MarkBarl Posted December 8, 2016 Share Posted December 8, 2016 I was in a theatre recently and had to have a pair of speakers flown. From the speaker spec they were 27kg each. Allowing additional weight for flying frames and cable, I estimated a weight of 75kg as a starting point for the fly man. At the end of the gig, I enquired how much weight they had to put on as this might be useful for future times when we have to fly a pair. I was told that the bar had 170kg on and that unladen it has 15kg on. When I expressed surprise, I was told that this was a double purchase system. With some assistance from Wikipedia do I understand correctly, that this is simply double the weight do to the limited movement distance of the arbor, meaning that the actual weight was 77.5kg which if not a DP system, 75kg is a reasonable place to start? Link to comment Share on other sites More sharing options...
andy_s Posted December 8, 2016 Share Posted December 8, 2016 Yes, double purchase counterweight systems require twice the 'balancing weight'but this means the counterweight only needs to travel half the distance that the load travels, which is sometimes useful. Link to comment Share on other sites More sharing options...
Bryson Posted December 9, 2016 Share Posted December 9, 2016 They also mean you can get nice wide wings. Ours are Double Purchase and the extra loading is a pain, but ultimately worth the effort. Link to comment Share on other sites More sharing options...
Just Some Bloke Posted December 20, 2016 Share Posted December 20, 2016 75 x 2 = 150 + 15 = 165kgs and they used 170kgs so your guess was remarkably close! Link to comment Share on other sites More sharing options...
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