Feedback / T1 ToneMatch® Audio Engine / Comp Gate
Use the CompGate - Noise Gate to effectively mute the microphone when there is not a strong vocal.
You will have to experiment to find the best setting.
From the Bose® Pro Portable PA Community
It seems so obvious now that the Noise Gate is the answer; still, your post prompted my epiphany. We play electric and definitely louder than an acoustic act. (ex: I use either two customized Blues Jr's in stereo, my '65 Super Reverb, or my ProTube Twin Amp on stage) The tonematch's Noise Gate solved the feedback resulting form my need to push the vocal mike to the max. Also, I don't have to stand in between the microphone and the Bose to avoid that ensuing ring. The band was awestruck by my the improvement in my "mixing prowess". Of course, I didn't tell them that you cued me in. Thanks, (and don't tell anyone you told me, ha!)
Feedback Problems - Esparka