INTERNATIONAL STANDARD ISO 16254 First edition 2016-05-01 Acoustics — Measurement of sound emitted by road vehicles of category M and N at standstill and low speed operation — Engineering method Acoustique — Mesurage du bruit émis par les véhicules routiers de catégories M et N l’arrêt et en fonctionnement basse vitesse — Méthode d’expertise Reference number ISO 16254:2016(E) I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 ISO 16254:2016(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2016, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Contents Page Foreword v Introduction vi Scope Normative references Terms and definitions Symbols and abbreviated terms Instrumentation 5.1 Instruments for acoustic measurement 5.1.1 General 5.1.2 Calibration 5.1.3 Compliance with requirements 5.2 Instrumentation for speed measurements 5.3 Meteorological instrumentation Acoustic environment, meteorological conditions, and background noise 6.1 Test site 6.1.1 General 6.1.2 Outdoor testing 6.1.3 Indoor hemi anechoic or anechoic testing 6.2 Meteorological conditions 6.2.1 General 6.2.2 Outdoor measurements 6.2.3 Indoor measurements 6.3 Background noise 6.3.1 Measurement criteria for A-weighted sound pressure level 6.3.2 Vehicle A-weighted sound pressure level measurement correction criteria 10 11 6.3.4 Measurement background noise when testing a component 12 Test procedures 12 7.1 Full vehicle testing 12 7.1.1 Microphone positions 12 7.1.2 Conditions of the vehicle 12 7.1.3 Test mass of vehicle 13 13 7.1.5 Operating conditions 13 7.1.6 Measurement readings and reported values 15 7.1.7 Data compilation 16 7.1.8 Standstill results 16 7.1.9 Slow speed cruise result at 10 km/h 16 7.1.10 Reported value 16 f f f 16 7.2.1 General 16 7.2.2 Instrumentation 17 7.2.3 Signal processing requirements 17 7.2.4 Test facilities 17 f 17 20 Test report 21 Annex A (informative) Information on development of ISO 16254 22 Annex B (informative) Development of frequency shift information 24 7.2 6.1 I ndo o r external s o und generatio n sys tem tes ting 6.3 B ackgro und no is e requirements when analys ing in o ne- third- o ctave b ands 7.1 Tyre s electio n and co nditio n M eas urement o 7.2 7.3 requency s hi t Frequency s hi t meas urement tes t p ro cedure M eas urement uncertainty © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n s o und to determine iii ISO 16254:2016(E) Annex C (informative) Relevance of objective acoustic data to pedestrian safety 26 Annex D (informative) Measurement uncertainty — Framework for analysis according to ISO/IEC Guide 98-3 (GUM) 28 Annex E (normative) Testing requirements for reduced uncertainty 34 Annex F (informative) f f f 35 Annex G (informative) Flowchart of the procedure for measurement and reporting of background noise 37 Annex H (informative) Flowchart for the procedure to correct A-weighted sound pressure levels38 Annex I (informative) Flowchart for the procedure to report A-weighted one-third-octaveband sound pressure levels 39 Bibliography 40 iv I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n F r e q u e n c y i d e n t i f i c a t i o n o t o n e s u s i n g t h e a s t F o u r i e r t r a n s o r m a t i o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso.org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the meaning o f ISO specific terms and expressions related to formity assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary in formation The committee responsible for this document is ISO/TC 43, Acoustics, Subcommittee SC 1, Noise, in collaboration with ISO/TC 22, Road vehicles © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n v ISO 16254:2016(E) Introduction The advent o f road transport vehicles that rely, in whole or in part, on alternative drive trains (e.g electromotive propulsion) are serving to reduce both air and noise pollution and their adverse impacts on citizens throughout the world However, the environmental benefits achieved to date by these “hybrid or pure electric” road vehicles have resulted in the unintended consequence o f removing a source o f audible signal that is used by various groups o f pedestrians (e.g in particular, blind and low vision persons) to detect the approach, presence and/or departure of road vehicles Therefore, this International Standard has been developed to provide a method to measure the sound emission o f road vehicles in standstill and low speed operation, as well as to quanti fy the characteristics o f any external sound-generation system installed for the purpose o f conveying acoustic in formation about the approach, presence and/or departure o f the vehicle to nearby pedestrians This International Standard was developed in cooperation with the Society o f Automotive Engineers (SAE) Vehicle Sound for Pedestrians Subcommittee vi I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved INTERNATIONAL STANDARD ISO 16254:2016(E) Acoustics — Measurement of sound emitted by road vehicles of category M and N at standstill and low speed operation — Engineering method Scope This International Standard is derived from ISO 362-1 and specifies an engineering method for measuring the sound emitted by M and N category road vehicles at standstill and low speed operating conditions The specifications reproduce the level o f sound which is generated by the principal vehicle sound sources consistent with stationary and low speed vehicle operating conditions relevant for pedestrian sa fety The method is designed to meet the requirements o f simplicity as far as they are consistent with reproducibility o f results under the operating conditions o f the vehicle The test method requires an acoustic environment which is only obtained in an extensive open space Such conditions usually exist during the following: — measurements o f vehicles for regulatory certification; — measurements at the manu facturing stage; — measurements at o fficial testing stations The results obtained by this method give an objective measure o f the sound emitted under the specified conditions o f test It is necessary to consider the fact that the subjective appraisal o f the annoyance, perceptibility, and/or detectability o f di fferent motor vehicles or classes o f motor vehicles due to their sound emission are not simply related to the indications o f a sound measurement system As annoyance, perceptibility and/or detectability are strongly related to personal human perception, physiological human condition, culture, and environmental conditions, there are large variations and therefore these terms are not use ful as parameters to describe a specific vehicle condition Spot checks o f vehicles chosen at random rarely occur in an ideal acoustic environment I f measurements are carried out on the road in an acoustic environment which does not fulfil the requirements stated in this International Standard, the results obtained might deviate appreciably from the results obtained using the specified conditions In addition, this International Standard provides an engineering method to measure the performance o f external sound generation systems intended for the purpose o f providing acoustic in formation to pedestrians on a vehicle’s operating condition This in formation is reported as objective criteria related to the external sound generation system’s sound pressure level, frequency content, and changes in sound pressure level and frequency content as a function o f vehicle speed As such, these measures can provide pedestrians with information on the location, speed, acceleration, and deceleration behaviour of a vehicle Annex A contains background information relevant in the development of this International Standard Normative references The following documents, in whole or in part, are normatively re ferenced in this document and are indispensable for its application For dated re ferences, only the edition cited applies For undated re ferences, the latest edition o f the re ferenced document (including any amendments) applies ISO 362–1, Measurement of noise emitted by accelerating road vehicles — Engineering method — Part 1: M and N categories © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n ISO 16254:2016(E) ISO 10844, Acoustics — Specification of test tracks for measuring noise emitted by road vehicles and their tyres ISO 26101, Acoustics — Test methods for the qualification of free-field environments IEC 60942, Electroacoustics — Sound calibrators IEC 61260–1, Electroacoustics — Octave-band and fractional-octave-band filters — Part 1: Specifications IEC 61672–1, Electroacoustics — Sound level meters — Part 1: Specifications SAE J2889–1, Measurement of Minimum Noise Emitted by Road Vehicles ISO/IEC Guide 98–3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) Terms and definitions For the purposes o f this document, the terms and definitions given in ISO 362–1 and SAE J2889–1 and the following apply 3.1 front reference plane vertical plane tangent to the leading edge of the vehicle 3.2 rear reference plane vertical plane tangent to the trailing edge of the vehicle 3.3 external sound generation system system that provides an acoustic signal to the external environment o f the vehicle for the purpose to provide information to pedestrians 3.4 component external sound generation system separately from the vehicle (3.3) intended to emit sound information which can be tested 3.5 kerb mass complete shipping mass o f a vehicle fitted with all equipment necessary for normal operation plus the mass of the following elements for M1, N1 and M2 having a maximum authorized mass not exceeding 500 kg: — lubricants, coolant (i f needed), washer fluid; — fuel (tank filled to at least 90 % o f the capacity specified by the manu facturer); — other equipment i f included as basic parts for the vehicle, such as spare wheel(s), wheel chocks, fire extinguisher(s), spare parts and tool kit Note to entry: The definition o f kerb mass can vary from country to country, but in this International Standard it re fers to the definition contained in ISO 1176 Note to entry: M and N vehicle categories are defined in SAE J2889–1 and ISO 362-1 3.6 mass in running order nominal mass of an N2, N3 or M2 vehicle having a maximum authorized mass greater than 500 kg, or an M3 vehicle as determined by the following conditions: I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) a) the mass in running order is taken as the sum o f the unladen vehicle mass and the driver’s mass; b) in the case o f category M2 and M3 vehicles that include seating positions for additional crewmembers, their mass is incorporated in the same way and equal to that o f the driver Note to entry: The driver’s mass is calculated in accordance with ISO 2416 Note to entry: Unladen vehicle mass is defined in ISO 362-1 3.7 full vehicle operation operation o f a vehicle with all systems and components operating according to the manu facturer’s specification for normal road use 3.8 simulated vehicle operation operation o f a vehicle with some systems or components disabled to reduce noise inter ference during testing which may include external signals applied to the vehicle to simulate actual in-use signals 3.9 lowest frequency of interest requency below which there is no signal content relevant to the measurement o f sound emission for f the vehicle under test Symbols and abbreviated terms T a b l e — S y m b o l s a n d a b b r e v i a t e d Symbol Unit Subclause AA′ — 7.1.5.1 BB′ — 7.1.5.1 δ1 - δ7 dB D.2 δ8 - δ14 dB D.3 δ15 - δ21 ,speed Hz — Hz D.4 6.1.3 7.2.5.2 ,ref Hz CC′ fi t e r m s a n d t h e p a r a g r a p h i n w h i c h t h e y a r e f i r s t u s e d Explanation Line perpendicular to vehicle travel which indicates the beginning of the zone to record sound pressure level during test Line perpendicular to vehicle travel which indicates end of the zone to record sound pressure level during test Input quantities to allow for any uncertainty in A-weighted sound pressure level Input quantities to allow for any uncertainty in one-third- octave-band A-weighted sound pressure level Input quantities to allow for any uncertainty in frequency measurement used for the determination o f frequency shi ft Centreline of vehicle travel Single frequency component o f external sound generation system at a given vehicle speed Single frequency component o f external sound generation system at re ference vehicle speed Frequency shi ft expressed in percent o f a re ference frequency Frequency resolution o f narrowband analysis used to measure frequency spectra for the purpose o f determining frequency del f % 7.2.5.2 7.2.5.2 ∆f Hz 7.2.3 s Hz — 5.1.1 6.3.2 vehicle m 6.1.3 Index for single test run within stopped or slow speed cruise test conditions Vehicle length used for determination of minimal space st,fwd dB 7.1.8 condition fi _ F j l L © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n shift information Sampling frequency used by digital signal processing system necessary to fulfil hemi-anechoic space requirements Vehicle A-weighted sound pressure level in stationary forward ISO 16254:2016(E) Table (continued) Symbol Unit Subclause L st,rev dB 7.1.8 L bgn dB dB dB dB dB 7.1.9 6.3.2 6.3.2 6.3.2 6.3.1 ∆ Lbgn,p-p dB 6.3.1 Lx dB D.2 L x,band dB D.3 L x,meas dB D.2 ∆L dB 6.3.2 N — 7.2.3 PP′ — 7.1.1 vAA′ km/h 5.2 Vehicle velocity when vehicle front re ference plane in forward motion passes line AA′ See 3.1 for definition o f front vBB′ km/h 5.2 Vehicle velocity when vehicle front re ference plane or rear o f vehicle in forward motion passes line BB′ See 3.1 for definition vPP′ km/h 5.2 f km/h km/h 7.2.5.2 7.1.5.2 L crs,10 L corr L test, j L testcorr, j vref vtest Explanation Vehicle A-weighted sound pressure level in stationary reverse condition Cruise vehicle A-weighted sound pressure level at a vehicle speed of 10 km/h Background noise correction A-weighted sound pressure level result of jth test run A-weighted sound pressure level result of jth test run corrected for background noise Background noise A-weighted sound pressure level Range of maximum to minimum value of the representative background noise A-weighted sound pressure level over a defined time period A-weighted sound pressure level for any stationary or cruise condition for use in assessment o f measurement uncertainty A-weighted sound pressure level per one-third-octave band or any stationary or cruise condition for use in assessment o f measurement uncertainty A-weighted sound pressure level for any stationary or cruise condition for use in assessment o f measurement uncertainty A-weighted sound pressure level of jth test result minus the A-weighted background noise level (∆ L = Ltest, j - L bgn) f Block size of digital sample used for discrete Fourier trans form or autopower spectrum analysis Line perpendicular to vehicle travel which indicates location of microphones reference plane of front reference plane Vehicle velocity when vehicle front re ference plane in orward motion passes line PP′ See 3.1 for definition o f front reference plane Re ference vehicle velocity used for calculating frequency shi ft percentage Target vehicle test velocity Instrumentation 5.1 5.1.1 Instruments for acoustic measurement General The apparatus used for measuring the sound pressure level shall be a sound level meter or equivalent measurement system meeting the requirements o f class instruments (inclusive o f the recommended windscreen, if used) These requirements are described in IEC 61672–1 The entire measurement system shall be checked by means o f a sound calibrator that fulfils the requirements of class sound calibrators in accordance with IEC 60942 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Annex D (informative) Measurement uncertainty — Framework for analysis according to ISO/IEC Guide 98-3 (GUM) D.1 General T he me a s u rement pro ce du re i s a ffe c te d b y s evera l the re s u lti ng level ob s er ve d for fac tors cau s i ng d i s tu rb a nce that le ad to va ri ation i n the s ame s ubj e c t T he s ou rce and natu re o f the s e p er turb ation s are no t comple tely known and s ome ti me s a ffe c t the end re s u lt i n a non-pre d ic table way T he accep te d for format e xpre s s ion o f u ncer tai ntie s genera l ly a s s o ci ate d with me tho d s o f me as u rement i s that given i n I S O/I E C Gu ide -3 T h i s format i ncorp orate s a n u ncer tai nty budge t, i n wh ich a l l the variou s s ou rce s o f u ncer tai nty are identi fie d a nd quanti fie d and from wh ich the combi ne d s ta nda rd u ncer tai nty c an b e obtained Uncertainties are due to the following factors: — variations in measurement devices, such as sound level meters, calibrators and speed-measuring device s; — variations in local environmental conditions that affect sound propagation at the time of measurement of Lst,fwd, Lst,rev ,and L x,band ; — va ri ation s i n veh icle s p e e d and i n veh icle p o s ition du ri ng the p as s-b y r u n; — va ri ation s i n lo c a l envi ron menta l cond ition s that a ffe c t the ch arac teri s tics o f the s ou rce; — e ffe c t o f envi ron menta l cond ition s (a i r pre s s u re, air den s ity, hum id ity, air temp erature) that i n fluence the me cha n ic a l charac teri s tics o f the s ou rce, ma i n ly engi ne p er formance; — e ffe c t o f envi ron menta l cond ition s that i n fluence the s ou nd pro duc tion o f the propu l s ion s ys tem (a i r pre s s u re, r den s ity, hu m id ity, r temp eratu re) and the rol l i ng s ound (tyre a nd ro ad s u r face temp eratu re, hu m id s ur face s) ; — test site properties (test surface texture and absorption, surface gradient) 7.3 T he uncer ta i nty de term i ne d accord i ng to repre s ents the u ncer tai nty as s o c iate d with th i s I nternationa l Sta nda rd I t e s no t cover the uncer ta i nty a s s o ci ate d with the variation i n the pro duc tion pro ce s s e s o f the ma nu fac turer T he vari ation s i n the s ou nd pre s s u re level or fre quenc y o f identic a l T he u ncer tai nty e ffe c ts may b e group e d i n the th re e are as comp o s e d o f the fol lowi ng of a production process are outside the scope of this International Standard a) u n its s ou rce s (s e e 7.3): u ncer tai nty due to cha nge s i n veh icle op eration with i n s e c utive ru n s , s ma l l change s i n we ather cond ition s , s ma l l ch ange s i n b ackgrou nd noi s e level s , and me as u rement s ys tem u ncer tai nty; the s e are re ferre d to as r un-to -r un variation s; b) u ncer tai nty due to change s i n we ather cond ition s th roughout the ye a r, ch angi ng prop er tie s o f a te s t s u r face over ti me, cha nge s i n me a s u rement s ys tem p er formance over longer p erio d s and cha nge s i n the veh icle op eration; the s e are re ferre d to as day-to - day va riation s; c) u ncer tai nty due to d i fferent te s t s ite lo c ation s , me as u rement s ys tem s , ro ad s u r face charac teri s tics and veh icle op eration; the s e are re ferre d to as s ite -to - s ite va riation s T he s ite -to - s ite va ri ation compri s e s u ncer tai nty s ou rce s compri s e s u ncer tai nty s ou rce s 28 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n from from a) , b) and c) T he day-to - d ay va ri ation a) and b) © ISO 2016 – All rights reserved ISO 16254:2016(E) D.2 Expression for the calculation of A-weighted sound pressure levels of vehicle low speed operation The general expression for the calculation of the low speed operation sound pressure level, L x, is given by Formula (D.1): L x = L x,meas + δ1 + δ2 + δ3 + δ4 + δ5 + δ6 + δ7 (D.1) where L x,meas is the A-weighted sound pressure level from any relevant test specified in this International Standard; δ1 is an input quantity to allow for any uncertainty in the measurement system; δ2 is an input quantity to allow for any uncertainty in the environmental conditions that a ffect sound propagation from the source at the time o f measurement; δ3 is an input quantity to allow for any uncertainty in the vehicle speed and position; δ4 is an input quantity to allow for any uncertainty in the local environmental conditions that a ffect characteristics o f the source; δ5 is an input quantity to allow for any uncertainty in the e ffect o f environmental conditions on the mechanical characteristics o f the power unit; δ6 is an input quantity to allow for any uncertainty in the e ffect o f environmental conditions on the sound production o f the propulsion system and the tyre/road noise; δ7 is an input quantity to allow for any uncertainty in the e ffect o f test site properties, primarily related to road sur face characteristics and sur face absorption characteristics NOTE The inputs included in Formula (D.1) to allow for errors are those considered applicable according to the state of knowledge at the time when this International Standard was being prepared, but further research could reveal that there are others NOTE The estimated values o f the delta functions can be principally positive or negative although they are considered to be zero for the given measurement (see Table D.1) Their uncertainties are not additive for the purpose of determining a measurement result NOTE The estimated value of δ7 is a nonlinear function o f vehicle speed It is e ffectively zero at zero km/h and increases nonlinearly with potential significance on the measurement result at any vehicle speed o f 20 km/h or higher D.3 Expression for the calculation of one-third-octave-band sound pressure levels of vehicle low speed operation The general expression for the calculation of the one-third-octave-band sound pressure level at a low speed operation condition, L x,band, is given by Formula (D.2): L x,band = L x,band,meas + δ8 + δ9 + δ10 + δ11 + δ12 + δ13 + δ14 (D.2) where © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n 29 ISO 16254:2016(E) ,band,meas is the A-weighted one-third-octave-band sound pressure level from any test specified in this International Standard at a band specified in IEC 61260–1; Lx δ8 is an input quantity to allow for any uncertainty in the measurement system; δ9 is an input quantity to allow for any uncertainty in the environmental conditions that a ffect sound propagation from the source at the time o f measurement; δ10 is an input quantity to allow for any uncertainty in the vehicle speed and position; δ11 is an input quantity to allow for any uncertainty in the local environmental conditions that a ffect characteristics o f the source; δ12 is an input quantity to allow for any uncertainty in the e ffect o f environmental conditions on the mechanical characteristics o f the power unit and any external sound generation system; δ13 is an input quantity to allow for any uncertainty in the e ffect o f environmental conditions on the sound production o f the propulsion system, any external sound generation system, and the tyre/road noise; δ14 is an input quantity to allow for any uncertainty in the effect of test site properties, primarily related to road surface characteristics and sur face absorption characteristics NOTE The inputs included in Formula (D.2) to allow for errors are those considered applicable according to the state of knowledge at the time when this International Standard was being prepared, but further research could reveal that there are others NOTE The estimated values o f the delta functions can be principally positive or negative although they are considered to be zero for the given measurement (see Table D.2) Their uncertainties are not additive for the purpose of determining a measurement result NOTE The estimated value of δ14 is a nonlinear function o f vehicle speed It is effectively zero at zero km/h and increases nonlinearly with potential significance on the measurement result at any vehicle speed o f 20 km/h or greater D.4 Expression for the calculation of frequency shift of vehicle low speed operation The general expression for the calculation o f the frequency shi ft a low speed operation condition, del_ f, is given by Formula (D.3): _ = {[( del f ,speed - f ,ref)/(vtest - vref)]/f ,ref} · 100+ δ15 + δ16 + δ17 + δ18 + δ19 + δ20 + δ21 fi i i (D.3) where ,ref fi is the frequency identified at the re ference vehicle speed which is defined as the re ference requency; f ,speed is the frequency identified at any vehicle speed higher than the re ference speed which is the shi fted re ference frequency due to the increase in vehicle speed; fi v test is the actual vehicle speed during the test; v ref is the re ference vehicle speed from which relative speed changes are calculated; δ15 30 is an input quantity to allow for any uncertainty in the measurement system; I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) δ16 for i s an i nput quantity to a l low for identi fic ation o f a any uncer ta i nty i n the s igna l pro ce s s i ng func tion s used fre quenc y; δ17 i s an i nput quantity to a l low for any uncer ta i nty i n the me as u re d veh icle s p e e d; δ18 i s an i nput quantity to a l low for any uncer ta i nty i n the i nput o f me a s ure d veh icle s p e e d to any ex terna l s ou nd generation s ys tem; δ19 for i s an i nput quantity to a l low s h i fte d δ20 fre quencie s any uncer ta i nty i n the identi fic ation o f re ference or by the re s p on s ible te s t engi ne er; for i s an i nput quantity to a l low any uncer ta i nty i n the e ffe c t o f envi ron menta l cond ition s on the s ound pro duc tion o f the propu l s ion s ys tem, a ny e xterna l s ou nd generation s ys tem, and the tyre/ro ad noi s e; δ21 for i s an i nput quantity to a l low any uncer ta i nty i n the e ffe c t o f te s t s ite prop er tie s NOTE The inputs included in Formula (D.3) to allow for errors are those considered applicable according to the state of knowledge at the time when this International Standard was being prepared, but further research could reveal that there are others T he e s ti m ate d va lue s o f the delta NO TE fu nc tion s c a n b e pr i nc ip a l l y p o s itive or ne gati ve a lthough they a re considered to be zero for the given measurement (see Table D.3) Their uncertainties are not additive for the purpose of determining a measurement result D.5 Uncertainty budget for determination of A-weighted sound pressure level Table D.1 — Uncertainty budget for determination of A-weighted sound pressure level of vehicle low speed operation Quantity Estimate in dB L x,meas Lx 0 0 0 δ1 δ2 δ3 δ4 δ5 δ6 δ7 Standard uncertainty, Probability distribution ui in dB — — — — — — — — coe fficient, Uncertainty contribution, 1 1 1 1 in dB — — — — — — — — Sensitivity ci — — — — — — — — u ic i u ici u , can be calculated according to the rules of ISO/IEC Guide 98-3, taking into account potential correlations between various input quantities From the NO TE i nd ividua l T he u ncer tai nty contribution s , u ncer ta i nty eva lu ation de s c r ib e d , the repre s ents combi ne d a s tanda rd fra me work th at uncer ta i nty, pro vide s u s e fu l i n for m ation to users of this International Standard This information represents the state of technical information at the information on all terms in Formula (D.1) and all interactions between such terms ti me when th i s I nter n atio n a l S ta nd a rd wa s b ei n g prep a re d Fu r ther wo rk i s ne ce s s a r y to p rovide u ncer ta i nty © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n 31 ISO 16254:2016(E) D.6 Uncertainty budget for determination of one-third-octave-band sound pressure levels Table D.2 — Uncertainty budget for determination of one-third-octave-band sound pressure levels of vehicle low speed operation Quantity L x,band,meas δ8 δ9 δ10 δ11 δ12 δ13 δ14 Estimate in dB L x, band 0 0 0 Standard uncertainty ui Probability distribution , in dB — — — — — — — — Sensitivity coe fficient ci — — — — — — — — , Uncertainty contribution u ic i , in dB — — — — — — — — 1 1 1 1 u ici u , can be calculated according to the rules of ISO/IEC Guide 98-3, taking into account potential correlations between various input quantities From the NO TE i nd ividua l uncer ta i nty contribution s , , the combi ne d T he u ncer ta i nty e va lu ation de s c rib e d rep re s ents a fra mework s ta ndard u ncer tai nty, th at p rovide s u s e fu l i n for m atio n to users of this International Standard This information represents the state of technical information at this time f Formula (D.2) and all interactions between such terms Fu r ther wo rk i s ne ce s s a r y to pro vide u ncer ta i nty i n o r m ation o n a l l ter m s i n D.7 Uncertainty budget for determination of frequency shift Table D.3 — Uncertainty budget for determination of frequency shift of vehicle low speed operation Quantity _ del fmeas δ15 δ16 δ17 δ18 δ19 δ20 δ21 Estimate in dB _ del f 0 0 0 Standard uncertainty, ui Probability distribution coe fficient, — — — — — — — — 1 1 1 1 in dB — — — — — — — — Sensitivity ci Uncertainty contribution, u ic i in dB — — — — — — — — u ici u , can be calculated according to the rules of ISO/IEC Guide 98-3, taking into account potential correlations between various input quantities From NO TE the i nd ividua l uncer ta i nty contribution s , , the combi ne d T he u ncer ta i nty e va lu ation de s c rib e d rep re s ents a fra mework s ta ndard u ncer tai nty, th at p rovide s u s e fu l i n for m atio n to users of this International Standard This information represents the state of technical information at this time f Formula (D.3) and all interactions between such terms Fu r ther wo rk i s ne ce s s a r y to p rovide u ncer ta i nty i n or m ation on a l l ter m s i n 32 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) D.8 Expanded uncertainty of measurement T he e xp a nde d u ncer tai nty, appropri ate coverage © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n U, i s c a lc u late d b y mu ltiplyi ng the combi ne d s tandard u ncer tai nty, u , b y the fac tor for the cho s en coverage prob abi l ity a s de s c rib e d i n I S O/I E C Gu ide -3 33 ISO 16254:2016(E) Annex E (normative) Testing requirements for reduced uncertainty Regu lator y u s age o f te s t pro ce du re s i s i n fluence d b y the ad m i n i s trative pro ce s s e s u s e d by variou s nationa l and i nternationa l re gu l ator y authoritie s T h i s I nternationa l Standard was develop e d with the exp e c tation that it wou ld b e uti l i ze d i n regu lator y a s s e s s ment where the veh icle manu fac tu rer has control over the te s t lo c ation, te s t e qu ipment, a nd de term i ne s the day o f te s t; however, the te s t i s ca rrie d out u nder d i re c t s up er vi s ion o f governmenta l ly accre d ite d te ch nic a l authoritie s T he s e typ e s o f re gu lator y pro ce s s e s typic a l ly a l s o i nclude form ity o f pro duc tion a s s e s s ment T he combi nation o f the s e me as u re s en s u re s the te s t re s u lts repre s ent the ac tua l veh icle p er formance wh i le applyi ng engi ne eri ng j udgement where ne ce s s a r y T he b as ic a s s u mp tion i s i f the veh icle me e ts the p er formance re qu i rements any where with i n the tolerance s s p e c i fie d i n the te s t, the veh icle wi l l provide s ati s fac tor y performance for all relevant operating conditions T here are re gu l ator y pro ce s s e s where th i s i s no t the c a s e For the regu lator y pro ce dure s where a th i rd p ar ty wi l l te s t a veh icle, add itiona l s tri ngenc y on the te s t pro ce du re i s re qu i re d to en s ure rep e atable and repro duc ible re s u lts I n the s e c a s e s , engi ne eri ng j udgement c a n no t b e appl ie d due to the re gu lator y pro ce s s as s u m i ng that a veh icle sh a l l me e t the regu lator y re qu i rements tolera nce s s p e ci fie d i n the te s t I f a veh icle c a n no t me e t re qu i rement for for all combi nation s of a l l p o s s ible cond ition s o f te s t, the veh icle i s de eme d u n s ati s fac tor y a nd noncompl i ant with re gu lator y re qu i rements 34 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Annex F (informative) F r e q u e n c y i d e n t i f i c f transformation a t i o n o t o n e s u s i n g t h e f a s t F o u r i e r F.1 General The fast Fourier trans formation or FFT is a power ful and commonly used algorithm to identi fy the spectral content of sampled time series The FFT algorithm is to be used with appropriate selected digital signal processing (DSP) parameters in order to guarantee optimal results The differences in DSP parameters depend on what aspect o f the signal needs identification or foreknowledge o f some characteristics o f the signal to be analysed The sampled representation o f a signal should not contain frequency content above the Nyquist requency or hal f o f the sampling frequency Measurement systems include anti-aliasing filters to guarantee this requirement The practical implementations o f anti-aliasing filters have their cut-o ff frequency set at 80 % to 90 % o f the Nyquist frequency f Applying an FFT on a block o f time data inherently assumes that this block repeats itsel f over time This implies that the end o f the block continues to the start o f the block without any transient behaviour This is rarely the case and transients can be observed This e ffect is re ferred to as leakage In order to keep the frequency content as close as possible to the exact frequencies, several time windows have been developed [7] These windows attenuate the signal on the extremes to minimize effects of transients The Hanning-, Flattop-, and Rectangular window are commonly used For the identification o f the frequency shi ft as a function o f vehicle speed, the frequency o f one or more tonal components in stationary signals is required F.2 Concept The identification o f tonal components requires an observation o f the signal for a su fficient time lapse This is commonly obtained by processing the time series to an averaged power spectrum This averaged power spectrum is the average of the power spectra of a number of overlapping time blocks A power spectrum is the square norm of the FFT spectrum of a time block multiplied with a time window o f the same length The square norm is obtained by the multiplication o f that FFT spectrum with its complex conjugate spectrum In order to give equal weight to all time samples from a signal energy point o f view, the overlap percentage has to be well chosen This overlap percentage depends on the type o f time window F.3 Implementation The sampling frequency o f the time series to be analysed should exceed the highest frequency o f concern with a factor o f 2,5 corresponding to an anti-aliasing filter placed at 80 % o f the Nyquist frequency However, it is recommended to use a higher factor (e.g 4) to have negligible impact o f that filter on the levels of the tonal components of interest The size o f each time block depends on the frequency resolution that is needed Tonal components can be identified with su fficient resolution i f this component is on a spectral line index 100 or higher The size o f the time block is determined by the lowest frequency o f interest © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n 35 ISO 16254:2016(E) In order to suppress leakage, the use of the Hanning window is recommended This window is a compromise between correct amplitude estimation and adequate frequency identification As a consequence, an overlap factor o f around 67 % is known to give equal weight to all time samples o f the time series being analysed F.4 Example Assume the case below: — Minimal frequency o f interest: Fmin = 125 Hz — Maximum frequency o f interest: Fmax = 400 Hz Minimal sampling frequency: — Fs ≥ Fmax × = 400 Hz × = 600 Hz Minimal duration and size of time block or maximum resolution of the spectrum: — T ≥ 100/Fmin = 100/125 Hz = 0,8 s — Bs = Fs · T = 600 Hz × 0,8 s = 680 samples — Δ F = Fs/Bs = 600/7 680 = 1,25 A wide number o f selections apply to the requirements above The selected sampling frequency should be equal or higher than the minimal sampling frequency and the frequency resolution equal or smaller than the maximum resolution: — Fs = 12 800 Hz > 600 Hz — Bs = 16 384 samples — Δ F = 12 800/16 384 = 0,781 25 < 0,8 — Fmin is at spectral line 125 Hz/0,781 25 = 160 Hz 36 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Annex G (informative) Flowchart of the procedure for measurement and reporting of background noise Figure G.1 — Measurement and reporting of background noise © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n 37 ISO 16254:2016(E) Annex H (informative) Flowchart for the procedure to correct A-weighted sound pressure levels Figure H.1 — Vehicle A-weighted sound pressure level measurement correction criteria 38 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved ISO 16254:2016(E) Annex I (informative) Flowchart for the procedure to report A-weighted one-thirdoctave-band sound pressure levels Figure I.1 — Background noise requirements for analysis in one-third-octave bands © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n 39 ISO 16254:2016(E) Bibliography [1] ISO 362-31) , Measurement of noise emitted by accelerating road vehicles — Engineering method — [2] [3] [4] [5] [6] [7] ISO 1176, Road vehicles — Masses — Vocabulary and codes ISO 2416, Passenger cars — Mass distribution ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results SAE J1715, Hybrid Electric Vehicle (HEV) and Electric Vehicle (EV) Terminology SAE J2805, Measurement of Noise Emitted by Accelerating Road Vehicles H arris f f Proc IEEE 1978 Jan., 66 (1) pp 51–83 B endat J.S., & P iersol A.G Random Data: Analysis and Measurement Procedures Interscience, New York, Second Edition, 1986 B endat J.S., & P iersol A.G Engineering Applications of Correlation and Spectral Analysis Interscience, New York, Second Edition, 1993 [8] [9] Part 3: Indoor testing M and N categories F J O n the u s e o wi ndows or h armon ic a na lys i s with the d i s cre te Fourier tran s form Wi ley- Wi ley- 1) To be published 40 I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n ISO 16254:2016(E) ICS 17.140.30 Price based on 40 pages © ISO 2016 – All rights reserved I n tern ati o n al Org an i z ati o n fo r S tan d ard i z ati o n