Iec 61094 5 2016

This p rt of IEC 610 4 des rib s method of determinin the pres ure sen itivity by comp rison with either a la oratory stan ard micro hone or another workin stan ard micro hone with known

THIS PUBLICATION IS COPYRIGHT PROT CTED

Copyright © 2 16 IEC, Ge e a, Switzerla d

Al rig ts reserv d Unles oth rwise sp cifie , n p rt of this p blc tio ma b re ro u e or uti ze in a y form

or b a y me ns,ele tro ic or me h nic l in lu in p oto o yin a d microfim, with ut p rmis io in writin from

eith r IEC or IEC's memb r Natio al Commite in th c u try of th re u ster If y u h v a y q estio s a o t IEC

c p rig t or h v a e q iry a o t o tainin a ditio al rig tsto this p blc tio , ple se c nta t th a dres b low or

y ur lo al IEC memb r Natio al Commite for furth r informatio

Droits d re ro u tio réserv s Sa f in ic tio c ntraire, a c n p rtie d c te p blc tio n p ut être re ro uite

ni uti sé so s q elq e forme q e c soit et p r a c n pro é é, éle tro iq e o mé a iq e, y c mpris la p oto o ie

et les microfims, sa s la c rd é rit d l EC o d Comité n tio al d l EC d p ys d d ma d ur Si v usa ez d s

q estio s sur le c p rig t d l EC o si v us d sirezo te ir d s droits su pléme taires sur c te p blc tio , uti sez

les c ord n é s ci-a rès o c nta tez le Comité n tio al d l EC d v tre p ysd résid n e

Th Intern tio al Ele trote h ic l Commis io (IEC) is th le din glo al org nizatio th t pre ares a d p blsh s

Intern tio al Sta d rds for al ele tric l ele tro ic a d relate te h olo ies

Ab ut IEC publ c tio s

Th te h ic l c nte t of IEC p blc tio s is k pt u d r c nsta t re iew b th IEC Ple se ma e sure th t y u h v th

latest e itio , a c rig n a or a ame dme t mig t h v b e p blsh d

IEC Catalog e - webstore.ie c / catalog e

Th sta d-alo e a plc tio for c nsultin th e tire

biblo ra hic l infor matio o IEC Inter natio al Sta d rds,

Te h ic l Sp cific tio s, Te h ic l Re orts a d oth r

d c me ts Av ia le for PC, Ma OS, An r oid Ta lets a d

iPa

IEC publc tio s s arc - w w.ie c /se rc pub

Th a v n e se rc e a les to fin IEC p blc tio s b a

v riety of crite a (r efer en e n mb r, te t, te h ic l

c mmite ,…) It also giv s informatio o pr oje ts, re la e

a d w ith r awn p blc tio s

IEC J st Publs ed - webstore.ie c / j stpubls ed

Sta u to d te o al n w IEC p blc tio s Just Pu lsh d

d tais al n w p blc tio s rele se Av ia le o ln a d

also o c a mo th b emai

Ele to edia - ww w.ele to edia.org

Th w or l 's le din o ln dictio ary of ele tro ic a d

ele tr i al terms c ntainin 2 0 0 ter ms a d d finitio s in

En lsh a d Fre c , w ith e uiv le t terms in 15 a ditio al

la g a es Also k now n as th Inter natio al Ele tr ote h ic l

Vo a ulary (IEV) o ln

IEC Glos ary - std.ie c / glos ary

6 0 0 ele trote h ic l ter min lo y e tr i s in En lsh a d

Fre c e tr acte from th Terms a d Definitio s cla se of

IEC p blc tio s is u d sin e 2 0 Some e tr i s h v b e

c le te fr om e r lier p blc tio s of IEC TC 3 , 7 , 8 a d

CIS R

IEC Cu tomer Serv ic Cente - webstore.ie c / cs

If y u w ish to giv us y our fe d a k o this p blc tio or

n e furth r as ista c ,ple se c nta t th Customer Ser vic

Ce tr e: csc@ie c

A pro os de lIEC

L Commis io Ele trote h iq e Intern tio ale (IEC) est la première org nisatio mo diale q i éla ore et p ble d s

Normes intern tio ales p ur to t c q i a trait à léle tricité, à léle tro iq e et a x te h olo ies a p re té s

A pro os de publc tio s IEC

L c nte u te h iq e d s p blc tio s IEC est c nstamme t re u Ve i ez v us as urer q e v us p s é ez lé itio la

plus ré e te, u c rig n um o ame d me t p ut a oir été p blé

Catalog e IEC - webstore.ie c / catalog e

Ap lc tio a to ome p ur c nsulter to s les r enseig eme ts

biblo ra hiq es sur les Normes intern tio ales,

Sp cific tio s te h iq es, Ra p r ts te h iq es et a tr es

d c me ts d l EC Disp nible p ur PC, Ma OS, ta letes

An roid et iPa

Re h rc e de publc tio s IEC - w w.ie c / se rc pub

L r ec er ch a a c e p rmet d tr ou er d s p blc tio s IEC

e uti sa t difér ents c tères (n mér o d référe c , te te,

c mité d’étu es,…) Ele d n e a s i d s infor matio s sur les

pr ojets et les p blc tio s rempla é s o r etir ées

IEC J st Publs ed - webstore.ie c / j stpubls ed

Restez infor mé sur les n u eles p blc tio s IEC Just

Pu lsh d d tai e les n u eles p blc t io s p r ues

Disp nible e lg e et a s i u e fois p r mois p r emai

Ele to edia - ww w.ele to edia.org

L pr emier dictio n ir e e lg e d ter mes éle tro iq es et

éle tr i u s I c ntie t 2 0 0 termes et d finitio s e a glais

et e fr an ais, ainsi q e les ter mes é uiv le ts d ns 15

la g es a ditio n les Eg leme t a p lé Vo a ulair e

Ele tr ote h iq e Inter natio al (IEV) e lg e

Glos aire IEC - std.ie c / glos ary

6 0 0 e tré s termin lo iq es éle tr ote h iq es, e a glais

et e fr an ais, e tr aites d s articles Ter mes et Définitio s d s

p blc tio s IEC p r ues d p is 2 0 Plus c rtain s e tr ées

a té e res e traites d s p blc tio s d s CE 3 , 7 , 8 et

CIS R d l EC

Serv ic Clents - webstore.ie c / cs

Si v us d sir ez n us d n er d s c mme tair es sur c te

p blc tio o si v us a ez d s q estio s c nta tez-n us:

csc@ie c

Partie 5: Méthodes pour l'étalonnage en pression par comparaison des

Warnin ! Mak e s re th t y ou o tain d this publc tion from a a thorize distributor

Ate tion! Ve i ez v ou a s rer qu v ou av ez o te u c te publc tion via u distribute r a ré

CONTENTS

FOREWORD 4

1 Sco e 6

2 Normative referen es 6

3 Terms an definition 6

4 Referen e en ironmental con ition 7

5 Prin iples of pres ure cal bration by comp rison 7

5.1 Prin iples 7

5.1.1 General prin iple 7

5.1.2 General prin iples u in simultane u ex itation 7

5.1.3 General prin iples u in seq ential ex itation 8

5.2 Me s rin the output voltages of the micro hones 8

6 Factors influen in the pres ure sen itivity 8

6.1 General 8

6.2 Micro hone pres ure eq al zation mec anism 8

6.3 Polarisin voltage 9

6.4 Referen e s ield config ration 9

6.5 Pres ure distribution over the dia hragms 9

6.6 De en en e on en ironmental con ition 10 6.7 Val dation 10 7 Calbration u certainty comp nents 10 7.1 General 10 7.2 Sen itivity of the referen e micro hone 10 7.3 Me s rements of micro hone output 1

7.4 Dif eren es b twe n the sou d pres ure at the test micro hone an that at the referen e micro hone 11 7.5 Acou tic imp dan es of the micro hones 1

7.6 Micro hone se aration distan e 1

7.7 Micro hone ca acitan e 11 7.8 Micro hone config ration d rin cal bration 1

7.9 Un ertainty on pres ure sen itivity level 12 An ex A (informative) Examples of couplers an j g for simultane u ex itation 13 A.1 A coupler for u e with WS2 micro hones at freq en ies up to 10 kHz 13 A.2 A j g for u e with WS2 or WS3 micro hones at freq en ies up to 2 kHz 14 An ex B (informative) Examples of couplers for seq ential ex itation 16 B.1 A coupler for u e with LS1 micro hones at freq en ies up to 8 kHz 16 B.2 A coupler for u e with WS2 micro hones at freq en ies up to 16 kHz 16 An ex C (informative) Determinin the o en-circ it sen itivity of a me s rement micro hone without u in the in ert voltage method 18 An ex D (informative) Typical u certainty analy is 19 D.1 Introd ction 19 D.2 Analy is 19 D.3 Combined an exp n ed u certainties 21

Bibl ogra h 2

Fig re A.2 – A j g fited with an LS2 an WS2 micro hone 14

Fig re A.3 – Example ar an ement of LS2 an WS2 micro hones in a j g 14

Fig re A.4 – Example ar an ement of LS2 an WS3 micro hones in a j g 14

Fig re B.1 – A coupler for u e with LS1 micro hones 16

Fig re B.2 – A coupler for u e with WS2 micro hones 17

Ta le A.1 – Calc lated cor ection to b ad ed to the sen itivity level of the WS3

micro hone when u in the ar an ement in Fig re A.4 15

Ta le D.1 – Example u certainty bu get 2

INTERNATIONAL ELECTROTECHNICAL COMMISSION

Part 5: Methods for pressure cal bration of working

standard microphones by comparison

1) Th Intern tio al Ele trote h ic l Commis io (IEC) is a worldwid org nizatio for sta d rdizatio c mprisin

al n tio al ele trote h ic l c mmite s (IEC Natio al Commite s) Th o je t of IEC is to promote

intern tio al c -o eratio o al q estio s c n ernin sta d rdizatio in th ele tric l a d ele tro ic fields To

this e d a d in a ditio to oth r a tivities, IEC p blsh s Intern tio al Sta d rds, Te h ic l Sp cific tio s,

Te h ic l Re orts, Pu lcly Av ia le Sp cific tio s (PAS) a d Guid s (h re fer refere to as “IEC

Pu lc tio (s)”) Th ir pre aratio is e truste to te h ic l c mmite s; a y IEC Natio al Commite intereste

in th su je t d alt with ma p rticip te in this pre aratory work Intern tio al g v rnme tal a d n

n-g v rnme tal org nizatio s laisin with th IEC also p rticip te in this pre aratio IEC c la orates closely

with th Intern tio al Org nizatio for Sta d rdizatio (ISO) in a c rd n e with c n itio s d termin d b

a re me t b twe n th two org nizatio s

2) Th formal d cisio s or a re me ts of IEC o te h ic l maters e pres , as n arly as p s ible, a intern tio al

c nse sus of o inio o th rele a t su je ts sin e e c te h ic l c mmite h s re rese tatio from al

intereste IEC Natio al Commite s

3) IEC Pu lc tio s h v th form of re omme d tio s for intern tio al use a d are a c pte b IEC Natio al

Commite s in th t se se Whie al re so a le eforts are ma e to e sure th t th te h ic l c nte t of IEC

Pu lc tio s is a c rate, IEC c n ot b h ld resp nsible for th wa in whic th y are use or for a y

misinterpretatio b a y e d user

4) In ord r to promote intern tio al u iformity, IEC Natio al Commite s u d rta e to a ply IEC Pu lc tio s

tra sp re tly to th ma imum e te t p s ible in th ir n tio al a d re io al p blc tio s An div rg n e

b twe n a y IEC Pu lc tio a d th c r esp n in n tio al or re io al p blc tio sh l b cle rly in ic te in

th later

5) IEC itself d es n t pro id a y atestatio of c nformity In e e d nt c rtific tio b dies pro id c nformity

as es me t servic s a d, in some are s, a c s to IEC marks of c nformity IEC is n t resp nsible for a y

servic s c rie o t b in e e d nt c rtific tio b dies

6) Al users sh uld e sure th t th y h v th latest e itio of this p blc tio

7) No la i ty sh l ata h to IEC or its dire tors, emplo e s, serv nts or a e ts in lu in in ivid al e p rts a d

memb rs of its te h ic l c mmite s a d IEC Natio al Commite s for a y p rso al injury, pro erty d ma e or

oth r d ma e of a y n ture wh tso v r, wh th r dire t or in ire t, or for c sts (in lu in le al fe s) a d

e p nses arisin o t of th p blc tio , use of, or rela c u o , this IEC Pu lc tio or a y oth r IEC

Pu lc tio s

8) Ate tio is drawn to th Normativ refere c s cite in this p blc tio Use of th refere c d p blc tio s is

in isp nsa le for th c re t a plc tio of this p blc tio

9) Ate tio is drawn to th p s ibi ty th t some of th eleme ts of this IEC Pu lc tio ma b th su je t of

p te t rig ts IEC sh l n t b h ld resp nsible for id ntifyin a y or al su h p te t rig ts

International Stan ard IEC 610 4-5 has b en pre ared by IEC tec nical commite 2 :

Electro cou tic

This edition can els an re laces the first edition publ s ed in 2 01 This edition con titutes a

tec nical revision

This edition in lu es the fol owin sig ificant tec nical c an es with resp ct to the previou

edition:

a) detai s of ad itional comp nents of u certainty;

b) revised cor ection for typ WS3 micro hones;

The text of this stan ard is b sed on the fol owin doc ments:

Ful information on the votin for the a proval of this stan ard can b fou d in the re ort on

votin in icated in the a ove ta le

This publcation has b en drafed in ac ordan e with the ISO/IEC Directives, Part 2

A l st of al p rts in the IEC 619 4 series, publ s ed u der the general title Me su reme nt

microp ho es, can b fou d on the IEC we site

The commit e has decided that the contents of this publcation wi remain u c an ed u ti

the sta i ty date in icated on the IEC we site u der "htp:/we store.iec.c " in the data

related to the sp cific publ cation At this date, the publ cation wi b

• reconfirmed,

• with rawn,

• re laced by a revised edition, or

• amen ed

ELECTROACOUSTICS – MEASUREMENT MICROPHONES –

Part 5: Methods for pressure cal bration of working

standard microphones by comparison

This p rt of IEC 610 4-5 is a pl ca le to workin stan ard micro hones with remova le

protection grid me tin the req irements of IEC 610 4-4 an to la oratory stan ard mi

cro-phones me tin the req irements of IEC 610 4-1

This p rt of IEC 610 4 des rib s method of determinin the pres ure sen itivity by

comp rison with either a la oratory stan ard micro hone or another workin stan ard

micro hone with known sen itivity in the resp ctive freq en y ran e

Alternative comp rison method b sed on the prin iples des rib d in IEC 610 4-2 are

p s ible but b yon the s o e of this p rt of IEC 610 4

The folowin doc ments, in whole or in p rt, are normatively referen ed in this doc ment an

are in isp n a le for its a pl cation For dated referen es, only the edition cited a pl es For

u dated referen es, the latest edition of the referen ed doc ment (in lu in an

3 Terms and definitions

For the purp ses of this doc ment, the terms an definition given in IEC 610 4-1 an the

la oratory stan ard micro hone or workin stan ard micro hone to b cal brated by

comp rison with a referen e micro hone

3.3

monitor microphone

3.4

coupler

device whic , when fited with micro hones, forms a cavity of predetermined s a e an

dimen ion an provides an acou tic coupl n element b twe n the micro hones an

b twe n the micro hones an the sou d source

3.5

j g

device whic , when fit ed with micro hones, hold them with their dia hragms face to face

se arated by a smal distan e but do s not en lose the sp ce b twe n them

4 Reference environmental conditions

The referen e en ironmental con ition are:

5.1.1 Ge eral principle

The pres ure sen itivity of a me s rement micro hone is defined in terms of a sou d

pres ure a pl ed u iformly over the dia hragm Con eq ently, the pres ure sen itivity can

only b re l sed in prin iple for micro hones from whic the protection grid can b removed

an the dia hragm exp sed to the sou d pres ure stimulu

The prin iple of these comp rison method is that when the referen e micro hone an the

test micro hone are exp sed to the same sou d pres ure either simultane u ly or

seq ential y, the ratio of their pres ure sen itivities is given by the ratio of their o en-circ it

output voltages The sen itivity (b th mod lu an phase) of the test micro hone can then b

calc lated from the sen itivity of the referen e micro hone

The prin iple of the method alows the test micro hone to b at ac ed to a p rtic lar

pre mpl fier an the sen itivity of the s stem may b refer ed to the output of that

pre mpl fier

Multi- req en y me s rements can b p rformed p rtic larly ra idly if a wide an sou d

source is u ed an the output voltages of the micro hones are analy ed in nar ow b n s

NOT If th refere c a d test micro h n s h v sig ific ntly difere t fre u n y resp nse c ara teristics, e.g

aro n reso a c fre u n ies, or wh n a pres ure resp nse micro h n is c mp re with a fre - ield resp nse

micro h n , this a pro c c n le d to erors wh n th inte tio is to d termin th pres ure se sitivity at th test

fre u n y, rath r th n th test fre u n y b n Du c nsid ratio of th a alysis b n width is a vise to a oid

su h erors Ty ic ly, a b n width of 1/6

th

-o ta e or n rower wi b suficie t to c nstrain a y eror to les th n

0,01 dB Howe er furth r c utio is a vise o re u in th b n width to se erely, as c n b p s ible with F T

( ast Fo rier tra sform) a alysers, as this c n hig lg t d ficie cies su h as sta din wa es in th so n field,

whic c n alsole d to erors (se [1]

1

for furth r d tais)

5.1.2 Ge eral principle using simulta eous e citation

In order for the two micro hones to b simultane u ly exp sed to es ential y the same sou d

pres ure it is u ual y neces ary for the front s rfaces of the two micro hones to b se arated

by a smal fraction of the wavelen th at the hig est freq en y of interest For freq en ies up

to 2 kHz, this can b ac ieved by mou tin the two micro hones face- o- ace se arated by

a proximately 1 mm in either a coupler or a j g

The o timum micro hone sep ration is somewhat de en ent on the acou tic en ironment an

s ould b determined for a p rtic lar set up Detai s of l k ly levels of p rforman e can b

fou d in [1]

1

Couplers u ual y contain an integral sou d source; j g mou ted micro hones are u ual y

exp sed to an external y prod ced sou d field In order to red ce the efect of s stematic

dif eren es in sou d pres ure b twe n the two micro hone p sition , for example cau ed by

some as mmetries, the fol owin proced re s al b u ed: af er the ratio of the micro hone

pres ure sen itivities is first determined, the micro hones s al b interc an ed, an the

me s rement re e ted The sen itivity is then calc lated from the me n of the two ratios

Examples of practical ar an ements an precaution to b ta en are given in An ex A

NOT Av idin asymmetry a d sta din wa es in th so n field, esp cialy in jg c nfig ratio s, h s a

sig ific nt b n ficial imp ct o th rela i ty of th results

5.1.3 Ge eral principle using s que tial e citation

In order for the two micro hones to b seq entialy exp sed to es ential y the same sou d

pres ure, either the ex han e of micro hones s al not c an e the sou d pres ure

sig ificantly or an sig ificant c an e s al b detected an cor ected This can b ac ieved

by in orp ratin a sou d source, a monitor micro hone, an the testreferen e micro hone in

a coupler In an desig of coupler, the monitor micro hone s al ac urately sen e c an es in

the sou d pres ure at the testreferen e micro hone p sition Examples of practical

ar an ements are given in An ex B

5.2 Me s ring the output volta e of the microphone

The output of a test or referen e micro hone may b determined as the o en-circ it voltage

by u e of the in ert voltage tec niq e (se 5.3 of IEC 610 4-2:2 0 ) or by u in a me s rin

s stem con istin of a hig input imp dan e micro hone pre mpl fier an a voltmeter (se

An ex C)

The method u ed to me s re the output voltage of the test micro hone s al b stated on an

cal bration certificate

6 Factors influencing the pressure sensitivity

The pres ure sen itivity of a me s rement micro hone can de en on en ironmental

con ition Further, the definition of the pres ure sen itivity impl es that certain req irements

b fulfi ed by the me s rements It is es ential d rin a calbration that these con ition are

controled s f iciently wel if the res ltin u certainty comp nents are to remain smal

6.2 Microphone pre s re e u l zation me ha ism

The normal con tru tion of a me s rement micro hone has the cavity b hin the dia hragm

fited with a nar ow pres ure-eq al zin tub to p rmit the static pres ure to b the same on

b th sides of the dia hragm Con eq ently, at very low freq en ies, this tub also p rtial y

eq al zes the sou d pres ure If, d rin the calbration, the sou d whic is coherent with that

on the dia hragm is in ident on the pres ure-eq al zin tub , then this could c an e the

a p rent sen itivity at low freq en ies an the res lt would not b the true pres ure

In a j g, where sou d is in ident on the pres ure eq al zin tub , the size of this c an e s al

b determined by comp rin cal bration made in the jg with cal bration made in a coupler

that do s not exp se the pres ure eq al zin tub to the sou d field

In a coupler an "O" rin can b u ed to se l the ga b twe n the coupler an the micro hone

If this is done, care s al b ta en to en ure that the "O" rin do s not exert u d e force on

the micro hone an cau e a c an e in sen itivity

6.3 Polarising volta e

If the test micro hone req ires an external p larisin voltage, then the p larisin voltage u ed

d rin the cal bration s al b re orted

If the referen e micro hone req ires an external p larisin voltage, then an diferen e

b twe n that a pl ed when it was cal brated an that a pl ed when it is u ed as the referen e

micro hone s al b alowed for in the u certainty calc lation (se An ex D)

6.4 Refere c s ield configuration

When the o en-circ it voltage is me s red, the s ield config ration given in IEC 610 4-1 or

IEC 610 4-4 s al b u ed

If a micro hone is inten ed to b u ed with a pre mpl fier havin a non-stan ard s ield

config ration, then it s al b calbrated as a s stem alon with its pre mpl fier

When in ert voltage cal bration are p rformed, it s al b stated whether output voltage from

the micro hone is a pl ed to the s ield (driven s ield config ration), or whether the s ield is

grou ded

If the in tru tion man al sp cifies a maximum mec anical force to b a pl ed to the central

electrical contact of the micro hone, this l mit s al not b ex e ded

6.5 Pre s re distribution ov r th diaphragms

The definition of the pres ure sen itivity as umes that the sou d pres ure over the dia hragm

is a pl ed u iformly The output voltage of a micro hone presented with a non-u iform

pres ure distribution over the s rface of the dia hragm wi difer from the output voltage of

the micro hone when presented with a u iform pres ure distribution havin the same me n

value, b cau e the micro hone is u ualy more sen itive to a sou d pres ure at the centre of

the dia hragm

Uniformity of sou d pres ure over the dia hragm of the micro hone can b o timised by

maintainin the radial s mmetry of the sou d field arou d the circ mferen es of the

micro hones This can b ac ieved u in a radial y s mmetric sou d source p sitioned

co xial y with the micro hones an , when the micro hones are mou ted in a j g, with the

micro hones p sitioned in the far field of the sou d source Althou h pres ure non-u iformity

over the s rface of the dia hragm can b minimised by u in a radial y s mmetric sou d

source, some non-u iformity at hig freq en ies can remain even with a p rfect source

It is dif ic lt to control the u iformity of the sou d field in an actual calbration set up

However, the combined ef ect of as mmetries in the sou d field an in the micro hones

b comes evident when the micro hones are rotated relative to e c other a out their axis of

s mmetry Th s, the related comp nent of me s rement u certainty can b red ced by

averagin res lts from a n mb r of s c me s rement config ration

NOT Wh n c mp rin micro h n s of th same mo el th re uireme t for u iformity of th so n field re u es

Alternatively, is ues with sou d field non-u iformity can b overcome if ex itation is made

with a difu e sou d field, for example in a reverb ration ro m Care s ould b ta en to avoid

cre tin stan in waves in the sou d field s r ou din the micro hones as these can cau e

sig ificant an u predicta le me s rement er ors A bro db n source, or re e ted

me s rements at dif erent p sition within the field, is also neces ary to ac ieve a s f iciently

low me s rement u certainty

The efect of a non-u iform pres ure distribution over the s rface of the dia hragm wi b

sig ificantly gre ter if the test an referen e micro hones are of dif erent diameters A

the retical model whic can b u ed to a ply cor ection an as es the u certainties in this

case is given in the lterature ( or example [1])

6.6 Depe de c on e vironme tal conditions

The sen itivity of a micro hone can de en on static pres ure, temp rature or h midity This

de en en e can b determined by comp rison with a wel c aracterised la oratory stan ard

micro hone over a ran e of con ition

If the referen e micro hone an the test micro hone are dif erent man facturer models, then

the sen itivity of the referen e micro hone s al b cor ected to the actual environmental

con ition d rin the test Alternatively, if they are of the same model, there can b an

ad antage in as umin that they have the same de en en e on en ironmental con ition so

that the cal bration of the test micro hone can b refer ed to the con ition at whic the

cal bration of the referen e micro hone is val d

Alternatively, when re ortin the res lts of a calbration, the pres ure sen itivity can b

cor ected to the referen e en ironmental con ition if rel a le cor ection data are avai a le

The actual con ition d rin the cal bration s al b re orted

6.7 Val dation

Calbration p rformed in an p rtic lar jg or coupler s al b valdated by comp rison with

cal bration p rformed in other j g an couplers an alternative sou d sources A se arate

val dation is neces ary for e c dif erent typ of micro hone If the test micro hone is a

la oratory stan ard micro hone, then the j g or coupler can b val dated by comp rin a

comp rison cal bration with a reciprocity cal bration For some micro hones, it can b

neces ary to u e more than one j g an /or coupler to cover a ful freq en y ran e with low

u certainty

7 Cal bration uncertainty compone ts

In ad ition to the factors influen in the pres ure sen itivity mentioned in Clau e 6, further

u certainty comp nents are introd ced by the method, the eq ipment an the degre of care

u der whic the cal bration is car ied out Factors whic afect the calbration in a known way

s ould b me s red or calc lated with an ac urac neces ary to ac ieve the desired overal

me s rement u certainty, an with as hig an ac urac as practica le if their influen e is to

b minimised

7.2 Se sitivity of the refere c microphone

The u certainty in the sen itivity of the referen e micro hone directly af ects the u certainty

7.3 Me s reme ts of microphone output

Un ertainties of ran om or time-varyin nature in the me s rement of the outputs of the

micro hones directly af ect the u certainty in the sen itivity of the test micro hone

Un ertainties of s stematic nature in the me s rement of the outputs of the micro hones can

af ect the u certainty in the sen itivity of the test micro hone The u certainty can b red ced

if the same s stem is u ed for b th the test an referen e micro hones

If test an referen e micro hone are me s red simultane u ly, s stematic u certainty can b

red ced u in the proced re des rib d in An ex C

7.4 Dif ere c s betwe n th soun pre s re at th te t microphone a d that at the

refere c microphone

With simultane u or seq ential ex itation, dif eren es in the acou tic imp dan e b twe n

the test an referen e micro hones can cau e the sou d pres ure at the test an referen e

micro hones to dif er A the retical model whic may b u ed to as es the res ltin

u certainty can b fou d in the l terature ( or example [2])

7.5 Acoustic impe a c s of the micro hon s

When the referen e micro hone an the test micro hone have sig ificantly dif erent acou tic

imp dan es ( or example, pres ure an fre - ield resp n e micro hones at freq en ies a ove

10 kHz), they can resp n diferently to the same sou d field b cau e of diferin volume

velocities at the dia hragms It is recommen ed that wherever p s ible a referen e

micro hone of simi ar acou tic imp dan e to that of the test micro hone b u ed If no

s ita le referen e micro hone is avai a le, the size of the er or cau ed s ould b estimated

an ad ed to the u certainty bu get

7.6 Microphone s paration dista c

The ide l micro hone se aration distan e u ed in simultane u ex itation me s rements

s ould b esta l s ed for e c acou tic en ironment in whic j g me s rements are to b

car ied out The distan e can b determined by ma in a series of me s rements at diferent

se aration an comp rin the res lts with a primary pres ure cal bration for the same

micro hone Me s rements made in some sou d field can b very sen itive to very smal

c an es in micro hone se aration distan e an micro hone p sition relative to the sou d

field In these cases it is prefera le to improve the sou d field rather than the p sitionin

s stem b cau e a very re rod cible p sitionin s stem can introd ce re e ta le s stematic

er ors that are not e siy detected

7.7 Microphone c pa ita c

In some cal bration method ( or example the a pro c outl ned in An ex C), the gain of the

micro hone pre mpl fier(s) u ed is as umed to b con tant when fit ed with diferent

micro hones However the gain of the pre mpl fier is typical y a fu ction of the at ac ed

micro hone ca acitan e

Therefore a cor ection s ould b made or a comp nent of u certainty alowed if the

ca acitan es of the referen e micro hone an test micro hone are s f iciently dif erent for

the influen e on the pre mpl fier gain to b sig ificant

NOT This efe t is a oid d if th insert v lta e te h iq eis use

7.8 Microphone config ration during c l bration

It may b neces ary to fit a micro hone with one or more ada ters s itin a p rtic lar

cal bration coupler or config ration Su h ada ters may have an influen e on the sen itivity of

NOT Both th refere c a d test micro h n s c n b influ n e b th fitin of a a ters.

7.9 Unc rtainty on pre s re s nsitivity lev l

For determinin the pres ure sen itivity level of workin stan ard micro hones, when the

referen e micro hone has b en cal brated in ac ordan e with IEC 610 4-2, it is estimated

that a comp rison cal bration of micro hones of the same diameter can ac ieve an exp n ed

u certainty with coverage factor 2 (se ISO/IEC Guide 9 -3) of a proximately 0,1 dB at low

an mid le freq en ies The u certainty in re ses to a out 0,2 dB at 10 kHz an 2 kHz for

WS1P an WS2P workin stan ard micro hones, respectively An ex D contain an example

of an u certainty analy is

Annex A

(informativ )

Examples of couplers and j gs for simultaneous excitation

A.1 A coupler for us with WS2 microphones at frequencies up to 10 kHz

The coupler s own in Fig re A.1 alows two micro hones with exp sed dia hragms to b

in erted face- o- ace se arated by a out 2 mm The coupler contain a radial sou d source

that generates a radial y s mmetric acou tic field b twe n the dia hragms In this example

the grid of the test micro hone has b en removed an re laced with an ada tor rin to give

the config ration of an LS2 micro hone Variation on the prin iple could in lu e a sl g tly

larger diameter coupler where the test micro hone would b s p orted by other me n

D ime sio s in mi imetres

7 Cyln ric lso rc dia hra m

Figure A.1 – A coupler for u e with WS2 microphone

This method may also b u ed without removin an protection grid from the test micro hone

provided that the presen e of the grid is al owed for in the u certainty calc lation The grid

can cau e an u ac e ta le level of me s rement u certainty at hig freq en ies, ef ectively

A.2 A j g for use with WS2 or WS3 microphones at frequencie up to 20 kHz

A simple ar an ement for holdin an p sitionin an LS2 micro hone an a WS2 micro hone

in a s ita le p sition for a simultane u calbration is s own in Fig re A.2 The j g is en losed

in an acou tic c amb r with a lou sp a er providin the sou d source The prefer ed location

for the sou d source is on the axis of s mmetry of the micro hones The detai ed p sitionin

for WS2 an WS3 micro hones is s own in Fig res A.3 an A.4 resp ctively Note that the

protection grid have b en removed

Figure A.2 – A j g fit e with a LS2 a d WS2 micro hon

D ime sio s in mi imetres

NOT Th dime sio sh wn is th dia hra m-o

-dia hra m se aratio

NOT Th dime sio sh wn is th dia hra m-

o-dia hra m se aratio This se aratio dista c is th

o ly o e for whic th c re tio s sp cifie in Ta le

When the ar an ement of Fig re A.4 is u ed, cor ection are req ired to ac ou t for the radial

sen itivity of the micro hones an the fact that the test micro hone is smal er than the

referen e micro hone Ta le A.1 gives cor ection to b ad ed to the sen itivity level of the

WS3 micro hone as umin that the referen e micro hone is of typ LS2 P (se [1]) an that

the sou d field is radial y s mmetrical The exp n ed u certainty on the cor ection is

estimated to b 10 % of their value (in dB) whic is a proximately the c an e o served by

IEC

0,5

IEC 1

IEC

If the sou d ar ives from a direction other than the axis of s mmetry of the j g, me s rements

s ould b made with the sou d ar ivin from several diferent direction an an average

ta en A con enient me n of ac ievin this is to u e a dif u e sou d field

Table A.1 – Calc late cor e tions to be a de to the s nsitivity le el

Annex B

(informativ )

Examples of couplers for sequential excitation

B.1 A coupler for us with LS1 microphones at frequencies up to 8 kHz

A coupler for u e with LS1 micro hones is s own in Fig re B.1 A WS1P micro hone, u ed as

the sou d source, is s rewed directly into the up er p rt of the coupler without an protection

grid or ada tor A pro e tub micro hone is in erted from the side of the coupler so that the

pro e tip is one- hird of the distan e alon a radiu from the wal , an is u ed to control the

sou d pres ure in the coupler The acou tic imp dan e of the pro e tub micro hone u ed

can afect the res lts, but a tub with an acou tic imp dan e of 8 0 MPa∙s∙m

–3

has b en

u ed s c es ful y The test an referen e micro hones are held in the coupler by a yo e an

sprin ar an ement

If b th test an referen e micro hones are WS1 micro hones con erted to the LS1

config ration with an ada tor rin , the same ada tor rin s ould b u ed on b th

5 Ap rture for test a d refere c micro h n

Figure B.1 – A coupler for us with LS1 microphone

B.2 A coupler for us with WS2 microphones at frequencies up to 16 kHz

Fig re B.2 s ows a coupler that can b u ed for seq ential comp rison cal bration of WS2

monitor micro hone detects the c an e in sou d pres ure when the test micro hone is

re laced by the referen e micro hone

D ime sio s in mi imetres

Ke

1 Mo itor micro h n

2 Testrefere c micro h n

3 Co pler c vity, diameter 9,3 mm

4 Cyln ric lso rc dia hra m

Figure B.2 – A coupler for u e with WS2 microphone

This method may also b u ed without removin an protection grid from the test micro hone

provided that the presen e of the grid is al owed for in the u certainty calc lation

Annex C

(informativ )

Determining the open-circuit sensitivity of a measurement

microphone without using the insert voltage method

When a comp rison cal bration is b in p rformed, it is p s ible to determine the o en-circ it

sen itivity of the test micro hone without u in the in ert voltage method It is neces ary for

the o en-circ it sen itivity of the referen e micro hone to b known an a cor ection (or

u certainty) to b in lu ed for an diferen e d e to the test an referen e micro hone

presentin a dif erent electrical source imp dan e to the pre mpl fier The prin iple is that by

interc an in the micro hones b twe n the two me s rin c an els an re e tin the

me s rements, an dif eren e in the gain of the two c an els (an some other s stematic

ef ects) can b el minated This can b demon trated by the fol owin

When two micro hones with their dia hragms facin are at close proximity to e c other, an

their outputs me s red as levels on two me s rement c an els, then the level re din

dif eren e, L

12, b twe n the two c an els (neglectin an influen e of micro hone

m1+ L

d1+ L

WA) – (L

2+ L

m2+ L

d1+ L

is the sou d pres ure level that the ex itation sou d source prod ces at the

centre p int mid-way b twe n the micro hone dia hragms;

Eq ation (C.1) as umes that the micro hones have dif erent sen itivities, but are otherwise

identical in their mec anical an electro cou tic c aracteristic

When the micro hones are interc an ed, the level re din diferen e b twe n the two

m1+ L

d+ L

WA) – (L

1+ L

m2+ L

d+ L

is the sou d pres ure level that the ex itation sou d source prod ces at the

centre p int mid-way b twe n the micro hone dia hragms afer the interc an e

From the dif eren e b twe n Eq ation (C.1) an Eq ation (C.2), the sen itivity level

dif eren e b twe n the two micro hones is

(L

1– L

2) = ½(L

12– L

m2, L

d1, L

d,

Annex D

(informativ )

Typical uncertainty analysis

D.1 Introduction

The fol owin is an example u certainty calc lation for a h p thetical cal bration protocol It

s ould not b ta en as an ex au tive lst of p s ible u certainty comp nents, or an in ication

of typical u certainty values

D.2 Analy is

The u certainties given in Ta le D.1 are calc lated for the example of a simultane u

cal bration of a low sen itivity typ WS2P micro hone u in an LS2P referen e micro hone

The coupler s own in Fig re A.1 is u ed, an there are thre re e ts of the cal bration The

micro hones are interc an ed in the coupler p rts an on the pre-ampl fiers to elminate the

ef ects of an as mmetry in the coupler an an dif eren es in gain in the two me s rement

c an els (se An ex C) The res lts are not refer ed to the referen e en ironmental

ref

× R

V/ R

red ced to u ity by the proces des rib d in An ex C an the cor ection s c as

those given in An ex B, but it wi have some resid al u certainty

For this example, fig res are given for a freq en y of 2 kHz only In practice, the calc lation

is re e ted for e c freq en y u ed The re orted u certainty is b sed on a stan ard

u certainty multipl ed by a coverage factor k = 2, providin a level of confiden e of

a proximately 9 %

The me s rement u certainty arises from eig t dif erent sources, but ad itional comp nents

can b req ired in p rtic lar set ups or micro hone config ration The comp nent d e to

re e ta i ty is evaluated as a typ B u certainty b sed on l mits esta l s ed by a large

n mb r of simi ar me s rements; the remainin comp nents are also evaluated as typ B It

is as umed that the sen itivity of the micro hone is l nearly de en ent on e c comp nent

an that the cal bration of the referen e micro hone refers to the actual me s rement

con ition

Table D.1 – Ex mple unc rtainty budg t

Comp nent

Stan ard

unc rainty

dB

Se sitivity of refere c micro h n

Th u c rtainty as o iate with th c lbratio of th la oratory sta d rd micro h n use as

th refere c , is q ote o itsc lbratio c rtific te as ± ,0 dB with a c v ra e fa tor of k = 2

This is e uiv le t to a sta d rd u c rtainty of 0,0 /2 dB = 0,0 5 dB

u c rtainty wi b intro u e From a k owle g of th in ut imp d n e of th pre-amplfiers

a d th ma ufa turer’s sp cific tio for th c p cita c of th micro h n s, it is p s ible to

c lc late th t, in this p rtic lar insta c , th semi-ra g of this c mp n nt is 0,01 dB with a

re ta g lar distrib tio This is e uiv le t to a sta d rd u c rtainty of 0,01/√3 dB =0,0 6 dB

0,0 6

No -ln arity

Th resp nse of th a alyser to sig als of difere t ma nitu es c uld b in eror b a smal

amo nt Tests of th a alyser are p rforme with two difere t c lbrate ate u tors whic are

se arately pla e to mimic th le el difere c s th t are e p cte to b me sure in th a tu l

c lbratio Th micro h n c lbratio is o ly alowe to pro e d if th difere c b twe n th

results of th se tests a d th k own v lu s of th ate u tors is within 0,0 dB He c th se

mi-ra g of this c mp n nt is 0,0 dB with a re ta g lar distrib tio This is e uiv le t to a

sta d rd u c rtainty of 0,0 /√3 dB= 0,017 dB

0,017

Micro h n imp d n e

Th a o stic l imp d n e of th micro h n a ts inseries with th t of th air in th sp c

b twe n th two micro h n s Micro h n swith difere t a o stic imp d n e th refore se

slg tly difere t pres ures wh n simulta e usly e p se to th same pres ure field (se 7.4 a d

[2] Th ma nitu e of th efe t wh n hig se sitivity a d low se sitivity ty e WS2P

micro h n s are c mp re , is a worse c se a d ta e as th u c rtainty in this e ample At 2

kHz, th semi-ra g of this c mp n nt is 0,0 5 dB with a re ta g lar distrib tio This is e uiv le t

to a sta d rd u c rtainty of 0,0 5/√3 dB = 0,0 3 dB Wh n micro h n s h v sig ific ntly diferin

imp d n es (or e ample WS2F micro h n c mp re a ainstLS2P at fre u n ies a o e 10

kHz), th me sureme t u c rtainty c n b c nsid ra ly larg r a d sh uld b esta lsh d

e p rime taly

0,0 3

Polarisin v lta e

Th p larisin v lta e afe ts th se sitivity of b thth refere c a d test micro h n s If th

same p larisin v lta e is a ple to b th micro h n s th efe t wi b n glgible Howe er if

o e micro h n is pre-p larise , this wi n t b th c se a d th eror wi p rsist Th

p larisin v lta e is set to (2 0,0 ± 0,2) V givin a semi-ra g for this c mp n nt of 2 lg

(2 0,2/2 0) dBwith are ta g lar distrib tio This is e uiv le t toa sta d rd u c rtainty of

Drif in refere c micro h n se sitivity sin e last c lbratio

Th se sitivity of th refere c micro h n c n h v c a g dsin e it was c lbrate Two

c lbrate refere c micro h n s are c mp re a ainst e c oth r as a c e k b foreth

c lbratio of test micro h n s Th c mp riso c lbratio a d th refere c c lbratio of th

refere c micro h n sh uld a re within 0,0 dB Howe er, th v lu use d rin a c lbratio

must b furth r re u e b th u c rtainty as o iate with th c mp riso me sureme t Th

sta d rd u c rtainty of this c mp n nt is 0,0 /√3 dB = 0,017 dB

0,017

Ro n in of re orte results

Th result is re orte with a resolutio of 0,01 dB, givin a semi-ra g of 0,0 5 dB with a

re ta g lar distrib tio This is e uiv le t to a sta d rd u c rtainty of 0,0 5/√3 dB = 0,0 3 dB

0,0 3

Ad itio al comp nents for spe ial c s s

Stan ard

unc r ainty

in dB

Core tio s for th difere c in dia hra m diameter wh n c lbratin aty e WS3

micro h n a ainst a ty e LS2 refere c micro h n

Th e p n e u c rtainty dire tly as o iate with th c lc late c r e tio is estimate to

b 10 % of th v lu of th c re tio (in d cib ls)

Th u a c u te for difere c b twe n th c re te c mp riso c lbratio of a WS2

micro h n c mp re a ainst a LS1 refere c micro h n a d a pres ure re ipro ity

Un ertainties as o iate with system c lbratio s

Wh n micro h n s arec lbrate as a system (i e in c nju ctio with a pre mplfier) th

efe t d e to a y d viatio from 2 0 V in th p larisatio v lta esu ple b th p wer

su ply u it is n t c n ele o t d rin th me sureme t

Th c mp n nt as o iate with micro h n c p cita c sh uld b re-c nsid re to a c u t

for th c p cita c prese te b th micro h n system to e c of th me sureme t system

D.3 Combined and expande unc rtainties

The combined stan ard u certainty is fou d from the ro t s m-s uare of the u certainty

comp nents, whic gives a value of 0,0 0 dB (a strict calc lation would req ire e c

comp nent to b con erted from logarithmic to l ne r form b fore doin the combination but

as the values are very smal , the res lt would b es ential y the same) The exp n ed

u certainty with a coverage factor of 2 is then 0,0 dB

Bibl ography

[1] BARHAM R BARRERA-FIGUEROA S an AVISON J E M Secon ary pres ure

cal bration of me s rement micro hones Metrologia 51 2 14

[2] JARVIS D.R Method for determinin the pres ure sen itivity of workin stan ard

micro hones – a re ort on Euromet project A31 NPL re ort CIRA(EXT)010, 19 6

[3] FEDTKE T In estigation of secon ary pres ure cal bration method for the phase

resp n e of me s rement micro hones Ac stica 8 Sup l 1, S 17 , 19 6

[4] JARVIS D.R an WATKINS S.A Method for determinin the pres ure sen itivity of

IEC typ WS3 me s rement micro hones NPL re ort CIRA(EXT)0 2, 19 7

[5] WONG G.S.K LIXUE Wu, Interc an e micro hone method for cal bration by

comparison Internoise 9

[6] WONG G.S.K EMBLETON T.F.W Thre -p rt two-micro hone cavity for acou tical

cal bration J Acou t Soc Am 71, p.12 6-12 7, 19 2

[7] WONG G.S.K Precision method for phase matc of micro hones J Acou t Soc Am

9 , p.12 3-12 5, 19 1

[8] IEC 610 4-2:2 0 , Me su reme nt microp ho es – Part 2: Primary meth d forpres ure

calb rato of lab oratory sta dard microp ho es b y th re cip rociy te ch ique

[9] ISO/IEC Guide 9 -3, Uncertainty of me sureme nt – Part 3: G uide to th e p re ssio of

unce rtainty in me sureme t (GUM: 1995)

_ _ _ _ _ _