Document ba701Lq8y7n6BBVxy3x0wmNao

-v ! =; , r1 v'v f LIA24108 ___JL 1 --i-* -> ---1 ' April lh, 1S6k SUBJECT: BOISE COBTSOL CASS HISTORt To Hesters of the Lead Industries Association, Inc.: Attached Is the third detailed report of a ease history of a successful experioental Installation of lead for noise control. o It fcllovs case histories sent to you with our letters of December t, 1962 and March 20, l$6h. Ve hope you will find the InfomatIon contained In this cost recent case history useful In your own prcootion and sale of lead for noise control. Very truly yours. RLZ:*k Znc. Executive Vice President - mm* nm ----------------------------- ----------- n"^r LIA 2 A10 9 itUiaiwtJti LEAD FOR SOLES CCt/TROL -- CASS HISTORT # 3 Hotel Ar.jrlca. Hartford Summary; When a change in floor plan of the new Hotel America io Hartford, Connecticut cade it necessary to thin a section of the vail between hotel rooms, the architect contacted LIA for help. He required the same sound Isolation la a vail not exceeding l" In thickness as he expected to achieve with a good conventional wall 4" thick. A basic construction was suggested by LIA and the final detailed drawing was worked out by Levis Goodfrlend through the ILZRO consulting arrangeoent. Tests of the com pleted wall show that the thin lead "fin" does not lower the transmission loss of that vail of the rocm. Testing conditions were poor and the per formance ratings are cade questionable by leakage of sound through cracks in both the conventional wall and the thin lead fin. We, therefore, prefer not to stress the numerical results (although they show the lead wall to be slightly better than the conventional vail). History and Problem: Mr. Hartln Ginsberg of the architectural fir* of Curtis and Davis phoned LIA January S3* 19^3. A revision of the floor plan of the Hotel America In Hartford, Conn., had made It necessary to bring the ccemon vail betveen hotel rooms to Join the front vail of the building at narrow millions Instead of on the columns. The specific problem was to find some wall construction which. In the allowable l" of wall thickness, would provide sound isolation equal to that of the con ventional wall used In the balance of the room. O This conventional wall was 3/8" plaster over 3/8" gypsum lath on both sides of 2$" steel studs. Glass fiber batting was called for In the space betveen. The performance of such * vail Is estimated to be 42 db ninefrequency average. -more- '\ N 1982.01 Hotel America, Hertford -2- April lU, 1964 Action talent Immediately following Glnsburg's call we viaited Cinsburg's office. The Job was past deadline and immediate action wo* called for. Preliminary estimate* showed what, type of structure waa called for. This wa* a laminate of gypsum board with fairly heavy aheet lead (6 or 8 pound). By early March, detailed drawings were in the hand* of the architect. The detail suggested for the thin wall (subsequently called the "fin" or "lead fin") 1* shown in the attached drawing. It should be noted that, a* installed and Inspected on February 6, 1964, the felt gasketing had been replaced with urethane foaa gasket and the calking had not been done though the roan was apparently finished. Furthermore, at one place the metal windcm frame passes into the Joint between the fin and the front wall of the building. At this point the gasketing had been cut away leaving a gap of about 3/l6"x 2". Rather great improvement in performance can be expected when this gap is closed xtb calking. This wa* not the only uncertain factor in making the test. There wa* no choice of roce* to be tested -- only one room was available which had a doer installed and which was not filled with supplies of same kind. The door wa* about 15 lnchea shorter than the door opening and obviously transom will be installed at a later date. This opening wa* blocked with corrugated card board during the tests, but noise pouring out of the doorway of the source rooa to the corridor sued frea the corridor through ths makeshift door barrier contributed to the noise level in the receiving room without any doubt. Despite a very high ambient noise in the receiving room (overall 56 db) due to construction work in progress and air diffuser noise, the signal level* were at least 6 db higher than the background. If the roam is retested under better conditions,it is almost certain that the high ambient noise will limit the test results unless a more powerful noise source is employed. Results: Figure 2 shows the measured noise reduction through the conventional wall and through the vail which had the short lead fin. It should be emphasised that both walls are probably much better than this. The measured reduction is severely limited by noise leakage. In both cases the curves are based on four readings in the source room and four in the receiving roaa. Except in the lowest frequency band, readings in either room agreed within about 3 <U> with the significant exceptions marked. The asterisk marks band* where the location nearest the cracks at the fln-frort wall Joint read high. The star indicate# band* with high readings for the location nearest the cracks in the conventional wall. By placing an extension microphone close to the crack* it wa* possible to record a sound spectrum which peaked in these bands. The relatively lev frequencies at which the conventional wall Joint peaked are quite unexpected and do not teem to be the tort of behavior normally assocleted with leakage through cracks. We have no explanation for this. It wa* quite easy to localise these leaks with a stethoscope and the quality of the sound (pitch of the noise) seemed to agree with the spectrum we metered. wi " -more- V I W L I. T"'WV i mi i.i" .. iwa mnunf LIA2A111 ub o Hotel America, Hartford -3- Aprll Ik, 1964 Technical addendum: The equipment used was loaned by the Research Lab of American Smelting and Refining Company and Hr. John Honan of their research staff participated In the. tests. The equipment was: Altec 755-C speaker in cn infinite baffle, a Grayson-Statler noise generator, EV 65IA calibrated microphone (calibration correction were not required or mad* In this test), and an IAC sound spec trometer rich'octave band analyzer. 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