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Author Topic: Measuring amplifier voltage output with a multimeter  (Read 50487 times)

jack smith

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #10 on: October 01, 2009, 08:37:43 am »

Look Ivan, stop bashing me alright? I dont want to try and get louder sound, louder than what my speakers can safely handle. I just want to make sure they get as much power as they need to sound as loud and clear as they can do. You can understand my confusion can't you? People say that I need to make sure i'm getting enough voltage to the amp to enable it to give out the power its rated at, and some people say that I may need to run the line level a tad past 0db in order to get the full power out of the amplifier. I kind of understand the idea, but i'm a little confused, thats all. Are you saying, that as long as I set the gain structure properly, and then go upto about 0db on the front end dj mixer after i've set gain structure, that i'll be giving the speakers enough power if I use a Crown K2 bridged into 4 ohms, with 1 JBL SRX728 sub running on the each amp?

Thats all I want to know. Simple hey?

Am I right in saying that any level past 0db is clipping the system, and go into the red lights is very serious clipping that could fry the speakers? At least am I right on this point?
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TJ (Tom) Cornish

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #11 on: October 01, 2009, 09:15:25 am »

OK - There are at least 3 different things at work here:

1: The input voltage and current available to your amp from the wall socket.  As others have pointed out, there's pretty much nothing you can do about this.  It also doesn't likely matter much - firstly because you can't fix it, and secondly because it won't affect the output very much.

2: Gain structure.  The idea here is to set your equipment so that you have access to all of the power your amp can deliver (if you need it), but also aren't using too much gain (amplification - either at your power amp or at some preamp stage inside your mixer or crossover) so that you get hiss.


3: Setting limiters to prevent clipping and reduce the chance of speaker damage.


I don't see at least in this thread what equipment you are using.  Please tell us which amps, what speakers, and if you have any kind of crossover or other processor in the middle.  This will help.

Read up on gain structure both by searching on the forum, and by reading stuff here:

http://www.rane.com/library.html

Also check out how limiters work.


One piece of good advice that you have received is to "have enough rig for the gig".  There are 2 ways to look at this - either lower your expectations to what the gear you currently own can handle, or get a bigger system.

Sound pressure and electrical power are not linear in this context.  After you get up a ways into the output of your speakers, it takes a lot more electrical power to make a small sound pressure difference.  This large electrical power difference also determines whether your speakers are humming along comfortably, or being pushed to the limit.  This is why Ivan and others are saying to not sweat the last little bit - even leaving 10% or 20% of your amp unused (if that's happening - I expect it's not), that only equals 1 or 2 dB of less output.


After you get the concepts sorted out you'll know where to go.  And don't feel bad about buying the meter - you'll use it plenty going forward.  I never bring gear without one.
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Ivan Beaver

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #12 on: October 01, 2009, 09:15:58 am »

It is NOT the distortion/clipping that damages most loudspeakers.  It is the (for the hundredth time) the AVERAGE POWER OVER TIME.  

That is NOT an easy thing to determine-as has been already beaten to death.

In any dynamic environment-saftey factors are much harder (read impossible as there are to many variables) to determine so that on occasion you come right up to the limit-but other times you are will below it.

No matter how hard you try- you CANNOT put a simple number/solution to a VERY complex problem.  That is simple.

And again-if people are suggesting you get enough voltage to the amp-I would ask THEM how do they go about gettting the AC line voltage up if it is low?

Let's assume you are not using a generator that you can adjust the voltage and are simply using the power companies line voltage.

You have what you have-and that is it.  Nothing you can do-so don't worry about it.

BTW it is not bashing you, but you seem to be having a hard time understanding what "how loud-peak output" etc means.

I guarantee that I could take the exact same system as you and get louder peaks out of it and still have it playing at the end of the night-assuming you are putting large amps on the system in order to "get the most out of the loudspeakers"-such as 6dB over the "minimum" rating.  In the case of the JBL728-if you put the max 6400w/cabinet as is on their spec sheet.

As long as you hit it with very short pulses (and the AVERAGE level is WELL below that)you may be fine-(depending on the freq and overexcursion), but try running your system where you have 0 on your console as the clip point-and allow people to run up to the 0 point.  BYE BYE subs.

HOW?  by playing material that has a much higher dynamic range (higher crest factor)less compressed.  That's it.  When you play the type of material you say you do, yes it will be "louder" than what I am talking about-but if you measure the peak loudness-I will be louder-but your average would be higher.  I am talking about a night of music-not just one song.

So what is "loudness" the peak-or the average.  It is exactly those types of questions that come into play when figuring out what your loudspeakers can take without being torn up.

Put the voltmeter away-it will tell you nothing of any real value.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs

jack smith

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #13 on: October 01, 2009, 09:46:41 am »

Well thats how i've set gain structure for years. Put about 1/5 more power through the system than its rms continuous rating (say 1,200 watts rms through a speaker rated at 1,000 watts rms continuous)and had not let the level for the whole system go past 0db on the front source (dj mixer) after i've set the gain structure, so make sure that all pieces of euipment clip at the same level.  I've never blown a driver or had any problems with anything. So once gain structure is set, is the red light the clip then? I thought 0db was the clip point. Maybe I was running my system about 4db lower than what I could of done all this time then due to me thinking that clipping was at 0db, when it was at +6 (which was the 1st red light on my dj mixer).

The equipment I was using years ago were JBL MP418 subs (I was using my friend's). But now my system is going to consist of 2 SRX728 subs, a Rane TTM56 dj mixer, Electrovoice AC One crossover, 2 JBL SRX722 mid/highs (t to you guys for recommending them), Crown K2 amps bridged into 4 ohng the 2 SRX728 subs and a Lab Gruppen LAB4000 amp running the 2 SRX722 mid/highs. I watch the levels very carefully and never let any dj go over the 0db light on the dj mixer all night (I keep checking every 5 minutes to make sure dj's aren't overdriving the system). I'm thinking about getting an XTA DP224 early next year after learning about limiters so to protect my system more by properly setting the DP224 up.
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TJ (Tom) Cornish

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #14 on: October 01, 2009, 10:11:09 am »

0dB the clpping point of what?  You have more than one clipping point in your system.  Many mixers don't clip until the output is +20dBu, but that input into an amp that clips with a lower input voltage will be a bad thing.

Ivan is trying to explain that clipping isn't the major factor that will determine whether you cook your speakers or not - average power is.  I'm going to take a leap (please correct me if I'm wrong) and guess that your music type is electronic or hip hop, which means that your source material has very little dynamic range - i.e. it's loud all the time, and not just on kick hits like rock and roll.  This means that your speakers will be stressed more than if you had lighter content music, even at the same volume.

How this happens is the driver never has time to cool down between peaks - continuous tones keep putting the heat on.  Your driver can handle this, but at a lower level than if you had short spikes with cool down time inbetween.

In the case of your 728s, that means the number that is important to you is 1600 watts.  Your K2 can put 2500 watts bridged at 4 ohms, which means it is possible to burn up the speakers if you are putting continuous tones into them with this amp.

Practically speaking, you're on the right track with picking a level on your DJ mixer as your target for everyone to hit.  Should it be the 0dB light?  Maybe - maybe not.  It depends on your gain structure.  If you want to know what the clip point of your amps are, you can do the following:

- Unplug your speakers.
- Get a test tone somewhere in the range that speaker will produce.  For subs - use 60 - 80Hz.
- Turn up the test tone until the amp clip light is lit.
- Note the position this happens on your mixer meter.
- If you don't like where the amp clip point happens on your mixer, you may be able to move it by changing the gain on your crossover.  If you want clip to be 0dB on your mixer, the crossover would be a good place to fine tune the gain so that happens.

This procecure can produce helpful information, but it won't necessarily tell the whole story as you are testing only one band of your system - the subs.  A song with tons of bass may clip the sub amp more quickly than a more balanced song.


As Ivan has said - this is a complicated problem, and there isn't a simple formula.  If you want simple, the best way to guarantee that you won't damage your speakers is to buy about 6 more 728s and run them all at an easy level.
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jack smith

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #15 on: October 01, 2009, 11:05:14 am »

The music i'll be playing is mainly music with a lot of bass in it thats pretty continuous and not a single bass stab sound in the songs. Its got as lot of continuous pulse bass, thats continuous. Now I understand. The Crown K2 is too powerful an amp to use with the SRX728 sub simply because of the music i'll be playing through it. So what would be a good amp to use on the SRX728 subs? What about a QSC PLX-1802 bridged on each sub, or maybe a still a Crown K2 but after i've set the gain structure on the system, turn the K2's attenuators down about 3db so the amp isn't giving the speakers so much power.

Actually I just thought, the other type of music i'll be playing is a lot of dance music like trance and techno that has only got single sinewave bass on top of the kick drums and no continuous bass. Its like a bang, bang, bang, bang. Thats how the techno and trance is i'll also be playing, wheras the the oldskool i'll be playing has bass that is like baaaaaaaaaaang, then at a differnt note, baaaaaaaaang continuous kind of bass.
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TJ (Tom) Cornish

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #16 on: October 01, 2009, 11:21:36 am »

Your K2 amps are fine - you just need to make sure they aren't run absolutely to the limit.
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jack smith

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #17 on: October 01, 2009, 12:02:47 pm »

Ok thanks. I won't run the amp to its limit because I know now (even though I havent used the new SRX728 & Crown K2 system yet) it'll be too powerful for the SRX728 sub when playing the sort of music I, and my fellow friends (djs) play. If I was playing something like opera or country and western i'd be ok with putting the full 2,500 watts through the SRX728 sub yeah? Does it sound like i'm understanding you correctly now?
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Ivan Beaver

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Re: Measuring amplifier voltage output with a multimeter-A better explanation
« Reply #18 on: October 01, 2009, 12:52:31 pm »

Let's try a different approach at power handling-ie sub damage.

Let's talk about your body and what it can take.

What is the highest temp your body/skin can take without pain-discomfort or damage?

120
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs

Ivan Beaver

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #19 on: October 01, 2009, 12:53:40 pm »

You're getting it now.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs
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