Live sound equipment + Generator?

[OneEng]

Up here in Michigan, we have been getting torrential rain and storms on a daily basis.  Last night at practice, our practice house was out of power, so we fired up the generator.

My furman power distribution box was showing some pretty unstable voltage (112-120) and every time the kick drum hit, the lights dimmed (no kidding).

We have done this before in a pinch, but last night was the first time that it occurred to me that this may not be the best thing for my expensive speakers and digital rack gear.

Everything seems fine, but it got me thinking.

Is this risky?

[agedhorse]

Risky? Certainly, given the generator type and size that you are using.

The problem with using smaller, non-commercial/industrial type generators is that they have poorer regulation and lower rotating mass (stored mechanical energy). With smaller generators, assuming they are of reasonable reliability type, in order to accomodate a dynamic load you will need to size the generator at ~2x-3x what you would need for a more continuous load. By doing this, you automatically increase the rotating mass and place less requirements on the AVR circuit. Also, goos maintenance is critical, especially on machines that use field winding brushes and sliprings.

There are 2 things that happen when a generator is undersized for a dynamic load, they are somewhat independent but also somewhat interrelated. The first is that with lower rotating mass, speed control becomes more difficult for the generator's prime mover to maintain through governing, and while this is not the sole determining factor for output voltage, it does play a part in it. The other factor is that the field strength is proportional to output voltage so as the output voltage falls the field must increase. This is done by the AVR circuit which generally (these days) is a PWM controlled signal fed back from the exciter into the field... just like the tracking power supply in the Lab Gruupen amps!!! Whenever you have a feedback/servo circuit like these, hunting can take place if the changes are too fast so the gain and acceleration ofthe control must be slow enough to be unconditionally stable, which is at odds to maintaining good dynamic regulation in an undersized machine.

So, either find an adequate sized generator of high quality or take a beer break and wait for utility power to become stable.

[Unalaska]

How about keeping it to a vocal only pa? Less demand for AC.

[Pro Sound Guy]

Kick drum in the monitors for rehearsal for a club band?

Really?

 

Ok

 

[WynnD]

I'll be honest. I don't understand where a drummer on an acoustic set gets off thinking that he needs drums to be in his own monitor. I also don't normally put the kick into the monitors. I can easily hear it from the FOH.

[OneEng]

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Pro Sound Guy wrote:

Kick drum in the monitors for rehearsal for a club band?

Really?

 

Ok

 

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We use IEMs, so I am guessing that the monitors weren't the problem

The subs were.  

I like to practice like we gig.  I do this for several reasons.  The most important is that I feel strongly that if there is something wrong with your live setup, it is much better to find out about it at practice rather than at a gig.  We also have a practice stage and all of us are setup as we are at a real gig.  That way any visual cues we use at practice work at live gigs as well vs. everyone facing each other at practice, then suddenly at a gig, you are missing important visual cues you have become used to having.

I take this philosophy clear down to the cables, stands and mic's we are using at practice.  These are packed up and used at the gig as well.  We have spares that we bring of nearly everything, but those are exactly that .... spares.  What we do at practice is what we do at a gig.

That is also true of running the setlist.  We have groups of different genre music that we play together.  That way once a group gets on the dance floor, they stay for the entire group.  We practice moving from song to song smoothly and with little or no delay.  We pause at the end of a group of songs, acknoledge the applause, then move into the next group of songs.

[OneEng]

 

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agedhorse wrote:

 

 

Risky? Certainly, given the generator type and size that you are using.

 

The problem with using smaller, non-commercial/industrial type generators is that they have poorer regulation and lower rotating mass (stored mechanical energy). With smaller generators, assuming they are of reasonable reliability type, in order to accomodate a dynamic load you will need to size the generator at ~2x-3x what you would need for a more continuous load. By doing this, you automatically increase the rotating mass and place less requirements on the AVR circuit. Also, goos maintenance is critical, especially on machines that use field winding brushes and sliprings.

 

There are 2 things that happen when a generator is undersized for a dynamic load, they are somewhat independent but also somewhat interrelated. The first is that with lower rotating mass, speed control becomes more difficult for the generator's prime mover to maintain through governing, and while this is not the sole determining factor for output voltage, it does play a part in it. The other factor is that the field strength is proportional to output voltage so as the output voltage falls the field must increase. This is done by the AVR circuit which generally (these days) is a PWM controlled signal fed back from the exciter into the field... just like the tracking power supply in the Lab Gruupen amps!!! Whenever you have a feedback/servo circuit like these, hunting can take place if the changes are too fast so the gain and acceleration ofthe control must be slow enough to be unconditionally stable, which is at odds to maintaining good dynamic regulation in an undersized machine.

 

So, either find an adequate sized generator of high quality or take a beer break and wait for utility power to become stable.

---

 

Thanks Andy.

Yea, I think his consumer grade Honda generator simply doesn't provide a very stable voltage source.

I should have turned off the mains and only ran on the IEM's in hind sight.  Stupid move on my part.  Fortunately, everything seems to have survived my ignorance.

I am more concerned about doing this once I move to a digital board.  Do you think that a digital board will be more susceptable to poor power than my rock solid MixWiz appears to be?  Also, what do you think about a cheep UPS used primarily for the purpose of smoothing out the voltage spikes.  I saw one at Walmart yesterday for $78.00.  In contrast, Furman makes some rack mount versions that run closer to $1000.00.

Finally, is it harder on the powered speakers?  I am assuming that the power supply built into the amp has some pretty decent caps on the input to handle voltage regulation.  My gut tells me that if the voltage drops on a big transient, that the current on the input stage of the regulator would increase which may pose an issue in putting more thermal load on the speaker.  Additionally, I assume that the DSP should work just fine as long as the voltage regulation on the input of the power module continues to provide good even power despite the fluctuations on the A/C input.

What do you think?