Is 40amps enough?

ademhayyu21

New Member
Hello friends!

I hope everyone is enjoying their summer. I've been contacted to provide a quote for AV equipment for a new outdoor stage being built. Fun!

Here's the catch, the site is only providing 2x 20amps to tie the equipment into. The stage is approximately 28'x30', will live on a pretty large field, and expected to host some big name performance organizations around the city so it would be safe to assume that audience sizes would range between 80-250. Just based on what I know about sound and consulting with audio engineers, this would call for some powerful speakers and subs to get some decent audio quality. Am I underestimating the power of 40amps?

Looking forward to whatever thoughts the pros have on this. I've consulted with some electricians and some companies who guided me towards finding some alternative more reasonable options in terms of power distros and company switches but I'm interested to hear folks thought's on this.

Thanks y'all!
 
Since I ran 60 amps (@ 120V) to power just the house lights, amps, computers, mixer, and wireless equipment in the booth for a 126 seat indoor theater, I'm going to say folks will tell you, as they said in Jaws, "You're going to need a bigger boat."
 
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Most likely it is enough if you amps are split equally. Keep in mind, "program" output is usually 5x the RMS draw as music and voice are quite dynamic. At 120 volts the 32 amps (cont duty from 2x20) will give you 3840 continuous watts. If you are running standard program ratio, (x5) that would allow you almost 20kw of program audio. Here's the thing, is the 2x20 just for sound? If other things are tied into it that would greatly reduce YOUR available sound power.
 
Most likely it is enough if you amps are split equally. Keep in mind, "program" output is usually 5x the RMS draw as music and voice are quite dynamic. At 120 volts the 32 amps (cont duty from 2x20) will give you 3840 continuous watts. If you are running standard program ratio, (x5) that would allow you almost 20kw of program audio. Here's the thing, is the 2x20 just for sound? If other things are tied into it that would greatly reduce YOUR available sound power.
Thanks for the response. Yeah I’m also expected to run lights, mixer, consoles, and reserve some power for projections for movie nights and such.
 
No. This is an unacceptable proposal.

What do they hope to accomplish with the limited amount of power?

If they're going to have entertainment or presentations by "people you've heard of" they'll be renting generators. Heck the average bar band needs more than 2 circuits.

My suggestion (snipped opinion of silly, short-sighted committees)... is a pair of 50 amp, 120/240v services on either NEMA 14-50 (electric cooking appliance-style) or appropriate Hubbell CS series (the kind your local Sunbelt or other rental shops have on their generators and spider boxes). If the max audience is 250, they deserve the same experience as the performer would give 2500, and that means electrical infrastructure is a bit more expensive, per patron.

Alternately, a 200 amp, 120/208v 3 phase company switch. Yeah, it seems big. It's cheaper to put in now than later. Think: LED walls.

What is the proposed programming, and is the organization animal, mineral, or vegetable... er, municipal, academic, or house of worship?
 
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Since you mentioned setting up[ an outdoor stage, it sounds like a generator and feeder is in order. You might be able to pull power from a nearby building (which sounds like what's being offered), but 2x20A isn't going to get you much. Like, production management might use up that much, just by themselves.

Is a 28 x 30 stage only going to draw 250 patrons? I'd look at the size of the park you're in, and assume you're going to fill it. Even if it doesn't sell out, you'll have patrons to prefer to sit further away from the stage, or in the shady area, and so on.
 
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I run a lunchtime outdoor stage on 1x L21-30... KW152 tops over KW118's with KW122 wedges... plus 2 drops of band power. No lights. That L21-30 is 90 amps total possible power, and we max it out with that system most days. 2x 20's you are talking to speakers on sticks and hope the bands don't show up with amps. Your going to be renting a generator for most show unless they pull in way more power.
 
Hello friends!

I hope everyone is enjoying their summer. I've been contacted to provide a quote for AV equipment for a new outdoor stage being built. Fun!

Here's the catch, the site is only providing 2x 20amps to tie the equipment into. The stage is approximately 28'x30', will live on a pretty large field, and expected to host some big name performance organizations around the city so it would be safe to assume that audience sizes would range between 80-250. Just based on what I know about sound and consulting with audio engineers, this would call for some powerful speakers and subs to get some decent audio quality. Am I underestimating the power of 40amps?

Looking forward to whatever thoughts the pros have on this. I've consulted with some electricians and some companies who guided me towards finding some alternative more reasonable options in terms of power distros and company switches but I'm interested to hear folks thought's on this.

Thanks y'all!
Projection outdoors competing with the sun?
No way, No F'in way.
Toodleoo!
Ron Hebbard
 
"We, the unwilling, led by the unknowing...."
 
While I too would recommend getting more power, and if its permanent, a genny probably isn't best to rely on for every show. Let me go down a rabbit hole though.

A 2 channel power amp that's rated at 8000w for 2 channels will pull about 9A of 110v power when running at "maximum level" at 8ohms and lightly clipping. (QSC PL380 PDF power draw download link)
To put this in perspective - a rated 2000w quad amplified powered speaker (500w/ ch), under my testing indoors in a 50'x100'x20' room, hitting 95db at 20 feet away, speakers on sticks at head level, playing Toto's Rosanna with no EQ, draws constantly under 20w at 110v AC.

It's truly about scope. If they have a tech budget of $1000 then they're obviously in over their head with everything, not just Audio and Lighting. Are there building plans yet?

I've absolutely run sound for a choir in a park before and had no issues with powered speakers running from a single plug from the bathroom. But it was 60 singers and no instruments. We could easily run 2 mains and 2 delay powered speakers on sticks with no worry about overloading a single 20A circuit.
July 4th announcer guy with recorded patriotic songs. Sure no worries.

Sometimes "parks" don't want it to be "loud" so maybe the 2x20A circuits is their way of safeguarding against that. But if a drummer, 2 electric guitars and a bass player show up, it's just going to pop the circuit 3 minutes into rehearsal, not automagically limit the guitar amp to volume notch 1/2.
 
I have a fair amount of doubt that the bikes are powering anything but the sound engineer's phone charger.
I started out with the same skepticism, but I was wrong. There's a guy who operated here in the SF Bay Area til moving up to gold country at the start of the pandemic who did exactly this. He had carefully rebuilt the power supplies in his amps for greater conversion efficiency, added some battery storage for buffering, and it really worked - well enough to fill a park over a square block in size. Another impressive use was at a large rally/protest for environmental justice and climate action Fall 2019. I ran fixed PA at the pre-march rally; then his rig, mounted on a 3 wheeled bike-towed trailer, provided sound for the march as it made its way down Market Street. I wouldn't do a Led Zeppelin concert this way (at least yet), but it was way more practical than I gave it credit for. Solar panels when not used in motion also added to the power available.
 

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