Measuring amps/power requirement for audio

Sayen

Active Member
I've measured power many times for lighting using my trusty clamp meter, but never for audio, and I'm a bit vague on how much power an audio system draws. Out of curiosity I ran a test on our portable audio system. I didn't think to look at what gear was included, but lets estimate it at 2 subs, 2 mains, three monitors, and four Crown amplifiers to run the entire thing, plus two mixers. At idle, I only measured around 5 amps, and at full volume close to 6. Those two numbers seem awful low, especially coming from the world of lighting.

So...what am I missing?
 
I am a student. This is a guess. Please don't make fun of me if I am wrong. Take with salt.

I know amps use capacitors, so could it be possible that, once this capacitor is charged, the amp needs to draw less power to maintain it? Or something?

I am a student. This is a guess. Please don't make fun of me if I am wrong. Take with salt.
 
Audio Watts are nebulous things, you will often see a "3000" Watt amplifier with a mains input rating of 2000 Watts or less, there are many ways to measure audio Watts, there's rms, peak to peak, peak instantaneous, etc etc.Basically an amplifier can be rated at any size you want.2000 wats of real audio power is seriously loud, I often see 4-6 1200 Watt amps plugged into a 10A socket and working perfectly happily.Best not to mention this to audio guys, they will explain how they need all this power for "headroom", in fact most audio guys need quite a lot of "headroom"
 
I am a student. This is a guess. Please don't make fun of me if I am wrong. Take with salt.

I know amps use capacitors, so could it be possible that, once this capacitor is charged, the amp needs to draw less power to maintain it? Or something?

I am a student. This is a guess. Please don't make fun of me if I am wrong. Take with salt.
You are actually quite correct in your hypothesis.
Inrush current is the term.
 
Stating the obvious, and preaching to the choir here, but...
that's because of their overly inflated cerebral appendages. ;)

/ducks and runs
But at least that prevents the cranial-rectal inversion syndrome from which some others suffer. ;)


To the OP, were all four amps and two mixers on one circuit and you measured the current for that circuit? What were the actual "full volume" conditions? I'm not real surprised that you measured less draw than you might expect, however I am surprised at the 6A "full volume" number relative to the 5A idle number.

As David noted, real world audio signals are constantly varying and audio has to be looked at in terms of both peak and average levels, which then also affects the associated power. For many types of music it is not unusual to have a 10-20dB crest factor, which represents a peak level 10 to 100 times the average level, so it is quite possible to have high level peaks and still have a much lower average level. People are often surprised by how much of the time their 1,000W amp is outputting double digit Watts during typical use. However, if the peak level remains the same then as the frequency of the peaks occurring increases or as the average level increases, the crest factor decreases and the power required increases.

So that often leaves the dilemma of providing power based on a 'worst case' scenario that may rarely apply or of making some assumptions and compromises knowing that they place some potential limits on the system.
 
I was testing to see if we could run our entire audio system off of generators for an up coming event. I had the entire system chained back to one circuit for the test, popped in my wire adapter and threw the clamp meter on it. Full volume was with an iPod playing and cranked - I guessed that the system would need more power when the speakers were pushing more sound. I'm assuming (?) that individual lines don't add up much because of the board's preamp and the minimal power levels there, so we figured one input (iPod) would give us a decent ballpark figure for power.

I did the measurements without the generator. We did note the inrush, but I didn't think to measure it. It was pretty brief, but you could hear the generator rev up briefly.
 
The load from the console, and things like EQs, processors, etc., is going to be pretty stable no matter what you do with it. The power amps are the ones that will vary a lot based on the audio demands.

I'm assuming that the gig is outside, since you need a generator. Keep in mind that if you made load measurements indoors, that the speakers and amps will be working harder outside. Floors, walls, and ceilings reflect sound and help it get from speaker to ear efficiently, but outside those things don't exist.
 
We pushed it to 11 for the test. I wasn't worried about measuring the console, and we didn't even plug in the pedal boards and whatnot for the test.

So audio really does just draw a minimal amount of power, especially compared to lighting?
 
We pushed it to 11 for the test. I wasn't worried about measuring the console, and we didn't even plug in the pedal boards and whatnot for the test.
I'm still not clear on how hard you were running the system but if you measured 6A for a circuit running four amps and two mixers then it was probably not being run hard. I've seen an entire system run off a single 15A circuit that got very loud but that was was a factor of the application and a testament to the efficiency of that particular system, it was able to get plenty loud for the application without being pushed at all. You did not note which amp models were involved, however looking at a few Crown amp models, the 1/8 power ratings (typical of program material right at clipping) show a current draw anywhere from 3A to 10A or more and 5 to 10 times that of idle. If you measured 6A total for four amps and two mixers then that's probably 1-1.5A per amplifier and seemingly well below the draw those amps potentially represent when run hard. Were the amps clipping even with proper system gain structure?

So audio really does just draw a minimal amount of power, especially compared to lighting?
It depends on how you look at it, but in typical theatrical applications then overall yes, audio requires much less power than lighting. There are audio amplifiers that require a 20A or 30A circuit to themselves and for which the output wiring has to be treated as Class 1 wiring, but in many situations it is common to run multiple amplifiers on a single circuit without any problems.
 
Did I miss something, or can't you just read this info off the back of the gear in question?

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Amp manufacturers seem to have settled on the average power being 1/8 of max on "normal" music and 1/3 of max on "heavily compressed" music. Search for "power consumption" and similar terms on the makers websites and you'll find the specs.
 
Did I miss something, or can't you just read this info off the back of the gear in question?

Sent from my DROIDX using Tapatalk

You can read it but can you believe it?
 
I was testing to see if we could run our entire audio system off of generators for an up coming event.
A major factor to bear in mind is the averaging, or the time constant, of the current meter. Amplifiers have have high peak current requirements, with the average current draw being a small fraction of the peak. Amplifiers need the peak current.

With utility provided power, there is enough current capability that this requirement is usually not significant. the generator(s) will have to be sized to handle the peak current draw.

Andre
 
Did I miss something, or can't you just read this info off the back of the gear in question?

Sent from my DROIDX using Tapatalk

You can read it but can you believe it?

Ummm, yes?

What reason do you have not to?

Sent from my DROIDX using Tapatalk
 
Ummm, yes?

What reason do you have not to?
Perhaps the question should be "What does the number on the rear panel represent?"
 
We are using five Behringer EP2500 amps, I was wrong about the Crowns. The back doesn't list anything other than the wattage of the individual units. 5*2400=12,000W, or around 100A by the math at full output. So audio folks, is it just a misunderstanding over how these work? I'm both confused and curious.
 
We are using five Behringer EP2500 amps, I was wrong about the Crowns. The back doesn't list anything other than the wattage of the individual units. 5*2400=12,000W, or around 100A by the math at full output. So audio folks, is it just a misunderstanding over how these work? I'm both confused and curious.

Are you running full duty sine wave into clipping on a regular basis?

If not, you're never going to see a sustained current consumption of anywhere near that.

You would be surprised on what you can run off of a single 20A breaker. In a pinch I have run a small outdoor festival off of a single circuit. Venue was a 200'x200' park in the middle of down town Portland using 4x RCF 6001A on top of 4x Dynacord Cobra PWH subwoofers powered by a PowerH 5k, 6 monitor mixes on LG Fp2600's, and stage power. Even when the headliner came on and we had sustained 95dBA levels at FOH, even when the bassist was really playing we only ever pulled 19A as measured by a Furman PL PRO.
 
We are using five Behringer EP2500 amps, I was wrong about the Crowns. The back doesn't list anything other than the wattage of the individual units. 5*2400=12,000W, or around 100A by the math at full output. So audio folks, is it just a misunderstanding over how these work? I'm both confused and curious.
If that's the maximum draw for the peak levels and the system was running full out then music with good dynamics (a 10-20dB crest factor) might equate to a 1A to 10A average draw while heavily compressed music (a 6dB or lower crest factor) might average 25A or more. That's really one of the major differences between lighting and audio, while the current and power associated with lighting may vary, you are typically not looking at the same variations in signal level or crest factors common to audio. It is not that difficult to conceive running a fixture at 100% for some period of time but you probably won't often see a pure sine wave at full level for long periods with a sound system.
 
I have read this thread and understand the power will be a strange thing going to sound. I too am a light guy but get involved in the power supply side for lights,sound and video on a regular basis. I usually just ask sound what they want but have never understood how it is figured. We occasionally get in tight power limits and frequently use generators for events. I would like to have some idea how figure their needs and this thread has done nothing to clear the mystery.
 

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