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How to rid the place of bad equipment

Discussion in 'Sound, Music, and Intercom' started by dunnohowto, Jan 8, 2008.

  1. dunnohowto

    dunnohowto Member

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    I have a problem at one of the places i started sound work at and i might ask here.
    ok, i have a system that always feedsback at you. multidirectional mics......
     
  2. museav

    museav CBMod CB Mods Departed Member

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    Okay, admitting you have a problem is the first step...:)

    Can you tell us anything more about the situation? What is the application? What are you doing? What equipment is involved? What do you mean by 'multidirectional' mic? Are there any factors that seem to affect the feedback? The more information you can provide on the specifics of the situation, the greater and more relevant the help that can be provided.

    Feedback is usually not just an equipment issue, it is an acoustic and overall system phenomena. Often the system setup, the relationships of mics and speakers, the physical environment and the operation of the system are more likely to be the cause of feedback than it being simply an equipment issue.
     
  3. dunnohowto

    dunnohowto Member

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    Ok the sound system is being used in a hall setting. It is being used for mass. There are 4 500W RMS 1000W max speakers powered by 4 power amplifiers from a yamaha mixer. We have 3 multidirectional speakers, one uni directional mic and two wireless mics. The current setup has two front speakers pointed at the back of the hall which probaly echos off the rear wall. The setup also has the rear speakers pointing at the stage at an angle. I dont know if it will cause problems. It also doesnt take too much gain and volume to cause feedback. Btw would adding an equaliser be better?

    Thanks
     
  4. Eboy87

    Eboy87 Well-Known Member

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    Where are your mics positioned in relation to the speakers? Are they in front of or behind? Are the rear speakers being used as monitors for people on-stage so to speak, or are they getting the same feed as the L-R mains? Also, when you say unidirectional mic, there's more than one kind of uni mic, i.e. cardioid, hypercardioid, supercardioid, etc. You wouldn't happen to know which kind of those it is, or make/model number.

    An EQ will help to a point, but only if the person using it actually knows how to use it. True, they are able to notch out the frequency feeding back, but they can cause a lot more harm than good when someone "helps" by hacking up the curve.

    Definitely place the speakers ahead of the mics, if possible. Putting them behind will just cause the mic to pick up the sound from the mains and reamplify it, thus creating feedback. I have a theory on what might be causing feedback, but need more information on the placement of speakers and mics to confirm/debunk it. You wouldn't happen to have a drawing of the space, would you?

    Also, try positioning the L-R mains on an angle down towards the seating. THe church I worked in had a marble back wall, and the reflections could and would make the system get away from you if you weren't watching. But the main thing is keeping the mics behind the speakers.

    Sorry if that didn't help at all
     
  5. dunnohowto

    dunnohowto Member

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    As you can see the picture is not to scale. Currently the placement of the system is a bit odd :) but our budget doesnt allow for moving to the back :( but need some help. btw i wouldnt have the brands of the mics on hand

    Thanks
     

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  6. museav

    museav CBMod CB Mods Departed Member

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    By 'multi-directional' mic, I assume you mean omnidirectional (although that could also define bipolar/figure 8 or hypercardioid) while the uni-directional is probably cardioid.

    What is the purpose of the rear speakers? Since you indicated that they are getting the same signal as the front speakers, my first thought is that they are probably causing more problems than they are providing any benefit. And getting the front speakers to be aimed at the audience while minimizing the sound hitting the walls would probably help.

    EQ may help, but there are certain things that may be related to your room and system that equalization cannot really address. For example, you might reduce the energy driving a particular room mode using an EQ but you can't actually fix the problem that way. And as Eboy noted, too often you end up with a conflict between the equalization necessary to correct problems and that equalization negatively impacting the sound quality. This is especially true with wide band, such as octave, equalizers since each band affects a fairly wide range of frequencies and problem frequencies often fall between two bands.

    Is this a traditional mass with all vocals and speech with no stage monitoring or is it a contemporary mass with live music, instruments on stage, stage monitors and higher sound levels? How are the mics being used both functionally (lead vocal, choir, instrument mic, etc.) and physically (handheld, stand, overhead and so on)?

    How big is the room and the audience? What are the room finishes? Do you get an echo off the rear wall even with the sound system off?
     
  7. jkowtko

    jkowtko Active Member

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    Some thoughts/comments:

    * rear speakers -- turn them off and see if the feedback goes away. If it does, then the rear speakers are probably playing too loud. Either leave them off, or you have to find a way to attenuate (lower the volume of) them. You can also EQ them to drop the feedback frequencies, but that requires an EQ -- do you have a 31-band EQ?

    * omni mics -- the term "omnidirectional" is generally used over "multi-direcftional". Are these just handheld mics? If so, they should not be omni's -- they should be cardiod. How much budget do you have to buy new cardoid mics? orangecountyspeaker.com has great Shure SM58 (the "staple" mic) knockoffs for very little money .. you can get three of them, including shipping, for under $100 total. I have one and it sounds the same as an SM58 to me, and also appears to be pretty durable, so in my opinion a great deal.

    * I also second the suggestion of the previous post to tile the main speakers down a bit. It can make all the difference in the world in killing reflections and reducing feedback.

    Please let us know what budget $$ you have for this -- it will help with the suggestions
     
  8. Eboy87

    Eboy87 Well-Known Member

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    I think we're all in agreement that the best starting solution is to lose the rear speakers, and to angle the front ones down.

    It would really help if you could get us make/model numbers for the mics. If it's for a church service, I'd be willing to bet they're 58's of the wired and wireless variety, or even a crown PCC.

    Also, to reiterate what Museav said, a few more details about the room itself would help out. I think it's an acoustic issue, so I don't think an EQ is really absolutely necessary at this point. Electronic solutions to acoustic problems usually don't end up well, especially in churches.
     
  9. dunnohowto

    dunnohowto Member

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    Thanks for the rear speaker cut suggestion. We have a congregation of about 200-300. The walls are made of wood with holes drilled in to it. The microphones sit on the lecturns and one on the altar. The room size i'll probaly say, i'll go check check, will be about 45m*20m and in the US thats about (don't mind the conversions) 147ft*65ft. btw since this is now an acoustics problem i'd like to show that the ceiling is low 3m 9ft and is angled then is about 8m 26ft as shown by this attachment. Theres a choir but theres no band, the organ does it all. It's more the traditional mass. We do have monitor/foldback speakers but their not used a lot. I currently don't have an 31 band EQ but the amp has a knob on it so i can turn it down or off, so i'll try down and then off the following week. I'll also try and get a budget for it. I also find that with the sound off theres a echo of people talking, but thats cause they talk so loud.
     

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  10. avkid

    avkid Not a New User Fight Leukemia

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    Hmm..you might actually need delays in a room that size.
    I think you should consult a professional.
     
  11. Eboy87

    Eboy87 Well-Known Member

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    You don't need delays. That adds a whole new set of problems. For 300, the L-R mains will do fine.
     
  12. avkid

    avkid Not a New User Fight Leukemia

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    I meant zoned, not delayed.
    Speakers recessed into the ceiling with a system processor that has been set up by a professional.
     
  13. dunnohowto

    dunnohowto Member

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    Ok can you try to explain that to me a little better

    Thanks
     
  14. avkid

    avkid Not a New User Fight Leukemia

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    What you need is a professional A/V installer.
     
  15. dunnohowto

    dunnohowto Member

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    Ok. Well we have a budget :( Would changing all of the mics to SM 58 be better (less feedback)?
     
  16. avkid

    avkid Not a New User Fight Leukemia

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    Alright, that question sealed the deal.
    You are in way over your head.
    I will contact you.
     
  17. cutlunch

    cutlunch Active Member

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    Dunnohowto
    Could you please explain something for me about the rear speakers. Are they actually right at the back of the room behind the last row of seats? Or are they part way down the rows moving towards the front? Roughly how old is this installation?

    How long has this feedback been a problem? If the feedback wasn't always there try and findout what has changed. A basic guide for microphones is to try and keep them behind the speakers.

    Let us know how you get on with disconnecting the rear speakers.
     
  18. dunnohowto

    dunnohowto Member

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    Hello,
    Ok the speakers are installed at about the second last row of seats. The installation was about 3 months ago. We usd to have another sound system but they retired it. Meanwhile we'll have to wait till the 13/1/08 when we have a mass to test it.
     
  19. cutlunch

    cutlunch Active Member

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    Who did the install? If it was professional company you should be going back to them to sort it out.
     
  20. dunnohowto

    dunnohowto Member

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    It was a DIY install :(
     

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