Hush Houses, Langley AFB VA

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AFOEHL REPORT 89-049EHO011FNACommunity Noise Survey of AF37/T-10Hush Houses, Langley AFB VACDJOHNCDC. ELLIS II, Maj, USAF, BSCWINSTON J. SHAFFER II, 1Lt, USAF, BSCJUNE989ULJUNE 1989UL3DTIC3 191199DFinal ReportDistribution is unlimited; approved for public releaseAF Occupational and Environmental Health Laboratory (AFSC)Human Systems DivisionBrooks Air Force Base, Texas 78235-550189

NOTICESWhen Government drawings, specifications, or other data are used for anypurpose other than a definitely related Government procurement operation, theGovernment incurs no responsibility or any obligation whatsoever.The factthat the Government may have formulated, or in any way supplied the drawing,specifications, or other data, is not to be regarded by implication, orotherwise, as in any manner licensing the holder or any other person orcorporation; or conveying any rights or permission to manufacture, use, orsell any patented invention that may in any way be related thereto.The mention of trade names or commercial products in this publication is forillustration purposes and does not constitute endorsement or recommendationfor use by the United States Air Force.The Public Affairs Office has reviewed this report, and it is releasable tothe National Technical Information Service, where it will be available to thegeneral public, including foreign nations.This report has been reviewed and is approved for publication.WINSTON J. SHAFFER II, XLt, USAF,Consultant, Industrial HygieneBSC/, DENNIS R. SKALKA, Lt Col, USAF, BSCChief, Consultant Services DivisionAir Force installations may direct requests for copies of this report to: AFOccupational and Environmental Health Laboratory (AFOEHL) Library, Brooks AFBTX 78235-5501.Other Government agencies and their contractors registered with the DTICshould direct requests for copies of this report to: Defense TechnicalInformation Center (DTIC), Cameron Station, Alexandria VA 22304-6145.Non-Government agencies may purchase copies of this report from: NationalTechnical Information Service (NTIS), 5285 Port Royal Road, Springfield VA22161JAMES C. ROCK,CommanderColonel,USAF,BSC

UNCLASSIFIEDSECL"ITY CLA5SIFCAT-ON OF TITISýA--,TForm Appr ovediREPORT DOCUMENTATION PAGEI& REPORT SECURITY CLASSIFiCATION1b RESTRICTIVE MARKINGSUNCLASSIFIEDNA2& SECURITY CLASSIFICATION AUTHORITY2t,OMBNO ON/AVALABI ,TYOF REPORTApprovedfor publicrelease;distributionis unlimited.SCHEDULENA4 PERFORMING ORGANiZATION REPORT NUMBER(S)S MONITORING ORGANIZATION REPORT NUMBER(S)89-049EH0101FNA6a NAME OF PERFORMNG ORGANIZATIONAF Occupational6b OFFICE SYMBOLand Environ-mental Health LaboratoryNAME OF MONITORING ORGANIZATION7bADDRESS (City, State, ard ZIP Code)FC.H6r- ADDRESS (City, State, and ZIPCodo)Brooks AFB TX74(Ifiiable)78235-55011Ba. NAME OF FUNDING , SPONSORINGORGANIZATIONBb OFFICE SYMBOL(if applicable)9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERISame as 6a8'. ADDRESS (City, State, anrd ZIP Code)10 SOURCE OF FUNDING NUMBERSPRO3RAMPROJECTTASKELEMENT NONONO1 1, 1ommun1,,ITLE (IncJ y* ýuriryNoise Qassification).Survey ofAF37/T-10 Hush Houses,WORK UNITACCESSION NOLangley AFB VA12 PERSONAL AUTI4OR(S)-aMl Major John C. Ellis II; 1Lt Winston J.Shaffer, II13a. TYPE OF REPORT13bFinalTIME COVEREDFROM14. DATE OF REPORT (Year, Month, Day)P715 PAGE COUNTJune 19897316 SUPPLEMENTARY NOTATION17COSATI CODESFIELDGROUPSUB-GROUP18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)Community noiseHush houseAnnoyanceVibration19 ABSTRACT (Continue on reverse ifnecessary and identify by block number)"-This report provides results of the survey of the AF37/T-1O Hush Houses at Langley AFB per-formed on 27-31 Jan 89 by AFOEHL.The base Bioenvironmental Engineering Service, 1 MedicalGroup/SGPB, requested this noise study to confirm their tentative conclusion that T-10 hushhouse operations are the cause of complaints of a civilian. The civilian contends hushhouse operations are vibrating his house and thus disturbing him and his wife, as well ascausing damage to his house. The condition of the two T-10 hush houses, as well as thebackground of problems with their installation, is discussed. The results of noise measurements taken at selected points 250 feet from each hush house under various operating conditions show the hush houses did not meet the design noise criteria. Measurements taken atthe complainant's property and at another house in the community showed the wind is causingthe low frequency energy to be directed downwind to produce an intermittent problem in thecommunity. Recommendations are made to operate in the short term under wind conditionswhich do not create community problems. The long term solution is to repair the hush houses20XDISTRIBUTION/ AVAILABILITY OF ABSTRACTC UNCLASSIFIED OIuLIMIrED0SAME AS RPTZI OF SOtDO Form 1473, JUN 8621CtM6J rSffyWAYCLASSIFICATION45DTIC uSERS I&JA UAF BC22,b'MPrevious editions are ObsoleteiOtUA 1 ricuea Code) 722A,%Lo ck6BOLSE( ulITY CLASSIFICATION OF T-,SUNCLASSIFIED.DA6E

INSTRUCTIONS FOR PREPARATION OF REPORT DOCUMENTATION PAGEGENERAL INFORMATIONThe accuracy and completeness of all in formation provided in trie DD Form ¶473 especially classification anddistribution limitation markings, are the responsomility of .he authoring or monitor ng Do-- activity,Because the data input on this form will be what others will retrieve from DT'C's bibliographic data base or maydetermine how the document can be accessed by future users, care should be taken to nave the form completed byknowledgeable peirsonnel For better communication and to facilitate more complete and accurate input from theoriginators of the form to those processing the data, space nas been provided in Block 22 for the name, te ephonenumber, and office symbol of the DoD person responsible for the input cited on the forrmAll information on the D0 Form 1473 should be typed.Only information appearing on or in theif there is any doubt, the block should be leftSome of the information on the forms (edescribe the content of the repor-t or identifyNOTE:repor-t, or applying specifically to the repor-t in hand, should be repor-tedblank.g-, title, abstract) vvs! oe machine indexed The terminology used shouldit as precisely as possible for future identification and retrievalUnclassified abstracts and titles describinq classified documents maXyaopear seearatelX from the documentsin an unclassified context. e.g.,.'n OTIC announcement bulletins and bibliographies. This must be consideredin the preparation and marking of unclassified abstracts and t-itles.The Defense Technical information Center (DTIC) is ready to offer assistance to anyone who needs and requests itCall Data Base input Division, Autovon 284-7044 or Commercial (202) 274-7044SECURITY CLASSIFICATION OF THE FORMin accordance with DoD 5200 1-R, information Security Program Regulation, Chapter IV Section 2, paragraph 4-200,classification markings are to be stain::asd, printed, or written at the top and bottom of the form .n capital ietters thatare larger than those used in tne t ext of the document. See also DoD 5220 22-M, industrial Secur-ty Manual forSafeguarding Classified Informatioo. Sec-tion 11,paragraph 1la(2). This form should be unclassified , if possible.SPECIFIC BLOCKSDsigate he ghstSlack 5 Monitoring Organization Report Numoeris) EnzerBlocecuityC'as-fiattn1 Reorts assgne by thc reor -imniiquei ficationaecurityMonitoring Agency This should be a numoer assigrned tiy a Coo20IR hpesisVII,XIr, ApenixsA.c) no h eotSe00viiXi.AppedixA lorother government agency and should be in accordance withANSI ST0 239 23-74 if tihe Monitoring Agency is the swme as thennztoetrterprubrilcPerfrigOBlock 1b. Restr cted 'A1arking. Enter vrie restricted marking orwafrning notice ofthe report eicg C tv0I. R0 NATO)lev5henterreor ume i lok4 nSecurity Class,f;ýatiom AuthorityEnter 'hestock 2.commonly Fised mark rigs n, accordance with 0O0 520 I -R. ChapterIV, Section 4, paragrapih 4-400 and 4.402 indicate classificationauthorityBlock 2bDeclassification ,Downgrading Schedule. 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JUN 86Block 6& Nonme of Performing Organization For in-h ous*reports, enter the name )f the performing activity For reporuprepared iinder contract or grant, enter the contractor or tiegrantee who generated the report and identify the appropriatecorporate division. schooi. laboratory. etc . of the authorBlock 6b Office SymboiPerforming OrganizationBlack 6cAddressEnter the office symbol of theEnier the address of the PerformingZP odOgnatct.saeadZPcdBlock 71 tmame of Monitoring OrganizationThis is theagency respo'rsioie for administering or monitorin g a project,co ntract, or grantif 'le monitor is also the Performin gin the case of jointOrganization. leave Biock 7a oianksponsorship, the Monrrtor n qorganization is itterrnined byadvance agreemenItiinietr'er an office a group. or acommittee reprosentint; more than one activity. service, oragencyBlack 7b Address Enter thie address of the Monioir nigOrganization inchide cty state and ZiP coaeBlock Ba Name or FundngiSponsoring Orga-nitat orEnter !15e' u official name of the organization ,wnder whose.moredato funding the jocu.ment was generated. whether 'hework ovas done in-house or by contractif the MonitoringOryanization is the same as the Funding Organization leave SaDiank-Block Sb Office 1., :;-1 - tie, re office symbol of !meFrunqn 15ponsor rrg Orga.' 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ACKNOWLEDGEMENTThe excellent support provided by Bioenvironmental Engineering Services, I MedThe work of Maj TerryGrp/SGPB, during this survey is very much appreciated.acquisition computerandin writing the data analysisM. Fairman, AFOEHL/ECR,Additionally, theprograms used for this project is gratefully acknowledged.efforts of the weather squadron and the photo lab were instrumental indocumenting this survey.II4,.:ts;ui:o rb;i.: TAHU J:"O',"*.: dy .ByCIIIr,( IbtrvJiIIA 'tvCodesA\,j,'o' 'ior

ContentsPageDO Form II. Discussion1I11. Conclusions13IV. Recommendations14References15AppendixA Measurement System Equipment List17B T-10/2 Installation Documentation21C One-Third Octave Band Data31Distribution List69iv

IllustrationsFigureTitlePage1Acceptance Test Noise Measurement Points22Map of Langley AFB and Local Area73Measurements at the Miller's Property withBoth T-10/1&2 in Afterburner, 2200 Hrs,28 Jan 8994Measurements at 1919 Seward Drive withT-10/2 in Afterburner, 2300 Hrs, 28 Jan 8911TableIZones of Influence (1:118)32Yearly Average Sound Leve s Identified to Protectthe Public Health and Welfare with an AdequateMargin of Safety (2:29)43Exclusion Distances Based on Human Effectsfor Maximum Sound Pressure Levels (1:117)4Acceptance Test on T-10 Hush Houses inAfterburner, Langley AFB, 28 Jan 895Measurements at the Miller's Property with BothT-10/1&2 in Afterburner, 2200 hrs, 28 Jan 89106Measurements at 1919 Seward Drive with T-10/2in Afterburner, 2300 Hrs, 28 Jan 8912v8

I.INTRODUCTIONA. Purpose: This report provides results of the survey of the twoAF37/T-10 Hush Houses at Langley AFB performed on 27-31 Jan 89 by AFOEHL.Thebase Bioenvironmental Engineering Service, 1 Medical Group/SGPB, requestedthis noise study to confirm their tentative conclusion that T-10 hush houseoperations are the cause of complaints by Mr Miller, a civilian.The baserequested we define and provide a solution to the problem.B. Problem: Mr Miller contends Hush House operations are vibrating hishouse.Not only is this disturbing him and his wife, but he claims this hascaused damage to his house.Aircraft maintenance operations are under arestricted work schedule to reduce night time complaints, creating amaintenance backlog.C. Scope:The condition of the two T-10 hush houses, as well as thebackground of problems with their installation, is discussed.The results ofnoise measurements taken at selected points 250 feet from each Hush Houseunder various operating conditions are reported.Measurements taken at thecomplainants property and at another house in the community are alsoexamined.Recommendations are made for both a short term and long termsolution to abate the problem.II.DISCUSSIONA.Standards.1. T-10 Hush Houses.Acceptance testing for noise on T-10 hushhouses consists of performing measurements at 20 locations on two 250 footsemi-circular arcs as shown in Figure 1.The A-weighted sound level shouldnot exceed 80 dB at any of these positions.It is necessary to control notonly audible noise, but low-frequencies which may induce vibrations insurrounding structures.Hush houses reduce audible noise by transferringconsiderable energy from the audible to the subaudible frequency range.Infrasound, frequencies below 30 Hz, are not perceived well by the human earand people do not usually notice these frequencies unless the levels are veryhigh.These low frequencies produce no adverse health effects below 145 dB.However, when sufficient energy is transmitted it may be felt directly or thevibrating material may produce audible sounds.The adverse effects of thislow frequency energy are controlled by the use of siting criteria to ensurebuildings are not within the zone of influence of these effects.The zones ofinfluence, or guidelines for minimum distances, are as shown in Table I.These zones of influence are based upon a worst case comparison of vibrationanalyses and a survey of base complaints and are not blanket criteria.

\LOCATION4 0f M1kJIAIWfvTST A TI0.4II325014rIl UIASLJPMINIS ARI 0kfOVIAfD 010004L Y TOO 1*4 POIN TI 0*40*4 10(&L LRE1ADINGS N1ED NOQTI( YAKE. 00d 0#41SIDE. Wit AtAOINGS MiJI1 rbt 4m13IAAI*4Ot*41 ATI.JviN"fN12PSIO**"OtDEFigure 1. Acceptance Test Noise Measurement Points278(

Table 1. Zones of Influence (1:118)Building FunctionWorkshop (full-time occupancy)Masonry with 15-25% door andwindow openings **Distance (ft)*550Prefabricated steel buildingssingle story500Office - masonry with 15-25% doorand window openings **single storymulti-story5001000Vibration sensitive equipment(e.g., optical microscopes, photointerpretation light tables)single story/concrete blocksingle story/prefab steelmulti-story/prefab yhousingmedical****1000-300020003000Radial distance as measured from both ends of exhaust tubeUsing a weighting factor of 1 to adjust for different buildingfunctions per ANSI S3.29-1983.HQ AFLC/DEPV, "Interim Site Planning Guidance for Aircraft JetEngine Hush House Facilities," 10 July 1984.2. Community Noise. The Environmental Protection Agency published areport (1) which outlines equivalent sound levels to protect public health andwelfare. A summary of these recommendations is shown at Table 2. The tableidentifies a 24-hour equivalent A-weighted sound level (Leq) of 70 dB toprotect public health (primarily to prevent hearing loss) and a day-nightaverage sound level (Ldn) of 55 dB(A) outdoors to prevent activityinterference in residential areas with outside space and farm residences.Table 3 shows the exclusion distances based on human effects for maximum soundpressure levels.3

Table 2.Yearly Average Sound Levels Identified to Protect thePublic Health and Welfare with an Adequate Margin ofSafety(2:29)IndoorActivity Heairing LossMeasureResidentual with Outside Space and FarmResidencesLdnResidcntial with NoOutsidv Sp'JcoLdniInterferenceConsidera-lion45To ProtectBoth Ef'-BohEInterBothfects (b)ference4545707Inside 5557070(a)557045Leq(24)(d)Leq(24)0(c)70Leq(24)Farm Land andGeneral 070(c)Code:a.b.L.d.Both Efts (b45Lcq(24)Recreational AreasConsidcraon70CommercialL-eq(24)To Protc. tA ant55770Leq( 24'.cq(24)EducationalOutdoorActivity Hearing LossSince different types of activities appear to be associated with different levels, identification of a maximum level for activity interference may be difficult except in thosecircumstances where speech communication is a critical activity. (See Figure D-2 fornoise levels as a function of distance which allow satisfactory communication.)Based on lowest level.Based only on hearing loss.An Leq(8I of 75 dB may be identified in these situations so long as the exposure overthe remaining 16 hours per day is low enough to result in a negligible contribution tothe 24-hour average. i.e. no greater than an Leq of 60 dB.Note.Explanation of identified level for hearing loss. The exposure period whichresults in hearing loss at tlte identified level is a period ot 40 years.*Ref'cr, to einergy rather than arithmetic averages.4

Table 3.Exclusion Distances Based on Human Effects for MaximumSound Pressure Levels (1:117)Source/Health EffectTarget Noise Level(Outside)Infrasound (15 Hz)ChronicAcute95 dB120 dBExclusion Distance *(ft)4000 Assuming nobuildingattenuation250 Assuming nobuildingattenuationNoiseHearing LossSpeech Interference80 dB(A)95 dB(A)80 dB(A) (assume15 dB Attenuation)65 dB(A) 250 Open work area200 Inside building(assuming 15dB Attenuation)800 95% indoorsentenceintelligibility4000 95% sentenceintelligibilityat 2 metersraised voiceDirectly behind augmentor tube.B. Methodology.A microphone with windscreen on a 1.6 meter pole wasswept up and down directly over the test point from approximately 0.3 to 3meters elevation with the microphone axis pointed directly at the hushhouse.During the approximately 30 second period of the sweep, tape recordingwas performed and the tapes were later analyzed using a real time analyzer.Spot checks with a hand held sound level meter were accomplished to comparewith analyzed results to ensure operational errors had not occurred duringdata collection. Calibration tapes were made both before and after the surveyto verify system performance and produce frequency response curves used tocorrect the data. Microphone calibration curves were also used to correct thedata. Calibration signals, produced by an acoustic calibrator, were recordedbefore and after each series of readings. A complete list of equipment isshown at Appendix A.Weather conditions, including temperature, relative humidity, windspeed and direction, and barometric pressure, were monitored at eachmeasurement location by a local weather observer. These data were used toensure weather conditions did not interfere with measurements and to correctreadings to standard conditions as appropriate.Recordings were made on 28 Jan 89 to determine if the hush housesstill met the acceptance criteria. Both hush houses, designated T-10/1 and5

T-10/2, were assessed independently at both military and afterburner powerlevels. T-10/1, installed in March 1986, is configured to test enginesinstalled in the F-15 aircraft. T-10/2, installed in March 1988, isconfigured to test bare F-100-PW-100 engines in a test stand.Only points 7through 11 for T-10/1 and 6 through 11 for T-10/2 (see Figure 1) were testedsince these included the loudest points for each configuration and were themost likely to create problems at Mr Miller's property (Figure 2).Recordingswere made on Mr Miller's property on 28 Jan 89 during the day and night.These tests were performed with T-10/1 and T-10/2 running both individuallyand together in both military and afterburner power.Readings were also takenat night on his daughter's property, located in another neighborhood (1919Seward Drive), with T-10/2 in afterburner.Background levels were recordedfor each series of tests for comparison to hush house noise levels.C.Findings:A discussion with Mr Art Woytek, Hush House Program Office, Kelly AFB,prior to our visit revealed previous hush house problems had been experiencedat Langley.At the time of installation of the second hush house (T-10/2) theCorps of Engineers allowed the contractor to install a sand foundation underand around the augmentor tube and deflector instead of the 3/4" aggregaterequired.This was in spite of the recommendation to the contrary by the HushHouse Program Office at Kelly AFB.Appendix B contains the documentationconcerning the foundation.The report shows that at initial fire up a cloudof sand was ejected from the deflector.After a foreign object damage (FOD)hazard was ruled out, testing showed the cell did not pass the acousticcriteria.Removal and inspection of the insulation disclosed the sand hadpacked the insulation, decreasing its ability to attenuate the noise.Afterinsulation replacement, the test cell passed acoustic testing.Thepresumption appears to have been the sand was no longer present in quantitiessufficient to create a problem.Our visual inspection of the test cells on28 Jan 89 revealed not only had the insulation become packed down in T-10/2,but T-10/1 had the same problem and also appeared not to have the requiredaggregate foundation.Both hush houses had sand and small gravel depositedinside the augmentor and deflector areas.6

qCCILLAMLftit factCOP-COCk.4 FAMPAT\,,42.1,idols.9SoulMiller"IW*hNOWG.AjýWksF Fe,ist1iFVAY,43,S"v.VI:r ISMrsIkeivOv IkitktooBUor"CrefkFigure 2. 14ap of Langley AFB and Local Area.7

As sunmnarized in Table 4, acoustic tests performed at 250 feet on bothhush houses revealed T-10/1 just met the 80 dB(A) criteria, but T-10/2 didnot.One-third octave band sound pressure levels for all points measured aregiven in tabular and graphic form in Appendix C. Even when properly working,hush houses testing bare engines produce higher noise levels than when testingengines installed in aircraft.Table 4.Acceptance Test on T-1O Hush Houses in AfterburnerLangley AFB, 28 Jan 89Hush HousePosition- T-10/1(F-15 Aircraft w/F-100 Engines)T-10/2(F-1O0,*OverallA-Weighted Sound Pressure 8.980.581.181.5Bare Engine)Not measured - in the shadow of T-10/2Noise tests at Mr Miller's property on the afternoon and evening of28 Jan 89 showed no appreciable difference between background noise levels andnoise produced by aircraft being tested in the hush houses, either bymeasurement or subjectively.The test results are shown at Table 5 and Figure3.As the tests at Mr Miller's property were coming to a close at 2230, hisdaughter called him to say she was experiencing effects similar to those hehad described to her.She named the exact times the hush houses had beenrunning in afterburner.Measurements taken on her property at 1919 SewardDrive (see Table 6 and Figure 4) later in the evening confirmed the presenceof increased low frequency energy during operation of T-10/2 in afterburner.The effect was also evident subjectively through both vibration sensations andaudible house vibrations.Complaints from others in the same area during thisperiod confirmed the existence of a problem.D.Observations:The degradation of the ability of the T-10 to attenuate noiseresulting from the improper foundation material allowing sand and small rocksto be drawn in by the jet engine intake and exhaust will continue unlessmeasures are taken to correct the problem.Both hush houses suffer from thisproblem.The effect is worse in T-10/2, since it is used to test bare engineswhich produce more noise than installed engines.Inspection of both hushhouses revealed gravel and sand had accumulated where the augmentor meets thedeflector section.About 50 percent of the insulation had been moved awayfrom the screen, seriously degrading the attenuation.8

MILLER BACKGROUND80-- UNWEIGHTED SPL (d9)IM-WIGHTED SL (dl(A)ý. .I.I.6 0.30J20ONE-THIRD OCTAVE BAND CENTER FREQUENCY (Hz)MILLER T-10/1&2 AFTERBURNER805II-WIHTED6SL (d (A260.20ONE-THIRD OCTAVE BAND CENTER FREQUENCY (Hz)Figure 3.Measurements at the Millers' Property with Both T-10/1 & 2 inAfterburner, 2200 Hrs, 28 Jan 19899

Table 5.Measuremnts at the Nillers' Property with Both T-10/1 A 2in Afterburner, 2200 Hrs, 28 Jan 89BackgroundSound PressureLevel(dB)T-10/1 & 2 ABSound One ThirdOctave BandFrequency(Hz)10T-10/1 & 2 70.10.30.20.10.00.3

1919 SEWARD DRIVE BACKGROUND A-WEIGHTEDSL (dll(A)ýLU0. . . . . . . . . . . . . . .40-40. .30.ONE-THIRD OCTAVE BAND CENTER FREQUENCY (Hz)1919 SEWARD DR T-10/2 AFTERBURNER80-I LU. .-WIGHTED SL (dU(A. .30ONE-THIRD OCTAVE BAND CENTER FREQUENCY (Hz)Figure 4. Measurements at 1919 Seward Drive with T-10/2 inAfterburner, 2300 Brs, 28 Jan 198911

Table 6.Measurements at 1919 Seward Drive with T-10/2 inAfterburner, 2300 Hrs, 28 Jan 89One-ThirdOctave BandFrequency(Hz)BackgroundSound PressureLevel(dB)T-10/2 ABSound PressureLevel(dB)T-10/2 1.820.010.74.62.11.20.90.2- 1.5- 2.4- 1.9- 0.10.1- 0.4- 0.5- 0.6- 0.3- .20.3AB-Afterburner12

Data collected the night of 28 Jan 89 at the Miller property isrepresented graphically in Figure 3. The background level is 42.9 dB(A).With both hush houses running in afterburner the level is 43.8 dB(A), aninsignificant difference, especially since these readings were collected atdifferent times. The low frequency data, below about 50 Hz, show very littledifference, with all frequencies indicating readings in the low 50 dB range.No audible difference existed and no rattling of the house occurred.Figure 4shows direct evidence of the problem collected at 1919 Seward Drive after MrMiller's daughter called. The background level of 42.9 dB(A) versus the levelof 43.2 dB(A) with T-10/2 in afterburner is again not meaningful.However, at50 Hz and below the change is dramatic.Differences of 14 to 22 dB (equal tolevels 25 to 158 times higher) make apparent the effect the wind has onshifting this effect. The wind was 11 degrees at less than 5 knots. Thislocation is at 191 degrees relative to the hush houses.Therefore, it wasdirectly downwind from the hush houses. Thus, the wind directs the noise,particularly at low frequencies, causing an intermittent problem at any oneparticular location.The A-weighted sound pressure level caused by hush house operations doesnot exceed background levels by any significant amount. The measuredafterburner noise level of less than 45 dB(A) would not contribute to the Ldnenough to cause the EPA recommended Ldn level of 55 dB(A) to be exceeded.Thus, technically there is no audible community noise problem created byoperation of the hush houses even in their presently degraded condition. Theexclusion distance levels for human effects are also not exceeded.III.CONCLUSIONSA. Both T-10 Hush Houses are out of specification and must be repaired.The first T-10 would probably not pass if a bare engine was installed. Thevisual evidence of packed insulation accompanied by the presence of sand andsmall gravel in T-10/1 and 2 indicates the same problem with both hushhouses. The performance of both will continue to degrade, creating morewidespread problems and complaints.B. The low frequency energy, increased because of the degradation of thehush houses (primarily T-10/2 at present), is being channeled by the wind tocreate problems downwind of the hush houses.The problem is intermittentsince only at certain times is a particular populated area downwind of thehush houses. The Environmental Protection Agency recommendation of an Ldn of55 dB(A) is not exceeded by hush house operation.C. The complaints by Mr Miller of the rattling of windows and otherobjects were validated during a visit by the base bioenvironmental engineeringand public affairs offices. Recordings taken during this AFOEHL survey at MrMiller's daughter's house objectively confirm t

The condition of the two T-10 hush houses, as well as the background of problems with their installation, is discussed. The results of noise measure-ments taken at selected points 250 feet from each hush house under various operating con-ditions show the hus

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