G.R.A.S. 50AI User manual

Instruction Manual
Sound Intensity Probe Type 50AI
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark www.gras.dk

Revision 6 June.2014
Sound-intensity Probe Type 50AI

G.R.A.S. Sound & Vibration
CONTENTS
1. Introduction and Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Main Components..................................................4
Microphones .............................................................4
Preampliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Available Versions..................................................6
2. Input Channels ..................................................9
2.1 PreamplierInputsAandB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Sound-intensityAxis ................................................9
3. Output Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1 UsewithPowerModuleType12AB ...................................11
4. Handling and Assembling the Probe ...............................12
4.1 TheMicrophones .................................................12
4.2 Probe Design ....................................................12
4.3 PhysicalStrength .................................................12
4.4 Assembling the Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.5 UsingtheWindscreen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Specications ..................................................16
5.1 All versions:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 VersionB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3 Version C .......................................................16
5.4 Version D .......................................................17
5.5 Version HP ......................................................17
5.6 Version LD ......................................................17

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 4
1. Introduction and Description
TheSound-intensityProbeType50AI(Fig.1.1)isatwo-microphonesoundintensityprobe.It
hasapairofG.R.A.S.phase-matched½″microphonesType40AI(Fig.1.2),twoG.R.A.S.¼″
microphonepreampliersType26AA,solidspacers,remotecontrolhandleandconnection
cable.Theprobeisadjustable,durableandfullycomplieswiththefollowingrequirements:
• IEC61043,Electroacoustics-InstrumentsfortheMeasurementofSoundIntensity-Meas-
urementswithPairsofPressureSensingMicrophones,1993forClass1Sound-intensity
probes.
Fig. 1.1 The Sound-intensity Probe Type 50AI

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 5
Fig. 1.2 The type of carrying case delivered with the Type 50AI
1.1 Main Components
ThemaincomponentsoftheSound-intensityProbeType50AIare:
• SoundIntensityMicrophonePairType40AK
• TwoMicrophonePreampliersType26AA
• Foursolidspacersofvariouslengthsandaspacercup(seeFig.1.5)
• Remote-controlhandlewith(whereapplicable)uptotwopushbuttonsforcontrollingmeas-
urements
SeealsoFig.1.8.
TheType50AIisdeliveredinacarryingcasesimilartotheoneshowninFig.1.2,completewith
microphones,preampliers,standardaccessoriesandaremote-controlhandle.
1.1.1 Microphones
Themicrophones(Fig.1.3)arehighsensitivity,free-eld½″condensermicrophoneswitha
uniquely-designedpressureequalizationsystemthatensuresextremelywelldenedphase
characteristics.Themicrophonesandpreampliersaremountedontheendofthetelescopic
armoftheRemote-controlhandle.Tocoverthefullfrequencyrangefrom50Hzto10kHz,the
Type50AIisdeliveredwithfoursolidinterchangeablespacersforspacingthemicrophonesat
12mm,25mm,50mmand100mm.

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 6
1.1.2 Preampliers
Thesmall¼″diameterand40mmlongmicrophonepreampliers(Fig.1.4)arehousedin
robust,stainlesssteelcasingswhichenablenovelprobedesignsthatreducedisturbancesto
thesoundeldotherwisebroughtaboutbytheeffectsofshadowsanddiffraction.Symmetryof
designenablesreliablecalibrationsasdescribedintheproposedstandard(ISO/DIS9614-2)for
soundpowermeasurementsusingsound-intensitymeasurements.
Fig. 1.3 Showing similar pairs of phase-matched ½″ microphone cartridges
Above: Type 40AK, which includes spacers and three adapters for
¼″ preampliers as supplied with the Type 50AI.
Below: Type 40AI, which includes cartridges only
Fig. 1.4 Pair of ¼″ Preampliers Type 26AA supplied with the Type 50AI
Fig. 1.5 Showing the various spacers and the spacer cup supplied with the Type 50AI
RA0263
100 mm spacer
RA0264
50 mm spacer
RA0265
25 mm spacer
RA0266
12 mm spacer
GR0040
Spacer cup

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 7
Fig. 1.6 Showing the markings and external features on the remote-control handles of the various
versions of the Type 50AI
1.2 Available Versions
VariousversionsoftheType50AIareavailablefordirectusewithawiderangeofgeneral-pur-
posefrequencyanalysersaswellasspecialisedsoundintensityanalysers.Fig.1.6showsthe
mainexternalfeaturesofthevariousversions.
Type 50AI version B
Hasbuilt-inremote-controlfunctionsfordirectconnectionto,andcontrolof,sound-intensity
measuringsystemsfromawiderangeofsupplierssuchas01dB,Müller-BBMandNeutrix-
Cortex.
CanbeuseddirectlywiththeG.R.A.S.IntensityModuleType12AB(seealsosection3.1),
whichprovidesallnecessaryvoltagesfortheremote-controlfunctionsandpoweringthepream-
pliers.
TheIntensityModuleType12AB(whichisbattery-operated)hastwostandardBNCoutput
socketsforconnectingtoanalysersthatdon’thavespecialmicrophone-preamplierinputsand
a9-pinD-subsocketwiredupforconnectingdirectlytotheRS232portofacomputer(Fig.3.2);
thusenablingsoftwaretobecontrolledbytheremotecontrolfacilitiesofthisversionofthe
Sound-intensityProbe.
UsewiththeType12ABenablesdirectusewith01dBSoundIntensitysystems.
Type50AI
version HP
Type50AI
version C
Type50AI
versionB
version D
version LD

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 8
Type 50AI version C
Canbeconnecteddirectlytoanyanalyserwithtwostandard7-pinLEMOmicrophone-preampli-
erinputs.
CanbeusedwiththefollowingG.R.A.S.PowerModules,whichprovideallnecessaryvoltages
forpoweringthepreampliers:
• IntensityModuleType12AB(seedescriptionaboveunderversionB)
• PowerModuleType12AA
(viatheincludedadaptercableAC0003,whichsplitstheoutputfroma12-pinLEMOsocket
intotwo7-pinLEMOplugs)
ThePowerModuleType12AA(whichisbattery-operated)hastwostandardBNCoutputsock-
etsforconnectingtoanalysersthatdon’thavespecialmicrophone-preamplierinputs.
Type 50AI version D
SimilartoversionBbutusesaninternal9-Vbattery(alreadyttedondelivery)forenablingits
remote-controlfunctions.Fig1.7showshowtogainaccesstothebattery.
Type 50AI version HP
Hasbuilt-inremote-controlfunctionsfordirectconnectionto,andcontrolof,Hewlett-Packard
analyserssuchasthetypesHP3569AandHP35670AOptUK4.
BothoftheseanalyserswillsupporttheLEDsmarkedOVERLOADandMEASURING as well as
thecontrolbuttonmarkedSTART/GATE.
Type 50AI version LD
Hasbuilt-inremotecontrolfunctionsfordirectuseandcontrolofLarsonDavisanalyserssuch
asthetypesLD2900andLD3000.
Fig. 1.7 Access to the 9 -V battery located inside the remote-control handle of the
Type 50AI version D. The battery should be disconnected / reconnected
while inside the remote-control handle
Unscrewand
remove
Slidecover
back

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 9
Fig. 1.8 Showing the main components of the Sound-intensity Probe Type 50AI prior to assembly
RA0263 100 mm spacer
RA0264 50 mm spacer
RA0265 25 mm spacer
RA0266 12 mm spacer
GR0040 Spacer cup
RA0003 Straightadapter
PairofType26AA ¼″preampliers
Type40AI Pairofphase-matched½″microphones
Pair of RA0001 Right-angledadapters
OutputsocketRemote-controlbuttonsTelescopicarmPreamplierinputsSwivelhead

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 10
2. Input Channels
TheType50AIhastwoinputchannels,one
foreachmicrophonepreamplier.Thechan-
nelsaremarkedAandBontheremote-control
handle,seeFig.2.1.
2.1 PreamplierInputsAandB
AandBrefertothetwochannelsoftheprobe.
ChannelAisreservedfortheleadingmicro-
phone,i.e.themicrophonerststruckbyan
acousticwavefront(seeFig.2.2).Whenthis
happens,thisshouldbeinterpretedasaposi-
tivecomponentofthesoundintensityinthe
directionfrommicrophoneAtomicrophoneB.
2.2 Sound-intensity Axis
Fig.2.2illustratestheoriginanddirectionof
positivesound-intensityvectors.Thispositive
directionisalwaysfrommicrophonesAtoB.
Theoriginofthesound-intensityaxisliesonthe
geometric centre of the pair of probe micro-
phones.
Fig. 2.1 Showing the inputs and markings for
the two preamplier inputs
InputforchannelB
InputforchannelA
Markingsforchan-
nelsAandB

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 11
Fig. 2.2 Showing the microphones ‘A’ and ‘B’ which correspond with channels
A and B respectively. ‘A’ is the leading microphone and is struck rst by a
sound wave
AB
+
Direction
of positive
intensity
Type40AKpair
Originofintensityaxis
A
leadingmic.
B
trailing mic.

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 12
3. Output Socket
ThepinconnectionsoftheLEMOoutputsocketatthebaseoftheType50AIareshownin
Fig.3.1.Thefourinnerpins,i.e.9,10,11and12areforenablingadialoguebetweenauser
andananalyser/computerviaanRS232port.Theyareusedto:
a)Transmitthestate(pressed/notpressed)ofthetwopushbuttonsonthehandleoftheType
50AI
Whenpressed:
the blue button transmits Data Set Ready
thegreybuttontransmitsClear To Send
b)SignaltheresponsesviathetwoLEDsalsoonthehandleoftheType50AI
When lit:
theredLEDissignallingRequest To Send
thewhiteLEDissignallingData Terminal Ready
Bysuitablyprogrammingtheanalyser’s/computer’ssoftware,measurementsanddataacquisi-
tioncanbecontrolledinteractivelyviathepushbuttonsandLEDs.
Fig. 3.1 12-pin LEMO female socket 1B (external view). The
four inner pins are for connecting directly to an RS232
computer port
Fig. 3.2 9-pin female D-sub connector socket of the Power
Module Type 12AB for connecting directly to an RS232
computer port (external view)
3.1 Use with Power Module Type 12AB
IftheType50AIisusedwithaG.R.A.S.PowerModuleType12AB,pins9,10,11and12
(Fig.3.1)automaticallyhaveanoutletviatheRS232portoftheType12AB(seeFig.3.2)for
furtherconnectiontoananalyser/computer.

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 13
4. Handling and Assembling the Probe
4.1 The Microphones
TheMicrophonesType40AI(Fig.1.3)areapairofspecialfree-eldmicrophoneswith
extremelywell-controlledphasecharacteristics.Theyaredeliveredasamatchedpaireachwith
individualcalibrationdataaswellasdataondifferencesbetweentheirphaseresponses.
Thesemicrophoneshaveauniquepressureequalisationsystemwhichensuresawelldened
lower-limitingfrequencyandanextremelylowsensitivitytosoundpressuresatthepressure
equalisationchannels.Therefore,theycanbecalibratedinsingle-portphasecalibratorssuchas
theG.R.A.S.IntensityCalibratorType51AB.
4.2 Probe Design
ThedesignoftheSound-intensityProbeminimisesacousticreectionsandtheinuenceof
diffraction.Thishasbeenachievedbyremovinganyphysical,reectivecomponentsfromthe
soundpathat0°incidence.Sincesoundwavesat0°incidencearethemaincontributorstothe
totalsoundintensitylevel,itisimportantthatdisturbancesinthisdirectionbeminimised.
Thethin,2mmdiameterpreampliercableswillhavenoinuenceonthesoundeldsincethey
constituteahighlyirregularsurfacewithnegligiblereections.Theeffectsofacousticdiffraction
andreectionfromthephysicalpartsoftheSound-intensityProbearebelow0.15dB.
Microphonesaresuppliedaspairs(Type40AI)orassets(Type40AK)whichincludespacers
andthreepreamplieradapters(tworight-angledandonestraight).
Thedistancesbetweenmicrophonesandpreampliershavebeenkepttoaminimuminorder
toavoidproblemswithanystraycapacitanceandsensitivitytovibration.Whileamplitude
characteristicsarelittleinuenced,thephasecharacteristicsofaSound-intensityProbecan
becriticallyaffectedbyevenverysmallvibrationsintheconductorscarryingtherawsignals
fromthemicrophones.Therefore,the¼″preampliersaremountedinrigidcontactwiththe½″
microphonesviashortadapters(right-angledand/orstraight).Thisalsoeliminatesproblems
withnon-matchingcapacitancesbetweenmicrophonesandpreampliers,whichcouldgiverise
to phase problems.
4.3 Physical Strength
Fromaphysicalpointofview,aSound-intensityProbeshouldberobustandeasytoassemble
anddismantle.Typically,therearetwopointsinaSound-intensityProbewhichcanbeidenti-
edascriticalforphysicalstrengthandarethemostlikelytosufferdamageandarethemost
difculttorepair.Thesepointsarethethreadsonmicrophonesandpreampliersaswellason
themicrophones’protectiongrids.Theconnectionsbetweenmicrophonesandpreampliersare
verydelicateandcarrybothmicrophonesignalsandmicrophonepolarisationvoltages.There-
fore,thepreamplierthreadsoftheType50AIaresupportedbystainlesssteel½″to¼″adapt-
ers.Thereisalsoaprotectiveguardwithinthe¼″housingofeachpreamplier.Inaddition,the
microphones’protectiongridsaremadeofstainlesssteeltowithstandroughphysicaltreatment
sinceabuckledordamagedprotectiongridwillalmostinvariablydamageamicrophone’sdia-
phragmbeyondrepair.
4.4 Assembling the Probe
TheSound-intensityProbecanbeassembledineitherastraightcongurationorasymmetri-
calcongurationThestraightconguration(Fig.4.1),isforintensitymeasurementscloseto
surfacesandgeneralsourcelocationmeasurements.Thesymmetricalconguration(Fig.4.2),
isidealforsoundpowermeasurements,forexampleaccordingtointernationalstandardISO
9614-2“Acoustics-Determinationofsoundpowerlevelsofnoisesourcesusingsoundinten-
sity”wherearotationtestisrequired.
TheprobeontheType50AIconsistsofthepartsshowninFig.4.4.Assembleasfollows.

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 14
* According to the investigations of Jacobsen, Keith, and Krishnappa, diffraction effects at the intensity probe com-
pensate for the insufciencies of the nite difference approximation. The frequency range of intensity measure-
ments may therefore be extended to frequencies up to 10kHz using ½″ probes with a 12 mm spacer.
1.MountoneofthemicrophonesontheRight-angledadapterRA0001andtheothermicro-
phoneoneithertheotherRight-angleadapterforasymmetricalprobeorontheStraight
adapterRA0003forastraight-probeconguration.
 RemovetheyellowprotectioncapsfromthetwoPreampliersType26AAandmountthe
microphone-adapterassembliesonthepreampliers.ScrewtheSpacercupGR0040
ontotheprotectiongridofoneofthemicrophones.Selectanappropriatespacer(see
Fig.5.1forworkingfrequencyranges)fromthefoursuppliedandscrewthisontothe
protectiongridoftheothermicrophone.Inmanycases,the12mmspacerRA0266will
beappropriateandwillcoverthefrequencyrangefrom100Hzto6.3kHz*.
Fig. 4.1 Straight setup using the 25-mm spacer
Fig. 4.2 Symmetrical setup using the 12-mm spacer

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 15
2.Nowassembletheprobeheadbypressingthefreeendofthespacer(mountedontheone
microphone)intothespacercupmountedontheothermicrophone.Tochangethespacer,
inordertocoveradifferentfrequencyrange,dismantletheprobeheadbypullingthespacer
outofthespacercup,unscrewthespacerandreplaceitwithanotherone(seeFig.4.3).
3.Mounttheprobeheadbyslidingoneofthepreampliersintotheclamp(whichcanbelocked
atanglesof0°,45°,90°,135°and180°)atthetopofthetelescopicarmandtightenthe
ngerscrew(seetheexamplesinFigs.4.1and4.2).Connectthetwopreamplierstothe
inputconnectorsatthetopofthetubesshowninFig.2.1.Theleftinputconnectorislabelled
aschannelAontheprobehandleandtheotherinputislabelledchannelB.Forthecorrect
signoftheintensityvector,thefront,orleadingmicrophoneshouldbeconnectedtoinput
channelA(seesection2.1).
4.Connecttheprobetotheanalyserviatheappropriateadaptercable(dependingonthe
specictypeofanalyser).ThefunctionsoftheoperatingbuttonsandindicatingLEDsonthe
controlhandlearedeterminedbytheanalyserinuseandinformationabouttheseshouldbe
foundintheinstructionmanualofthegivenanalyser(seealsosections1.2and3.1).
4.5 Using the Windscreen
TheSound-intensityProbeType50AIincludesanellipticalwindscreen(AI0001)whichcanbe
usedwhenevermakingoutdoormeasurementsorwhenmakingindoormeasurementsinthe
presenceofbulkairmovements.Useitonlywhenmeasurementsareinuencedbywind.It
givesgoodprotectionatwindspeedsgreaterthan0.5m/sandcanreducepressureuctuations
causedbyturbulencebyasmuchas20dBwiththistechniqueofintensitymeasurements.
Fig. 4.3 Changing the spacer: Pull the two halves of the probe
apart, unscrew the spacer from the microphone grid,
screw another spacer on and push the two halves of the
probe together again.
Pull apart
Push together

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 16
Fig. 4.4 Exploded view of probe assembly. On the left: straight setup. On the right the branch for a
symmetrical setup
RA0003
Straightadapter
RA0001
Right-angledadapter
GR0040
Spacer cup
RA0266
Spacer
Type40AI
Matchedpairof
microphones
Type26AA
¼″Preamplier
Type26AA
¼″Preamplier
RA0001
Right-angledadapter
Type26AA
¼″Preamplier
Straight
Symmetrical

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 17
5. Specications
5.1 All versions:
Sound-intensity microphone set Type 40AK comprising:
Matchedpair½″mics. Type40AI
12 mm spacer RA0266
25 mm spacer RA0265
50 mm spacer RA0264
100 mm spacer RA0263
SeeFig.5.1forworkingfrequencyranges
Preampliers:
Pair¼″   Type26AA
with4-pinLEMOconnectortypeFGGOB
Frequency response and phase matching:
IEC1043Class1
Operating Temperature Range:
+5°Cto+40°C
Weight:
0.4kg(0.9lbs)VersionB
Accessories included:
Windscreen   AI0001
5.2 Version B
Remote-control handle:
Built-inremotecontrolfunctionsfor01dBanalysers.Twobuttonsforaveragingcontrolandtwo
LEDsforstatusindicationandoverloadindication.
Accessories included:
5 m cable AA0021
Adaptercable  AC0002(12-pinLEMOto2x7-pinLEMO,plusremote- 
    controlmale6-pinminiDINplug)
5.3 Version C
Remote-control handle:
General-purposeintensityhandlewithtwo7-pinLEMO1Boutputconnectors.
Accessories included:
5 m cable AA0021
Adaptercable  AC0003(12-pinLEMOto2x7-pinLEMO)

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 18
5.4 Version D
Remote-control handle:
SimilartoversionBbutusesaninternal9-Vbatteryforenablingitsremote-controlfunctions.
Accessories included:
5 m cable AA0021
Adaptercable  AC0005(12-pinLEMOto2x7-pinLEMO,plusremote- 
    controlfemale9-pinD-subplug)
5.5 Version HP
Remote-control handle:
Built-inremotecontrolfunctionsforHewlett-Pakardanalysers.Onebuttonformeasurement
control.LEDsforstatusindicationandoverloadindication.
Accessories included:
3 m cable AA0040
Adaptercable  AC0006(12-pinLEMOto2x7-pinLEMO,plusremote- 
    controlmale15-pinD-subplug)
5.6 Version LD
Remote-control handle:
Built-inremotecontrolfunctionsforLarsonDaviesanalysers(LD3000orLD2900).Onebutton
formeasurementcontrol.LEDsforstatusindicationandoverloadindication.
Accessories included:
5 m cable AA0021
Adapterbox   AC0007(forLD3000)
   or AC0004(forLD2900)

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 19
Fig. 5.1 Working frequency ranges covered by the various spacer lengths. The top bar is for the case when a Type
50AI is equipped with a pair of ¼″ intensity microphones (Type 40BI) and a 6 mm spacer (note the extend-
ed high-frequency range).
WEEEdirective:
2002/96/EC
CEmarkingdirective:
93/68/EEC
Manufacturedtoconformwith:
RoHSdirective:
2002/95/EC
G.R.A.S. Sound & Vibration continually strives to improve the quality of our products for our customers; therefore, the
specifications and accessories are subject to change.
100 1k 10k 10 100k
12 mm (RA0266)
25 mm (RA0265)
50 mm (RA0264)
100 mm (RA0263)
d
Frequency Hz
With ¼" Mics. Type 40BI and 6 mm spacer (RA0267)