http://www.prosoundweb.com/article/the_wall_of_sound_to_now_a_pa_evolution_odyssey/http://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/40220-ozzy-plant-2-mics-taped-together.html::They were supposed to kill feedback. Two microphones were wired out of phase. In close proximity like that will cancel each other out if the same signal, with the same strength is applied to both. If you sing into the closest one, your voice won't be canceled out (that signal being much stronger than the one going in to the second mic). The sound returning from the pa speakers though would enter both mics at pretty much the same level and at the same time, causing phase cancellation and avoiding feedback.
Try it. It really works. Nowadays, the intelligent graphic equalizers will solve the issue in a more elegant way..::
OR
Join Date: Sep 2007
Location: ontario, canada
Posts: 150
yes, the two mic taped together thing is indeed to eliminate feedback, as monitor systems were in their infancy (if they were used at all), and most times there was either the PA on its own, or very large sidewash systems. if you look at old footage of the stones, mick can be seen using this technique.
also, as a sidenote re: the grateful dead's massive system...everyone did in fact have their own stack behind them, but the reason why the FOH guy had no control over anyone's sound was because there WAS no FOH guy. there were people giving feedback to the band so it remained more or less balanced, but there was no console to be wrangled. (this VERY large system was run completely on tube powered amps as well, making it the most labour-intensive PA to ever be built, and ultimately led to its demise due to the unbelievable cost involved in its upkeep.)