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SettingAccurateLimiterThresholds
ThelimitersbuiltintotheDSO480 isintendedtobeusedforloudspeakerdriverprotection,asopposedto
amplifierprotection.Allmodernprofessionalpoweramplifiersdesignedforlivesoundusehavetheirown
limiters,whicharetailoredtoprotectingtheamplifierfromclipping.
Thefollowingsectiondescribeshowtosetuptheuni
ts’limiterstoprovideexceptionalprotectionagainst
driveroverheating,andconeover‐excursion.
MostspeakersystemsaregivenapowerratinginWattsRMS.Thisisthemaximumcontinuo uspowerthatthe
systemwillhandleandoftenappearsveryconservative.Inreality,asmusicprogramisfarfromcontinuousin
nature,thepeakpowerofthesystemismuchhi
gher–uptotentimesthecontinuousfigure.Anylimiter,
whichistoprotectthedriverfromdamage,mustbeabletofulfilthefollowing tasks.
• HaveanattacktimewhichiscalculatedtoallowtransientsthroughbutkeeptheRMSlevelbel
owthe
speakermanufacturersspecification;
• Haveareleasetimewhichissufficientlylongtoavoidthelimiteritselfmodulatingtheprogram;
• Beintelligentenoughtoadjusttheenvelopeofthelimiteraccordingtothefre quencycontentofthe
programmaterial.
Theprogramlimitersarecapableofperform
ingallthesetasks.Theonlyparameterthattheusermustset
manuallyisthethreshold,anditiscrucialthatthisisdonecorrectly.Considerthetablebelow.
dB Ratio Vrms
Pwr8 Ω Pwr4 Ω Pwr2 Ω
45 177.83 137.74 2371.71 4743.42 9486.83
44 158.49 122.77 1883.91 3767.83 7535.66
43 141.25 109.41 1496.45 2992.89 5985.79
42 125.89 97.52 1188.67 2377.34 4754.68
41 112.20 86.91 944.19 1888.39 3776.78
40 100.00 77.46 750.00 1500.00 3000.00
39 89.13 69.04 595.75 1191.49 2382.98
38 79.43 61.53 473.22 946.44 1892.87
37 70.79 54.84 375.89 751.78 1503.56
36 63.10 48.87 298.58 597.16 1194.32
35 56.23 43.56 237.17 474.34 948.68
34 50.12 38.82 188.39 376.78 753.57
33 44.67 34.60 149.64 299.29 598.58
32 39.81 30.84 118.87 237.73 475.47
31 35.48 27.48 94.42 188.84 377.68
30 31.62 24.49 75.00 150.00 300.00
Usingthistableitisastraightforwardproceduretoworkouttherequiredsettingofthelimiterthresholdsfor
thesystem.
First,checktheRMSpow erratingofthespeakersystem,anditsimpedance.
Lookupthisvalueinthetableabove,usingtheclosestvaluebelowtheratedpowerofthespeaker
system.Notethecorresponding‘dB’value.
Checkthegainofyouramplifier,whichneedstobein‘dB’.
Subtr
actFROMthisgainfigurethatobtainedfromthetabletofindtherequiredabsolutesettingfor
thelimiterthresholds.
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