"Flying boxes/arrays" may be the culprit??

[Mike Monte]

Hello:
In light of the recent stage collapses in Indiana and Belguim one common factor that I have noticed is that both stages had "flown line arrays".
Flying Line Arrays seem to be the rage these days (because they sound great) BUT hanging thousands of pounds of speakers on stage truss
does raise the structure's "center of gravity" to unsafe levels in my book.

Could the stage collapse(s) been avoided if the sound rig(s) used consisted of "ground-stacked" speakers??

I think so....

Properly secured or not, I'd rather take my chances in a potential high-wind situation with a "properly secured" ground stack rig than a flown rig...

Has the practice of "flying rigs" increased the incidence of stage failure?

Food for thought.

Mike Monte

 

[Tim McCulloch]

Re: "Flying boxes/arrays" may be the culprit??

Weight and balance are issues with anything in the air. Properly engineered and assembled structures can deal with these, but it's up to the operator to know those limits and enforce them when clients think you're being too picky.

We fly lots of VerTec 4889 with 4880 subs and use both bungee cords and ratchet straps. As has been pointed out in other posts here and at PSW, both ridged attachment and pendulum swinging are bad. Ridged transfers 100% of the wind load laterally to the towers; swinging creates a dynamic load of unknown energy loading the structure in ways the engineer cannot account for on an individual basis. We let a small bit of swing happen as it reduces the wind load (hence the bungees) but if it gets to the point where the ratchet straps take tension it's time to have a talk with the promoter about the weather.

Ground stacks blow over, too, even when strapped down. I've had pSeudo-4 speakers blown off scaffolding (2" ratchet straps holding them down) in storms. That said, you can't ground stack a line array and get the results the act/client require or that the audience deserves. And think about it: if the winds are that high there are other issues that related to the safety of the artists, crew and audience that need to be addressed. I'd rather pick up pieces of gear at an evacuated site than clean the blood off equipment (and my hands, so to speak).

So yes, flying speakers can and is done safely on a routine basis and groundstacking is not the panacea one might think.

Have fun, good luck.

Tim Mc

 

[Bennett Prescott]

Re: "Flying boxes/arrays" may be the culprit??

So yes, flying speakers can and is done safely on a routine basis and groundstacking is not the panacea one might think.

Eugh, God, it is not a panacea at all. It is simply impossible to cover a medium sized (2,000 people?) or larger audience well with a ground stacked system, except maybe if you build enormous scaffolding towers, and then you're back in the same ball game again so you might as well just fly an array off them.

 

[Rob Timmerman]

Re: "Flying boxes/arrays" may be the culprit??

If hanging 5 tons worth of equipment from the roof structure is changing the center of mass to any significant degree, you don't have enough weight on your anchor points. This goes doubly for any stage that has a roof or solid backdrop. A 60MPH wind exerts ~10lbs per square foot on a flat surface. I'll leave it as an exercise to the reader to determine how much weight that requires as ballast on the guy wires to hold down the roof.

 

[Matt Errend]

Re: "Flying boxes/arrays" may be the culprit??

The weight of the PA rig is relatively small when compared to the the rest of the production. A hang of 16x V-DOSC is only about #5000 including bumpers and pick. Let's say the entire weight of the PA is 10,000lbs, maybe 16,000lbs if you're flying subs. Compared to a modern lighting and video hang carried by an 'A' list artist, that's pretty minor. A large roof system like the one in Indiana was designed to support a UDL of ~100,000lbs. Sure taking the mass of the PA out of the roof would lighten the load, but then you're looking at other means of trying to support that same system, none of which are going to be any more resilient against toppling than a properly designed and deployed truss superstructure when presented with serious wind loads.

Really what it all comes down to is ballast. One point raised earlier (I can't recall if it was on this forum or another) is why venues like the Indiana state fair grounds, where the same structure is erected on a regular basis, aren't installing permanent attachment points for the towers and guy lines in the form of concrete pads that extend down several feet into the ground and weigh several tons. This would provide the rough equivalent to a permanent structures foundation, while still keeping the main structure available for use and deployment in other situations. When the permanent anchors are not being used, they should be able to be covered so that normal use of the field or track area would not be impacted.

 

[Brad Weber]

Re: "Flying boxes/arrays" may be the culprit??

The weight of the PA rig is relatively small when compared to the the rest of the production. A hang of 16x V-DOSC is only about #5000 including bumpers and pick. Let's say the entire weight of the PA is 10,000lbs, maybe 16,000lbs if you're flying subs. Compared to a modern lighting and video hang carried by an 'A' list artist, that's pretty minor. A large roof system like the one in Indiana was designed to support a UDL of ~100,000lbs. Sure taking the mass of the PA out of the roof would lighten the load, but then you're looking at other means of trying to support that same system, none of which are going to be any more resilient against toppling than a properly designed and deployed truss superstructure when presented with serious wind loads.

But it is not just the mass, it is where it is, the resulting moments and shear, tension and compression loads that exist in addition to the simple vertical static loads. And that may be what get some people into trouble, the overall system may be rated for the overall load but who is responsible for assessing the structural integrity with the actual loads placed on the structure?