PA and Feedback?
low_light
Posts: 251
Okay, I have a Yamaha PA with two Peavey stack speakers. Each speaker stack holds two 10's and two 12's. got a couple of good shure mics. and we get feedback a lot and sometimes even current through the mic that shocks my mouth now and then. mainly happens when i have my electric strapped on.. we've moved the main PA around the room and made sure it's not close to the Mics. so there is no current shocking my mouth anymore. but we cant get a clean level of volume over our instruments.
The obvious answer is turn down, but the drums dont have a volume knob. I guess my main question is what exactly causes feedback? I dont know enough about gear to be able to isolate the problem.
anyone?
-low
The obvious answer is turn down, but the drums dont have a volume knob. I guess my main question is what exactly causes feedback? I dont know enough about gear to be able to isolate the problem.
anyone?
-low
www.myspace.com/eotoband
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That is something we havent playd with yet is the EQ. Ill try that. thanks again
-dm
Also you may have an underpowered PA for all those speakers so the gain may be too high in order for the set up to work. Check the power ratings on the speakers and the Amp My guess is Ex is right. Adjust the eq and gain accordingly to get the best sound without feedback.
Feedback is caused by over driving the microphone or causing to much gain before distortion. The shures (SM 58's?) are good mic's with a substantial gain threshold so the EQ especially in the high region must be set to high for the gain (volume) setting you are using.
Check the logical stuff too, like making sure the speakers aren't throwing sound at the mikes. Keep them out in front of the mikes. Deaden the room with carpet, quilts, old clothes.
this is the PA I have..
"YAMAHA- If you don't need more than 6 channels, but do need ample power and monitoring capability, the EMX66M is the mixer for you. 2 mono 300W amps can both drive mains or monitors or both, or can be bridged for a whoppin' 600W of output. Mixer section features 3-band mono channel EQs, dual 7-band graphics, 8 digital effects programs (echo and reverb selections), 2 aux sends (monitor and effects), phantom power (+15V), and Yamaha speaker processing. XLR and TRS input connectors on channels 1-4, XLR and TRS pairs on 5-6. "
Features:
6 channels
2 mono 300W amplifiers (600W bridged)
3-band channel EQ
Dual 7-band graphic equalizers
8 digital effects programs (echoes and reverbs)
2 aux sends (monitor and effects)
Phantom power (+15V)
Yamaha speaker processing
XLR and TRS input connectors on channels 1-4, XLR and TRS pairs on 5-6
18-15/16"W x 12"H x 12-7/8"D
We dont have monitors so we have the speakers facing us but we are across the room. I'll try everything you guys have suggested next practice.
thanks again
Feedback is caused by sound from the speakers re-entering the microphone. When more than 50% of the sound entering the mic is from the sound of that mic in the speakers, it causes feedback. Essentially, the sound loops back into the mic, becoming a little louder in the speakers, thereby becoming louder again in the mic, becoming louder in the speakers, louder in the mic, etc. and just gets worse and worse. Of course, electronic signals travel fast, so this happens almost instantaneously.
Usually, feedback from one frequency (one place in the EQ spectrum) is the cause of the problem. That's why feedback sounds like one note that just gets louder and louder. Therefor, if you can figure out what frequency that note is, you can cut it in the EQ and solve your problem. Sometimes there are harmonic feedback frequencies, i.e. octaves. Octaves in the EQ frequency band are either doubles (1k [1000] would be 2k, 2k would be 4k, etc) or halves (1k would be 500, 500 would be 250, etc).
If you cut more than 2 frequencies on a 7-band graphic, you're really just reducing the gain in the system. Try to find the worst two frequencies, notch the worst all the way and the other about half-way, then just keep the volume right below feedback level. And another note: reverb tends to make feedback worse, so try not to use any 'verb (or other effects).
When using a regular Shure SM 58, the feedback rejection is directly off-axis. So, having the mic's cable end pointed straight at the nearest speaker is best (in monitors). Beta 58's and other mics that are super- or hyper-cardiod have 120-degree rejection angles. So, have the speaker 60 degrees to the left or right of the cable-end of the mic.
If you need more help or advice, PM me. I'm more than happy to help. Hope you understand everything I wrote here... and good luck.
this is a great forum
-low
-dm