Mackie SRM1850 - The Ins and Outs of Polarity

Owner’s Manual
11
Owner’s Manual
Placement
SRMsubwoofersaredesignedtositontheoor
orstage.Theyarenotdesignedtobepole-mounted
orsuspended.
Whenpole-mountingloudspeakers,besurethat
thesubwoofersarestabilizedandsecuredfromfalling
overorbeingaccidentallypushedover.
PleasenotethatSRM750loudspeakers
shouldbestacked,notpole-mounted.
Failuretofollowtheseprecautionsmayresult
indamagetotheequipment,personalinjury,ordeath.
Speakingofstacking,SRM2850subwoofershave
footholeslocatedonthetopofeachcabinet.Whilewe
realizethatcrowdswillfallheadoverheelsattheir
beauty,believeitornot,thesefootholesdoindeedserve
apurpose.
ShouldyoudecidetostackanadditionalSRM2850–
creatingamonsterPA–thefeetlocatedonthebottom
ofeachsubwooferlineupnicelywiththefootholes
locatedonthetopofeachsubwoofer.Thesamecanbe
saidofthefourfeetofanSRM750andthefourfootholes
locatednearthecenteroftheSRM2850.
Foreitherofthesestackedscenarios,itishighly
suggestedthatstrapsareutilized.Toreiterate,failure
tofollowtheseprecautionsmayresultindamageto
theequipment,personalinjury,ordeath.
Thesecabinetshavenoriggingpointsand
arenotsuitableforrigging.NEVERattempt
tosuspendanSRMsubwooferbyitshandles.
The Ins and Outs of Polarity
SRMsubwoofersincludeaswitchthatallowsyouto
quicklyinvertthepolarityofthesubwoofer’soutput
relativetotheinputsignalitisreceivingfromthe
mixerorothersoundsource.Butwhatexactlydoesthat
mean?Asubwooferworksbyliterallypumpingairas
thewooferconemovesinandoutwithrespecttothe
cabinetinwhichitishoused.Itdoessoaccordingtothe
low-frequencyportionofthesignalitreceivesfromthe
soundsource.
Thewooferconeissimplyfollowingthewaveformas
seeninthesinewaveinFigure1.Asthesinewaverises,
thewooferconepushesout.Likewise,asthesinewave
falls,thewooferconepullsintothecabinet.Amusical
signalismuchmorecomplex,ofcourse,butthesame
principleapplies.Movementofthewooferconecauses
airpressurechangesthatweperceiveassound.
Whenthenormal/invert[polarity]switch[4]is
engaged,theoriginalwaveformissimplyreversed180˚
[seeFigure2].Again,thesubwooferconefollowsthe
waveform.However,thistimethewooferconestarts
bypullingintothecabinetfollowedbythewoofercone
pushingout.Ifyouhaveeverexperimentedwitha
subwooferpolarityswitch,youmaynothavenoticed
anychangestothesoundregardlessofitsposition,
especiallyifyouarelisteningtojustthesubwoofer.
Thisisnormal,asourearsperceivethembothatthe
sametime.
Thenormal/invert[polarity]switchcomesintoplay
whenthesubwooferispairedwithaloudspeaker.
Ideally,thewooferconesofthesubwooferandfull
rangeloudspeakerwouldworktogetherbypushing
andpullinginunison.SRMsubwoofersaredesignedto
beusedinabroadrangeofapplications.Theexibility
providedbythepolarityswitchisnecessarytoensure
thatyouarereceivingthebestpossiblesoundfrom
yoursystem,regardlessofyoursetup.
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Figure 1: Normal [0˚]
Amplitude Amplitude
Figure 2: Invert [180˚]
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Polarity Waveforms