PA and Feedback?

low_lightlow_light Posts: 251
edited October 2003 in Musicians and Gearheads
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
www.myspace.com/eotoband
Post edited by Unknown User on

Comments

  • exhaustedexhausted Posts: 6,638
    play with the graphic eq on the PA's amp. you can roll off the frequencies where the feedback is occurring.
  • low_lightlow_light Posts: 251
    thanks Ex. I was hoping you'd reply hehe.

    That is something we havent playd with yet is the EQ. Ill try that. thanks again

    -dm
    www.myspace.com/eotoband
  • Pacomc79Pacomc79 Posts: 9,404
    yeah roll off the highs, another quick answer is to get the .99cent foam pop filters and cover the mic windscreens. this will cut back on the sound wash (bad feedback) from all those amps and cymbals in the room.

    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.
    My Girlfriend said to me..."How many guitars do you need?" and I replied...."How many pairs of shoes do you need?" She got really quiet.
  • robrob Posts: 142
    Paco and exhausted are right
    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.
    How,,,,,did I GET here?!

  • low_lightlow_light Posts: 251
    thanks Pac and Rob.

    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
    www.myspace.com/eotoband
  • mccreadyisgodmccreadyisgod Bumfuq, MTPosts: 6,395
    Yeah, EQ is definitely the solution... try notching 1k on the 7-band graphic. That's a typical feedback problem with Shure mics.

    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.
    ...and if you don't like it, you can suck on an egg.
  • low_lightlow_light Posts: 251
    yeah, MC i understood. thanks for the reply. I think I have a good idea now on what to do.

    this is a great forum

    -low
    www.myspace.com/eotoband
  • I have the same PA. Except I have a pair of JBL dual 15s. The eq is the trick. also put the main speaker volume at 95% the max volume. Then adjust the mic volume on it's own channel leaving the main volume the same. I would adjust the eq knobs from the top down on the mic channel. Since the top knobs control the higher frequencies. Use the tab buttion. If you have a digitech vocal processor like I do or another vocal effects unit other then the built in use the low z channel to plug the mic into then use pad. This makes it possible to use the effects with out the feed back. Always have the mic as far as possible from the mains and if you only have mains dont point it twoards the speakers. Try not to point it twoards the monitors also. If you want to use the effects built in the pa have the effect on and then tube the eq to get rid of the frequency that causes the feed back. Good luck.
  • low_lightlow_light Posts: 251
    ahh thanks man i appreciate it. that helped give me some insight to that unit as well. im a novice when it comes to gear experience. thanks again

    -dm
    www.myspace.com/eotoband
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