Document O1kXpwB3KbnXZNyaXe79DnpQQ

ms^m LlA17323 i I I Industry Development Cocreittee's j Subcommittee on Sound and Vibration Mlnutas S & H 1 St 1 X "A* August 2S, 1964 i1 IL>a 1Lm*:Z ..( :-gi zrr 7"^ r>t t>t, rw tr*^ V i vTiti"rrTrr THIN ISM gU.T IS A POOD BARRIER iUTUslAl, for reducing the trans mission of air bonis sound. par? IS TSC'-MCAU-T COOP because it combines high density, natural limpness end good damping capacity. LEAD 13 KECKANICAtiT POOD because it is easily forced or fitted, requires no special tools, can be readily adhered or fastened to other materials and provides a non porous aesfcrane. LEAD IS ACPUSTICALLT POOD becauae pound for pound it is a better sound barrier than ary other conventional building caterlal. LEAD IS rCfyJJCALrr POOP because it is reasonable in cost, takes less space, often saves weight, is easy to install and Is salvageable. This pamphlet contains additional inforaatioa on: The nature of sound. What constitutes a good barrier, irhat are the pitfalls to be avoided. i Examples of effective barriers containing lead, i jMiscellaneous infcreation helpful in working with sound. 1 tkvsiz cr sxyp The sounds we hear are the result of air pressure waves impinging upon our ultra sensitive ears. The frequency pitch of audible pressure waves can vary free 20-20,000 cycles p*r second. The intensity of these pressure waves and the physical energy Involved varies over a fantastic range and accordingly it is expressed logarithmically in units known as decibels. Sound can be pleasant, acceptable, tolerable, objectionable or injurious. Noise is unwanted sound and in today's society the control of noise is fast becoming s problem of major proportions involving petty annoyances, loss of privacy, lowerod working efficiency, higher accident -- rstes and piiysical inpairoerrt of hearing. 3 Tho inforestion presented here is concerned with air-borne noise rather than impact or structural borne noise. This includes familiar sources such as the crying baby, TV U HiFi sets, loud conversation, offios machines, motors, punpa, manufacturing operations, etc. It does not include noise from articles dropped or foot traffic on bare floors above, water hammer In pipes, vibration from heavy machinery or the rumble of a subway train, which is transmitted pa-iaarily through tho ground or the structure involved. VWi!l^*PBWWaWff*w WWW >35?* DOCUMENT LIA17331 WAS CREADTED ON OR AFTER JANURY 1, 1974, AND IS THEREFORE NOT SUBJECT TO PRODUCTION IN RENITA JACKSON, ET AL. V. THE GLIDDEN COMPANY ET AL. f^ummru >qn y'* ag*^**uiw LIA1733? .n'uyi|f,i j t i s. i i Industry Developcerrt Ccexdttee' Subcocnlttee os Sound and Vibration Kirmt*. xi-T,, . 'ufe*r^.-- * mini "A* -2- August 28, 1964 Air-borne sound la a aerie* of air pressure wav*a radiating Is all dir act lona frco a aourca such Ilka the ripples In a pool front dropping atonaa. That* pressure mvas will readily penetrate porous materials but will act rigid barriers Into vibration 'ditch. In turn, generates new aound of lower intensity on tha opposite aide of the barrier. WHAT COiSTmrTES a po o d s o w d b a k p j z r A good aound barrier well la one which will reduce offending nolee from adjacent area* to the level of the background nolee normally praaant and accepted In the desired quiet area or to setae slightly higher level which ie still detoed acceptable to the occupant of the quiet area and will provide speech privacy or freedcn fresa annoyance or distraction. For example, an SO db (decibel) noise impinging on a JO db til will generate a 50 db noise on the other side, if the normal and accepted level of background noise In the quiet area la 50 db, no annoyance will be experienced. If, however, the normal background noise level Is 40 <#>, it will now increase to 50 db indicating that the barrier Is inadequate. ; The physical properties of a material or s composite wall that go to aaka up a good sound barrier are high density, freedom from stiffness t and good Jar.ping capacity. Lead has all of these desired properties to s greater extent than any other common building material. The proper use of lead in combination with other materials will compensate for their deficiencies end will improve the acoustical performance of the composite barrier. To select or design s barrier one must have * measure of Its effectiveness. This is known as its Transmission Loss (TL) and represents the reduction in the level of air-borne sound that will pass through s giver, barrier. The TL is expressed in decibels as s single figure which, in turn, represents the arithmetic average of nine separate TL measurements taken et specified frequency rengee between 125-4000 cycles per second. This portion of the sound spectrua encompasses tbs frequencies of most of the sound waves to which we are subjected. Transmission Lost Is fixed property of s barrier but varies with tha frequency of the sound. Thus, In appraising the capacity of a barrier one should consider both the stated TL figure and the frequency plotting of the separate values that make up the figure. A more recent means of expressing the sound attenuation capacity of a barrier is known as the Sound Transmission Class (STC) number. This method has gained acceptance because It give# a more reliable measure of barriers which hare sharp dips In TL at certain frequencies. i Bg'nj<.-i >?!.,` > . T ^ f'*y*gy f i I\-r* LI A 1? 33 3 ] Industry Development Coc*ri.tt*, 3ufccc=.icitte on Sound and Vibration Minute* sifliaii v -3- August 28, 1964 i There 1* * further lcjiroved net hoi of expressing the attenuation capacity, known e* the Speech Privacy Index which narrow* the field of attention to the 200-4000 epa range and takes into account the factor* 4i of Intelligibility and background conditions. In ranking teat* of various materials cr panels for barrier performance, as arithmetic average of the noise reduction in the speech range freo 200-4000 cp* provide# a useful single figure rating. | The TL of all material* and barrier* increase* with frequency but at scoe point in the curve a pilateau or dip will occur with most material* when* the barrier developes travelling wave* (like microscopic vereion* of th* vmve? in a shaken rug) in sympathy with the disturbing mould waves. Uben this coincidence occurs, the amplitude of vibration in the barrier increase* aid more sound is transmitted. Lead as a material does not have this detrimental property in the frequency range* with which we are concerned. Thus, when combined with other material*. It will Improve their weak spot*. i ' i isi. Th# required TL for a barrier in any given situation will depend upon the amount of background noise present, the degree of quiet desired, the amount of absorptive material present and the character and intensity of the offending noise. for example in a typical office without air conditioning and where reasonable quiet 1* desired, the partition barrier or well should usually have a minimum average TL of 40 db. Recently revised P.H.A. wd !-i Standard Requirements for Apartment House construction call for partition walls with substantially higher 5TC ratings. See table. p i PITPAUS TO BE AVOIDED Th* installed barrier when tested in place will frequently fall short of the TL test rating for the barrier. This can be due to a highly absorptive receiving room but more frequently can result fras faulty installation in failing to allmlnat* aound leaks in seams, doors and perimeter Joints. In many cases this lowered performance stems from th* existence of numerous flanking paths vis which the sound tmves can circurrent th# barrier wall. Cocoon flanking paths include windows, back to back electrical fixtures, medicine cabinets or wall Joints; door louvres, heating ducts; open plenum above hung ceiling; low TL ' S'