Amplifier power vs power draw

[s1962a]

I am a bit confused about what mains power draw an amplifier would have, if I know it's rough max/rms output. So if an amplifer says 1300 watt max, does that mean it will potentially draw 1.3kw from the mains? Like a kettle for example.

The reason i'm asking is i'm trying to work out the power requirements for an off grid amp/speaker setup where no mains power is available, but using those 240v lithium battery packs. If i had a 250w battery pack, could it power a 1300 watt amp and speakers?

[annodomini2]

No there will be efficiency factors based on the type of amplifier, the design and the sound being played and at what volume.

As audio is usually not a flat signal the power draw for the amp will be RMS (Root Mean Squared) of signal * Gain * amp efficiency + static amp draw.

This is not everything, but will get you in the ballpark.

If you put a power monitor (current probe with logging) on for say an hour at the volume you interested in using, this will give you some data to work from and probably be more accurate than above.

E.T.A. you would either need bigger batteries or capacitors to cover the peaks

[Zad]

It all depends how honest the amp marketing people are and what sort of amplifier it is. Class B amplifiers run at half the maximum current even with no signal, so they are generally restricted to audiophiles. Modern amps can be Class D (digital) which may run 80/90% efficiency, depending on the power supply and the amp design.

Generally, say an amplifier has a real world average power of 100W:
RMS power (root mean square) is 100*1.414 = 141W
Now it gets into vague marketing speak:
"Music power" = 2*RMS Power = 282W
Some can choose to combine both channels
"Peak Music Power" is whatever the amp can deliver for a tiny amount of time, in a sudden peak. Basically dumping the contents of the power supply caps across the speaker. So possibly 2* again. or 4* if the marketing people are feeling enthusiastic.

An averagely efficient Class C 1300W real world amp could easily need to deliver 2000W of power for periods of time.

[cml24]

Do you have a specific amplifier in mind? Do you have a battery / ups system selected?

It's a substantial amplifier if it's drawing 1300w for any length of time.

What space are you trying to fill with sound? My car stereo has an actual total output of 12w by way of a small comparison.

[s1962a]

Thanks for the info

So the deal is that there is a local club that wants to have a socially distanced meeting in the park or other open space (no idea how that works with the rule of six). My job is to find out how to run 1 or 2 PA speakers to play some music / use microphones etc.

Doing some research, I can either go for 12v battery speakers - something like this which you just charge up

https://www.gear4music.com/PA-DJ-and-Lighting/SubZ...

But in case the batteries dont last very long or more power is needed I was looking into proper powered speakers with an inverter type setup, or one of those lithium battery packs. But the speakers are quoted as 1000w so I dont know if i can power them from a 250w or 400w power bank. Ideally speakers should be powered at maybe half volume for 4 or 5 hours in one go.

Speakers with built in amp
https://www.gear4music.com/PA-DJ-and-Lighting/Mack...

Power Bank
https://www.amazon.co.uk/POWEROAK-Generator-220V-2...
https://www.amazon.co.uk/UKing-Generator-60000mAh-...

Cheers

[blitzracing]

Fist get your speakers above head night as human bodies absorb sound quite nicely, as this will reduce your power requirments. Why not run it off a generator, they are not a lot to buy or hire at say 2.5 kw?

[thebraketester]

blitzracing said:

Fist get your speakers above head night as human bodies absorb sound quite nicely, as this will reduce your power requirments. Why not run it off a generator, they are not a lot to buy or hire at say 2.5 kw?

That would be my thought. Hire a small generator.

[jet_noise]

blitzracing said:

Fist get your speakers above head night as human bodies absorb sound quite nicely, as this will reduce your power requirments. Why not run it off a generator, they are not a lot to buy or hire at say 2.5 kw?

+1
Stands are available or you could do the '70s disco thing and have a stack of tables (before H&S was a thing ).
Be a little cautious on the gennie - IIRC it needs to be a good (true) sine wave for audio stuff.
And don't turn the gennie off with the power on. The transient is quite destructive. I've seen much of a system taken out - blown amps and speakers blasted completely off their mountings!

It's a long time since I did this stuff so things may have moved on.
I get the idea of battery/inverter pack - clean, simple, quiet, solid state but my feeling is they are not suited to the oomph you need, neither peak nor capacity. If you were powering a couple of lights or a TV but not a PA.

[Zad]

Gennies aren't the only things that don't produce sine wave Ac output, most battery powered inverters generate something closer to square wave unless they have the correct load.

[spikeyhead]

Zad said:

It all depends how honest the amp marketing people are and what sort of amplifier it is. Class B amplifiers run at half the maximum current even with no signal, so they are generally restricted to audiophiles. Modern amps can be Class D (digital) which may run 80/90% efficiency, depending on the power supply and the amp design.
...

Class A amps run at half the maximum current with no signal in, class B consume no current with no input, but suffer from cross-over distortion.

[spyder dryver]

blitzracing said:

... as human bodies absorb sound quite nicely...

One of our sound engineers often refers to the audience as "meat baffles".