead is to be mechanicallyfastened or hung loosely it is nowready for use. If it is to be mountedwith an adhesive, the oil film presenton rolled sheet lead must be removed.A solution of trisodium phosphate orany heavy duty alkaline cleaner doesthis quickly. Traces of the alkali arebest flushed off with warm water. Sol-vent degreasing can also be employed.Continuous cast lead sheet has no oilfilm and requires no treatment.

Mechanically fastened con-struction poses no special problems.Because lead is soft, it should not benailed or screwed without some sortof bearing pad to distribute the load.Otherwise it is liable to tear. It can benailed through a batten or secured byscrews with large washers, etc. It isalso good practice to use a cement orcalking compound to "butter" studsor furring strips which will receivesheet lead. Where the calking oradhesive has some strength, sheet leadcan be nailed to the wood grid with-out any load distributors.

Lead adhesively bonded to a sup-porting panel is usually more conven-ient to work with and provides ex-cellent acoustic results. Viscoelasticadhesives (rubber base "Contact" andsimilar types) give an added bonuswith lead by aiding in damping panelvibration. Once the lead has been pre-pared for lamination the adhesive canbe used following the manufacturer's

directions. Wire brushing the lead willimprove the adhesive bond.

Lead can be readily adhered tothin panels of plywood, hardboard,gypsum or asbestos cement board foruse as a sub-assembly in finishing thewall. Such lead laminates can beworked with the tools appropriate toth(: base stratum and represent theeasiest method of physically gettingthe lead into the wall. the use of leadsheet of equal or greater weight thanthe substrate will usually entirely elim-inate the coincidence dip found in allconventional panel materials.

To get the best acoustical per-formance from any wall there are fourcardinal points to be observed:

Plug all leaks. The amountof sound that can leak through thetiniest gap or crack is unbelievable.The penalty imposed by these leaksbecomes much greater as the wall'sperformance is improved. It is obvi-ously unwise to jeopardize the im-proved performance of a leaded wallby neglecting to eliminate the leaks.When in doubt, use a gasket, tape,calking compound or paint. Design-ing skill and meticulous care in actualconstruction are absolutely necessary.

Always avoid constructiondetails that needlessly stiffenthe wall. Part of lead's effectivenesscomes from its limpness. If lead isrigidly adhered to a stiff wall, the im-provement it affords will be minimal.In using lead to improve a cinderblockwall, for example, it is first adheredto 1/4" plywood or other surface skinand then installed on furring stripsaway from the wall. This has beenshown to give a 6 db improvement.*Adhered directly to a leak-free stiffwall of this type, the same lead wouldhave produced a negligible improve-ment.

In solid walls, where there is noisolating air space to allow the lead toassume its natural limpness, place thestiffest materials near the core of thewall, the more flexible near the sur-faces.

* See curve 3B, page 7.9

Provide an inner air spacewhen wall thickness allows. Thesame weight of materials properlysplit into two separate layers and sep-arated will nearly always outperforma single solid wall acoustically. Themore air space between the layers,generally, the better the eesult will be.There can be exceptions 'o this whenthe two layers are so mechanicallytied together that they act as one. Inthis case the stiffness will be muchgreater and the wall will suffer. Thecommon 2 x 4 stud wall is a case inpoint. Thin double wall surface skinsof plywood, hardboard or gypsumboard when backed with light gaugelead sheet will give better performancethan unleaded skins of any single ma-terial of equal weight. Staggered studsand/or resilient ties between the twofaces of the wall will provide furtherimprovement for such walls.

Absorption inside hollowwalls boosts the TL. The hollowcores described above can act as reso-nating chambers unless they containsufficient absorptive material. Inexpen-sive glass fiber or mineral wool battingin these spaces, particularly when incontact with the lead backed panelskins, will provide substantial improvement. It also provides some dampingwhich improves the wall's impact noisebehavior and helps produce the charac-teristic deadness associated with sound-proofing.

70

so

50

40

" 30

20

10

050 100 200 400 800 1600 3200 6400

Frequency In cycles per second

Two 1separated

pound ead sheetsby 3W'

Two 1- poundseparated

leadby

shoe1%" .4

rAl<*Single 1-lead sheet

pound

VEFFECTTWO

as noiseroom -

would

OFSHEETS'SPACE

THEM

reduction'transmission

be similar)

, A) USINGB) INCREASING

BETWEEN

(Plottedin test

loss curves

I

Lead PlenumBarriers

Thin sheet lead makes an excel-lent plenum barrier and is simple toinstall. Inexpensive wallboard has fre-quently been used above the partitionto carry it to the slab. A well-installedbarrier of this type can be adequatethough it is expensive in view of thelabor needed to get the required fitaround piping, wiring, ducts, etc. Inpractice a good fit is seldom achievedand thus the effort is wasted. A lessexpensive method employing thin leadsheet produces better results.

BLOCKING THE PLENUM PATHWherever partitions between rooms

stop short of the slab above leaving aspace or plenum between the hungceiling and the slab, there is a poten-tial sound path through this space.Since this common construction usuallymakes use of a lightweight acousticalceiling, the flanking through the ple-num is usually quite serious. Ceilingtiles and other acoustic surfacing ma-terials are light and porousas theymust be to fill their role of absorbingsound generated in the room. It is thisproperty that brings about the mutedor hushed quality in the room in whichthe noise is being produced. But light-ness and porosity necessary for absorp-tion cannot fill the need fot a barriermaterial. Thus it is relatively easy fornoise to pass through one ceiling,bounce from the slab, and enter anearby room through its ceiling.

Thin sheet lead is an economicand convenient material to use inblocking the plenum path. There aretwo methods by which it can be ap-plied. It may be laid over the ceilingtiles or it may be used as a curtainto continue the vertical partition fromthe hung ceiling to the slab. The firstmethod is usually called an "over theceiling" barrier; the second, a plenumbarrier.

Ventilation and lighting systems,as well as construction details of theceiling will usually govern the choicebetween these two methods. The easeof cutting and forming the thin sheetto achieve a good fit around lightingfixtures, sprinkler heads, piping andconduit, etc., makes application fairlysimple and inexpensive.

Over the ceiling barriers ofone pound lead were tested understandard conditions with a ceiling oflightweight (0.6 pounds/sq ft) ceilingtile. The attenuation was improvedfrom ?1 db to 39 db in this test. Seefigure at right.

INSTALLATION

For barriers with no penetrations

Attach wood cleat or metal partitionceiling channel to underside of floorslab. CIA desired length of lead sheet

several inches longer than plenumheight. Fold 1" of top edge over thinfiber board, wood batten or gypsumboard strip 1" wide.

Fasten to cleat with heavy duty stapleson 4" centers through 2 thicknesses oflead and the batten strip, or with roundhead screws and 3/4" flat washers on8" centers to metal channel.

Push top edge of lead against ceilingslab.

1

j

70

60

.0V

c40

oa

30

20

10

0

I I IATTENUATION OF A

LOW.TL CEILING BOARDWITH AND WITHOUT LEAD

Tested atGeiger & Hamme Labs

With 1 lb. sheet lead

Without lead


PROCEDURE

Overlap vertical edges 1".

Turn up overlapping edges and foldinto a tight standing seam.Drape of 1" will self-seal at bottom.Apply tape if desired.

For penetrations up to 2"in diameterFold a vertical 1" tuck in the lead 1"beyond the center line of penetrationin direction of work.

Slit the tuck the shortest distance fromtop or bottom to point of penetration.

Snip or cut the tuck at the location ofpipe or wires.

10

i

Drape the barrier foil over the pipe orwires. Squeeze-fit the lead around pipeor wires. Tape if desired.

Fold over the slit edges of the tuckand form a tight standing seam.

For small circular or squarepenetrating ductsFold a vertical tuck and slit as above.

Make two diagonal cuts in the tuck atpenetrat: -, point to accommodate sizeof duct.

Fold the pie-shaped flaps against theduct and tape in place.

For large rectangular ductsDrape the barrier foil from the cleatonto the top of the duct.

Fold top edge of a shorter barrier sheetover a batten strip and fasten to bot-tom of duct with sheet metal screwsand washers on 8" centers.

Make usual standing seams at verticaledges of duct and tape the flaps to theduct edges.

Lay a few feet of barrier foil on topof the duct on both sides of partitionsto reduce drumming noise.

For patching holesCut a piece of barrier lead 4" larger inall dimensions than the hole. Turnup 1" of the lead barrier all aroundthe hole and also on the patch. Insertand fold edges together and crimp toform standing seams.

for spaces with critical require-mentsLay additional lead barrier with 1"overlap over the acoustical ceiling tilein the area 6 ft. from the partition inthe noisy room.

Precautions to keep in mindBe certain that the top edge of the leadbarrier is folded over a batten strip orother smooth edge, cleat or bracket sothat the sheet is fully supported acrossits width rather than just at points ofattachment. This will effectively elim-inate any danger of tearing at fasteners.

50

0

1- pound sheet%' gypsum(2.6 pounds

NO PLENUMI I

lead

boardsq. ft

BARRIER

PLENUMBARRIER

I I


Battens, calked and fastened to slab

1- pound sheet lead

Self drape

Partition

Miscellaneous Helpful InformationWEIGHTS OF MATERIAL

Weights given are average

LBS. per LBS. perMASONRY & CONCRETE MATERIALS CU. FT. MORTAR & PLASTER CU. FT.

Cinders or ashes 40-45 Plaster 96Granite, without mortar 158-168Limestone, marble, without mortarSand or gravel, dry & loose

16590-105 EXTERIOR WALLS & WALL MATERIALS

Sand or gravel, dry & packedSandstone, bluestone, witn mortar

100-120147

Masonry (Incl. mortar;no plaster unless noted) lb/sq. ft.

WOOD (12% MOISTURE CONTENT)4" brickwork8" brickwork

3574

Birch, red oak 44 8" concrete, reinforced stone or gravel 100Cedar 22 12" concrete, reinforced stone or gravel 150Douglas fir, (coast region) 34 4" concrete block, stone or gravel 27-33Oak, white 47 8" concrete block, stone or gravel 50-60Pine, long-leaf southern 29Pine, short leaf southern 36

PARTITIONS

CONCRETE3" Gypsum block, plaster 2S 21

Cinder, concrete fill 60 4" Gypsum block, plaster 2S 25Cinder, reinforced 100-115 6" Gypsum block, plaster 2S 31Stone 144 Gypsum board, 'A" thick 2.1

Lath & plaster, 2" x 4" wood studs 14-16BRICK MASONRY (INCLUDING MORTAR) Plaster 4-5

Common 120 2" Solid plaster partition . 18

11

WHAT TRANSMISSION LOSSIS REQUIRED?

Ideally, each acoustical problemwould be solved by measuring the levelof background noise and the level ofthe noise to be shut out or containedby the barrier. The transmission lossof the barrier, at each frequency, wouldthen have to be at least the differencebetween allowable background leveland the level of disturbing noise.

The allowable background noiseis often distributed over the frequencyspectrum with most of the sound en-ergy at low frequencies. In other words,the normal noise background thecombined noise of traffic, air diffusers,distant and unintelligible conversation,etc. is somewhat predictable. Whereno specific data is available, a "normal"background can be assumed. The NC,or Noise Criteria, curves shown hereare very commonly used to representbackground level. The accompanying

90

80.0

70

60

43 50

40

a.0

30

20

1002

7575 150 300 600 1,200 2,400150 300 600 1,200 2,400 4,800

Frequency band in cycles per second

4,80010,000

Noise criteria for different typos of spaces

NC Curve Typical Applications

NC-20 to NC-30 Executive offices and confer-ence rooms for 50 people

NC-30 to NC-35 Private or semiprivate offices,reception rooms, and smallconference rooms for 20people

NC-35 to NC-40 Medium-sized offices and in-dustriel business offices

NC-40 to NC-50 Large engineering and draft-ing rooms, etc.

NC-.50 to NC-55 Secretarial areas (typing),accounting areas (businessmachines), blueprint rooms,etc.

Above NC-SS Not recommended for anytype of office

50

40.0

In2 300VI

2 20

10

MINIMUM TL REQUIRED FOR

Very quiet offices

Quiet offices

Moderatelyno sy offices

0125 250 500 1000 2000 4000 8000

Third octave band centerFrequency in cycles per second

table gives a rough gauge of back-ground level by listing the NC curvewhich commonly applies to severallocations.

Where intense noiseas from apiece of machineryis anticipated, itis usually possible to get informationfrom the manufacturer about the noiselevels it will produce. This can varywidely between manufacturers. Gar-bage disposal units, for example, man-ufactured by two companies had noiseratings (overall) of 76 and 85 db.Similar discrepancies are often foundbetween different make' of pumps,fans, air conditioners and office ma-chines. Care in purchase and installa-tion of such equipment will help re-duce the problems of sound transmis-sion.

Where it is impossible to pindown source levels, there are databased on past studies which can beused. The curves (see above) and

TRANSMISSIONLOSS OF WALL

30 db. or less

Table (see below) represent such"average requirements."

Properly designed barriers willreduce the sound transmission to ac-ceptable levels.

What to do about leaks.The unaided ear held to but nottouching the walls can locate leaksrather well. Better still, a doctor'sstethoscope, with the head removed sothat the open rubber tube scan bemoved along over cracks or joints, willlocate leaks accurately.

Most such leaks will be gaps orcracks and the remedy is calking,spackling, or plugging with an ap-propriate material. Where the gap doesnot exceed about 1/16", duct sealingtape will do a credible job.

Where no gap or crack is presentand the leaky area is large, suspectstructural flanking by a nail or bolt,electrical box, piping, etc. There isoften no simple solution to such built-in flanking. Isolating the offendingstructural elements with air or a resil-ient material is desirable but usuallyentails expensive alterationsthey arebest designed out of the wall to startand kept out by close policing duringconstruction.

Painting and finishing leadposes one possible problem. The metalis soft and even though most paintsadhere well, it can be cut or abradedby physical contact. Veneers, laminates,fabric finish, and other finishing mate-rials are best used over exposed sur-faces of lead. Where no physical con-tact is expected, lea i may be paintedwith any quality paitlt.

HEARING CONDITIONS RATING

Normal speech can be understoodquite easily and distinctly throughthe wall.

Poor

30 to 35 db. Loud speech can be understoodfairly well. Normal speech can beheard but not easily understood.

Fair

35 to 40 db. Loud speech can be heard, but is noteasily intelligible. Normal speechcan be heard only faintly, if at all.

Good

40 to 45 db. Loud speech can be faintly hoardbut not understood. Normal speechis inaudible.

Very good recommendedfor dividing walls betweenapartments.

45 db. or greater

Look Ahead with Lea

Very loud sounds, such as loud sing-ing, brass musical instruments, or aradio at full volume can be heardonly faintly or not at all.

Excellent recommendedfor band rooms, music prac-tice rooms, radio andsound studios.

Lead Industries Association292 Madison Ave.New York, New York 10017

PV/ 3/63 (35M) Printed in U.S.

sound barrier a material should consist of the capacity, and (4) … · 2013. 11. 6. · documsnt...

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