Feedback is all about the relationship of microphone and speakers. Anyone that has access to a mike needs to be aware of this. I've seen a ton of "musicians" that point the mic right into a monitor inbetween songs and wonder who is doing this. Moving monitors or mics can go a long way to reducing feedback. Also make sure monitors are pointing to the back of the mic (singer is singing into the front).
How do you get rock volumes without feedback? Easy answer. Lower your your stage volume and let FOH speakers do the work. Your guitard will say "if I turn down my Marshal stack down I'll loose my tone". Fire him. You will always have a hard time with feedback when you compete with a narrow minded guitard. There are a lot of guitards around.
Adjusting equipment? Each and every mic, cable, mixer, efx processor, amp, speaker cab and room has frequencies that they like and dislike. This makes for a complex mess that makes a sound man work for his pay. A graphic EQ will go a long way to dealing with this mess. I recommend a 31 band EQ on every amp. After a while you will hear a ring and know what freq it is and your finger will just lower that freq and it will be gone. You will also hear a ring and not know what freq it is. I used to boost each freq one at a time till I found the freq cuz it just got worse. This method will not make you any friends but it works.
Me??? I'm usually the singer, bass player and sound man. My brain ain't big enough to do all three at the same time. So I go for high quality equipment. First of all I throw away the 58's. 58's are great mics but they make a sound man work. I like Audix OM-3's but there are a lot of mics that have a close proximity effect and that means good feedback rejection. If everyone is using the same mic, your job will be easier cuz when the first mic is dialed in the rest fall right into place.
Summary: Change out the mics, add EQ's and turn down.
Good luck.
