Quote:
Originally Posted by mnfreelancer
Those who argue for the mic level scenario say:
-There is more gain before feedback when using open mics in close proximity (this seems counter-intuitive except than with electronics you find out quickly that every component in a circuit has a sweet spot where it operates the most efficiently and in audio this translates directly to frequency response and sensitivity...my theory is that the electronics in the amps are configured in such a way that frequencies that typically ring and feed-back in a live room are attenuated out of coincidence because of the behavior of the electronics involved.)
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Think of the system in terms of simple math. You have a microphone that is putting out a mic level signal.
On one hand that signal is routed to the preamp section of the powered speaker, where it is stepped up to some higher level to be sent to the main amp section. We'll call this signal level Y (more or less line level). The amp then does it's thing, however many db it is, and you get a speaker level, which goes to the speakers and gets turned into acoustic energy to produce a given SPL in the room. On the other hand, that same mic puts out the mic level which then gets routed to the board, and stepped up by the board's preamps to a line level. Either way, the signal hits the amp section at line level. By padding down your mixer's outputs to line level, you just make the preamp on the powered speaker have to re-amplify your signal, along with any noise injected into whole system.
If you experience significantly more feedback when using the mixer at line level, that would suggest that the "line level" of the mixer is hotter than the "line level" of the pre-amp in the speaker. No great surprise there, especially given what MuseAV mentioned about the mixer and the powered speaker having the same pre-amp. The mixer would then add summing amps on the stereo buss and possibly a final stage at the output of the board, which would make for a hotter output. Which would drive the amp harder, which would result in more SPL in the room, which could result in feedback sooner. I would expect the level knob on the speaker could be adjusted to account for this slight difference in signal levels.
For the reasons that you stated, driving the amp with the mixer at line level is the right way of doing things.
Matt