David, same question as above ... What would you say are most important things to consider in getting the most volume before feedback w/ a mic going thru your amp and not a PA?
Your position (and the mic's position) relative to the speaker?
Relative to the other instruments to control bleed?
Notch filter? Is there a typical frequency range that most often triggers that awful high-pitched elec. squealing from a mic?
Let's assume that one can at least get a decent amount and quality of sound unamped, for the sake of discussion. My bass is not a cannon, but it doesn't exactly whimper w/ my technique either. It's just sort of ... average.
Thanks for any info or advice you or anyone else would care to provide.
First, you need to understand the pattern the mic throws. For example, an omnidirectional mic picks up sound from 360 degrees, I think hyper-cardiod is less then 90. Some mics, eg. Shure SM57 are even more directional.
With the knowledge of the mic's pattern, try to position yourself so the mic is facing away from other instruments and your amp as much as possible. I like placing my mic infront of the treble side F-hole. If there's a drummer, the ideal position would be on the drummer's left, my bass and I are angled facing slightly right, so the mic is turned away from the drums, and my amp, an AI Contra is behind me and to the right. By having the amp there, my body acts as a buffer between the mic and amp. Set-up like this, volume levels have to be really high to cause problems for me.
Remember, feedback is caused by a mic amplifying the sound from a speaker it's sending a signal to, hence re-amplifying itself. So the way to avoid feedback is by preventing the mic from picking up the sound from it's own speaker. A lot of times I can't set-up the way I described above so I adapt. Sometimes that means there's a little bleed, but as I mentioned before, it's only audible when I'm not playing. In extreme cases, I've placed my amp in front of me.
I don't know which frequency is usually the problem and I don't have experience with notch filters. When I used to do live sound around Philadelphia we had a full spectrum graphic eq. The only frequencies it was ever used to boost were around 550hz, which is approximately the freqency of the human voice, if the singer was weak. Otherwise it was only used to cut frequencies; maybe some bass frequencies if boominess was a problem; if there was a feedback problem we'd find the frequency and cut it back. It's very exact. That's the way I'd deal with problems now if I had the equipment.
