First of all, it's not just the voltage that is dangerous. Though, higher voltage means the arc is more probable, of course. A foam cover is a poor insulator, b

First of all, it's not just the voltage that is dangerous. Though, higher voltage means the arc is more probable, of course. A foam cover is a poor insulator, but at least it helps keeping the minimal distance from the conductive microphone grill. In this case we're talking mostly about avoiding unpleasant shocks, not some life-endangering situations.