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  #1  
Old February 20th, 2007, 07:20 PM
jahern jahern is offline
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Advice on Microphone feedback

My Church had a get together last Friday 2/16 and in addition to singing a few songs, I provided a lot of the music (basically based on love songs as it was based on Valentine's day) When another singer started doing Angel Baby, I thought it would be cute to grab a mic and start doing doobadeedoo. It was OK except no matter where I went with the mic we were getting high pitched feedback. What are factors that I need to be aware of? Anybody?
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Old February 20th, 2007, 08:31 PM
George George is offline
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Sounds like you may have been in proximity to some speakers that caused feedback. If that were the case, turning the amp volume or the mike gain down may alleviate the situation.

Perhaps someone else may have a different suggestion. I's say that would be the first place to look.
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Old February 20th, 2007, 11:43 PM
Dave Heidersche Dave Heidersche is offline
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Along with turning down the volume, it is always a good idea to reduce or eliminate the echo or reverb when more than one mic is being used. Another sure fire cause of feedback is when the singer covers the microphone screen with his/her hands. I'm not sure why it does it but it leads to feedback.

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  #4  
Old February 20th, 2007, 11:49 PM
jahern jahern is offline
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Volume Question

By Volume, are we only talking about the gain on the mixer or on the amplifier as well. Do better machines handle more power? etc.
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Old February 21st, 2007, 12:31 AM
ddouglass ddouglass is offline
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Quote:
Originally Posted by jahern View Post
By Volume, are we only talking about the gain on the mixer or on the amplifier as well. Do better machines handle more power? etc.
It isn't a machine problem per se. The feedback is a sound loop created by sound from the speaker regenerating through the microphone. There are several things you can do to help prevent it.
Adjusting the amplifier will adjust the total volume (music and vocal) which isn't going to help if you want the audience to still be able to hear.
Adjusting the mixer levels is what you want. Hopefully you have a mixer with separate controls for each microphone and also for the music. That way you can adjust the offending microphone without changing the rest. If your mixer has treble and bass adjustments for each mic then you can lower the treble to stop the feedback. Also as Dave said it is a good idea to turn off the reverb/echo when using multiple microphones to help prevent the feedback.
An equalizer (a good one) can really help prevent feedback too, because you can lower the offending frequency's volume without effecting the rest of the frequencies of the final output. This would be a big help to you as the acoustics in most churches are not designed for amplified systems. They are usually built to allow the naked voice to carry well in the hall without having to have a microphone.

And Dave when a singer cups his hands around the microphone it is like yelling in a hall. Their voice is echoing off of their hands and can act just as a reverb....so they think, but it also channels the speaker sound into the mic at a higher level.
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  #6  
Old February 21st, 2007, 12:51 AM
TKaraoke TKaraoke is offline
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Feedback!

Too much bass on a mic will also give you feedback. You can use a feedback eliminator, I started with a Beringer, now use a DBX Drive Rack PA, pretty pricey but it's worth its' weight in gold. Covers a number of individual units all in one, Limiter, Compressor, Feedback Eliminator, EQ, Pink Noise (if you get the RTA Mic), adjusts for a number of mfg's speakers, amplifiers, speaker configurations, actually probably does more than you'll or I need. Just how much $ do you want to spend is all that matters. Just remember: he who dies with the most toys wins!
TKaraoke
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  #7  
Old February 25th, 2007, 05:31 AM
kilith kilith is offline
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Also the quality of the mic can make a HUGE difference! I have had audio-technica mic that has a switch (on and off) and I got HORRIBLE feedback no matter what I did. (forgot one mic at home by misplacing it and had to use the backup... I disconnected the backup and put it away and used my mic and the other orginal mic) If you can stay away from mics with an on off switch and having someone always back adjusting your volumes you might be able to stay away from feedback.
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Old March 1st, 2007, 04:56 PM
billyo billyo is offline
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Quote:
Originally Posted by jahern View Post
My Church had a get together last Friday 2/16 and in addition to singing a few songs, I provided a lot of the music (basically based on love songs as it was based on Valentine's day) When another singer started doing Angel Baby, I thought it would be cute to grab a mic and start doing doobadeedoo. It was OK except no matter where I went with the mic we were getting high pitched feedback. What are factors that I need to be aware of? Anybody?
just turn the highs ( treble ) down of the offensive mic and , never point the mic down on the floor, that would create a feedback you wouldnt believe..too much bass on the mic will give you a loud hum..the back end of the mic should be facing the ( back or front ) of speakers..
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Old March 1st, 2007, 10:46 PM
kilith kilith is offline
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Quote:
Originally Posted by billyo View Post
just turn the highs ( treble ) down of the offensive mic and , never point the mic down on the floor, that would create a feedback you wouldnt believe..too much bass on the mic will give you a loud hum..the back end of the mic should be facing the ( back or front ) of speakers..
Problem is most speakers in churches are now up by the ceiling pointing down so that is some what hard to control how the mic faces now days
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  #10  
Old March 1st, 2007, 11:36 PM
billyo billyo is offline
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Wink

Quote:
Originally Posted by kilith View Post
Problem is most speakers in churches are now up by the ceiling pointing down so that is some what hard to control how the mic faces now days

i believe thats true and you're right,but he said something about a get together.so i took that as an outside of church function..
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Old March 2nd, 2007, 06:47 AM
mindonstrike mindonstrike is offline
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Pure speculation here:
If you had to hold the mic a foot away from you to not overpower the other singer, I'd say the mic was too hot.
If this was not the case I would suspect you picked up an omni-directional mic which picks up sound from all directions instead of a uni-directional mic which for all intents and purposes picks up sound from only one direction - typically through the top.

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Old March 2nd, 2007, 09:31 AM
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Whatya mean exactly by "too hot" ?
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Old March 2nd, 2007, 10:06 AM
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In general, when you think of feedback, think of holding a mirror up to another mirror so that you can see yourself holding a mirror in a mirror of you holding a mirror, in a mirror of you holding a mirror, etc. If you hold the mirrors at just the right angle to each other, you can see your image repeated into infinity.

The same happens with a mic and speaker. The mic is taking in sound and the sound is coming out of the speaker. The more you increase the volume, the more sound is coming out of the speaker and then more sound can be picked up by the mic. If the mic is too close to the speaker, then the mic begins picking up the sound from the speaker and the speaker is then reproducing that extra sound from the mic and it creates a loop that feeds on itself into infinity.

Omnidirectional mics which pick up sound from many directions are particularly prone to this. Unidirectional mics are definitely a plus, but intelligent speaker placement may solve your problem. In a tight space, you may not have room to keep your speakers a safe distance from your mics, but you can still try to turn them away. Sometimes, if you have a long narrow room with solid walls, you can point the speakers at a 45degree angle to the walls and bounce the sound into the audience. This diffuses the sound, while still distributing it throughout the room.

You may also want to consider getting monitor speakers. This allows you to turn your main speakers out to the audience while having the monitors pointed to the volacists and adjusting your monitor volumes to accomodate.

Also, properly setting your system volumes and equalizing for the room is critical. For best results, use a separate power amp and mixing board. I have never been a fan of mixing amplifiers. I am partial to the QSC PXL series power amps. They are plenty powerful, have built in limiters and for the road systems, they are only 21 lbs. Any good mixing board will do so long as you have separate controls for each mic and music input.

For best quality sound, set your mixing board's Main volume to the halfway or 12:00 position, bring down all channel slides to zero and turn all gain levels down to the 9:00 position. Turn on your amp and set the amp volumes to FULL. Now start with one channel at a time on your mixing board and bring the volume slide slowly up until you reach the halfway point on the slide. If you find the volume doesn't fill the empty room, begin increasing the gain on that channel. Try not to exceed the 12:00 position on the gain unless you are still really weak in the room. If you cannot fill an empty room with sound, with your amp at full and your mixing board settings all at half full, then you need a more powerful amp and speakers. Once the room fills up with people, you can adjust the mixer's Master volume, gain and slide volumes to accommodate.

Avoid cranking everything to full. You will get distortion in your sound and you run the risk of overloading what your speakers can handle.

Remember to understand the difference between gain and volume - most people don't. Here's a nutshell version: Gain is how much signal you are allowing into a channel and volume is how much you're sending out. If you allow too much signal into a channel it can create distortion that gets sent out to the speakers as you increase the volume. Someone who cups their hands around a mic is forcing more sound into that mic and therefore more sound into that channel on the mixing board. Reducing the gain and increasing the volume will reduce the distortion from the mic while maintaining the volume of the output. You see?

Now, about the amp settings. Many people seem surprised when I tell them to set the amp to full volume, but I tell them to stop and think of the logic behind it. Your mixing board is your master control through which all your devices flow. Every mixing board can produce a degree of hiss and background noise. If there is going to be distortion in the sound, it's going to come from here. If your amp volumes are at full, then your mixing board volumes shouldn't ever have to be set at more than 3/4. The less signal you have to send out of the mixing board, the less distortion, hiss and background noise will be sent as well. Let your amp do the work. It wants to power your system, so let it. Your mixing board wants to coordinate your system, not power it, so let each component do what it's intended to do.

- Alan Ross

PS - bryant just posted the question, what is "too hot"? Too Hot means that either the volume or gain on the mic is too high. When you have to hold the mic a foot away from your face, it's because it's too loud. Bringing down the volume slide on mixing board is usually the solution, but you could have your gain set way too high as well. Properly adjusting your mic channel will cure this problem. A singer should be able to hold the mic two to four inches from their mouth. With a unidirectional mic, the singer should hold the mic in such a way as to be singing into the top of the mic, not the side.
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  #14  
Old March 4th, 2007, 06:17 PM
quaizywabbit quaizywabbit is offline
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quite often i've seen numerous hosts(and even larger multiriggers) that use a 'global' eq improperly.

the global eq should only compensate for room acoustics and/or to balance speaker response. Every change on the global eq affects the mic's, so use it very sparingly.

misuse of the mic eq's is also quite common:

for example a female singer with virtually no bass in her voice and the bass on the mic channel turned up - all this does is expose this mic to the lower freq's that cause feedback, especially in the presence of a subwoofer. You can't add something that isn't there in the first place, so concentrate on adjusting/balancing the frequencies that are present.

on my rig i instead use my sweepable midrange and leave the bass zero'd.

with duets (particularly with female groups) panning each mic off center (where no mics share the same pan setting) as well as slightly varying each mics eq(again none sharing a setting) helps dramatically with clarity and feedback problems...

I also use a Dbx Driverack PA.........worth every penny!
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