overview of metrics pertinent to human response to uam noise
TRANSCRIPT
OverviewofMetricspertinenttoHumanResponsetoUAMNoise
AdvancedControls&DisplaysGroupHumanSystemsIntegrationResearchDivision
NASAAmesResearchCenterMoffettField,California
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• Noisedosemetrics;DNL,CTL• Statisticalmetrics;exemplarcommunitynoiseordinance
• Spectrum-basedmetrics
• Metricsbasedoneventfrequency
• Metricsbasedonpartialloudnessanddetection
OUTLINE
EXEMPLARROTORCRAFTAPPROACHSPECTRUM•SOUNDEVENTISTIME-VARYING•LOUDER&DISTINCTFROMTHEBACKGROUNDNOISE(AMBIENT)
• Soundexposurelevel(dose-based)
• AverageandMaximumlevels• Tone–correctedlevels• “Numberabove”levels(threshold-based)
• TimeAudible(audibilityabovebackground)
AEDTACOUSTICPREDICTIONMETRICS
Weightingsappliedtoacousticalmeasurements•TimeWeighting
• Instantaneouslevels(“peak”)• Integrationofsoundenergyoverspecific
timeperiod(125ms“fast”;1s“slow”)•FrequencyWeighting
• A-weighting(loudnessasafunctionoffrequency,atonesoundlevel)
• Unweighted(“Z”weighting)
• ”C”weighting,“B”,“D”…….
• Leq:equivalentcontinuoussoundpressurelevel (averageleveloveraperiodoftime)• Lmax:maximumlevel
• Lpk:Peaksoundpressurelevel
• L90:NinetiethPercentileSoundLevel(L90)(levelexceeded90%ofatimeperiod)
Average,StatisticalandMaximumLevels
SoundExposureLevel(SEL):Normalizationofsoundenergytoaconstanttimeinterval• Thesoundenergywithinthedurationofasoundevent(e.g.ajet
flyover)isnormalizedbyintegrationtoafixedduration,e.g.,1second.• Theenergyintegrationstarts&endsretoapeaklevel(e.g.,10dBa
singleaircraftflyoverrethemaximumlevel).• Thelongerthedurationofasoundevent,thehighertheSEL• SEL=AverageA-weightedlevel(LeqA)+10*log10(duration)
TwoSoundEvents(aircraftflyovers)AandB• Ahasahigher
maximumlevelthanB
• ButAhasalowerSELthanBbecauseitsdurationisshorter
• SELcalculatesanormalizationoftotalsoundenergytoaconstanttimeinterval
LaMAX=7874
Energyintegrationto1s
A. B.
SEL=82 SEL=87SEL=82
A. B.
MetricsbasedonSOUNDDOSE(SOUNDEXPOSURELEVEL:SEL)• Usedforhearingconservation(e.g.,OSHA)
–calculatingpermissiblesoundexposuretonoiseoveraworkday(“dosage-HL”relationship).
• A-weightedfrequencytypicallyapplied
• UsedforcalculatingtheDay-NightAverageSoundLevel,orDNL,acommunitynoiseexposuremetric.
• Percentageofpersonshighlyannoyed(%HA)byaircraftsoundcanbecalculatedbyadosage-responserelationship.
• DNLmetric(Ldn)sumsenergyacrossmultipleSELs• 10dBpenaltyfornighttimehours• Effectively,a24hournoisedose
7am 10pm 7am
80dBLeq,10s=90dBSELeach 80dB+10dBpenalty 80+10dB
Example:o TwoVTOLflyoversduringtheday,averagelevel(Leq)80dBo Oneflyoveratnight=10daytimeflyovers(dueto10dBpenalty)o Durationofoverflight=10s(90dBSELfordaytimeflights)o Soundexposuressummedandadjustedfora24hourperiodo ResultingDNL=51.4
510seconds 10seconds
• FAAcriteriaforsignificance:atleast1.5dBabove65DNL• FICON(1992)predicts~12%highlyannoyed@65DNL• ISO1996.1(2003)predicts~27%highlyannoyed
65
~12%
~27%
CurvefitstohighlySkeweddata
CTL(communitytolerancelevel,Lct):ISO1996-1
• Lct=DNLlevelatwhich50%ofthepeopleinaparticularcommunityarepredictedtobehighlyannoyed(%HA)bynoiseexposure
• Calculates%HAandDNLforaspecificcommunityasopposedtohypothetical“average”
• Thevariationinsensitivitybetweendifferentcommunitiescanbe
wide-ranging
EXEMPLARURBANRESIDENTIALNOISEORDINANCE(SANFRANCISCO)
•Thelevelsandmetricscitedincommunitynoiseordinancescouldaffectexpectationsandsensitivity
EXEMPLARURBANRESIDENTIALNOISEORDINANCE(SANFRANCISCO)
Maximumallowableinteriornoise:45dBAbetween10:00p.m.-7:00a.m.55dBAbetween7:00a.m.to10:00p.m.fromasourceoutsideofadwelling….
Article29ofthePoliceCodedefines“Ambient”asthelowestsoundlevelrepeatingitselfduringaminimumten-minuteperiod…withthenoisesourceatissuesilent,andinthesamelocationasthemeasurementofthenoiselevelofthesourceorsourcesatissue…theL90(thelevelofnoiseexceeded90%ofthetime)isaconservativerepresentationoftheambient….Innocaseshalltheambientlevelbeconsideredtobelessthan35dBAforinteriorresidentialmeasurementsand45dBAinallotherlocations.
Maximumallowableexteriornoise:5dBAabovetheambientatanypointoutsideofthepropertyplane...orthreefeetfromanywallbetweendwellings(apartments,condos,etc.)
SPECTRUMBASEDMETRICSconsiderationoflevelandfrequency
TonalCorrectionmetrics• Appliedinmanycommunitynoiseordinances• Accountsfortherelativeincreaseinnoiseloudnesswhenindividual
tonesarepredominantwithinanoverallspectrum• Examplesofsources:motors,bladepassagefrequency,electrical“buzz”• Thepresenceoftonescanadd5-8dBtomeasuredsoundsourceasa
penalty(e.g.,LPNT–Tone-correctedPerceivedNoiseLevel-foraircraftcertification).
One-thirdoctavebandspectrumofanoisewithtwosignificanttones(arrows)
Loudness adjusted sound exposure level: LLSEL • DescribedinannextoANSIS12.9part4• UseofISO226equalloudnesscontoursinsteadofA-weighting:
basedonlevelandfrequency(butaveragesovertime)• Appliespenaltiesfortypesofsound(characteristic,impulsiveness)• Tonalpenalties:5dBexceedanceinadjacent1/3octavebandsfrom
500Hz-10kHz,8dBfor160-400Hz
• MetricsbasedonNUMBEROFEVENTSaboveathreshold
AsingleDNLvaluecanresultfromdifferentcombinationsofsoundlevelsandeventfrequencyThesethreeexamplesareallequivalentto65DNLTime-energydosagemetricisnotintuitiveforcommunitiesrespondingtonoise
SEL=114dBX1event
SEL=104dBX10events
SEL=94dBX100events
Event Frequency compared to Noise Contours
20
N70(#events>70dBA)Nthreshold(#events
detectableabovebckgdnoise)
Noisecontours(Leq)
• TALAtimeaboveA-weightedSEL• TALCtimeaboveC-weightedSEL
• TAPNLtimeabovePNL-weightedSEL
• NANLnumberabovenoiselevel•Numberofeventsaboveauditorythreshold
Exampleeventfrequencymetrics
• MetricsbasedonDETECTIONand
TIME-VARYINGPARTIALLOUDNESS
GiventhesameA-weightedlevel,intermittentsoundislouderandmoredetectable
Loudnessisaffectedbyitsvarianceovertime(intermittency)
a.b.
Time:
Time:
Soun
dlevel
Loudnessisaffectedbythephenomenonofmasking:howonesoundcanaffecttheperceptionofanothersound
Twotonesthatarecloseinfrequencycaninteractsuchthataquietertoneismadeinaudible.Thisistermedthe“maskingthreshold”Thisfigureshowsamaskingtoneat1000Hertzwithasecondtone(blue-redarrow)slightlylowerinfrequencyThesecondtoneinquietisaudibleatthebluelevel(10dB).Withthemaskingtonepresent,Itslevelmustbeattheredlevel(42dB)tobeaudible
Partialloudness:LoudnessofaVTOLinthepresenceofanothersound•Redarrowsindicatefrequenciesthatwouldbeaudible(notmasked)
Partialloudness:LoudnessofaVTOLinthepresenceofanothersound
TotalLoudness
VTOLloudness
Time-varyingpartialloudnessapproach(futureISO532.3,532.4) 1.Characterizebackground
noiseintermsofstandardizedtime-varyingloudnessspectra
2.Determinethetime-varyingpartialloudnessofaVTOLtodetermineitslevelofdetectionforthathour
7am 7:30am 8:00am
Soun
dlevel
Time:
OverviewofMetricspertinenttoHumanResponsetoUAMNoise
AdvancedControls&DisplaysGroupHumanSystemsIntegrationResearchDivision
NASAAmesResearchCenterMoffettField,California
_______