Feedback Issues

[tycobb73]

My band practices in my bassment. It is about a 15 x 20 room, drywalled. I know nothing about sound, would like to learn but when we gig I'm looking at hiring it out. I still need to have something good enough for practice. So right now I've pieced together a PA for practice. Its this old 12 channel peavey board that goes into my Gallien Krueger 1001RBII that goes into my Dr Bass 210. The mics of which there are 2 are SM58. I have the amps and mixer all along the short wall. The drummer is next to them. All Amps except my bass amp are about 2 to 4 ft in the air. The singers are about 15 ft away from the amps and directly face them. They stand about 5 ft apart. Our volume isn't what I'd call loud, as the drummer isn't loud and we can hear him fine. I also am very good friends with my nighbors as our houses are about 20 ft apart and he said he couldn't hear us at all with my slider door closed. I'm getting feedback issues. One of the other mixers I try is a 4 channel line mixer that is better, but because of the line inputs and mic adapters I don't have room to add a 3rd singer (the drummer) and I still have issues. I have most everything on the mixer flat, except the sliders which I manipulate until its on the verge of feeding back. If I lower it enough so that it doesn't feed back I have trouble hearing it over the rest of the 2 guitar band. Any suggestions? I don't care about quality as I just want to get through practice but volume and feedback are an issue.

[KeithAlanK]

The note that feedback makes is a function of distance from mic to speaker.
The farther away, the lower the note produced.
This is why when a singer drops the mic close to a stage monitor it squeals a high pitch--the distance travelled is short so it can run around "the loop" of mic-->spkr-->mic-->spkr etc much faster. If it loops 1000 times in a second, the feedback node frequency is 1Khz, so reducing 1K with an EQ can reduce feedback or kill it entirely.

In your situation, it can be a direct feedback loop but more likely the reflected sound off walls etc is a major contributing factor.
A 31-band graphic is the best tool for this, but simply experimenting with mic location can really pay off.

Mics are least sensitive at the 10 and 2 o'clock positions as you face it to sing, so just turning the singers a bit can help.
Another thing to try is some treatment to the walls to lessen reflected sound.
Carpeting, blankets, a mattress...you get the idea.

Hope this helps.
Good luck!