hi all,
am hoping to get some help confirming whether or not my maths is right for setting the limiters on my system to protect the subs. I have a dcx2496 dsp which has inbuilt limiters.
I was planning to run 2x fane colossus 18xb (1000W Rms) in parallel off the xti4000 bridged. this would give me 3200W of power which is way too much. I've been advised strongly elsewhere that i'm better off just running them one on each channel at 650W. but was wondering whether i can make sure the drivers are safe by using limiters so that im still able to take the subs closer to full power?
From what i've managed to work out from research, i've put together some calculations that supposedly would limit the signal reaching the amp to keep the subs safe. That being said i am fairly new to this and still trying to wrap my head around it so they could be way off. any advice would be very appreciated (an an explanation as to why something is wrong!) would really like to understand the maths/physics behind this if possible.
formulas are from these threads:
https://forum.speakerplans.com/output-levels-input-sensitivity-dbu-dbfs-ummmm_topic23486.html?KW=+22dBu
https://forum.speakerplans.com/setting-limiters-on-berry-lms_topic27651_page1.html
so: wanting to limit the output of amp from 3200W to 2000W
1) The ultradrive meters in dBfs with 0dBfs = +22dBu
2) The amplifier in requires 1.4vrms for full output (+5.14dbu)
to work out the dB ratio of these two powers:
10 Log (3200/2000) = 2.041db
then to find limiter setting:
-22 - 2.041 + 5.14 = -18.9dbu
From what i've been able to work out, this would theoretically limit the output to the subs to 2000W regardless of the signal coming into the dcx? if this is completely wrong pls explain why!
would probably set to -20dbu to be safe as apprently can't guarantee 1000W rms is accurate and they're gonna be used for bass music (dub reggae etc.)
am hoping to get some help confirming whether or not my maths is right for setting the limiters on my system to protect the subs. I have a dcx2496 dsp which has inbuilt limiters.
I was planning to run 2x fane colossus 18xb (1000W Rms) in parallel off the xti4000 bridged. this would give me 3200W of power which is way too much. I've been advised strongly elsewhere that i'm better off just running them one on each channel at 650W. but was wondering whether i can make sure the drivers are safe by using limiters so that im still able to take the subs closer to full power?
From what i've managed to work out from research, i've put together some calculations that supposedly would limit the signal reaching the amp to keep the subs safe. That being said i am fairly new to this and still trying to wrap my head around it so they could be way off. any advice would be very appreciated (an an explanation as to why something is wrong!) would really like to understand the maths/physics behind this if possible.
formulas are from these threads:
https://forum.speakerplans.com/output-levels-input-sensitivity-dbu-dbfs-ummmm_topic23486.html?KW=+22dBu
https://forum.speakerplans.com/setting-limiters-on-berry-lms_topic27651_page1.html
so: wanting to limit the output of amp from 3200W to 2000W
1) The ultradrive meters in dBfs with 0dBfs = +22dBu
2) The amplifier in requires 1.4vrms for full output (+5.14dbu)
to work out the dB ratio of these two powers:
10 Log (3200/2000) = 2.041db
then to find limiter setting:
-22 - 2.041 + 5.14 = -18.9dbu
From what i've been able to work out, this would theoretically limit the output to the subs to 2000W regardless of the signal coming into the dcx? if this is completely wrong pls explain why!
would probably set to -20dbu to be safe as apprently can't guarantee 1000W rms is accurate and they're gonna be used for bass music (dub reggae etc.)
Hi,
+22dbu= 9,75 Vrms.
1,4Vrms= approx +5,5dbu.
22dbu-5,5dbu= 16,5db
You then need something along 16,5db attenuation for your amp max out, if 2db are needed to pad to 2kw then -18,5dbfs is in the ballpark. But... limiters works on peaks/transients not on rms levels! So i would lessen a bit more just to be sure...
Overall your math is not this off, and yes something along -20dbfs is not a bad figure imho ( you don't need ten digit accuracy and you probably won't run your sub at max all the time.. i hope!).
Here is a useful link to play with dbu if needed:
https://www.sowter.co.uk/decibels.php
The system will be run by dj? Analog or digital desk? Cause if analog they can overdrive their desk without too much hassle so it can be dangerous for your subs... with bass heavy music the high rms levels are dangerous.
That said this is not how i determined the number of box and amp power needed when we had a soundsystem, things like level required on dancefloor and distance of said dancefloor, number of hour of play and headroom have to be taken into account to have safe margin of operation ime.
+22dbu= 9,75 Vrms.
1,4Vrms= approx +5,5dbu.
22dbu-5,5dbu= 16,5db
You then need something along 16,5db attenuation for your amp max out, if 2db are needed to pad to 2kw then -18,5dbfs is in the ballpark. But... limiters works on peaks/transients not on rms levels! So i would lessen a bit more just to be sure...
Overall your math is not this off, and yes something along -20dbfs is not a bad figure imho ( you don't need ten digit accuracy and you probably won't run your sub at max all the time.. i hope!).
Here is a useful link to play with dbu if needed:
https://www.sowter.co.uk/decibels.php
The system will be run by dj? Analog or digital desk? Cause if analog they can overdrive their desk without too much hassle so it can be dangerous for your subs... with bass heavy music the high rms levels are dangerous.
That said this is not how i determined the number of box and amp power needed when we had a soundsystem, things like level required on dancefloor and distance of said dancefloor, number of hour of play and headroom have to be taken into account to have safe margin of operation ime.
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thanks a lot for the reply, really helpful.
im not expecting to run the subs at full all night and i trust the djs playing so generally make sure they're well off the red. this was more for interest/understanding than cause im planning to max them out all night
gonna be playing for 5 straight hours of pretty continuous bass so definitely gonna be careful.
also forgot to mention but on advice from the threads above^ i keep my limiters at 4000ms release time for safety.
im gonna be on the controls for the soundsystem on and off all night (between dancing) but gonna be having djs play bass music all night. I have the dj mixer (digital) running into an analog mackie profxv2. Normally what i do is set the max out from the dj mixer (red lining hard) when setting up so that it comes up at -2db on the mackie (the xlr outs on this mixer are +2db).
im not expecting to run the subs at full all night and i trust the djs playing so generally make sure they're well off the red. this was more for interest/understanding than cause im planning to max them out all night
gonna be playing for 5 straight hours of pretty continuous bass so definitely gonna be careful.also forgot to mention but on advice from the threads above^ i keep my limiters at 4000ms release time for safety.
It's not actually these are very robust drivers. Your calculations are fine you just have to ensure the amp gain controls are set to max and that the DJ doesn't redline thier mixer/controller, if the music maintains dynamics and doesn't get compressed then your subs will easily handle everything that amp has to offer.
I have a DCX that has been sucessfully protecting one of my sound systems for several years, in my case the sub drivers are being powered at thier program rating which is 2x rms with no issues.
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any chance i could get a slight explanation on this? Up until this point, i've been using the limiters to cap the signal and then essentially amp gain controls as a kind of "volume" knob (and also to balance the highs, mids and lows). This was under the assumption that, as long as i keep the signal going into the dcx at just bouncing off the limiters, i would essentially be getting a loosely constant signal into the amps, which i can then use the amp level knob to control how much power i fed the drivers.
from responses on here and another thread it seems this is a complete misunderstanding of how they work/are best used. I only recently discovered the norm was to set amp gain controls to max and do all the gain staging earlier in the chain. should i really be maintaining appopriate signal level entirely on the mixing desk (bearing in mind i can't always control the dj and their obsession with turning up the gain)? and would it be best to set the relative levels of high-mids-lows on the gain settings in the dcx?
didnt realise this was something that could be done safely! would you say that if being used for bass-driven dance music this would generally be unsafe for subs? have seen warnings on other threads that for dub/dubstep type music the continuous basslines mean that going over the rms is risky
Most Gain Control found on amp are passive attenuator. As such they have 2 main drawbacks: depending on thetype of attenuator choosen their input Z ( impedance) can vary, they'll bring ( a bit) of noise changing S/N ratio a bit.
To my view what Conanski recommend is related to your calcul which will change the threshold point of limiters if not fully open but it's on the safe way imho ( except if you try to compensate the input signal by upping it's level to reach 5,5dbu...).
Varying Z can change freq response but it will depend of your amp input Z, usually they are high on recent amp so you rarely compromise the 'bridging transmission' sheme.
Noise... well it might lower s/n ratio a bit. But i would not have concern as you don't drive a compression drivers with 120db/1w/1m...
Gain stagging should respect the nominal level and associated headroom of each link in the chain. Otherwise you'll compromise S/N ratio of the whole chain...
The second desk in your setup doesn't protect you from a dj playing with the pre gain on his mixer or using bass eq at +15db ( max out volume) but it'll give you a way to cut his signal before it destroy the FOH.
I was low confidence in dj as i am one myself: few are the one who understand you should never saturate the main mix ( foh) and are able to maintain a constant output level without upping gain during a mix, or not boost low end at insane amount...
D&B , Dubstep, Dub are amongst the worst signals for a PA: low end often equal to full blast modified high rms sinus running continously during long period of time.
It's a torture for subs hence being cautious not to overdrive them at the source ( the dj's desk gain pot and eq).
To my view what Conanski recommend is related to your calcul which will change the threshold point of limiters if not fully open but it's on the safe way imho ( except if you try to compensate the input signal by upping it's level to reach 5,5dbu...).
Varying Z can change freq response but it will depend of your amp input Z, usually they are high on recent amp so you rarely compromise the 'bridging transmission' sheme.
Noise... well it might lower s/n ratio a bit. But i would not have concern as you don't drive a compression drivers with 120db/1w/1m...
Gain stagging should respect the nominal level and associated headroom of each link in the chain. Otherwise you'll compromise S/N ratio of the whole chain...
The second desk in your setup doesn't protect you from a dj playing with the pre gain on his mixer or using bass eq at +15db ( max out volume) but it'll give you a way to cut his signal before it destroy the FOH.
I was low confidence in dj as i am one myself: few are the one who understand you should never saturate the main mix ( foh) and are able to maintain a constant output level without upping gain during a mix, or not boost low end at insane amount...
D&B , Dubstep, Dub are amongst the worst signals for a PA: low end often equal to full blast modified high rms sinus running continously during long period of time.
It's a torture for subs hence being cautious not to overdrive them at the source ( the dj's desk gain pot and eq).
It's headroom related: your amp power can be many times the recommended power of your drivers as long as you don't let the amp drive at full power.
By doing so you are sure the electronic circuit will never distort ( especially on peaks) and as such your drivers are safer than if the amp driving them clip ( as clipping result in a square wave and for the driver it mean being pushed at it's limit of travel in/out for 'long' period of time ( relatively speaking, 50% of frequency related time), the inverse of what an audio signal should be...).
That said when you do such things you have to be sure an idiot will not push the outlevel too far... hence it's rarely recommended to do such in a PA : there was always a drunk punk who wanted 'more sound' pushing the fader on our back when we had the sound system despite we been cautious...
In studio i often installed 1kw amps to drive 250w passive speakers, sometime lower power loudspeakers ( Ns10) but the 'main' level controls were hidden into a machine room and no idiots were allowed to have the key. The only level knob on the console set max output level which were 'safe' to drive the amp without killing the monitors.
Here is some good reading about the pro and con of multiamped systems even if it is for home it suit PA too:
https://sound-au.com/bi-amp.htm
https://sound-au.com/bi-amp2.htm
https://sound-au.com/tweeters.htm
You can balance L/M/H levels inside the DCX. The limiter calculations you have done depend on the amp gains bing at max, if they aren't then the signal level required to activate them goes up and all that work was for nothing. And.. having the amp gains set anywhere other than at max position at an event exposes your rig to medling fingers that could crank them up at any moment.
Yes.. and I know what you mean about the DJs. Every one that comes to the stage wants to be a bit louder than the last guy, and some just keep tweaking thier levels over the duration of a set until they are solidly into the red. I see this all the time and just walk over and calmly ask them to roll the levels back out of the red, I want the DJ rig and the downstream mixer to be flashing yellow leds at most.. because it sounds better. and I make sure to mention this at the beginning of an event. My rig.. my rules. They don't seem to understand hearing fatigue or have no self control. Or both!
Yes it is going to be program genre dependent. I do a lot of work with south asian groups and caribean DJs, there are lots of bass heavy tracks but I don't know if it's quite as demanding as Dub so you are wise to err on the safe side.