So we played a 4th celebration yesterday in Big Lake TX. Pretty normal city park/fairgrounds. Had the concrete stage with a metal roof.
This was the first time this event has been held. I don't think anyone has put a significant system on this stage before! Here's the video:
http://youtu.be/0giPDmHiTDcIt was so bad. The rattle was every bit as loud as the pa.
The city people we were dealing with were super cool and I suggested finding some tires to throw on the roof. They found about a dozen old tires and out them up there. It helped tremendously! The roof still rattled but it was greatly muted and did not "sustain" like it does in the video.
Show went smoothly and everyone was happy!