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[Chris Poynter]

Hi Everyone,

I have a couple JBL SRX 815P speakers that I use for mobile DJ (and the occasional live sound) use, and they are fantastic for small to medium sized events; however, I am looking to add a couple SRX818SP subs for larger gigs.

Right now, I run my speakers and small light show off one 15 amp circuit, and when I'm chugging along at full-tilt the whole thing draws 14.3 amps MAX.

I have a Ultratec Radiance hazer as well, and it's listed power consumption is approximately 8 amps. I always find a second 15 amp circuit to plug this into.

I don't currently have a distro box or anything, so my current practice is to just use two separate 15 amp circuits in the venues I play. In some of these venues it's difficult to find a third!

Anyways, back to the PA: The tops and the subs both have a listed power consumption of 2.2A (1/8th Power) and 5.6A (1/3rd Power). I never really push my gear that hard, so if I'm just barely tapping into the "limit" light, is 2.2 amps (each) a fair estimate of their power consumption?

TL;DR - I'm wondering if anyone in here uses two JBL SRX815p tops and two SRX 818SP subs and has measured the total power consumption in a real world scenario. I want to make sure I have a plan for powering everything before I proceed with the subs.

Thanks!

Christopher Poynter
Victoria, BC, Canada
www.chrispoynter.ca

[Chris Grimshaw]

1/8th power is pink noise just tickling the limiters. Chances are the program material will be more dynamic than pink noise, so the 2.2A would be a safe bet.
If you're playing bass-heavy music with continuous sine waves (happy to provide examples), the power consumption on the subs will be much higher. Most music will fall under the 1/8th power category, so allowing 9A for the PA system would be pretty reasonable IMO.

Chris

[Chris Poynter]

1/8th power is pink noise just tickling the limiters. Chances are the program material will be more dynamic than pink noise, so the 2.2A would be a safe bet.
If you're playing bass-heavy music with continuous sine waves (happy to provide examples), the power consumption on the subs will be much higher. Most music will fall under the 1/8th power category, so allowing 9A for the PA system would be pretty reasonable IMO.

Chris

Thanks for the reply, Chris. I appreciate it! No crazy bass-heavy music... just lots of top40, lol.

[Mike Monte]

Thanks for the reply, Chris. I appreciate it! No crazy bass-heavy music... just lots of top40, lol.

My observation: most young people are listening to their songs on earbuds thus they are not used to hearing "crazy bass"....
You are all set.

[Luke Geis]

I would look for a third circuit to plug the subs in on. 14 amps is A LOT. While class D amps have come a long way, the truth is they still demand immediate power from the wall. Subs are a little more demanding. They may have the same basic spec, but they will draw more over a period of time.

I have a pair of PRX 518 subs that will essentially shut down if they don't have their own power source when asked to do some heavy work. As long as they have their own circuit they will pretty much do as I ask. These subs are only rated to 129db!!!!! So you can see how they spend a fair amount of time doing some work. They are also rated at close to 5 amps, so that may be the difference? In either case, I notice a difference when they share power with anything.

Another thing to keep in mind is the specs. While it says X amps at 1/8th power, you have to realize how much power you are truly consuming. 1/8th power is the equivalent of a sine wave -6db from clipping if I am not mistaken? A sine wave is NOT program media. Program media these days   carries a crest factor close to that of a sine wave ( -3db )!!! So when you have that type of media playing at what seems a modest level, you are actually asking quite a bit. The 14 amps you state, seems evident of that. 5.6 amps per speaker is still only 11.2 amps, there is still 3 amps left to go! That means while being modest in volume, you are still closer to 1/2 power or -3db ( sine wave at full output ) type levels. You can turn up if you want, but the speaker probably wont really allow it. Once the limiter starts working, you don't really gain SPL as much as apparent level. It actually compresses the media enough to reduce its crest factor and give the impression of being louder. With consumer media, this is rather difficult to do since the media is already at that apparent level. So more compression just makes it sound even more squashed and compressed ( often crunchy and distorted sounding with lack of bass and highs ). With live media its not as abrupt or brash and it gives that live media a more processed type of sound; I.E. It more or less helps more so than destroys it. 

Plan on at least one more circuit plane and simple.

[Chris Poynter]

I would look for a third circuit to plug the subs in on. 14 amps is A LOT. While class D amps have come a long way, the truth is they still demand immediate power from the wall. Subs are a little more demanding. They may have the same basic spec, but they will draw more over a period of time.

I have a pair of PRX 518 subs that will essentially shut down if they don't have their own power source when asked to do some heavy work. As long as they have their own circuit they will pretty much do as I ask. These subs are only rated to 129db!!!!! So you can see how they spend a fair amount of time doing some work. They are also rated at close to 5 amps, so that may be the difference? In either case, I notice a difference when they share power with anything.

Another thing to keep in mind is the specs. While it says X amps at 1/8th power, you have to realize how much power you are truly consuming. 1/8th power is the equivalent of a sine wave -6db from clipping if I am not mistaken? A sine wave is NOT program media. Program media these days   carries a crest factor close to that of a sine wave ( -3db )!!! So when you have that type of media playing at what seems a modest level, you are actually asking quite a bit. The 14 amps you state, seems evident of that. 5.6 amps per speaker is still only 11.2 amps, there is still 3 amps left to go! That means while being modest in volume, you are still closer to 1/2 power or -3db ( sine wave at full output ) type levels. You can turn up if you want, but the speaker probably wont really allow it. Once the limiter starts working, you don't really gain SPL as much as apparent level. It actually compresses the media enough to reduce its crest factor and give the impression of being louder. With consumer media, this is rather difficult to do since the media is already at that apparent level. So more compression just makes it sound even more squashed and compressed ( often crunchy and distorted sounding with lack of bass and highs ). With live media its not as abrupt or brash and it gives that live media a more processed type of sound; I.E. It more or less helps more so than destroys it. 

Plan on at least one more circuit plane and simple.

Hi Luke,

Thanks for the input.

As I mentioned, "I run my speakers and small light show off one 15A circuit, and when I'm chugging along at full-tilt the whole thing draws 14.3A MAX." That is to say, when I look at my little power meter at the end of the night, 14.3A is the peak number I pulled at any point in the night. I've done this over the course of several gigs, one of which I was pushing the system fairly hard.

My light show theoretically draws 9.3A at the most, but I haven't measured it separately from the sound system.

This would mean that theoretically my speakers are pulling a combined total of 5A, or 2.5A each... a little more than the listed 2.2A at 1/8 power.

I should probably measure the speakers and lights separately at some point, but I just thought I would ask around to see if anyone in here uses that same JBL system, and if they find that one 15A circuit is enough for the speakers and subs together... since the subs have the same specs.

Cheers,

Christopher

[Larry Sheehan]

Hi Luke,

Thanks for the input.

As I mentioned, "I run my speakers and small light show off one 15A circuit, and when I'm chugging along at full-tilt the whole thing draws 14.3A MAX." That is to say, when I look at my little power meter at the end of the night, 14.3A is the peak number I pulled at any point in the night. I've done this over the course of several gigs, one of which I was pushing the system fairly hard.

My light show theoretically draws 9.3A at the most, but I haven't measured it separately from the sound system.

This would mean that theoretically my speakers are pulling a combined total of 5A, or 2.5A each... a little more than the listed 2.2A at 1/8 power.

I should probably measure the speakers and lights separately at some point, but I just thought I would ask around to see if anyone in here uses that same JBL system, and if they find that one 15A circuit is enough for the speakers and subs together... since the subs have the same specs.

Cheers,

Christopher

Since the hazer is already on it's own circuit, just move the rest of the lights to that circuit and you should be fine.

[Luke Geis]

I know for a fact that when pushed, all 4 speakers on one circuit will not work very well. While they will function, my guess is that they will clip early or simply start reducing level.

The way the amps work is simple. They demand current to convert into output voltage. When you have a large bass hit all 4 speakers are then trying to pull current from one outlet. That outlet will only " Flow " so much current before it chokes out due to the demand. In other words it just can't keep up. If ran this way long enough it will generate enough heat and trip the breaker, or you simply utilize better than the 15 amp breaker will allow and it trips or a combination of both. What you can usually see with this high current draw is a loss in voltage seen at the outlet. You can loose as much as 5-10 volts every bass hit if the speakers are being ran nearer their limits. In either case you have to expect the worst. If the speakers will pull up to 5 amps  at modest use, then 4 of them at 5 amps will be 20 amps!!! A 15 amp circuit will not tolerate that draw for long before it says no more and trips.

I would run all the lights on one circuit and then split the PA into another 2 circuits.

[Chris Grimshaw]

Luke,

The 5.6A current rating is 1/3rd power, which is just tickling the limiters on a 33% duty cycle signal. FWIW, sine waves are 50% duty cycle, and square waves are 100%. With pop music, you'll have to really really mash into the limiters to see current draw that high. It'll sound very very bad before the breakers pop. Note that with a crossover in place, the tops shouldn't pull much current when the bass drops.

It's a fair point about voltage sag. I'd rather hope the amplifiers would have regulated supplies that wouldn't care about voltage fluctuations, but that's not always the case. Even if the supplies aren't regulated, I'd expect them to still run okay, unless the voltage goes low enough to switch the cabinets off completely (usually around 90v). As a reference, I used a set of amps with unregulated PSUs on the end of a few hundred feet of 32A 240v feed. The mains was reading 212v with everything at idle. When things got going, the lights were dimming - I expect it was dropping to well below 200v. Given that the amps were expecting 240v, those are difficult working conditions. Everything went fine, though. There was plenty of rig for the gig, so even operating on reduced power there was enough grunt.

Chris

[Art Welter]

1/8th power is the equivalent of a sine wave -6db from clipping if I am not mistaken? A sine wave is NOT program media. Program media these days   carries a crest factor close to that of a sine wave ( -3db )!!! So when you have that type of media playing at what seems a modest level, you are actually asking quite a bit. The 14 amps you state, seems evident of that. 5.6 amps per speaker is still only 11.2 amps, there is still 3 amps left to go! That means while being modest in volume, you are still closer to 1/2 power or -3db ( sine wave at full output ) type levels.

Plan on at least one more circuit plane and simple.

Luke,
 
Full "RMS" power is determined by measuring the voltage of a sine wave,  voltage x voltage /resistance ="watts RMS". A sine wave has a crest factor of 3 dB, but "full power" is considered to be that, -6 dB would be 1/4 power, still twice as much average power as 1/8 power, pink noise (12 dB crest factor) "tickling the limiters" as Chris noted.

Circuit quantity has nothing to do with low voltage "brown out", (which will generally reduce the power an amplifier can produce) wire gauge and distance to the mains transformer determine that. A single circuit run of 10 AWG 50' from the mains will be far more "stiff" (less voltage drop) than two circuits of 14 AWG running 150'.

Art

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