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Practical Application of Sheet Lead for Sound Barriers

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Practical Application of Sheet Lead for Sound Barriers I DOCUMSNT RISUN ED 031905 EF 003 340 Practical Application of Sheet Lead for SoundBarriers. Lead Industries Association, New York,N.Y. Report No -AIA -39; CSI -DIV -13 Pub Date May. 65 Note-12p. Available from-Lead Industries Association.292 Madison Avenue, New York, New York10017 EDRS PriceMF-S025 HC 10.70 Descriptors -*Acoustical Environment. *AcousticInsulation, *Acoustics, Building Design. *BuildingMaterials. Construction (Process) Identifiers -*Sound Barriers Techniques for improving sound barriersthrough the use of lead sheeting are described. To achieve an idealsound barrier a material should consistof the following properties--(1) high density.(2) freedom from stiffness. (3) gooddamping capacity, and (4) integrity as anon-permeable membrane. Lead combinesthese desired properties to a greater extentthan any other common buildingmaterial. The proper use of lead incombination with other materials cancompensate for their deficiencies and improve the acousticalperformance of the composite barrier.Three ways in which barriers arerated for their effectiveness arediscussed and compared. Practical tips for designing better soundbarriers as well as pitfalls to beavoided are listed.Design and construction informationfor installing practical lead walls is presented and guidelines arerecommended. (TO PRACTICALAPPLICATION 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 is U 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 ASSOCIATION 292 Madison Ave. New York, N. Y. 10017 ook Ahead with Lead Practical Sound Barriers Employing Lead THE NATURE OF SOUND air-borne sound of lower intensity on ness. This is known as its Transmis- The sounds we hear are the re- the opposite side of the barrier. This sion Loss (TL) and represents the is how sound "passes through" a wall. reductioninthelevelof air-borne sult of air pressure waves impinging sound transmitted by a given barrier upon our ultra sensitive ears. The fre- quency (pitch)of audible pressure WHAT CONSTITUTES as determined under controlled condi- waves ranges from 20-20,000 cycles A GOOD SOUND BARRIER tions. The TL is expressed in decibels per second. The intensity of these pres- A good sound barrier wall is one as a single figure which, in turn, repre- sure waves in terms of their physical whichwillreduceoffendingnoise sents the arithmetic average of nine energy varies over a fantastic range from adjacent areas to the level of the separate TL measurements takenat and accordingly, itis expressed loga- backgroundnoisenormallypresent specifiedfrequencyrangesbetween rithmically in units known as decibels. and accepted in the desired quiet area 125-4000 cycles per second. This por- Sound can be pleasant, acceptable, or to some slightly higher level which tion of the sound spectrum encom- tolerable,objectionable or injurious. is still deemed acceptable to the occu- passes the frequencies most commonly Noise is unwanted sound and in to- pant of the quiet area and which will encountered and most critical in effect day's society the control of noise is fast provide speechprivacyor freedom upon speech intelligibility. becoming a problem of major propor- from annoyance or distraction.For TransmissionLossisafixed tions. Unsuppressed noise can cause example, an 80 db (decibel)noise property of a barrier but varies with petty annoyance, loss of privacy, low- impinging on a 30 db wall will gen- the frequency of the sound. The TL ered working efficiency, higher acci- erate a 50 db noise on the other side. of all materials and barriers increases dent rates and physical impairment of If the normal and accepted level of with frequency but at some point in hearing. background noise in the quiet area is the curve a plateau or dip will occur The information presented here is 50 db, no annoyance will be experi- with most materials where the barrier concerned with air-borne noise rather mced. If, however, the normal back- develops traveling waves (like micro- than impact or structure-borne noise. ground noise levelis 40 db,it will scopicversions of the waves ina Air-bornenoiseincludesfamiliar now increase to 50 db indicating that shaken rug) in sympathy with the dis- sources such as the crying baby, TV the barrier is inadequate. turbing sound waves. & HiFi sets, loud conversation, office The physical properties of a ma- terialor a composite wallthat go When this "coincidence" occurs, machines, motors, pumps, manufac- the amplitude of vibration in the bar- turing operations, etc. It does not in- to make up an ideal sound barrier clude noise from objects dropped or are high density, freedom from stiff- rier increases and more sound is trans- mitted.Thus, in appraising the ca- foot traffic on bare floors above, water ness, good damping capacity and in- pacity of a barrier one should consider hammerinpipes,vibrationfrom tegrity as a non-permeable membrane. heavy machinery or the rumble of a Lead combines these desired proper- both the stated TL figure and the fre- subway train, all of which are trans- ties to a greater extent than any other quency plotting of the separate values mitted primarily through the ground common building material. The that make up the figure. or the structure involved. proper use of lead in combination with Lead, by virtue of its limpness The pressure waves in air-borne other materials will compensate for and density, does not exhibit this co- sound radiate inall directions from their deficiencies and will improve the incidence dip in the frequency range their source much like ripples in a acousticalperformance of the com- with which we are concerned. Thus, pool radiate from a dropped pebble. posite barrier. when properly combined with other These pressure waves will readily pen- materials, it will improve or dominate etrate a porous barrier. They will also HOW A BARRIER IS RATED their inherent weak spots and improve set a rigid barrier into unnoticed vi- T-) select or design a barrier one the acoustical performance of the com- bration which, in turn, generates new must have a measure of its effective- posite barrier. - 2 Three Ways Barriers Are Rated 70 Ø. 60 4ce*. Solid curve 35 db average 50 NINE-FREQUENCY AVERAGE In 0 40 The average of the TL at nine speci- 0 fied frequencies(125, 170, 250, 350, E 500, 700, 1000, 2000,and4000cycles LC' 30 per second)is the most usual rating for sound barriers. Note that the solid Dashed curve 20 40 db curve averages 35 db and the dashed average curve averages40db on this basis. 10 0 50 100 200 400 800 1600 3200 640012,800 Frequency in cycles per second 70 60 SOUND TRANSMISSION CLASS(STC) A standard STC "profile" can be lo- 50 --r- cated just under the performance curve so that the center sectionof the profile 0 oue is just tangent to the curve. The two STC 40 40 outer portions of the profile may aver- Solid curve I the test curve. al I pow wow ems age one db higher than STC 30 F30 1# When this is done the high end of the 40 Dashed curve 4.44 410" profile is at the STC for the barrier. de Note that the solid curve has a better 20 , STC than the dashed, even though its average performance is not ashigh. 10 / 0 50 100 200 400 800 1600 , Frequency in cyclts per second 70 <-N 64 so PRIVACY ANALYZER 50 A standard "dot field" for one of sev- In eral types of environment is adjusted 40 0 over the test curve until exactly ten In In dots exceed the curve. The index of E _., 30 the dot field template then shows the I privacy analyzer rating.In this case 20 (same solid curve as above), the rat- ing with an "N" dot field is 64. 10 0 50 100 200 400 800 1600 3200640012,800 Frequency in cycles per second 3 A more recently accepted means performance, an arithmetic average of of expressing the sound attenuation the noise reduction in the speech rarlge capacity of a barrier is known as the from 200-4000 cps also provides a use- Sound Transmission Class (STC) num- ful single figure rating. ber. This method has gained accept- The required index for a barrier in ance because it gives a more reliable any given situation will depend upon singlefiguremeasureofbarriers the amount of background noise pres- which have sharp dips in TL at cer- ent, the degree of quiet desired, the Lead( d Vinyl tain frequencies. amount of absorptive material present There isa furtherimproved and the character and intensity of the method which expresses the adequacy offending noise. Leaded vinyl sheet is a composite of a barrier in the form of a specific For example in a typical private material comprising two vinyl sheets Speech Privacy Index. It narrows the officewithoutairconditioning and with a filler of lead powder embedded field of attention to the 200-4000 cps where reasonable quiet is desired, the invinyl.Itisavailablein weights range, takes into account the type of partition barrier or wall should prefer- from 1/2 to 3 lbs. per sq. ft., up to 1/8" background conditions and rates the ably have a minimum STC rating of in thickness and is completely limp in barrier according toitscapacityto 45 db.
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