Simple thought, this is more for experimenting than anything else. I am well aware the end result may sound horrible, so please don't presume to preach to me here.
I play music. I have a battery powered amplifier / speaker which I modded with a bigger battery and power jacks for my small mixer and DI box. The sound balance is pretty shitty, but it's for fun and gets the job done for outdoor gigs.
I have a couple of battery powered omnidirectional collar mics that I want to use. The problem is, they're pretty sensitive and I can only crank them up so far before feedback starts, at a few different frequencies. The microphone inputs on the amp have no tone adjustment.
20Hz-20kHz response, omnidirectional
Simply put, I want to open up the microphone jack and solder a couple of resistors and caps in there to make a band-pass filter solely for the human vocal range. Now I am completely aware this could mess up the sound pretty badly, but I'm not using this system to record anything, ever. I just want to eliminate the feedback by isolating/passing only the human vocal range with a passive filter. If it sounds nasty (which, again, it probably will) it's a simple matter of desoldering stuff and putting the original wire back.
So, the question:
What range of frequencies best describes the human voice, and for the electrically-inclined, could you help me determine the resistor/capacitor values that will likely work best without killing the sound of my voice?