They have a stack of about 10,000 watts about 100 metres away.

I have read 95 dB(C) several hundred metres away in previous years. They think by putting these empty steel boxes in the way, that they will QUOTE reduce the rumble UNQUOTE. They will guarantee increased reflections, thus increased feedback. They have the stage and speakers elevated ABOVE the top of the specially built earth berm around the sunken auditorium - and they are stacking these hollow boxes 5 metres high on the narrow top of this earth berm.

Chooks will not walk on the ground at that distance away in previous years! They sit off the ground and grumble all day.

The wavelength of the rumble is longer than even the length of these boxes! The massive bass boost they use such that 120 dB(C) equates to 60 dB(A) is right in the resonant range - not to forget that a mostly sealed box is a good Helmholtz style Resonator (depends on Volume), and at that size, the overtones (a totally different series from the ones that occur in open pipes, rods, etc) will be right up in the music range.

They will resonate!