How Much Power Do I Need?

To many ads? Support ODJT and see no ads!
I wrote a proposal for a homecoming set up this fall, and they are booking me for it. But since I'm used to doing smaller wedding oriented set ups, I'm not sure exactly what will be needed for this. The set up will end up being as follows:

- 4 QSC 181 Subs
- 2 Pioneer XPRS-12 tops
- K12 (run as a monitor)
- 2 Chauvet Intimidator 355 IRCs
- 4 Chauvet H6 SlimPar LED Fixtures
- My controller and laptop, etc.

The lights are all LED and should be pretty efficient. But I'm worried the subs would be too much for a single circuit. If I split the subs 2 x 2 on different circuits, do you think they'll blow?

I don't really know how to do the math, but would like to be a little more scientific than "just bring a crapload of extension cords"



Music is dynamic, and the only time that the amps in the speakers would require maximum input current would be on a test bench testing with sine waves. Music is equivalent to 1/8 power consumption ratings tested with pink noise. You would be ok with the items listed on two 15 amp circuits. Also remember that a 15 amp breaker is not going short burst of 15 amp draw. Some reading material is linked below.

https://www.qsc.com/resource-files/productresources/spk/kw/q_spk_kw_usermanual_en.pdf

Duty cycle
 
Music is dynamic, and the only time that the amps in the speakers would require maximum input current would be on a test bench testing with sine waves. Music is equivalent to 1/8 power consumption ratings tested with pink noise. You would be ok with the items listed on two 15 amp circuits. Also remember that a 15 amp breaker is not going short burst of 15 amp draw. Some reading material is linked below.

https://www.qsc.com/resource-files/productresources/spk/kw/q_spk_kw_usermanual_en.pdf

Duty cycle


Screen Shot 2018-07-04 at 12.33.07 PM.png

I had looked at the manual but hadn't found that line before. If I assume that an outlet is delivering at least 100 volts (my Monster Power Conditioner generally reads between 110-125) - then the draw from 4 181s would be 9.3 Amps, but likely a bit less.
 
I have only had a problem once time on a 15 Amp Circuit. That was at a Halloween Party at a old house in D.C. years ago. I turned on my old MBT Enticer 300 wattx2 Lamp Fixture, and it would trip the breaker. I think it was more because it was a real old house rather than being just a 15 amp circuit. It held my sound system fine, but once that light was turned on, I would be shut down, and have to go to the breaker box. After two times, I just did not use the light any more. That was probably 11 years ago.

I have NEVER had a problem on a 20 amp Circuit. Even with 2 Subs, and a large LED Lighting display going on the same outlet. Of course, I don't use mega power drawing subs....just 2 12s
 
Unless the outlets are marked, the only way you'll know if they're regular 20A breakers, or 15A GFCI breakers (that trip if you sneeze at them) is by looking inside the panel box.
 
Unless the outlets are marked, the only way you'll know if they're regular 20A breakers, or 15A GFCI breakers (that trip if you sneeze at them) is by looking inside the panel box.
Actually, by code, the 20A rated receptacles have a different prong design ...

main-qimg-53bb28bdae90d657161dab67a726a883.jpg
 
Correct if there is only a single outlet on the circuit, but NEC code allows multiple 15A outlets going to a single 20A breaker. Look in the panel box.
I agree, but if you NEED 20A, you need a 20A outlet. I would never try to draw a 20A load through a 15A outlet, regardless of the breaker size.
 
I think it's unlikely that I get back to the breaker box. I'm going to assume that they are 15 amp circuits.

The last time I had a big power consideration, the outlets were actually numbered as to what circuit they were on. So it made it easy to split between 4 breakers in that case (that was much bigger gear than what I'm bringing this time).

If they aren't numbered, is there any way to tell if two outlets are on the same circuit together?
 
  • Like
Reactions: ittigger
I think it's unlikely that I get back to the breaker box. I'm going to assume that they are 15 amp circuits.

The last time I had a big power consideration, the outlets were actually numbered as to what circuit they were on. So it made it easy to split between 4 breakers in that case (that was much bigger gear than what I'm bringing this time).

If they aren't numbered, is there any way to tell if two outlets are on the same circuit together?
Not without tracing them back to the panel. I have a breaker identification tool (similar to this .. Klein Tools Digital Circuit Breaker Finder-ET300 - The Home Depot) I use around the house (and have used at 1 event space) to determine what breaker is attached to an outlet or light (I have a screw in adapter for lights). Trace 1 outlet, then the next, so on .. tedious and does require access to the panel (don't need to touch wiring).
 
If they aren't numbered, is there any way to tell if two outlets are on the same circuit together?
Without access to the panel (so you can trip the breakers), what you can do is measure the voltage at the outlet with nothing plugged in. Now put a really big load on the outlet (like a portable electric grill oven), enough that you can see a voltage drop - it's a duplex outlet, measure the receptacle not being used. All the other outlets on the same circuit will show that same voltage drop.

So, YES you can do it, but for you, a big NO!!!!!
 
Without access to the panel (so you can trip the breakers), what you can do is measure the voltage at the outlet with nothing plugged in. Now put a really big load on the outlet (like a portable electric grill oven), enough that you can see a voltage drop - it's a duplex outlet, measure the receptacle not being used. All the other outlets on the same circuit will show that same voltage drop.

So, YES you can do it, but for you, a big NO!!!!!

I suggest bringing a high wattage hair-dryer as it is much easier to transport than a portable grill over. :headbang:
 
I suggest bringing a high wattage hair-dryer as it is much easier to transport than a portable grill over. :headbang:
Except the last time I tried holding a hair dryer in one hand, and a multimeter measuring 115VAC in the other - well, let's just say it didn't go well!! :cheers:
 
  • Like
Reactions: ittigger
I see a bunch of items that seem like hum eliminators ranging from $20 - $100. I don't know that I've ever experienced a ground loop (or if I did, I didn't know what it was). But what are you guys using... and where should it be in the signal chain?
 
I see a bunch of items that seem like hum eliminators ranging from $20 - $100. I don't know that I've ever experienced a ground loop (or if I did, I didn't know what it was). But what are you guys using... and where should it be in the signal chain?

I keep a few of these around just in case. I prefer these since they are not added to the audio chain that could further degrade the audio.
 

Attachments

  • humxsplashbanner.jpg
    humxsplashbanner.jpg
    112.1 KB · Views: 10
  • Like
Reactions: ittigger
I have both, and the hum x never seems to work. The audio XLR ones work wonders. I don't find it degrades the audio at all.
 
  • Like
Reactions: Albatross
I have both, and the hum x never seems to work. The audio XLR ones work wonders. I don't find it degrades the audio at all.
...and it's probably safer as well. Some are critical of the HumX because it's not UL approved

earth-f1.gif
The dotted line is the ground loop. The 'loop" can be broken anyplace. The "audio" hum eliminators obviously break it on the signal side - they are usually transformers with totally seperate primaries and secondaries. In nearly all cases, transformers are more effective than breaking the loop on the AC ground side, but good ones come at high cost, and cheap ones may seriously affect the frequency response of the equipment. The switch is usually labled "Ground Lift".

img2B.jpg
 
There are generally 3 ways to break a ground loop, 2 on the signal lines and 1 on the power side.

On the signal side, and on the simple side, you can remove the connection between signal ground and chassis ground, either by using a ground lift adapter (or switch) or by cutting the jumper between the signal ground (pin 1) and the shield (chassis ground) in the cable. If you screw off the XLR boot, you'll find many cables have a little wire jumper between pin 1 and the shell. Cut it at one end (normally the male plug side) and many times you'll remove the noise. The reason is some AC powered devices (mixers, amps, etc.) ground the metal case they are in and tie the shell of XLRs to it as well (the cheaper all plastic connectors ironically avoid that. By cutting the jumper, you isolate the balanced signal from the AC noise.

Up next would be what Handinon shows above .. a combination of breaking the signal/chassis ground bond AND isolating the 2 signal lines with a transformer. More efficient, though transformer balancing can introduce issues as well.

On the power side, the Hum-X works using 2 large capacity diodes in a clipping circuit (in reverse parallel - anode to cathode) to "rectify" the signal so the hum is basically clipped out.